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7a301c1b8c
When using bit tests for hole checks, we call AddPredecessorToBlock to give the phi node a value from the bit test block. This would break if we've previously called removePredecessor on the default destination because the switch is fully covered. Test case by Mark Lacey. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235771 91177308-0d34-0410-b5e6-96231b3b80d8
4704 lines
182 KiB
C++
4704 lines
182 KiB
C++
//===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// Peephole optimize the CFG.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/SetVector.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/ConstantFolding.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/TargetTransformInfo.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/CFG.h"
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#include "llvm/IR/ConstantRange.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/DerivedTypes.h"
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#include "llvm/IR/GlobalVariable.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/IR/MDBuilder.h"
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#include "llvm/IR/Metadata.h"
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#include "llvm/IR/Module.h"
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#include "llvm/IR/NoFolder.h"
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#include "llvm/IR/Operator.h"
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#include "llvm/IR/PatternMatch.h"
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#include "llvm/IR/Type.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Transforms/Utils/ValueMapper.h"
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#include <algorithm>
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#include <map>
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#include <set>
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using namespace llvm;
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using namespace PatternMatch;
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#define DEBUG_TYPE "simplifycfg"
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// Chosen as 2 so as to be cheap, but still to have enough power to fold
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// a select, so the "clamp" idiom (of a min followed by a max) will be caught.
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// To catch this, we need to fold a compare and a select, hence '2' being the
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// minimum reasonable default.
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static cl::opt<unsigned>
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PHINodeFoldingThreshold("phi-node-folding-threshold", cl::Hidden, cl::init(2),
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cl::desc("Control the amount of phi node folding to perform (default = 2)"));
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static cl::opt<bool>
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DupRet("simplifycfg-dup-ret", cl::Hidden, cl::init(false),
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cl::desc("Duplicate return instructions into unconditional branches"));
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static cl::opt<bool>
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SinkCommon("simplifycfg-sink-common", cl::Hidden, cl::init(true),
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cl::desc("Sink common instructions down to the end block"));
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static cl::opt<bool> HoistCondStores(
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"simplifycfg-hoist-cond-stores", cl::Hidden, cl::init(true),
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cl::desc("Hoist conditional stores if an unconditional store precedes"));
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STATISTIC(NumBitMaps, "Number of switch instructions turned into bitmaps");
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STATISTIC(NumLinearMaps, "Number of switch instructions turned into linear mapping");
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STATISTIC(NumLookupTables, "Number of switch instructions turned into lookup tables");
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STATISTIC(NumLookupTablesHoles, "Number of switch instructions turned into lookup tables (holes checked)");
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STATISTIC(NumTableCmpReuses, "Number of reused switch table lookup compares");
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STATISTIC(NumSinkCommons, "Number of common instructions sunk down to the end block");
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STATISTIC(NumSpeculations, "Number of speculative executed instructions");
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namespace {
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// The first field contains the value that the switch produces when a certain
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// case group is selected, and the second field is a vector containing the cases
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// composing the case group.
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typedef SmallVector<std::pair<Constant *, SmallVector<ConstantInt *, 4>>, 2>
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SwitchCaseResultVectorTy;
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// The first field contains the phi node that generates a result of the switch
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// and the second field contains the value generated for a certain case in the switch
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// for that PHI.
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typedef SmallVector<std::pair<PHINode *, Constant *>, 4> SwitchCaseResultsTy;
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/// ValueEqualityComparisonCase - Represents a case of a switch.
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struct ValueEqualityComparisonCase {
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ConstantInt *Value;
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BasicBlock *Dest;
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ValueEqualityComparisonCase(ConstantInt *Value, BasicBlock *Dest)
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: Value(Value), Dest(Dest) {}
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bool operator<(ValueEqualityComparisonCase RHS) const {
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// Comparing pointers is ok as we only rely on the order for uniquing.
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return Value < RHS.Value;
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}
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bool operator==(BasicBlock *RHSDest) const { return Dest == RHSDest; }
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};
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class SimplifyCFGOpt {
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const TargetTransformInfo &TTI;
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const DataLayout &DL;
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unsigned BonusInstThreshold;
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AssumptionCache *AC;
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Value *isValueEqualityComparison(TerminatorInst *TI);
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BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
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std::vector<ValueEqualityComparisonCase> &Cases);
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bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
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BasicBlock *Pred,
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IRBuilder<> &Builder);
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bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
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IRBuilder<> &Builder);
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bool SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder);
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bool SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder);
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bool SimplifyUnreachable(UnreachableInst *UI);
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bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder);
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bool SimplifyIndirectBr(IndirectBrInst *IBI);
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bool SimplifyUncondBranch(BranchInst *BI, IRBuilder <> &Builder);
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bool SimplifyCondBranch(BranchInst *BI, IRBuilder <>&Builder);
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public:
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SimplifyCFGOpt(const TargetTransformInfo &TTI, const DataLayout &DL,
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unsigned BonusInstThreshold, AssumptionCache *AC)
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: TTI(TTI), DL(DL), BonusInstThreshold(BonusInstThreshold), AC(AC) {}
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bool run(BasicBlock *BB);
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};
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}
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/// SafeToMergeTerminators - Return true if it is safe to merge these two
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/// terminator instructions together.
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///
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static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
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if (SI1 == SI2) return false; // Can't merge with self!
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// It is not safe to merge these two switch instructions if they have a common
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// successor, and if that successor has a PHI node, and if *that* PHI node has
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// conflicting incoming values from the two switch blocks.
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BasicBlock *SI1BB = SI1->getParent();
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BasicBlock *SI2BB = SI2->getParent();
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SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
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for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
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if (SI1Succs.count(*I))
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for (BasicBlock::iterator BBI = (*I)->begin();
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isa<PHINode>(BBI); ++BBI) {
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PHINode *PN = cast<PHINode>(BBI);
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if (PN->getIncomingValueForBlock(SI1BB) !=
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PN->getIncomingValueForBlock(SI2BB))
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return false;
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}
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return true;
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}
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/// isProfitableToFoldUnconditional - Return true if it is safe and profitable
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/// to merge these two terminator instructions together, where SI1 is an
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/// unconditional branch. PhiNodes will store all PHI nodes in common
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/// successors.
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///
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static bool isProfitableToFoldUnconditional(BranchInst *SI1,
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BranchInst *SI2,
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Instruction *Cond,
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SmallVectorImpl<PHINode*> &PhiNodes) {
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if (SI1 == SI2) return false; // Can't merge with self!
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assert(SI1->isUnconditional() && SI2->isConditional());
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// We fold the unconditional branch if we can easily update all PHI nodes in
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// common successors:
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// 1> We have a constant incoming value for the conditional branch;
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// 2> We have "Cond" as the incoming value for the unconditional branch;
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// 3> SI2->getCondition() and Cond have same operands.
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CmpInst *Ci2 = dyn_cast<CmpInst>(SI2->getCondition());
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if (!Ci2) return false;
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if (!(Cond->getOperand(0) == Ci2->getOperand(0) &&
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Cond->getOperand(1) == Ci2->getOperand(1)) &&
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!(Cond->getOperand(0) == Ci2->getOperand(1) &&
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Cond->getOperand(1) == Ci2->getOperand(0)))
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return false;
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BasicBlock *SI1BB = SI1->getParent();
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BasicBlock *SI2BB = SI2->getParent();
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SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
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for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
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if (SI1Succs.count(*I))
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for (BasicBlock::iterator BBI = (*I)->begin();
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isa<PHINode>(BBI); ++BBI) {
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PHINode *PN = cast<PHINode>(BBI);
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if (PN->getIncomingValueForBlock(SI1BB) != Cond ||
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!isa<ConstantInt>(PN->getIncomingValueForBlock(SI2BB)))
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return false;
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PhiNodes.push_back(PN);
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}
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return true;
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}
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/// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
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/// now be entries in it from the 'NewPred' block. The values that will be
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/// flowing into the PHI nodes will be the same as those coming in from
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/// ExistPred, an existing predecessor of Succ.
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static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
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BasicBlock *ExistPred) {
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if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
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PHINode *PN;
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for (BasicBlock::iterator I = Succ->begin();
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(PN = dyn_cast<PHINode>(I)); ++I)
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PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
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}
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/// ComputeSpeculationCost - Compute an abstract "cost" of speculating the
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/// given instruction, which is assumed to be safe to speculate. TCC_Free means
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/// cheap, TCC_Basic means less cheap, and TCC_Expensive means prohibitively
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/// expensive.
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static unsigned ComputeSpeculationCost(const User *I,
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const TargetTransformInfo &TTI) {
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assert(isSafeToSpeculativelyExecute(I) &&
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"Instruction is not safe to speculatively execute!");
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return TTI.getUserCost(I);
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}
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/// DominatesMergePoint - If we have a merge point of an "if condition" as
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/// accepted above, return true if the specified value dominates the block. We
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/// don't handle the true generality of domination here, just a special case
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/// which works well enough for us.
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///
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/// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
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/// see if V (which must be an instruction) and its recursive operands
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/// that do not dominate BB have a combined cost lower than CostRemaining and
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/// are non-trapping. If both are true, the instruction is inserted into the
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/// set and true is returned.
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///
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/// The cost for most non-trapping instructions is defined as 1 except for
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/// Select whose cost is 2.
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///
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/// After this function returns, CostRemaining is decreased by the cost of
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/// V plus its non-dominating operands. If that cost is greater than
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/// CostRemaining, false is returned and CostRemaining is undefined.
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static bool DominatesMergePoint(Value *V, BasicBlock *BB,
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SmallPtrSetImpl<Instruction*> *AggressiveInsts,
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unsigned &CostRemaining,
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const TargetTransformInfo &TTI) {
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Instruction *I = dyn_cast<Instruction>(V);
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if (!I) {
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// Non-instructions all dominate instructions, but not all constantexprs
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// can be executed unconditionally.
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if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
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if (C->canTrap())
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return false;
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return true;
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}
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BasicBlock *PBB = I->getParent();
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// We don't want to allow weird loops that might have the "if condition" in
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// the bottom of this block.
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if (PBB == BB) return false;
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// If this instruction is defined in a block that contains an unconditional
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// branch to BB, then it must be in the 'conditional' part of the "if
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// statement". If not, it definitely dominates the region.
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BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
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if (!BI || BI->isConditional() || BI->getSuccessor(0) != BB)
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return true;
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// If we aren't allowing aggressive promotion anymore, then don't consider
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// instructions in the 'if region'.
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if (!AggressiveInsts) return false;
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// If we have seen this instruction before, don't count it again.
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if (AggressiveInsts->count(I)) return true;
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// Okay, it looks like the instruction IS in the "condition". Check to
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// see if it's a cheap instruction to unconditionally compute, and if it
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// only uses stuff defined outside of the condition. If so, hoist it out.
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if (!isSafeToSpeculativelyExecute(I))
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return false;
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unsigned Cost = ComputeSpeculationCost(I, TTI);
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if (Cost > CostRemaining)
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return false;
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CostRemaining -= Cost;
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// Okay, we can only really hoist these out if their operands do
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// not take us over the cost threshold.
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for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
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if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining, TTI))
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return false;
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// Okay, it's safe to do this! Remember this instruction.
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AggressiveInsts->insert(I);
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return true;
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}
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/// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
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/// and PointerNullValue. Return NULL if value is not a constant int.
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static ConstantInt *GetConstantInt(Value *V, const DataLayout &DL) {
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// Normal constant int.
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ConstantInt *CI = dyn_cast<ConstantInt>(V);
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if (CI || !isa<Constant>(V) || !V->getType()->isPointerTy())
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return CI;
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// This is some kind of pointer constant. Turn it into a pointer-sized
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// ConstantInt if possible.
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IntegerType *PtrTy = cast<IntegerType>(DL.getIntPtrType(V->getType()));
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// Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
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if (isa<ConstantPointerNull>(V))
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return ConstantInt::get(PtrTy, 0);
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// IntToPtr const int.
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if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
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if (CE->getOpcode() == Instruction::IntToPtr)
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if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
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// The constant is very likely to have the right type already.
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if (CI->getType() == PtrTy)
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return CI;
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else
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return cast<ConstantInt>
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(ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
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}
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return nullptr;
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}
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namespace {
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/// Given a chain of or (||) or and (&&) comparison of a value against a
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/// constant, this will try to recover the information required for a switch
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/// structure.
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/// It will depth-first traverse the chain of comparison, seeking for patterns
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/// like %a == 12 or %a < 4 and combine them to produce a set of integer
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/// representing the different cases for the switch.
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/// Note that if the chain is composed of '||' it will build the set of elements
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/// that matches the comparisons (i.e. any of this value validate the chain)
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/// while for a chain of '&&' it will build the set elements that make the test
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/// fail.
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struct ConstantComparesGatherer {
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const DataLayout &DL;
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Value *CompValue; /// Value found for the switch comparison
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Value *Extra; /// Extra clause to be checked before the switch
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SmallVector<ConstantInt *, 8> Vals; /// Set of integers to match in switch
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unsigned UsedICmps; /// Number of comparisons matched in the and/or chain
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/// Construct and compute the result for the comparison instruction Cond
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ConstantComparesGatherer(Instruction *Cond, const DataLayout &DL)
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: DL(DL), CompValue(nullptr), Extra(nullptr), UsedICmps(0) {
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gather(Cond);
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}
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/// Prevent copy
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ConstantComparesGatherer(const ConstantComparesGatherer &) = delete;
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ConstantComparesGatherer &
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operator=(const ConstantComparesGatherer &) = delete;
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private:
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/// Try to set the current value used for the comparison, it succeeds only if
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/// it wasn't set before or if the new value is the same as the old one
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bool setValueOnce(Value *NewVal) {
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if(CompValue && CompValue != NewVal) return false;
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CompValue = NewVal;
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return (CompValue != nullptr);
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}
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/// Try to match Instruction "I" as a comparison against a constant and
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/// populates the array Vals with the set of values that match (or do not
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/// match depending on isEQ).
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/// Return false on failure. On success, the Value the comparison matched
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/// against is placed in CompValue.
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/// If CompValue is already set, the function is expected to fail if a match
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/// is found but the value compared to is different.
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bool matchInstruction(Instruction *I, bool isEQ) {
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// If this is an icmp against a constant, handle this as one of the cases.
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ICmpInst *ICI;
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ConstantInt *C;
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if (!((ICI = dyn_cast<ICmpInst>(I)) &&
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(C = GetConstantInt(I->getOperand(1), DL)))) {
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return false;
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}
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Value *RHSVal;
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ConstantInt *RHSC;
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// Pattern match a special case
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// (x & ~2^x) == y --> x == y || x == y|2^x
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// This undoes a transformation done by instcombine to fuse 2 compares.
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if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
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if (match(ICI->getOperand(0),
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m_And(m_Value(RHSVal), m_ConstantInt(RHSC)))) {
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APInt Not = ~RHSC->getValue();
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if (Not.isPowerOf2()) {
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// If we already have a value for the switch, it has to match!
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if(!setValueOnce(RHSVal))
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return false;
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Vals.push_back(C);
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Vals.push_back(ConstantInt::get(C->getContext(),
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C->getValue() | Not));
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UsedICmps++;
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return true;
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}
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}
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// If we already have a value for the switch, it has to match!
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if(!setValueOnce(ICI->getOperand(0)))
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return false;
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UsedICmps++;
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Vals.push_back(C);
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return ICI->getOperand(0);
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}
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// If we have "x ult 3", for example, then we can add 0,1,2 to the set.
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ConstantRange Span = ConstantRange::makeAllowedICmpRegion(
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ICI->getPredicate(), C->getValue());
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// Shift the range if the compare is fed by an add. This is the range
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// compare idiom as emitted by instcombine.
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Value *CandidateVal = I->getOperand(0);
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if(match(I->getOperand(0), m_Add(m_Value(RHSVal), m_ConstantInt(RHSC)))) {
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Span = Span.subtract(RHSC->getValue());
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CandidateVal = RHSVal;
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}
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|
|
// If this is an and/!= check, then we are looking to build the set of
|
|
// value that *don't* pass the and chain. I.e. to turn "x ugt 2" into
|
|
// x != 0 && x != 1.
|
|
if (!isEQ)
|
|
Span = Span.inverse();
|
|
|
|
// If there are a ton of values, we don't want to make a ginormous switch.
|
|
if (Span.getSetSize().ugt(8) || Span.isEmptySet()) {
|
|
return false;
|
|
}
|
|
|
|
// If we already have a value for the switch, it has to match!
|
|
if(!setValueOnce(CandidateVal))
|
|
return false;
|
|
|
|
// Add all values from the range to the set
|
|
for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
|
|
Vals.push_back(ConstantInt::get(I->getContext(), Tmp));
|
|
|
|
UsedICmps++;
|
|
return true;
|
|
|
|
}
|
|
|
|
/// gather - Given a potentially 'or'd or 'and'd together collection of icmp
|
|
/// eq/ne/lt/gt instructions that compare a value against a constant, extract
|
|
/// the value being compared, and stick the list constants into the Vals
|
|
/// vector.
|
|
/// One "Extra" case is allowed to differ from the other.
|
|
void gather(Value *V) {
|
|
Instruction *I = dyn_cast<Instruction>(V);
|
|
bool isEQ = (I->getOpcode() == Instruction::Or);
|
|
|
|
// Keep a stack (SmallVector for efficiency) for depth-first traversal
|
|
SmallVector<Value *, 8> DFT;
|
|
|
|
// Initialize
|
|
DFT.push_back(V);
|
|
|
|
while(!DFT.empty()) {
|
|
V = DFT.pop_back_val();
|
|
|
|
if (Instruction *I = dyn_cast<Instruction>(V)) {
|
|
// If it is a || (or && depending on isEQ), process the operands.
|
|
if (I->getOpcode() == (isEQ ? Instruction::Or : Instruction::And)) {
|
|
DFT.push_back(I->getOperand(1));
|
|
DFT.push_back(I->getOperand(0));
|
|
continue;
|
|
}
|
|
|
|
// Try to match the current instruction
|
|
if (matchInstruction(I, isEQ))
|
|
// Match succeed, continue the loop
|
|
continue;
|
|
}
|
|
|
|
// One element of the sequence of || (or &&) could not be match as a
|
|
// comparison against the same value as the others.
|
|
// We allow only one "Extra" case to be checked before the switch
|
|
if (!Extra) {
|
|
Extra = V;
|
|
continue;
|
|
}
|
|
// Failed to parse a proper sequence, abort now
|
|
CompValue = nullptr;
|
|
break;
|
|
}
|
|
}
|
|
};
|
|
|
|
}
|
|
|
|
static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
|
|
Instruction *Cond = nullptr;
|
|
if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
|
|
Cond = dyn_cast<Instruction>(SI->getCondition());
|
|
} else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
|
|
if (BI->isConditional())
|
|
Cond = dyn_cast<Instruction>(BI->getCondition());
|
|
} else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
|
|
Cond = dyn_cast<Instruction>(IBI->getAddress());
|
|
}
|
|
|
|
TI->eraseFromParent();
|
|
if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
|
|
}
|
|
|
|
/// isValueEqualityComparison - Return true if the specified terminator checks
|
|
/// to see if a value is equal to constant integer value.
|
|
Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
|
|
Value *CV = nullptr;
|
|
if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
|
|
// Do not permit merging of large switch instructions into their
|
|
// predecessors unless there is only one predecessor.
|
|
if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
|
|
pred_end(SI->getParent())) <= 128)
|
|
CV = SI->getCondition();
|
|
} else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
|
|
if (BI->isConditional() && BI->getCondition()->hasOneUse())
|
|
if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition())) {
|
|
if (ICI->isEquality() && GetConstantInt(ICI->getOperand(1), DL))
|
|
CV = ICI->getOperand(0);
|
|
}
|
|
|
|
// Unwrap any lossless ptrtoint cast.
|
|
if (CV) {
|
|
if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV)) {
|
|
Value *Ptr = PTII->getPointerOperand();
|
|
if (PTII->getType() == DL.getIntPtrType(Ptr->getType()))
|
|
CV = Ptr;
|
|
}
|
|
}
|
|
return CV;
|
|
}
|
|
|
|
/// GetValueEqualityComparisonCases - Given a value comparison instruction,
|
|
/// decode all of the 'cases' that it represents and return the 'default' block.
|
|
BasicBlock *SimplifyCFGOpt::
|
|
GetValueEqualityComparisonCases(TerminatorInst *TI,
|
|
std::vector<ValueEqualityComparisonCase>
|
|
&Cases) {
|
|
if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
|
|
Cases.reserve(SI->getNumCases());
|
|
for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); i != e; ++i)
|
|
Cases.push_back(ValueEqualityComparisonCase(i.getCaseValue(),
|
|
i.getCaseSuccessor()));
|
|
return SI->getDefaultDest();
|
|
}
|
|
|
|
BranchInst *BI = cast<BranchInst>(TI);
|
|
ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
|
|
BasicBlock *Succ = BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_NE);
|
|
Cases.push_back(ValueEqualityComparisonCase(GetConstantInt(ICI->getOperand(1),
|
|
DL),
|
|
Succ));
|
|
return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
|
|
}
|
|
|
|
|
|
/// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
|
|
/// in the list that match the specified block.
|
|
static void EliminateBlockCases(BasicBlock *BB,
|
|
std::vector<ValueEqualityComparisonCase> &Cases) {
|
|
Cases.erase(std::remove(Cases.begin(), Cases.end(), BB), Cases.end());
|
|
}
|
|
|
|
/// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
|
|
/// well.
|
|
static bool
|
|
ValuesOverlap(std::vector<ValueEqualityComparisonCase> &C1,
|
|
std::vector<ValueEqualityComparisonCase > &C2) {
|
|
std::vector<ValueEqualityComparisonCase> *V1 = &C1, *V2 = &C2;
|
|
|
|
// Make V1 be smaller than V2.
|
|
if (V1->size() > V2->size())
|
|
std::swap(V1, V2);
|
|
|
|
if (V1->size() == 0) return false;
|
|
if (V1->size() == 1) {
|
|
// Just scan V2.
|
|
ConstantInt *TheVal = (*V1)[0].Value;
|
|
for (unsigned i = 0, e = V2->size(); i != e; ++i)
|
|
if (TheVal == (*V2)[i].Value)
|
|
return true;
|
|
}
|
|
|
|
// Otherwise, just sort both lists and compare element by element.
|
|
array_pod_sort(V1->begin(), V1->end());
|
|
array_pod_sort(V2->begin(), V2->end());
|
|
unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
|
|
while (i1 != e1 && i2 != e2) {
|
|
if ((*V1)[i1].Value == (*V2)[i2].Value)
|
|
return true;
|
|
if ((*V1)[i1].Value < (*V2)[i2].Value)
|
|
++i1;
|
|
else
|
|
++i2;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
|
|
/// terminator instruction and its block is known to only have a single
|
|
/// predecessor block, check to see if that predecessor is also a value
|
|
/// comparison with the same value, and if that comparison determines the
|
|
/// outcome of this comparison. If so, simplify TI. This does a very limited
|
|
/// form of jump threading.
|
|
bool SimplifyCFGOpt::
|
|
SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
|
|
BasicBlock *Pred,
|
|
IRBuilder<> &Builder) {
|
|
Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
|
|
if (!PredVal) return false; // Not a value comparison in predecessor.
|
|
|
|
Value *ThisVal = isValueEqualityComparison(TI);
|
|
assert(ThisVal && "This isn't a value comparison!!");
|
|
if (ThisVal != PredVal) return false; // Different predicates.
|
|
|
|
// TODO: Preserve branch weight metadata, similarly to how
|
|
// FoldValueComparisonIntoPredecessors preserves it.
|
|
|
|
// Find out information about when control will move from Pred to TI's block.
|
|
std::vector<ValueEqualityComparisonCase> PredCases;
|
|
BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
|
|
PredCases);
|
|
EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
|
|
|
|
// Find information about how control leaves this block.
|
|
std::vector<ValueEqualityComparisonCase> ThisCases;
|
|
BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
|
|
EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
|
|
|
|
// If TI's block is the default block from Pred's comparison, potentially
|
|
// simplify TI based on this knowledge.
|
|
if (PredDef == TI->getParent()) {
|
|
// If we are here, we know that the value is none of those cases listed in
|
|
// PredCases. If there are any cases in ThisCases that are in PredCases, we
|
|
// can simplify TI.
|
|
if (!ValuesOverlap(PredCases, ThisCases))
|
|
return false;
|
|
|
|
if (isa<BranchInst>(TI)) {
|
|
// Okay, one of the successors of this condbr is dead. Convert it to a
|
|
// uncond br.
|
|
assert(ThisCases.size() == 1 && "Branch can only have one case!");
|
|
// Insert the new branch.
|
|
Instruction *NI = Builder.CreateBr(ThisDef);
|
|
(void) NI;
|
|
|
|
// Remove PHI node entries for the dead edge.
|
|
ThisCases[0].Dest->removePredecessor(TI->getParent());
|
|
|
|
DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
|
|
<< "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
|
|
|
|
EraseTerminatorInstAndDCECond(TI);
|
|
return true;
|
|
}
|
|
|
|
SwitchInst *SI = cast<SwitchInst>(TI);
|
|
// Okay, TI has cases that are statically dead, prune them away.
|
|
SmallPtrSet<Constant*, 16> DeadCases;
|
|
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
|
|
DeadCases.insert(PredCases[i].Value);
|
|
|
|
DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
|
|
<< "Through successor TI: " << *TI);
|
|
|
|
// Collect branch weights into a vector.
|
|
SmallVector<uint32_t, 8> Weights;
|
|
MDNode *MD = SI->getMetadata(LLVMContext::MD_prof);
|
|
bool HasWeight = MD && (MD->getNumOperands() == 2 + SI->getNumCases());
|
|
if (HasWeight)
|
|
for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
|
|
++MD_i) {
|
|
ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(MD_i));
|
|
Weights.push_back(CI->getValue().getZExtValue());
|
|
}
|
|
for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) {
|
|
--i;
|
|
if (DeadCases.count(i.getCaseValue())) {
|
|
if (HasWeight) {
|
|
std::swap(Weights[i.getCaseIndex()+1], Weights.back());
|
|
Weights.pop_back();
|
|
}
|
|
i.getCaseSuccessor()->removePredecessor(TI->getParent());
|
|
SI->removeCase(i);
|
|
}
|
|
}
|
|
if (HasWeight && Weights.size() >= 2)
|
|
SI->setMetadata(LLVMContext::MD_prof,
|
|
MDBuilder(SI->getParent()->getContext()).
|
|
createBranchWeights(Weights));
|
|
|
|
DEBUG(dbgs() << "Leaving: " << *TI << "\n");
|
|
return true;
|
|
}
|
|
|
|
// Otherwise, TI's block must correspond to some matched value. Find out
|
|
// which value (or set of values) this is.
|
|
ConstantInt *TIV = nullptr;
|
|
BasicBlock *TIBB = TI->getParent();
|
|
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
|
|
if (PredCases[i].Dest == TIBB) {
|
|
if (TIV)
|
|
return false; // Cannot handle multiple values coming to this block.
|
|
TIV = PredCases[i].Value;
|
|
}
|
|
assert(TIV && "No edge from pred to succ?");
|
|
|
|
// Okay, we found the one constant that our value can be if we get into TI's
|
|
// BB. Find out which successor will unconditionally be branched to.
|
|
BasicBlock *TheRealDest = nullptr;
|
|
for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
|
|
if (ThisCases[i].Value == TIV) {
|
|
TheRealDest = ThisCases[i].Dest;
|
|
break;
|
|
}
|
|
|
|
// If not handled by any explicit cases, it is handled by the default case.
|
|
if (!TheRealDest) TheRealDest = ThisDef;
|
|
|
|
// Remove PHI node entries for dead edges.
|
|
BasicBlock *CheckEdge = TheRealDest;
|
|
for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
|
|
if (*SI != CheckEdge)
|
|
(*SI)->removePredecessor(TIBB);
|
|
else
|
|
CheckEdge = nullptr;
|
|
|
|
// Insert the new branch.
|
|
Instruction *NI = Builder.CreateBr(TheRealDest);
|
|
(void) NI;
|
|
|
|
DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
|
|
<< "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
|
|
|
|
EraseTerminatorInstAndDCECond(TI);
|
|
return true;
|
|
}
|
|
|
|
namespace {
|
|
/// ConstantIntOrdering - This class implements a stable ordering of constant
|
|
/// integers that does not depend on their address. This is important for
|
|
/// applications that sort ConstantInt's to ensure uniqueness.
|
|
struct ConstantIntOrdering {
|
|
bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
|
|
return LHS->getValue().ult(RHS->getValue());
|
|
}
|
|
};
|
|
}
|
|
|
|
static int ConstantIntSortPredicate(ConstantInt *const *P1,
|
|
ConstantInt *const *P2) {
|
|
const ConstantInt *LHS = *P1;
|
|
const ConstantInt *RHS = *P2;
|
|
if (LHS->getValue().ult(RHS->getValue()))
|
|
return 1;
|
|
if (LHS->getValue() == RHS->getValue())
|
|
return 0;
|
|
return -1;
|
|
}
|
|
|
|
static inline bool HasBranchWeights(const Instruction* I) {
|
|
MDNode *ProfMD = I->getMetadata(LLVMContext::MD_prof);
|
|
if (ProfMD && ProfMD->getOperand(0))
|
|
if (MDString* MDS = dyn_cast<MDString>(ProfMD->getOperand(0)))
|
|
return MDS->getString().equals("branch_weights");
|
|
|
|
return false;
|
|
}
|
|
|
|
/// Get Weights of a given TerminatorInst, the default weight is at the front
|
|
/// of the vector. If TI is a conditional eq, we need to swap the branch-weight
|
|
/// metadata.
|
|
static void GetBranchWeights(TerminatorInst *TI,
|
|
SmallVectorImpl<uint64_t> &Weights) {
|
|
MDNode *MD = TI->getMetadata(LLVMContext::MD_prof);
|
|
assert(MD);
|
|
for (unsigned i = 1, e = MD->getNumOperands(); i < e; ++i) {
|
|
ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(i));
|
|
Weights.push_back(CI->getValue().getZExtValue());
|
|
}
|
|
|
|
// If TI is a conditional eq, the default case is the false case,
|
|
// and the corresponding branch-weight data is at index 2. We swap the
|
|
// default weight to be the first entry.
|
|
if (BranchInst* BI = dyn_cast<BranchInst>(TI)) {
|
|
assert(Weights.size() == 2);
|
|
ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
|
|
if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
|
|
std::swap(Weights.front(), Weights.back());
|
|
}
|
|
}
|
|
|
|
/// Keep halving the weights until all can fit in uint32_t.
|
|
static void FitWeights(MutableArrayRef<uint64_t> Weights) {
|
|
uint64_t Max = *std::max_element(Weights.begin(), Weights.end());
|
|
if (Max > UINT_MAX) {
|
|
unsigned Offset = 32 - countLeadingZeros(Max);
|
|
for (uint64_t &I : Weights)
|
|
I >>= Offset;
|
|
}
|
|
}
|
|
|
|
/// FoldValueComparisonIntoPredecessors - The specified terminator is a value
|
|
/// equality comparison instruction (either a switch or a branch on "X == c").
|
|
/// See if any of the predecessors of the terminator block are value comparisons
|
|
/// on the same value. If so, and if safe to do so, fold them together.
|
|
bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
|
|
IRBuilder<> &Builder) {
|
|
BasicBlock *BB = TI->getParent();
|
|
Value *CV = isValueEqualityComparison(TI); // CondVal
|
|
assert(CV && "Not a comparison?");
|
|
bool Changed = false;
|
|
|
|
SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
|
|
while (!Preds.empty()) {
|
|
BasicBlock *Pred = Preds.pop_back_val();
|
|
|
|
// See if the predecessor is a comparison with the same value.
|
|
TerminatorInst *PTI = Pred->getTerminator();
|
|
Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
|
|
|
|
if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
|
|
// Figure out which 'cases' to copy from SI to PSI.
|
|
std::vector<ValueEqualityComparisonCase> BBCases;
|
|
BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
|
|
|
|
std::vector<ValueEqualityComparisonCase> PredCases;
|
|
BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
|
|
|
|
// Based on whether the default edge from PTI goes to BB or not, fill in
|
|
// PredCases and PredDefault with the new switch cases we would like to
|
|
// build.
|
|
SmallVector<BasicBlock*, 8> NewSuccessors;
|
|
|
|
// Update the branch weight metadata along the way
|
|
SmallVector<uint64_t, 8> Weights;
|
|
bool PredHasWeights = HasBranchWeights(PTI);
|
|
bool SuccHasWeights = HasBranchWeights(TI);
|
|
|
|
if (PredHasWeights) {
|
|
GetBranchWeights(PTI, Weights);
|
|
// branch-weight metadata is inconsistent here.
|
|
if (Weights.size() != 1 + PredCases.size())
|
|
PredHasWeights = SuccHasWeights = false;
|
|
} else if (SuccHasWeights)
|
|
// If there are no predecessor weights but there are successor weights,
|
|
// populate Weights with 1, which will later be scaled to the sum of
|
|
// successor's weights
|
|
Weights.assign(1 + PredCases.size(), 1);
|
|
|
|
SmallVector<uint64_t, 8> SuccWeights;
|
|
if (SuccHasWeights) {
|
|
GetBranchWeights(TI, SuccWeights);
|
|
// branch-weight metadata is inconsistent here.
|
|
if (SuccWeights.size() != 1 + BBCases.size())
|
|
PredHasWeights = SuccHasWeights = false;
|
|
} else if (PredHasWeights)
|
|
SuccWeights.assign(1 + BBCases.size(), 1);
|
|
|
|
if (PredDefault == BB) {
|
|
// If this is the default destination from PTI, only the edges in TI
|
|
// that don't occur in PTI, or that branch to BB will be activated.
|
|
std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
|
|
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
|
|
if (PredCases[i].Dest != BB)
|
|
PTIHandled.insert(PredCases[i].Value);
|
|
else {
|
|
// The default destination is BB, we don't need explicit targets.
|
|
std::swap(PredCases[i], PredCases.back());
|
|
|
|
if (PredHasWeights || SuccHasWeights) {
|
|
// Increase weight for the default case.
|
|
Weights[0] += Weights[i+1];
|
|
std::swap(Weights[i+1], Weights.back());
|
|
Weights.pop_back();
|
|
}
|
|
|
|
PredCases.pop_back();
|
|
--i; --e;
|
|
}
|
|
|
|
// Reconstruct the new switch statement we will be building.
|
|
if (PredDefault != BBDefault) {
|
|
PredDefault->removePredecessor(Pred);
|
|
PredDefault = BBDefault;
|
|
NewSuccessors.push_back(BBDefault);
|
|
}
|
|
|
|
unsigned CasesFromPred = Weights.size();
|
|
uint64_t ValidTotalSuccWeight = 0;
|
|
for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
|
|
if (!PTIHandled.count(BBCases[i].Value) &&
|
|
BBCases[i].Dest != BBDefault) {
|
|
PredCases.push_back(BBCases[i]);
|
|
NewSuccessors.push_back(BBCases[i].Dest);
|
|
if (SuccHasWeights || PredHasWeights) {
|
|
// The default weight is at index 0, so weight for the ith case
|
|
// should be at index i+1. Scale the cases from successor by
|
|
// PredDefaultWeight (Weights[0]).
|
|
Weights.push_back(Weights[0] * SuccWeights[i+1]);
|
|
ValidTotalSuccWeight += SuccWeights[i+1];
|
|
}
|
|
}
|
|
|
|
if (SuccHasWeights || PredHasWeights) {
|
|
ValidTotalSuccWeight += SuccWeights[0];
|
|
// Scale the cases from predecessor by ValidTotalSuccWeight.
|
|
for (unsigned i = 1; i < CasesFromPred; ++i)
|
|
Weights[i] *= ValidTotalSuccWeight;
|
|
// Scale the default weight by SuccDefaultWeight (SuccWeights[0]).
|
|
Weights[0] *= SuccWeights[0];
|
|
}
|
|
} else {
|
|
// If this is not the default destination from PSI, only the edges
|
|
// in SI that occur in PSI with a destination of BB will be
|
|
// activated.
|
|
std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
|
|
std::map<ConstantInt*, uint64_t> WeightsForHandled;
|
|
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
|
|
if (PredCases[i].Dest == BB) {
|
|
PTIHandled.insert(PredCases[i].Value);
|
|
|
|
if (PredHasWeights || SuccHasWeights) {
|
|
WeightsForHandled[PredCases[i].Value] = Weights[i+1];
|
|
std::swap(Weights[i+1], Weights.back());
|
|
Weights.pop_back();
|
|
}
|
|
|
|
std::swap(PredCases[i], PredCases.back());
|
|
PredCases.pop_back();
|
|
--i; --e;
|
|
}
|
|
|
|
// Okay, now we know which constants were sent to BB from the
|
|
// predecessor. Figure out where they will all go now.
|
|
for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
|
|
if (PTIHandled.count(BBCases[i].Value)) {
|
|
// If this is one we are capable of getting...
|
|
if (PredHasWeights || SuccHasWeights)
|
|
Weights.push_back(WeightsForHandled[BBCases[i].Value]);
|
|
PredCases.push_back(BBCases[i]);
|
|
NewSuccessors.push_back(BBCases[i].Dest);
|
|
PTIHandled.erase(BBCases[i].Value);// This constant is taken care of
|
|
}
|
|
|
|
// If there are any constants vectored to BB that TI doesn't handle,
|
|
// they must go to the default destination of TI.
|
|
for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
|
|
PTIHandled.begin(),
|
|
E = PTIHandled.end(); I != E; ++I) {
|
|
if (PredHasWeights || SuccHasWeights)
|
|
Weights.push_back(WeightsForHandled[*I]);
|
|
PredCases.push_back(ValueEqualityComparisonCase(*I, BBDefault));
|
|
NewSuccessors.push_back(BBDefault);
|
|
}
|
|
}
|
|
|
|
// Okay, at this point, we know which new successor Pred will get. Make
|
|
// sure we update the number of entries in the PHI nodes for these
|
|
// successors.
|
|
for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
|
|
AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
|
|
|
|
Builder.SetInsertPoint(PTI);
|
|
// Convert pointer to int before we switch.
|
|
if (CV->getType()->isPointerTy()) {
|
|
CV = Builder.CreatePtrToInt(CV, DL.getIntPtrType(CV->getType()),
|
|
"magicptr");
|
|
}
|
|
|
|
// Now that the successors are updated, create the new Switch instruction.
|
|
SwitchInst *NewSI = Builder.CreateSwitch(CV, PredDefault,
|
|
PredCases.size());
|
|
NewSI->setDebugLoc(PTI->getDebugLoc());
|
|
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
|
|
NewSI->addCase(PredCases[i].Value, PredCases[i].Dest);
|
|
|
|
if (PredHasWeights || SuccHasWeights) {
|
|
// Halve the weights if any of them cannot fit in an uint32_t
|
|
FitWeights(Weights);
|
|
|
|
SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
|
|
|
|
NewSI->setMetadata(LLVMContext::MD_prof,
|
|
MDBuilder(BB->getContext()).
|
|
createBranchWeights(MDWeights));
|
|
}
|
|
|
|
EraseTerminatorInstAndDCECond(PTI);
|
|
|
|
// Okay, last check. If BB is still a successor of PSI, then we must
|
|
// have an infinite loop case. If so, add an infinitely looping block
|
|
// to handle the case to preserve the behavior of the code.
|
|
BasicBlock *InfLoopBlock = nullptr;
|
|
for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
|
|
if (NewSI->getSuccessor(i) == BB) {
|
|
if (!InfLoopBlock) {
|
|
// Insert it at the end of the function, because it's either code,
|
|
// or it won't matter if it's hot. :)
|
|
InfLoopBlock = BasicBlock::Create(BB->getContext(),
|
|
"infloop", BB->getParent());
|
|
BranchInst::Create(InfLoopBlock, InfLoopBlock);
|
|
}
|
|
NewSI->setSuccessor(i, InfLoopBlock);
|
|
}
|
|
|
|
Changed = true;
|
|
}
|
|
}
|
|
return Changed;
|
|
}
|
|
|
|
// isSafeToHoistInvoke - If we would need to insert a select that uses the
|
|
// value of this invoke (comments in HoistThenElseCodeToIf explain why we
|
|
// would need to do this), we can't hoist the invoke, as there is nowhere
|
|
// to put the select in this case.
|
|
static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
|
|
Instruction *I1, Instruction *I2) {
|
|
for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
|
|
PHINode *PN;
|
|
for (BasicBlock::iterator BBI = SI->begin();
|
|
(PN = dyn_cast<PHINode>(BBI)); ++BBI) {
|
|
Value *BB1V = PN->getIncomingValueForBlock(BB1);
|
|
Value *BB2V = PN->getIncomingValueForBlock(BB2);
|
|
if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
|
|
return false;
|
|
}
|
|
}
|
|
}
|
|
return true;
|
|
}
|
|
|
|
static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I);
|
|
|
|
/// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
|
|
/// BB2, hoist any common code in the two blocks up into the branch block. The
|
|
/// caller of this function guarantees that BI's block dominates BB1 and BB2.
|
|
static bool HoistThenElseCodeToIf(BranchInst *BI,
|
|
const TargetTransformInfo &TTI) {
|
|
// This does very trivial matching, with limited scanning, to find identical
|
|
// instructions in the two blocks. In particular, we don't want to get into
|
|
// O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
|
|
// such, we currently just scan for obviously identical instructions in an
|
|
// identical order.
|
|
BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
|
|
BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
|
|
|
|
BasicBlock::iterator BB1_Itr = BB1->begin();
|
|
BasicBlock::iterator BB2_Itr = BB2->begin();
|
|
|
|
Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
|
|
// Skip debug info if it is not identical.
|
|
DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
|
|
DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
|
|
if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
|
|
while (isa<DbgInfoIntrinsic>(I1))
|
|
I1 = BB1_Itr++;
|
|
while (isa<DbgInfoIntrinsic>(I2))
|
|
I2 = BB2_Itr++;
|
|
}
|
|
if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
|
|
(isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
|
|
return false;
|
|
|
|
BasicBlock *BIParent = BI->getParent();
|
|
|
|
bool Changed = false;
|
|
do {
|
|
// If we are hoisting the terminator instruction, don't move one (making a
|
|
// broken BB), instead clone it, and remove BI.
|
|
if (isa<TerminatorInst>(I1))
|
|
goto HoistTerminator;
|
|
|
|
if (!TTI.isProfitableToHoist(I1) || !TTI.isProfitableToHoist(I2))
|
|
return Changed;
|
|
|
|
// For a normal instruction, we just move one to right before the branch,
|
|
// then replace all uses of the other with the first. Finally, we remove
|
|
// the now redundant second instruction.
|
|
BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
|
|
if (!I2->use_empty())
|
|
I2->replaceAllUsesWith(I1);
|
|
I1->intersectOptionalDataWith(I2);
|
|
unsigned KnownIDs[] = {
|
|
LLVMContext::MD_tbaa,
|
|
LLVMContext::MD_range,
|
|
LLVMContext::MD_fpmath,
|
|
LLVMContext::MD_invariant_load,
|
|
LLVMContext::MD_nonnull
|
|
};
|
|
combineMetadata(I1, I2, KnownIDs);
|
|
I2->eraseFromParent();
|
|
Changed = true;
|
|
|
|
I1 = BB1_Itr++;
|
|
I2 = BB2_Itr++;
|
|
// Skip debug info if it is not identical.
|
|
DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
|
|
DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
|
|
if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
|
|
while (isa<DbgInfoIntrinsic>(I1))
|
|
I1 = BB1_Itr++;
|
|
while (isa<DbgInfoIntrinsic>(I2))
|
|
I2 = BB2_Itr++;
|
|
}
|
|
} while (I1->isIdenticalToWhenDefined(I2));
|
|
|
|
return true;
|
|
|
|
HoistTerminator:
|
|
// It may not be possible to hoist an invoke.
|
|
if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
|
|
return Changed;
|
|
|
|
for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
|
|
PHINode *PN;
|
|
for (BasicBlock::iterator BBI = SI->begin();
|
|
(PN = dyn_cast<PHINode>(BBI)); ++BBI) {
|
|
Value *BB1V = PN->getIncomingValueForBlock(BB1);
|
|
Value *BB2V = PN->getIncomingValueForBlock(BB2);
|
|
if (BB1V == BB2V)
|
|
continue;
|
|
|
|
// Check for passingValueIsAlwaysUndefined here because we would rather
|
|
// eliminate undefined control flow then converting it to a select.
|
|
if (passingValueIsAlwaysUndefined(BB1V, PN) ||
|
|
passingValueIsAlwaysUndefined(BB2V, PN))
|
|
return Changed;
|
|
|
|
if (isa<ConstantExpr>(BB1V) && !isSafeToSpeculativelyExecute(BB1V))
|
|
return Changed;
|
|
if (isa<ConstantExpr>(BB2V) && !isSafeToSpeculativelyExecute(BB2V))
|
|
return Changed;
|
|
}
|
|
}
|
|
|
|
// Okay, it is safe to hoist the terminator.
|
|
Instruction *NT = I1->clone();
|
|
BIParent->getInstList().insert(BI, NT);
|
|
if (!NT->getType()->isVoidTy()) {
|
|
I1->replaceAllUsesWith(NT);
|
|
I2->replaceAllUsesWith(NT);
|
|
NT->takeName(I1);
|
|
}
|
|
|
|
IRBuilder<true, NoFolder> Builder(NT);
|
|
// Hoisting one of the terminators from our successor is a great thing.
|
|
// Unfortunately, the successors of the if/else blocks may have PHI nodes in
|
|
// them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
|
|
// nodes, so we insert select instruction to compute the final result.
|
|
std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
|
|
for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
|
|
PHINode *PN;
|
|
for (BasicBlock::iterator BBI = SI->begin();
|
|
(PN = dyn_cast<PHINode>(BBI)); ++BBI) {
|
|
Value *BB1V = PN->getIncomingValueForBlock(BB1);
|
|
Value *BB2V = PN->getIncomingValueForBlock(BB2);
|
|
if (BB1V == BB2V) continue;
|
|
|
|
// These values do not agree. Insert a select instruction before NT
|
|
// that determines the right value.
|
|
SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
|
|
if (!SI)
|
|
SI = cast<SelectInst>
|
|
(Builder.CreateSelect(BI->getCondition(), BB1V, BB2V,
|
|
BB1V->getName()+"."+BB2V->getName()));
|
|
|
|
// Make the PHI node use the select for all incoming values for BB1/BB2
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
|
|
if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
|
|
PN->setIncomingValue(i, SI);
|
|
}
|
|
}
|
|
|
|
// Update any PHI nodes in our new successors.
|
|
for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
|
|
AddPredecessorToBlock(*SI, BIParent, BB1);
|
|
|
|
EraseTerminatorInstAndDCECond(BI);
|
|
return true;
|
|
}
|
|
|
|
/// SinkThenElseCodeToEnd - Given an unconditional branch that goes to BBEnd,
|
|
/// check whether BBEnd has only two predecessors and the other predecessor
|
|
/// ends with an unconditional branch. If it is true, sink any common code
|
|
/// in the two predecessors to BBEnd.
|
|
static bool SinkThenElseCodeToEnd(BranchInst *BI1) {
|
|
assert(BI1->isUnconditional());
|
|
BasicBlock *BB1 = BI1->getParent();
|
|
BasicBlock *BBEnd = BI1->getSuccessor(0);
|
|
|
|
// Check that BBEnd has two predecessors and the other predecessor ends with
|
|
// an unconditional branch.
|
|
pred_iterator PI = pred_begin(BBEnd), PE = pred_end(BBEnd);
|
|
BasicBlock *Pred0 = *PI++;
|
|
if (PI == PE) // Only one predecessor.
|
|
return false;
|
|
BasicBlock *Pred1 = *PI++;
|
|
if (PI != PE) // More than two predecessors.
|
|
return false;
|
|
BasicBlock *BB2 = (Pred0 == BB1) ? Pred1 : Pred0;
|
|
BranchInst *BI2 = dyn_cast<BranchInst>(BB2->getTerminator());
|
|
if (!BI2 || !BI2->isUnconditional())
|
|
return false;
|
|
|
|
// Gather the PHI nodes in BBEnd.
|
|
SmallDenseMap<std::pair<Value *, Value *>, PHINode *> JointValueMap;
|
|
Instruction *FirstNonPhiInBBEnd = nullptr;
|
|
for (BasicBlock::iterator I = BBEnd->begin(), E = BBEnd->end(); I != E; ++I) {
|
|
if (PHINode *PN = dyn_cast<PHINode>(I)) {
|
|
Value *BB1V = PN->getIncomingValueForBlock(BB1);
|
|
Value *BB2V = PN->getIncomingValueForBlock(BB2);
|
|
JointValueMap[std::make_pair(BB1V, BB2V)] = PN;
|
|
} else {
|
|
FirstNonPhiInBBEnd = &*I;
|
|
break;
|
|
}
|
|
}
|
|
if (!FirstNonPhiInBBEnd)
|
|
return false;
|
|
|
|
// This does very trivial matching, with limited scanning, to find identical
|
|
// instructions in the two blocks. We scan backward for obviously identical
|
|
// instructions in an identical order.
|
|
BasicBlock::InstListType::reverse_iterator RI1 = BB1->getInstList().rbegin(),
|
|
RE1 = BB1->getInstList().rend(),
|
|
RI2 = BB2->getInstList().rbegin(),
|
|
RE2 = BB2->getInstList().rend();
|
|
// Skip debug info.
|
|
while (RI1 != RE1 && isa<DbgInfoIntrinsic>(&*RI1)) ++RI1;
|
|
if (RI1 == RE1)
|
|
return false;
|
|
while (RI2 != RE2 && isa<DbgInfoIntrinsic>(&*RI2)) ++RI2;
|
|
if (RI2 == RE2)
|
|
return false;
|
|
// Skip the unconditional branches.
|
|
++RI1;
|
|
++RI2;
|
|
|
|
bool Changed = false;
|
|
while (RI1 != RE1 && RI2 != RE2) {
|
|
// Skip debug info.
|
|
while (RI1 != RE1 && isa<DbgInfoIntrinsic>(&*RI1)) ++RI1;
|
|
if (RI1 == RE1)
|
|
return Changed;
|
|
while (RI2 != RE2 && isa<DbgInfoIntrinsic>(&*RI2)) ++RI2;
|
|
if (RI2 == RE2)
|
|
return Changed;
|
|
|
|
Instruction *I1 = &*RI1, *I2 = &*RI2;
|
|
auto InstPair = std::make_pair(I1, I2);
|
|
// I1 and I2 should have a single use in the same PHI node, and they
|
|
// perform the same operation.
|
|
// Cannot move control-flow-involving, volatile loads, vaarg, etc.
|
|
if (isa<PHINode>(I1) || isa<PHINode>(I2) ||
|
|
isa<TerminatorInst>(I1) || isa<TerminatorInst>(I2) ||
|
|
isa<LandingPadInst>(I1) || isa<LandingPadInst>(I2) ||
|
|
isa<AllocaInst>(I1) || isa<AllocaInst>(I2) ||
|
|
I1->mayHaveSideEffects() || I2->mayHaveSideEffects() ||
|
|
I1->mayReadOrWriteMemory() || I2->mayReadOrWriteMemory() ||
|
|
!I1->hasOneUse() || !I2->hasOneUse() ||
|
|
!JointValueMap.count(InstPair))
|
|
return Changed;
|
|
|
|
// Check whether we should swap the operands of ICmpInst.
|
|
// TODO: Add support of communativity.
|
|
ICmpInst *ICmp1 = dyn_cast<ICmpInst>(I1), *ICmp2 = dyn_cast<ICmpInst>(I2);
|
|
bool SwapOpnds = false;
|
|
if (ICmp1 && ICmp2 &&
|
|
ICmp1->getOperand(0) != ICmp2->getOperand(0) &&
|
|
ICmp1->getOperand(1) != ICmp2->getOperand(1) &&
|
|
(ICmp1->getOperand(0) == ICmp2->getOperand(1) ||
|
|
ICmp1->getOperand(1) == ICmp2->getOperand(0))) {
|
|
ICmp2->swapOperands();
|
|
SwapOpnds = true;
|
|
}
|
|
if (!I1->isSameOperationAs(I2)) {
|
|
if (SwapOpnds)
|
|
ICmp2->swapOperands();
|
|
return Changed;
|
|
}
|
|
|
|
// The operands should be either the same or they need to be generated
|
|
// with a PHI node after sinking. We only handle the case where there is
|
|
// a single pair of different operands.
|
|
Value *DifferentOp1 = nullptr, *DifferentOp2 = nullptr;
|
|
unsigned Op1Idx = ~0U;
|
|
for (unsigned I = 0, E = I1->getNumOperands(); I != E; ++I) {
|
|
if (I1->getOperand(I) == I2->getOperand(I))
|
|
continue;
|
|
// Early exit if we have more-than one pair of different operands or if
|
|
// we need a PHI node to replace a constant.
|
|
if (Op1Idx != ~0U ||
|
|
isa<Constant>(I1->getOperand(I)) ||
|
|
isa<Constant>(I2->getOperand(I))) {
|
|
// If we can't sink the instructions, undo the swapping.
|
|
if (SwapOpnds)
|
|
ICmp2->swapOperands();
|
|
return Changed;
|
|
}
|
|
DifferentOp1 = I1->getOperand(I);
|
|
Op1Idx = I;
|
|
DifferentOp2 = I2->getOperand(I);
|
|
}
|
|
|
|
DEBUG(dbgs() << "SINK common instructions " << *I1 << "\n");
|
|
DEBUG(dbgs() << " " << *I2 << "\n");
|
|
|
|
// We insert the pair of different operands to JointValueMap and
|
|
// remove (I1, I2) from JointValueMap.
|
|
if (Op1Idx != ~0U) {
|
|
auto &NewPN = JointValueMap[std::make_pair(DifferentOp1, DifferentOp2)];
|
|
if (!NewPN) {
|
|
NewPN =
|
|
PHINode::Create(DifferentOp1->getType(), 2,
|
|
DifferentOp1->getName() + ".sink", BBEnd->begin());
|
|
NewPN->addIncoming(DifferentOp1, BB1);
|
|
NewPN->addIncoming(DifferentOp2, BB2);
|
|
DEBUG(dbgs() << "Create PHI node " << *NewPN << "\n";);
|
|
}
|
|
// I1 should use NewPN instead of DifferentOp1.
|
|
I1->setOperand(Op1Idx, NewPN);
|
|
}
|
|
PHINode *OldPN = JointValueMap[InstPair];
|
|
JointValueMap.erase(InstPair);
|
|
|
|
// We need to update RE1 and RE2 if we are going to sink the first
|
|
// instruction in the basic block down.
|
|
bool UpdateRE1 = (I1 == BB1->begin()), UpdateRE2 = (I2 == BB2->begin());
|
|
// Sink the instruction.
|
|
BBEnd->getInstList().splice(FirstNonPhiInBBEnd, BB1->getInstList(), I1);
|
|
if (!OldPN->use_empty())
|
|
OldPN->replaceAllUsesWith(I1);
|
|
OldPN->eraseFromParent();
|
|
|
|
if (!I2->use_empty())
|
|
I2->replaceAllUsesWith(I1);
|
|
I1->intersectOptionalDataWith(I2);
|
|
// TODO: Use combineMetadata here to preserve what metadata we can
|
|
// (analogous to the hoisting case above).
|
|
I2->eraseFromParent();
|
|
|
|
if (UpdateRE1)
|
|
RE1 = BB1->getInstList().rend();
|
|
if (UpdateRE2)
|
|
RE2 = BB2->getInstList().rend();
|
|
FirstNonPhiInBBEnd = I1;
|
|
NumSinkCommons++;
|
|
Changed = true;
|
|
}
|
|
return Changed;
|
|
}
|
|
|
|
/// \brief Determine if we can hoist sink a sole store instruction out of a
|
|
/// conditional block.
|
|
///
|
|
/// We are looking for code like the following:
|
|
/// BrBB:
|
|
/// store i32 %add, i32* %arrayidx2
|
|
/// ... // No other stores or function calls (we could be calling a memory
|
|
/// ... // function).
|
|
/// %cmp = icmp ult %x, %y
|
|
/// br i1 %cmp, label %EndBB, label %ThenBB
|
|
/// ThenBB:
|
|
/// store i32 %add5, i32* %arrayidx2
|
|
/// br label EndBB
|
|
/// EndBB:
|
|
/// ...
|
|
/// We are going to transform this into:
|
|
/// BrBB:
|
|
/// store i32 %add, i32* %arrayidx2
|
|
/// ... //
|
|
/// %cmp = icmp ult %x, %y
|
|
/// %add.add5 = select i1 %cmp, i32 %add, %add5
|
|
/// store i32 %add.add5, i32* %arrayidx2
|
|
/// ...
|
|
///
|
|
/// \return The pointer to the value of the previous store if the store can be
|
|
/// hoisted into the predecessor block. 0 otherwise.
|
|
static Value *isSafeToSpeculateStore(Instruction *I, BasicBlock *BrBB,
|
|
BasicBlock *StoreBB, BasicBlock *EndBB) {
|
|
StoreInst *StoreToHoist = dyn_cast<StoreInst>(I);
|
|
if (!StoreToHoist)
|
|
return nullptr;
|
|
|
|
// Volatile or atomic.
|
|
if (!StoreToHoist->isSimple())
|
|
return nullptr;
|
|
|
|
Value *StorePtr = StoreToHoist->getPointerOperand();
|
|
|
|
// Look for a store to the same pointer in BrBB.
|
|
unsigned MaxNumInstToLookAt = 10;
|
|
for (BasicBlock::reverse_iterator RI = BrBB->rbegin(),
|
|
RE = BrBB->rend(); RI != RE && (--MaxNumInstToLookAt); ++RI) {
|
|
Instruction *CurI = &*RI;
|
|
|
|
// Could be calling an instruction that effects memory like free().
|
|
if (CurI->mayHaveSideEffects() && !isa<StoreInst>(CurI))
|
|
return nullptr;
|
|
|
|
StoreInst *SI = dyn_cast<StoreInst>(CurI);
|
|
// Found the previous store make sure it stores to the same location.
|
|
if (SI && SI->getPointerOperand() == StorePtr)
|
|
// Found the previous store, return its value operand.
|
|
return SI->getValueOperand();
|
|
else if (SI)
|
|
return nullptr; // Unknown store.
|
|
}
|
|
|
|
return nullptr;
|
|
}
|
|
|
|
/// \brief Speculate a conditional basic block flattening the CFG.
|
|
///
|
|
/// Note that this is a very risky transform currently. Speculating
|
|
/// instructions like this is most often not desirable. Instead, there is an MI
|
|
/// pass which can do it with full awareness of the resource constraints.
|
|
/// However, some cases are "obvious" and we should do directly. An example of
|
|
/// this is speculating a single, reasonably cheap instruction.
|
|
///
|
|
/// There is only one distinct advantage to flattening the CFG at the IR level:
|
|
/// it makes very common but simplistic optimizations such as are common in
|
|
/// instcombine and the DAG combiner more powerful by removing CFG edges and
|
|
/// modeling their effects with easier to reason about SSA value graphs.
|
|
///
|
|
///
|
|
/// An illustration of this transform is turning this IR:
|
|
/// \code
|
|
/// BB:
|
|
/// %cmp = icmp ult %x, %y
|
|
/// br i1 %cmp, label %EndBB, label %ThenBB
|
|
/// ThenBB:
|
|
/// %sub = sub %x, %y
|
|
/// br label BB2
|
|
/// EndBB:
|
|
/// %phi = phi [ %sub, %ThenBB ], [ 0, %EndBB ]
|
|
/// ...
|
|
/// \endcode
|
|
///
|
|
/// Into this IR:
|
|
/// \code
|
|
/// BB:
|
|
/// %cmp = icmp ult %x, %y
|
|
/// %sub = sub %x, %y
|
|
/// %cond = select i1 %cmp, 0, %sub
|
|
/// ...
|
|
/// \endcode
|
|
///
|
|
/// \returns true if the conditional block is removed.
|
|
static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
|
|
const TargetTransformInfo &TTI) {
|
|
// Be conservative for now. FP select instruction can often be expensive.
|
|
Value *BrCond = BI->getCondition();
|
|
if (isa<FCmpInst>(BrCond))
|
|
return false;
|
|
|
|
BasicBlock *BB = BI->getParent();
|
|
BasicBlock *EndBB = ThenBB->getTerminator()->getSuccessor(0);
|
|
|
|
// If ThenBB is actually on the false edge of the conditional branch, remember
|
|
// to swap the select operands later.
|
|
bool Invert = false;
|
|
if (ThenBB != BI->getSuccessor(0)) {
|
|
assert(ThenBB == BI->getSuccessor(1) && "No edge from 'if' block?");
|
|
Invert = true;
|
|
}
|
|
assert(EndBB == BI->getSuccessor(!Invert) && "No edge from to end block");
|
|
|
|
// Keep a count of how many times instructions are used within CondBB when
|
|
// they are candidates for sinking into CondBB. Specifically:
|
|
// - They are defined in BB, and
|
|
// - They have no side effects, and
|
|
// - All of their uses are in CondBB.
|
|
SmallDenseMap<Instruction *, unsigned, 4> SinkCandidateUseCounts;
|
|
|
|
unsigned SpeculationCost = 0;
|
|
Value *SpeculatedStoreValue = nullptr;
|
|
StoreInst *SpeculatedStore = nullptr;
|
|
for (BasicBlock::iterator BBI = ThenBB->begin(),
|
|
BBE = std::prev(ThenBB->end());
|
|
BBI != BBE; ++BBI) {
|
|
Instruction *I = BBI;
|
|
// Skip debug info.
|
|
if (isa<DbgInfoIntrinsic>(I))
|
|
continue;
|
|
|
|
// Only speculatively execute a single instruction (not counting the
|
|
// terminator) for now.
|
|
++SpeculationCost;
|
|
if (SpeculationCost > 1)
|
|
return false;
|
|
|
|
// Don't hoist the instruction if it's unsafe or expensive.
|
|
if (!isSafeToSpeculativelyExecute(I) &&
|
|
!(HoistCondStores && (SpeculatedStoreValue = isSafeToSpeculateStore(
|
|
I, BB, ThenBB, EndBB))))
|
|
return false;
|
|
if (!SpeculatedStoreValue &&
|
|
ComputeSpeculationCost(I, TTI) >
|
|
PHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic)
|
|
return false;
|
|
|
|
// Store the store speculation candidate.
|
|
if (SpeculatedStoreValue)
|
|
SpeculatedStore = cast<StoreInst>(I);
|
|
|
|
// Do not hoist the instruction if any of its operands are defined but not
|
|
// used in BB. The transformation will prevent the operand from
|
|
// being sunk into the use block.
|
|
for (User::op_iterator i = I->op_begin(), e = I->op_end();
|
|
i != e; ++i) {
|
|
Instruction *OpI = dyn_cast<Instruction>(*i);
|
|
if (!OpI || OpI->getParent() != BB ||
|
|
OpI->mayHaveSideEffects())
|
|
continue; // Not a candidate for sinking.
|
|
|
|
++SinkCandidateUseCounts[OpI];
|
|
}
|
|
}
|
|
|
|
// Consider any sink candidates which are only used in CondBB as costs for
|
|
// speculation. Note, while we iterate over a DenseMap here, we are summing
|
|
// and so iteration order isn't significant.
|
|
for (SmallDenseMap<Instruction *, unsigned, 4>::iterator I =
|
|
SinkCandidateUseCounts.begin(), E = SinkCandidateUseCounts.end();
|
|
I != E; ++I)
|
|
if (I->first->getNumUses() == I->second) {
|
|
++SpeculationCost;
|
|
if (SpeculationCost > 1)
|
|
return false;
|
|
}
|
|
|
|
// Check that the PHI nodes can be converted to selects.
|
|
bool HaveRewritablePHIs = false;
|
|
for (BasicBlock::iterator I = EndBB->begin();
|
|
PHINode *PN = dyn_cast<PHINode>(I); ++I) {
|
|
Value *OrigV = PN->getIncomingValueForBlock(BB);
|
|
Value *ThenV = PN->getIncomingValueForBlock(ThenBB);
|
|
|
|
// FIXME: Try to remove some of the duplication with HoistThenElseCodeToIf.
|
|
// Skip PHIs which are trivial.
|
|
if (ThenV == OrigV)
|
|
continue;
|
|
|
|
// Don't convert to selects if we could remove undefined behavior instead.
|
|
if (passingValueIsAlwaysUndefined(OrigV, PN) ||
|
|
passingValueIsAlwaysUndefined(ThenV, PN))
|
|
return false;
|
|
|
|
HaveRewritablePHIs = true;
|
|
ConstantExpr *OrigCE = dyn_cast<ConstantExpr>(OrigV);
|
|
ConstantExpr *ThenCE = dyn_cast<ConstantExpr>(ThenV);
|
|
if (!OrigCE && !ThenCE)
|
|
continue; // Known safe and cheap.
|
|
|
|
if ((ThenCE && !isSafeToSpeculativelyExecute(ThenCE)) ||
|
|
(OrigCE && !isSafeToSpeculativelyExecute(OrigCE)))
|
|
return false;
|
|
unsigned OrigCost = OrigCE ? ComputeSpeculationCost(OrigCE, TTI) : 0;
|
|
unsigned ThenCost = ThenCE ? ComputeSpeculationCost(ThenCE, TTI) : 0;
|
|
unsigned MaxCost = 2 * PHINodeFoldingThreshold *
|
|
TargetTransformInfo::TCC_Basic;
|
|
if (OrigCost + ThenCost > MaxCost)
|
|
return false;
|
|
|
|
// Account for the cost of an unfolded ConstantExpr which could end up
|
|
// getting expanded into Instructions.
|
|
// FIXME: This doesn't account for how many operations are combined in the
|
|
// constant expression.
|
|
++SpeculationCost;
|
|
if (SpeculationCost > 1)
|
|
return false;
|
|
}
|
|
|
|
// If there are no PHIs to process, bail early. This helps ensure idempotence
|
|
// as well.
|
|
if (!HaveRewritablePHIs && !(HoistCondStores && SpeculatedStoreValue))
|
|
return false;
|
|
|
|
// If we get here, we can hoist the instruction and if-convert.
|
|
DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *ThenBB << "\n";);
|
|
|
|
// Insert a select of the value of the speculated store.
|
|
if (SpeculatedStoreValue) {
|
|
IRBuilder<true, NoFolder> Builder(BI);
|
|
Value *TrueV = SpeculatedStore->getValueOperand();
|
|
Value *FalseV = SpeculatedStoreValue;
|
|
if (Invert)
|
|
std::swap(TrueV, FalseV);
|
|
Value *S = Builder.CreateSelect(BrCond, TrueV, FalseV, TrueV->getName() +
|
|
"." + FalseV->getName());
|
|
SpeculatedStore->setOperand(0, S);
|
|
}
|
|
|
|
// Hoist the instructions.
|
|
BB->getInstList().splice(BI, ThenBB->getInstList(), ThenBB->begin(),
|
|
std::prev(ThenBB->end()));
|
|
|
|
// Insert selects and rewrite the PHI operands.
|
|
IRBuilder<true, NoFolder> Builder(BI);
|
|
for (BasicBlock::iterator I = EndBB->begin();
|
|
PHINode *PN = dyn_cast<PHINode>(I); ++I) {
|
|
unsigned OrigI = PN->getBasicBlockIndex(BB);
|
|
unsigned ThenI = PN->getBasicBlockIndex(ThenBB);
|
|
Value *OrigV = PN->getIncomingValue(OrigI);
|
|
Value *ThenV = PN->getIncomingValue(ThenI);
|
|
|
|
// Skip PHIs which are trivial.
|
|
if (OrigV == ThenV)
|
|
continue;
|
|
|
|
// Create a select whose true value is the speculatively executed value and
|
|
// false value is the preexisting value. Swap them if the branch
|
|
// destinations were inverted.
|
|
Value *TrueV = ThenV, *FalseV = OrigV;
|
|
if (Invert)
|
|
std::swap(TrueV, FalseV);
|
|
Value *V = Builder.CreateSelect(BrCond, TrueV, FalseV,
|
|
TrueV->getName() + "." + FalseV->getName());
|
|
PN->setIncomingValue(OrigI, V);
|
|
PN->setIncomingValue(ThenI, V);
|
|
}
|
|
|
|
++NumSpeculations;
|
|
return true;
|
|
}
|
|
|
|
/// \returns True if this block contains a CallInst with the NoDuplicate
|
|
/// attribute.
|
|
static bool HasNoDuplicateCall(const BasicBlock *BB) {
|
|
for (BasicBlock::const_iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
|
|
const CallInst *CI = dyn_cast<CallInst>(I);
|
|
if (!CI)
|
|
continue;
|
|
if (CI->cannotDuplicate())
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
|
|
/// across this block.
|
|
static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
|
|
BranchInst *BI = cast<BranchInst>(BB->getTerminator());
|
|
unsigned Size = 0;
|
|
|
|
for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
|
|
if (isa<DbgInfoIntrinsic>(BBI))
|
|
continue;
|
|
if (Size > 10) return false; // Don't clone large BB's.
|
|
++Size;
|
|
|
|
// We can only support instructions that do not define values that are
|
|
// live outside of the current basic block.
|
|
for (User *U : BBI->users()) {
|
|
Instruction *UI = cast<Instruction>(U);
|
|
if (UI->getParent() != BB || isa<PHINode>(UI)) return false;
|
|
}
|
|
|
|
// Looks ok, continue checking.
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
/// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
|
|
/// that is defined in the same block as the branch and if any PHI entries are
|
|
/// constants, thread edges corresponding to that entry to be branches to their
|
|
/// ultimate destination.
|
|
static bool FoldCondBranchOnPHI(BranchInst *BI, const DataLayout &DL) {
|
|
BasicBlock *BB = BI->getParent();
|
|
PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
|
|
// NOTE: we currently cannot transform this case if the PHI node is used
|
|
// outside of the block.
|
|
if (!PN || PN->getParent() != BB || !PN->hasOneUse())
|
|
return false;
|
|
|
|
// Degenerate case of a single entry PHI.
|
|
if (PN->getNumIncomingValues() == 1) {
|
|
FoldSingleEntryPHINodes(PN->getParent());
|
|
return true;
|
|
}
|
|
|
|
// Now we know that this block has multiple preds and two succs.
|
|
if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
|
|
|
|
if (HasNoDuplicateCall(BB)) return false;
|
|
|
|
// Okay, this is a simple enough basic block. See if any phi values are
|
|
// constants.
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
|
|
if (!CB || !CB->getType()->isIntegerTy(1)) continue;
|
|
|
|
// Okay, we now know that all edges from PredBB should be revectored to
|
|
// branch to RealDest.
|
|
BasicBlock *PredBB = PN->getIncomingBlock(i);
|
|
BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
|
|
|
|
if (RealDest == BB) continue; // Skip self loops.
|
|
// Skip if the predecessor's terminator is an indirect branch.
|
|
if (isa<IndirectBrInst>(PredBB->getTerminator())) continue;
|
|
|
|
// The dest block might have PHI nodes, other predecessors and other
|
|
// difficult cases. Instead of being smart about this, just insert a new
|
|
// block that jumps to the destination block, effectively splitting
|
|
// the edge we are about to create.
|
|
BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
|
|
RealDest->getName()+".critedge",
|
|
RealDest->getParent(), RealDest);
|
|
BranchInst::Create(RealDest, EdgeBB);
|
|
|
|
// Update PHI nodes.
|
|
AddPredecessorToBlock(RealDest, EdgeBB, BB);
|
|
|
|
// BB may have instructions that are being threaded over. Clone these
|
|
// instructions into EdgeBB. We know that there will be no uses of the
|
|
// cloned instructions outside of EdgeBB.
|
|
BasicBlock::iterator InsertPt = EdgeBB->begin();
|
|
DenseMap<Value*, Value*> TranslateMap; // Track translated values.
|
|
for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
|
|
if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
|
|
TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
|
|
continue;
|
|
}
|
|
// Clone the instruction.
|
|
Instruction *N = BBI->clone();
|
|
if (BBI->hasName()) N->setName(BBI->getName()+".c");
|
|
|
|
// Update operands due to translation.
|
|
for (User::op_iterator i = N->op_begin(), e = N->op_end();
|
|
i != e; ++i) {
|
|
DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
|
|
if (PI != TranslateMap.end())
|
|
*i = PI->second;
|
|
}
|
|
|
|
// Check for trivial simplification.
|
|
if (Value *V = SimplifyInstruction(N, DL)) {
|
|
TranslateMap[BBI] = V;
|
|
delete N; // Instruction folded away, don't need actual inst
|
|
} else {
|
|
// Insert the new instruction into its new home.
|
|
EdgeBB->getInstList().insert(InsertPt, N);
|
|
if (!BBI->use_empty())
|
|
TranslateMap[BBI] = N;
|
|
}
|
|
}
|
|
|
|
// Loop over all of the edges from PredBB to BB, changing them to branch
|
|
// to EdgeBB instead.
|
|
TerminatorInst *PredBBTI = PredBB->getTerminator();
|
|
for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
|
|
if (PredBBTI->getSuccessor(i) == BB) {
|
|
BB->removePredecessor(PredBB);
|
|
PredBBTI->setSuccessor(i, EdgeBB);
|
|
}
|
|
|
|
// Recurse, simplifying any other constants.
|
|
return FoldCondBranchOnPHI(BI, DL) | true;
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
/// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
|
|
/// PHI node, see if we can eliminate it.
|
|
static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
|
|
const DataLayout &DL) {
|
|
// Ok, this is a two entry PHI node. Check to see if this is a simple "if
|
|
// statement", which has a very simple dominance structure. Basically, we
|
|
// are trying to find the condition that is being branched on, which
|
|
// subsequently causes this merge to happen. We really want control
|
|
// dependence information for this check, but simplifycfg can't keep it up
|
|
// to date, and this catches most of the cases we care about anyway.
|
|
BasicBlock *BB = PN->getParent();
|
|
BasicBlock *IfTrue, *IfFalse;
|
|
Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
|
|
if (!IfCond ||
|
|
// Don't bother if the branch will be constant folded trivially.
|
|
isa<ConstantInt>(IfCond))
|
|
return false;
|
|
|
|
// Okay, we found that we can merge this two-entry phi node into a select.
|
|
// Doing so would require us to fold *all* two entry phi nodes in this block.
|
|
// At some point this becomes non-profitable (particularly if the target
|
|
// doesn't support cmov's). Only do this transformation if there are two or
|
|
// fewer PHI nodes in this block.
|
|
unsigned NumPhis = 0;
|
|
for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
|
|
if (NumPhis > 2)
|
|
return false;
|
|
|
|
// Loop over the PHI's seeing if we can promote them all to select
|
|
// instructions. While we are at it, keep track of the instructions
|
|
// that need to be moved to the dominating block.
|
|
SmallPtrSet<Instruction*, 4> AggressiveInsts;
|
|
unsigned MaxCostVal0 = PHINodeFoldingThreshold,
|
|
MaxCostVal1 = PHINodeFoldingThreshold;
|
|
MaxCostVal0 *= TargetTransformInfo::TCC_Basic;
|
|
MaxCostVal1 *= TargetTransformInfo::TCC_Basic;
|
|
|
|
for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
|
|
PHINode *PN = cast<PHINode>(II++);
|
|
if (Value *V = SimplifyInstruction(PN, DL)) {
|
|
PN->replaceAllUsesWith(V);
|
|
PN->eraseFromParent();
|
|
continue;
|
|
}
|
|
|
|
if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
|
|
MaxCostVal0, TTI) ||
|
|
!DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
|
|
MaxCostVal1, TTI))
|
|
return false;
|
|
}
|
|
|
|
// If we folded the first phi, PN dangles at this point. Refresh it. If
|
|
// we ran out of PHIs then we simplified them all.
|
|
PN = dyn_cast<PHINode>(BB->begin());
|
|
if (!PN) return true;
|
|
|
|
// Don't fold i1 branches on PHIs which contain binary operators. These can
|
|
// often be turned into switches and other things.
|
|
if (PN->getType()->isIntegerTy(1) &&
|
|
(isa<BinaryOperator>(PN->getIncomingValue(0)) ||
|
|
isa<BinaryOperator>(PN->getIncomingValue(1)) ||
|
|
isa<BinaryOperator>(IfCond)))
|
|
return false;
|
|
|
|
// If we all PHI nodes are promotable, check to make sure that all
|
|
// instructions in the predecessor blocks can be promoted as well. If
|
|
// not, we won't be able to get rid of the control flow, so it's not
|
|
// worth promoting to select instructions.
|
|
BasicBlock *DomBlock = nullptr;
|
|
BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
|
|
BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
|
|
if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
|
|
IfBlock1 = nullptr;
|
|
} else {
|
|
DomBlock = *pred_begin(IfBlock1);
|
|
for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
|
|
if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
|
|
// This is not an aggressive instruction that we can promote.
|
|
// Because of this, we won't be able to get rid of the control
|
|
// flow, so the xform is not worth it.
|
|
return false;
|
|
}
|
|
}
|
|
|
|
if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
|
|
IfBlock2 = nullptr;
|
|
} else {
|
|
DomBlock = *pred_begin(IfBlock2);
|
|
for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
|
|
if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
|
|
// This is not an aggressive instruction that we can promote.
|
|
// Because of this, we won't be able to get rid of the control
|
|
// flow, so the xform is not worth it.
|
|
return false;
|
|
}
|
|
}
|
|
|
|
DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
|
|
<< IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
|
|
|
|
// If we can still promote the PHI nodes after this gauntlet of tests,
|
|
// do all of the PHI's now.
|
|
Instruction *InsertPt = DomBlock->getTerminator();
|
|
IRBuilder<true, NoFolder> Builder(InsertPt);
|
|
|
|
// Move all 'aggressive' instructions, which are defined in the
|
|
// conditional parts of the if's up to the dominating block.
|
|
if (IfBlock1)
|
|
DomBlock->getInstList().splice(InsertPt,
|
|
IfBlock1->getInstList(), IfBlock1->begin(),
|
|
IfBlock1->getTerminator());
|
|
if (IfBlock2)
|
|
DomBlock->getInstList().splice(InsertPt,
|
|
IfBlock2->getInstList(), IfBlock2->begin(),
|
|
IfBlock2->getTerminator());
|
|
|
|
while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
|
|
// Change the PHI node into a select instruction.
|
|
Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
|
|
Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
|
|
|
|
SelectInst *NV =
|
|
cast<SelectInst>(Builder.CreateSelect(IfCond, TrueVal, FalseVal, ""));
|
|
PN->replaceAllUsesWith(NV);
|
|
NV->takeName(PN);
|
|
PN->eraseFromParent();
|
|
}
|
|
|
|
// At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
|
|
// has been flattened. Change DomBlock to jump directly to our new block to
|
|
// avoid other simplifycfg's kicking in on the diamond.
|
|
TerminatorInst *OldTI = DomBlock->getTerminator();
|
|
Builder.SetInsertPoint(OldTI);
|
|
Builder.CreateBr(BB);
|
|
OldTI->eraseFromParent();
|
|
return true;
|
|
}
|
|
|
|
/// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
|
|
/// to two returning blocks, try to merge them together into one return,
|
|
/// introducing a select if the return values disagree.
|
|
static bool SimplifyCondBranchToTwoReturns(BranchInst *BI,
|
|
IRBuilder<> &Builder) {
|
|
assert(BI->isConditional() && "Must be a conditional branch");
|
|
BasicBlock *TrueSucc = BI->getSuccessor(0);
|
|
BasicBlock *FalseSucc = BI->getSuccessor(1);
|
|
ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
|
|
ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
|
|
|
|
// Check to ensure both blocks are empty (just a return) or optionally empty
|
|
// with PHI nodes. If there are other instructions, merging would cause extra
|
|
// computation on one path or the other.
|
|
if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
|
|
return false;
|
|
if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
|
|
return false;
|
|
|
|
Builder.SetInsertPoint(BI);
|
|
// Okay, we found a branch that is going to two return nodes. If
|
|
// there is no return value for this function, just change the
|
|
// branch into a return.
|
|
if (FalseRet->getNumOperands() == 0) {
|
|
TrueSucc->removePredecessor(BI->getParent());
|
|
FalseSucc->removePredecessor(BI->getParent());
|
|
Builder.CreateRetVoid();
|
|
EraseTerminatorInstAndDCECond(BI);
|
|
return true;
|
|
}
|
|
|
|
// Otherwise, figure out what the true and false return values are
|
|
// so we can insert a new select instruction.
|
|
Value *TrueValue = TrueRet->getReturnValue();
|
|
Value *FalseValue = FalseRet->getReturnValue();
|
|
|
|
// Unwrap any PHI nodes in the return blocks.
|
|
if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
|
|
if (TVPN->getParent() == TrueSucc)
|
|
TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
|
|
if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
|
|
if (FVPN->getParent() == FalseSucc)
|
|
FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
|
|
|
|
// In order for this transformation to be safe, we must be able to
|
|
// unconditionally execute both operands to the return. This is
|
|
// normally the case, but we could have a potentially-trapping
|
|
// constant expression that prevents this transformation from being
|
|
// safe.
|
|
if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
|
|
if (TCV->canTrap())
|
|
return false;
|
|
if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
|
|
if (FCV->canTrap())
|
|
return false;
|
|
|
|
// Okay, we collected all the mapped values and checked them for sanity, and
|
|
// defined to really do this transformation. First, update the CFG.
|
|
TrueSucc->removePredecessor(BI->getParent());
|
|
FalseSucc->removePredecessor(BI->getParent());
|
|
|
|
// Insert select instructions where needed.
|
|
Value *BrCond = BI->getCondition();
|
|
if (TrueValue) {
|
|
// Insert a select if the results differ.
|
|
if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
|
|
} else if (isa<UndefValue>(TrueValue)) {
|
|
TrueValue = FalseValue;
|
|
} else {
|
|
TrueValue = Builder.CreateSelect(BrCond, TrueValue,
|
|
FalseValue, "retval");
|
|
}
|
|
}
|
|
|
|
Value *RI = !TrueValue ?
|
|
Builder.CreateRetVoid() : Builder.CreateRet(TrueValue);
|
|
|
|
(void) RI;
|
|
|
|
DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
|
|
<< "\n " << *BI << "NewRet = " << *RI
|
|
<< "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
|
|
|
|
EraseTerminatorInstAndDCECond(BI);
|
|
|
|
return true;
|
|
}
|
|
|
|
/// ExtractBranchMetadata - Given a conditional BranchInstruction, retrieve the
|
|
/// probabilities of the branch taking each edge. Fills in the two APInt
|
|
/// parameters and return true, or returns false if no or invalid metadata was
|
|
/// found.
|
|
static bool ExtractBranchMetadata(BranchInst *BI,
|
|
uint64_t &ProbTrue, uint64_t &ProbFalse) {
|
|
assert(BI->isConditional() &&
|
|
"Looking for probabilities on unconditional branch?");
|
|
MDNode *ProfileData = BI->getMetadata(LLVMContext::MD_prof);
|
|
if (!ProfileData || ProfileData->getNumOperands() != 3) return false;
|
|
ConstantInt *CITrue =
|
|
mdconst::dyn_extract<ConstantInt>(ProfileData->getOperand(1));
|
|
ConstantInt *CIFalse =
|
|
mdconst::dyn_extract<ConstantInt>(ProfileData->getOperand(2));
|
|
if (!CITrue || !CIFalse) return false;
|
|
ProbTrue = CITrue->getValue().getZExtValue();
|
|
ProbFalse = CIFalse->getValue().getZExtValue();
|
|
return true;
|
|
}
|
|
|
|
/// checkCSEInPredecessor - Return true if the given instruction is available
|
|
/// in its predecessor block. If yes, the instruction will be removed.
|
|
///
|
|
static bool checkCSEInPredecessor(Instruction *Inst, BasicBlock *PB) {
|
|
if (!isa<BinaryOperator>(Inst) && !isa<CmpInst>(Inst))
|
|
return false;
|
|
for (BasicBlock::iterator I = PB->begin(), E = PB->end(); I != E; I++) {
|
|
Instruction *PBI = &*I;
|
|
// Check whether Inst and PBI generate the same value.
|
|
if (Inst->isIdenticalTo(PBI)) {
|
|
Inst->replaceAllUsesWith(PBI);
|
|
Inst->eraseFromParent();
|
|
return true;
|
|
}
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/// FoldBranchToCommonDest - If this basic block is simple enough, and if a
|
|
/// predecessor branches to us and one of our successors, fold the block into
|
|
/// the predecessor and use logical operations to pick the right destination.
|
|
bool llvm::FoldBranchToCommonDest(BranchInst *BI, unsigned BonusInstThreshold) {
|
|
BasicBlock *BB = BI->getParent();
|
|
|
|
Instruction *Cond = nullptr;
|
|
if (BI->isConditional())
|
|
Cond = dyn_cast<Instruction>(BI->getCondition());
|
|
else {
|
|
// For unconditional branch, check for a simple CFG pattern, where
|
|
// BB has a single predecessor and BB's successor is also its predecessor's
|
|
// successor. If such pattern exisits, check for CSE between BB and its
|
|
// predecessor.
|
|
if (BasicBlock *PB = BB->getSinglePredecessor())
|
|
if (BranchInst *PBI = dyn_cast<BranchInst>(PB->getTerminator()))
|
|
if (PBI->isConditional() &&
|
|
(BI->getSuccessor(0) == PBI->getSuccessor(0) ||
|
|
BI->getSuccessor(0) == PBI->getSuccessor(1))) {
|
|
for (BasicBlock::iterator I = BB->begin(), E = BB->end();
|
|
I != E; ) {
|
|
Instruction *Curr = I++;
|
|
if (isa<CmpInst>(Curr)) {
|
|
Cond = Curr;
|
|
break;
|
|
}
|
|
// Quit if we can't remove this instruction.
|
|
if (!checkCSEInPredecessor(Curr, PB))
|
|
return false;
|
|
}
|
|
}
|
|
|
|
if (!Cond)
|
|
return false;
|
|
}
|
|
|
|
if (!Cond || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
|
|
Cond->getParent() != BB || !Cond->hasOneUse())
|
|
return false;
|
|
|
|
// Make sure the instruction after the condition is the cond branch.
|
|
BasicBlock::iterator CondIt = Cond; ++CondIt;
|
|
|
|
// Ignore dbg intrinsics.
|
|
while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt;
|
|
|
|
if (&*CondIt != BI)
|
|
return false;
|
|
|
|
// Only allow this transformation if computing the condition doesn't involve
|
|
// too many instructions and these involved instructions can be executed
|
|
// unconditionally. We denote all involved instructions except the condition
|
|
// as "bonus instructions", and only allow this transformation when the
|
|
// number of the bonus instructions does not exceed a certain threshold.
|
|
unsigned NumBonusInsts = 0;
|
|
for (auto I = BB->begin(); Cond != I; ++I) {
|
|
// Ignore dbg intrinsics.
|
|
if (isa<DbgInfoIntrinsic>(I))
|
|
continue;
|
|
if (!I->hasOneUse() || !isSafeToSpeculativelyExecute(I))
|
|
return false;
|
|
// I has only one use and can be executed unconditionally.
|
|
Instruction *User = dyn_cast<Instruction>(I->user_back());
|
|
if (User == nullptr || User->getParent() != BB)
|
|
return false;
|
|
// I is used in the same BB. Since BI uses Cond and doesn't have more slots
|
|
// to use any other instruction, User must be an instruction between next(I)
|
|
// and Cond.
|
|
++NumBonusInsts;
|
|
// Early exits once we reach the limit.
|
|
if (NumBonusInsts > BonusInstThreshold)
|
|
return false;
|
|
}
|
|
|
|
// Cond is known to be a compare or binary operator. Check to make sure that
|
|
// neither operand is a potentially-trapping constant expression.
|
|
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
|
|
if (CE->canTrap())
|
|
return false;
|
|
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
|
|
if (CE->canTrap())
|
|
return false;
|
|
|
|
// Finally, don't infinitely unroll conditional loops.
|
|
BasicBlock *TrueDest = BI->getSuccessor(0);
|
|
BasicBlock *FalseDest = (BI->isConditional()) ? BI->getSuccessor(1) : nullptr;
|
|
if (TrueDest == BB || FalseDest == BB)
|
|
return false;
|
|
|
|
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
|
|
BasicBlock *PredBlock = *PI;
|
|
BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
|
|
|
|
// Check that we have two conditional branches. If there is a PHI node in
|
|
// the common successor, verify that the same value flows in from both
|
|
// blocks.
|
|
SmallVector<PHINode*, 4> PHIs;
|
|
if (!PBI || PBI->isUnconditional() ||
|
|
(BI->isConditional() &&
|
|
!SafeToMergeTerminators(BI, PBI)) ||
|
|
(!BI->isConditional() &&
|
|
!isProfitableToFoldUnconditional(BI, PBI, Cond, PHIs)))
|
|
continue;
|
|
|
|
// Determine if the two branches share a common destination.
|
|
Instruction::BinaryOps Opc = Instruction::BinaryOpsEnd;
|
|
bool InvertPredCond = false;
|
|
|
|
if (BI->isConditional()) {
|
|
if (PBI->getSuccessor(0) == TrueDest)
|
|
Opc = Instruction::Or;
|
|
else if (PBI->getSuccessor(1) == FalseDest)
|
|
Opc = Instruction::And;
|
|
else if (PBI->getSuccessor(0) == FalseDest)
|
|
Opc = Instruction::And, InvertPredCond = true;
|
|
else if (PBI->getSuccessor(1) == TrueDest)
|
|
Opc = Instruction::Or, InvertPredCond = true;
|
|
else
|
|
continue;
|
|
} else {
|
|
if (PBI->getSuccessor(0) != TrueDest && PBI->getSuccessor(1) != TrueDest)
|
|
continue;
|
|
}
|
|
|
|
DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
|
|
IRBuilder<> Builder(PBI);
|
|
|
|
// If we need to invert the condition in the pred block to match, do so now.
|
|
if (InvertPredCond) {
|
|
Value *NewCond = PBI->getCondition();
|
|
|
|
if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
|
|
CmpInst *CI = cast<CmpInst>(NewCond);
|
|
CI->setPredicate(CI->getInversePredicate());
|
|
} else {
|
|
NewCond = Builder.CreateNot(NewCond,
|
|
PBI->getCondition()->getName()+".not");
|
|
}
|
|
|
|
PBI->setCondition(NewCond);
|
|
PBI->swapSuccessors();
|
|
}
|
|
|
|
// If we have bonus instructions, clone them into the predecessor block.
|
|
// Note that there may be mutliple predecessor blocks, so we cannot move
|
|
// bonus instructions to a predecessor block.
|
|
ValueToValueMapTy VMap; // maps original values to cloned values
|
|
// We already make sure Cond is the last instruction before BI. Therefore,
|
|
// every instructions before Cond other than DbgInfoIntrinsic are bonus
|
|
// instructions.
|
|
for (auto BonusInst = BB->begin(); Cond != BonusInst; ++BonusInst) {
|
|
if (isa<DbgInfoIntrinsic>(BonusInst))
|
|
continue;
|
|
Instruction *NewBonusInst = BonusInst->clone();
|
|
RemapInstruction(NewBonusInst, VMap,
|
|
RF_NoModuleLevelChanges | RF_IgnoreMissingEntries);
|
|
VMap[BonusInst] = NewBonusInst;
|
|
|
|
// If we moved a load, we cannot any longer claim any knowledge about
|
|
// its potential value. The previous information might have been valid
|
|
// only given the branch precondition.
|
|
// For an analogous reason, we must also drop all the metadata whose
|
|
// semantics we don't understand.
|
|
NewBonusInst->dropUnknownMetadata(LLVMContext::MD_dbg);
|
|
|
|
PredBlock->getInstList().insert(PBI, NewBonusInst);
|
|
NewBonusInst->takeName(BonusInst);
|
|
BonusInst->setName(BonusInst->getName() + ".old");
|
|
}
|
|
|
|
// Clone Cond into the predecessor basic block, and or/and the
|
|
// two conditions together.
|
|
Instruction *New = Cond->clone();
|
|
RemapInstruction(New, VMap,
|
|
RF_NoModuleLevelChanges | RF_IgnoreMissingEntries);
|
|
PredBlock->getInstList().insert(PBI, New);
|
|
New->takeName(Cond);
|
|
Cond->setName(New->getName() + ".old");
|
|
|
|
if (BI->isConditional()) {
|
|
Instruction *NewCond =
|
|
cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(),
|
|
New, "or.cond"));
|
|
PBI->setCondition(NewCond);
|
|
|
|
uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
|
|
bool PredHasWeights = ExtractBranchMetadata(PBI, PredTrueWeight,
|
|
PredFalseWeight);
|
|
bool SuccHasWeights = ExtractBranchMetadata(BI, SuccTrueWeight,
|
|
SuccFalseWeight);
|
|
SmallVector<uint64_t, 8> NewWeights;
|
|
|
|
if (PBI->getSuccessor(0) == BB) {
|
|
if (PredHasWeights && SuccHasWeights) {
|
|
// PBI: br i1 %x, BB, FalseDest
|
|
// BI: br i1 %y, TrueDest, FalseDest
|
|
//TrueWeight is TrueWeight for PBI * TrueWeight for BI.
|
|
NewWeights.push_back(PredTrueWeight * SuccTrueWeight);
|
|
//FalseWeight is FalseWeight for PBI * TotalWeight for BI +
|
|
// TrueWeight for PBI * FalseWeight for BI.
|
|
// We assume that total weights of a BranchInst can fit into 32 bits.
|
|
// Therefore, we will not have overflow using 64-bit arithmetic.
|
|
NewWeights.push_back(PredFalseWeight * (SuccFalseWeight +
|
|
SuccTrueWeight) + PredTrueWeight * SuccFalseWeight);
|
|
}
|
|
AddPredecessorToBlock(TrueDest, PredBlock, BB);
|
|
PBI->setSuccessor(0, TrueDest);
|
|
}
|
|
if (PBI->getSuccessor(1) == BB) {
|
|
if (PredHasWeights && SuccHasWeights) {
|
|
// PBI: br i1 %x, TrueDest, BB
|
|
// BI: br i1 %y, TrueDest, FalseDest
|
|
//TrueWeight is TrueWeight for PBI * TotalWeight for BI +
|
|
// FalseWeight for PBI * TrueWeight for BI.
|
|
NewWeights.push_back(PredTrueWeight * (SuccFalseWeight +
|
|
SuccTrueWeight) + PredFalseWeight * SuccTrueWeight);
|
|
//FalseWeight is FalseWeight for PBI * FalseWeight for BI.
|
|
NewWeights.push_back(PredFalseWeight * SuccFalseWeight);
|
|
}
|
|
AddPredecessorToBlock(FalseDest, PredBlock, BB);
|
|
PBI->setSuccessor(1, FalseDest);
|
|
}
|
|
if (NewWeights.size() == 2) {
|
|
// Halve the weights if any of them cannot fit in an uint32_t
|
|
FitWeights(NewWeights);
|
|
|
|
SmallVector<uint32_t, 8> MDWeights(NewWeights.begin(),NewWeights.end());
|
|
PBI->setMetadata(LLVMContext::MD_prof,
|
|
MDBuilder(BI->getContext()).
|
|
createBranchWeights(MDWeights));
|
|
} else
|
|
PBI->setMetadata(LLVMContext::MD_prof, nullptr);
|
|
} else {
|
|
// Update PHI nodes in the common successors.
|
|
for (unsigned i = 0, e = PHIs.size(); i != e; ++i) {
|
|
ConstantInt *PBI_C = cast<ConstantInt>(
|
|
PHIs[i]->getIncomingValueForBlock(PBI->getParent()));
|
|
assert(PBI_C->getType()->isIntegerTy(1));
|
|
Instruction *MergedCond = nullptr;
|
|
if (PBI->getSuccessor(0) == TrueDest) {
|
|
// Create (PBI_Cond and PBI_C) or (!PBI_Cond and BI_Value)
|
|
// PBI_C is true: PBI_Cond or (!PBI_Cond and BI_Value)
|
|
// is false: !PBI_Cond and BI_Value
|
|
Instruction *NotCond =
|
|
cast<Instruction>(Builder.CreateNot(PBI->getCondition(),
|
|
"not.cond"));
|
|
MergedCond =
|
|
cast<Instruction>(Builder.CreateBinOp(Instruction::And,
|
|
NotCond, New,
|
|
"and.cond"));
|
|
if (PBI_C->isOne())
|
|
MergedCond =
|
|
cast<Instruction>(Builder.CreateBinOp(Instruction::Or,
|
|
PBI->getCondition(), MergedCond,
|
|
"or.cond"));
|
|
} else {
|
|
// Create (PBI_Cond and BI_Value) or (!PBI_Cond and PBI_C)
|
|
// PBI_C is true: (PBI_Cond and BI_Value) or (!PBI_Cond)
|
|
// is false: PBI_Cond and BI_Value
|
|
MergedCond =
|
|
cast<Instruction>(Builder.CreateBinOp(Instruction::And,
|
|
PBI->getCondition(), New,
|
|
"and.cond"));
|
|
if (PBI_C->isOne()) {
|
|
Instruction *NotCond =
|
|
cast<Instruction>(Builder.CreateNot(PBI->getCondition(),
|
|
"not.cond"));
|
|
MergedCond =
|
|
cast<Instruction>(Builder.CreateBinOp(Instruction::Or,
|
|
NotCond, MergedCond,
|
|
"or.cond"));
|
|
}
|
|
}
|
|
// Update PHI Node.
|
|
PHIs[i]->setIncomingValue(PHIs[i]->getBasicBlockIndex(PBI->getParent()),
|
|
MergedCond);
|
|
}
|
|
// Change PBI from Conditional to Unconditional.
|
|
BranchInst *New_PBI = BranchInst::Create(TrueDest, PBI);
|
|
EraseTerminatorInstAndDCECond(PBI);
|
|
PBI = New_PBI;
|
|
}
|
|
|
|
// TODO: If BB is reachable from all paths through PredBlock, then we
|
|
// could replace PBI's branch probabilities with BI's.
|
|
|
|
// Copy any debug value intrinsics into the end of PredBlock.
|
|
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
|
|
if (isa<DbgInfoIntrinsic>(*I))
|
|
I->clone()->insertBefore(PBI);
|
|
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
|
|
/// predecessor of another block, this function tries to simplify it. We know
|
|
/// that PBI and BI are both conditional branches, and BI is in one of the
|
|
/// successor blocks of PBI - PBI branches to BI.
|
|
static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
|
|
assert(PBI->isConditional() && BI->isConditional());
|
|
BasicBlock *BB = BI->getParent();
|
|
|
|
// If this block ends with a branch instruction, and if there is a
|
|
// predecessor that ends on a branch of the same condition, make
|
|
// this conditional branch redundant.
|
|
if (PBI->getCondition() == BI->getCondition() &&
|
|
PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
|
|
// Okay, the outcome of this conditional branch is statically
|
|
// knowable. If this block had a single pred, handle specially.
|
|
if (BB->getSinglePredecessor()) {
|
|
// Turn this into a branch on constant.
|
|
bool CondIsTrue = PBI->getSuccessor(0) == BB;
|
|
BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
|
|
CondIsTrue));
|
|
return true; // Nuke the branch on constant.
|
|
}
|
|
|
|
// Otherwise, if there are multiple predecessors, insert a PHI that merges
|
|
// in the constant and simplify the block result. Subsequent passes of
|
|
// simplifycfg will thread the block.
|
|
if (BlockIsSimpleEnoughToThreadThrough(BB)) {
|
|
pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
|
|
PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
|
|
std::distance(PB, PE),
|
|
BI->getCondition()->getName() + ".pr",
|
|
BB->begin());
|
|
// Okay, we're going to insert the PHI node. Since PBI is not the only
|
|
// predecessor, compute the PHI'd conditional value for all of the preds.
|
|
// Any predecessor where the condition is not computable we keep symbolic.
|
|
for (pred_iterator PI = PB; PI != PE; ++PI) {
|
|
BasicBlock *P = *PI;
|
|
if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
|
|
PBI != BI && PBI->isConditional() &&
|
|
PBI->getCondition() == BI->getCondition() &&
|
|
PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
|
|
bool CondIsTrue = PBI->getSuccessor(0) == BB;
|
|
NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
|
|
CondIsTrue), P);
|
|
} else {
|
|
NewPN->addIncoming(BI->getCondition(), P);
|
|
}
|
|
}
|
|
|
|
BI->setCondition(NewPN);
|
|
return true;
|
|
}
|
|
}
|
|
|
|
// If this is a conditional branch in an empty block, and if any
|
|
// predecessors are a conditional branch to one of our destinations,
|
|
// fold the conditions into logical ops and one cond br.
|
|
BasicBlock::iterator BBI = BB->begin();
|
|
// Ignore dbg intrinsics.
|
|
while (isa<DbgInfoIntrinsic>(BBI))
|
|
++BBI;
|
|
if (&*BBI != BI)
|
|
return false;
|
|
|
|
|
|
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
|
|
if (CE->canTrap())
|
|
return false;
|
|
|
|
int PBIOp, BIOp;
|
|
if (PBI->getSuccessor(0) == BI->getSuccessor(0))
|
|
PBIOp = BIOp = 0;
|
|
else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
|
|
PBIOp = 0, BIOp = 1;
|
|
else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
|
|
PBIOp = 1, BIOp = 0;
|
|
else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
|
|
PBIOp = BIOp = 1;
|
|
else
|
|
return false;
|
|
|
|
// Check to make sure that the other destination of this branch
|
|
// isn't BB itself. If so, this is an infinite loop that will
|
|
// keep getting unwound.
|
|
if (PBI->getSuccessor(PBIOp) == BB)
|
|
return false;
|
|
|
|
// Do not perform this transformation if it would require
|
|
// insertion of a large number of select instructions. For targets
|
|
// without predication/cmovs, this is a big pessimization.
|
|
|
|
// Also do not perform this transformation if any phi node in the common
|
|
// destination block can trap when reached by BB or PBB (PR17073). In that
|
|
// case, it would be unsafe to hoist the operation into a select instruction.
|
|
|
|
BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
|
|
unsigned NumPhis = 0;
|
|
for (BasicBlock::iterator II = CommonDest->begin();
|
|
isa<PHINode>(II); ++II, ++NumPhis) {
|
|
if (NumPhis > 2) // Disable this xform.
|
|
return false;
|
|
|
|
PHINode *PN = cast<PHINode>(II);
|
|
Value *BIV = PN->getIncomingValueForBlock(BB);
|
|
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BIV))
|
|
if (CE->canTrap())
|
|
return false;
|
|
|
|
unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
|
|
Value *PBIV = PN->getIncomingValue(PBBIdx);
|
|
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(PBIV))
|
|
if (CE->canTrap())
|
|
return false;
|
|
}
|
|
|
|
// Finally, if everything is ok, fold the branches to logical ops.
|
|
BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
|
|
|
|
DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
|
|
<< "AND: " << *BI->getParent());
|
|
|
|
|
|
// If OtherDest *is* BB, then BB is a basic block with a single conditional
|
|
// branch in it, where one edge (OtherDest) goes back to itself but the other
|
|
// exits. We don't *know* that the program avoids the infinite loop
|
|
// (even though that seems likely). If we do this xform naively, we'll end up
|
|
// recursively unpeeling the loop. Since we know that (after the xform is
|
|
// done) that the block *is* infinite if reached, we just make it an obviously
|
|
// infinite loop with no cond branch.
|
|
if (OtherDest == BB) {
|
|
// Insert it at the end of the function, because it's either code,
|
|
// or it won't matter if it's hot. :)
|
|
BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
|
|
"infloop", BB->getParent());
|
|
BranchInst::Create(InfLoopBlock, InfLoopBlock);
|
|
OtherDest = InfLoopBlock;
|
|
}
|
|
|
|
DEBUG(dbgs() << *PBI->getParent()->getParent());
|
|
|
|
// BI may have other predecessors. Because of this, we leave
|
|
// it alone, but modify PBI.
|
|
|
|
// Make sure we get to CommonDest on True&True directions.
|
|
Value *PBICond = PBI->getCondition();
|
|
IRBuilder<true, NoFolder> Builder(PBI);
|
|
if (PBIOp)
|
|
PBICond = Builder.CreateNot(PBICond, PBICond->getName()+".not");
|
|
|
|
Value *BICond = BI->getCondition();
|
|
if (BIOp)
|
|
BICond = Builder.CreateNot(BICond, BICond->getName()+".not");
|
|
|
|
// Merge the conditions.
|
|
Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge");
|
|
|
|
// Modify PBI to branch on the new condition to the new dests.
|
|
PBI->setCondition(Cond);
|
|
PBI->setSuccessor(0, CommonDest);
|
|
PBI->setSuccessor(1, OtherDest);
|
|
|
|
// Update branch weight for PBI.
|
|
uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
|
|
bool PredHasWeights = ExtractBranchMetadata(PBI, PredTrueWeight,
|
|
PredFalseWeight);
|
|
bool SuccHasWeights = ExtractBranchMetadata(BI, SuccTrueWeight,
|
|
SuccFalseWeight);
|
|
if (PredHasWeights && SuccHasWeights) {
|
|
uint64_t PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
|
|
uint64_t PredOther = PBIOp ?PredTrueWeight : PredFalseWeight;
|
|
uint64_t SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
|
|
uint64_t SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
|
|
// The weight to CommonDest should be PredCommon * SuccTotal +
|
|
// PredOther * SuccCommon.
|
|
// The weight to OtherDest should be PredOther * SuccOther.
|
|
uint64_t NewWeights[2] = {PredCommon * (SuccCommon + SuccOther) +
|
|
PredOther * SuccCommon,
|
|
PredOther * SuccOther};
|
|
// Halve the weights if any of them cannot fit in an uint32_t
|
|
FitWeights(NewWeights);
|
|
|
|
PBI->setMetadata(LLVMContext::MD_prof,
|
|
MDBuilder(BI->getContext())
|
|
.createBranchWeights(NewWeights[0], NewWeights[1]));
|
|
}
|
|
|
|
// OtherDest may have phi nodes. If so, add an entry from PBI's
|
|
// block that are identical to the entries for BI's block.
|
|
AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
|
|
|
|
// We know that the CommonDest already had an edge from PBI to
|
|
// it. If it has PHIs though, the PHIs may have different
|
|
// entries for BB and PBI's BB. If so, insert a select to make
|
|
// them agree.
|
|
PHINode *PN;
|
|
for (BasicBlock::iterator II = CommonDest->begin();
|
|
(PN = dyn_cast<PHINode>(II)); ++II) {
|
|
Value *BIV = PN->getIncomingValueForBlock(BB);
|
|
unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
|
|
Value *PBIV = PN->getIncomingValue(PBBIdx);
|
|
if (BIV != PBIV) {
|
|
// Insert a select in PBI to pick the right value.
|
|
Value *NV = cast<SelectInst>
|
|
(Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName()+".mux"));
|
|
PN->setIncomingValue(PBBIdx, NV);
|
|
}
|
|
}
|
|
|
|
DEBUG(dbgs() << "INTO: " << *PBI->getParent());
|
|
DEBUG(dbgs() << *PBI->getParent()->getParent());
|
|
|
|
// This basic block is probably dead. We know it has at least
|
|
// one fewer predecessor.
|
|
return true;
|
|
}
|
|
|
|
// SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
|
|
// branch to TrueBB if Cond is true or to FalseBB if Cond is false.
|
|
// Takes care of updating the successors and removing the old terminator.
|
|
// Also makes sure not to introduce new successors by assuming that edges to
|
|
// non-successor TrueBBs and FalseBBs aren't reachable.
|
|
static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
|
|
BasicBlock *TrueBB, BasicBlock *FalseBB,
|
|
uint32_t TrueWeight,
|
|
uint32_t FalseWeight){
|
|
// Remove any superfluous successor edges from the CFG.
|
|
// First, figure out which successors to preserve.
|
|
// If TrueBB and FalseBB are equal, only try to preserve one copy of that
|
|
// successor.
|
|
BasicBlock *KeepEdge1 = TrueBB;
|
|
BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : nullptr;
|
|
|
|
// Then remove the rest.
|
|
for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
|
|
BasicBlock *Succ = OldTerm->getSuccessor(I);
|
|
// Make sure only to keep exactly one copy of each edge.
|
|
if (Succ == KeepEdge1)
|
|
KeepEdge1 = nullptr;
|
|
else if (Succ == KeepEdge2)
|
|
KeepEdge2 = nullptr;
|
|
else
|
|
Succ->removePredecessor(OldTerm->getParent());
|
|
}
|
|
|
|
IRBuilder<> Builder(OldTerm);
|
|
Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
|
|
|
|
// Insert an appropriate new terminator.
|
|
if (!KeepEdge1 && !KeepEdge2) {
|
|
if (TrueBB == FalseBB)
|
|
// We were only looking for one successor, and it was present.
|
|
// Create an unconditional branch to it.
|
|
Builder.CreateBr(TrueBB);
|
|
else {
|
|
// We found both of the successors we were looking for.
|
|
// Create a conditional branch sharing the condition of the select.
|
|
BranchInst *NewBI = Builder.CreateCondBr(Cond, TrueBB, FalseBB);
|
|
if (TrueWeight != FalseWeight)
|
|
NewBI->setMetadata(LLVMContext::MD_prof,
|
|
MDBuilder(OldTerm->getContext()).
|
|
createBranchWeights(TrueWeight, FalseWeight));
|
|
}
|
|
} else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
|
|
// Neither of the selected blocks were successors, so this
|
|
// terminator must be unreachable.
|
|
new UnreachableInst(OldTerm->getContext(), OldTerm);
|
|
} else {
|
|
// One of the selected values was a successor, but the other wasn't.
|
|
// Insert an unconditional branch to the one that was found;
|
|
// the edge to the one that wasn't must be unreachable.
|
|
if (!KeepEdge1)
|
|
// Only TrueBB was found.
|
|
Builder.CreateBr(TrueBB);
|
|
else
|
|
// Only FalseBB was found.
|
|
Builder.CreateBr(FalseBB);
|
|
}
|
|
|
|
EraseTerminatorInstAndDCECond(OldTerm);
|
|
return true;
|
|
}
|
|
|
|
// SimplifySwitchOnSelect - Replaces
|
|
// (switch (select cond, X, Y)) on constant X, Y
|
|
// with a branch - conditional if X and Y lead to distinct BBs,
|
|
// unconditional otherwise.
|
|
static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
|
|
// Check for constant integer values in the select.
|
|
ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
|
|
ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
|
|
if (!TrueVal || !FalseVal)
|
|
return false;
|
|
|
|
// Find the relevant condition and destinations.
|
|
Value *Condition = Select->getCondition();
|
|
BasicBlock *TrueBB = SI->findCaseValue(TrueVal).getCaseSuccessor();
|
|
BasicBlock *FalseBB = SI->findCaseValue(FalseVal).getCaseSuccessor();
|
|
|
|
// Get weight for TrueBB and FalseBB.
|
|
uint32_t TrueWeight = 0, FalseWeight = 0;
|
|
SmallVector<uint64_t, 8> Weights;
|
|
bool HasWeights = HasBranchWeights(SI);
|
|
if (HasWeights) {
|
|
GetBranchWeights(SI, Weights);
|
|
if (Weights.size() == 1 + SI->getNumCases()) {
|
|
TrueWeight = (uint32_t)Weights[SI->findCaseValue(TrueVal).
|
|
getSuccessorIndex()];
|
|
FalseWeight = (uint32_t)Weights[SI->findCaseValue(FalseVal).
|
|
getSuccessorIndex()];
|
|
}
|
|
}
|
|
|
|
// Perform the actual simplification.
|
|
return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB,
|
|
TrueWeight, FalseWeight);
|
|
}
|
|
|
|
// SimplifyIndirectBrOnSelect - Replaces
|
|
// (indirectbr (select cond, blockaddress(@fn, BlockA),
|
|
// blockaddress(@fn, BlockB)))
|
|
// with
|
|
// (br cond, BlockA, BlockB).
|
|
static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
|
|
// Check that both operands of the select are block addresses.
|
|
BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
|
|
BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
|
|
if (!TBA || !FBA)
|
|
return false;
|
|
|
|
// Extract the actual blocks.
|
|
BasicBlock *TrueBB = TBA->getBasicBlock();
|
|
BasicBlock *FalseBB = FBA->getBasicBlock();
|
|
|
|
// Perform the actual simplification.
|
|
return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB,
|
|
0, 0);
|
|
}
|
|
|
|
/// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
|
|
/// instruction (a seteq/setne with a constant) as the only instruction in a
|
|
/// block that ends with an uncond branch. We are looking for a very specific
|
|
/// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
|
|
/// this case, we merge the first two "or's of icmp" into a switch, but then the
|
|
/// default value goes to an uncond block with a seteq in it, we get something
|
|
/// like:
|
|
///
|
|
/// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
|
|
/// DEFAULT:
|
|
/// %tmp = icmp eq i8 %A, 92
|
|
/// br label %end
|
|
/// end:
|
|
/// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
|
|
///
|
|
/// We prefer to split the edge to 'end' so that there is a true/false entry to
|
|
/// the PHI, merging the third icmp into the switch.
|
|
static bool TryToSimplifyUncondBranchWithICmpInIt(
|
|
ICmpInst *ICI, IRBuilder<> &Builder, const DataLayout &DL,
|
|
const TargetTransformInfo &TTI, unsigned BonusInstThreshold,
|
|
AssumptionCache *AC) {
|
|
BasicBlock *BB = ICI->getParent();
|
|
|
|
// If the block has any PHIs in it or the icmp has multiple uses, it is too
|
|
// complex.
|
|
if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
|
|
|
|
Value *V = ICI->getOperand(0);
|
|
ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
|
|
|
|
// The pattern we're looking for is where our only predecessor is a switch on
|
|
// 'V' and this block is the default case for the switch. In this case we can
|
|
// fold the compared value into the switch to simplify things.
|
|
BasicBlock *Pred = BB->getSinglePredecessor();
|
|
if (!Pred || !isa<SwitchInst>(Pred->getTerminator())) return false;
|
|
|
|
SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
|
|
if (SI->getCondition() != V)
|
|
return false;
|
|
|
|
// If BB is reachable on a non-default case, then we simply know the value of
|
|
// V in this block. Substitute it and constant fold the icmp instruction
|
|
// away.
|
|
if (SI->getDefaultDest() != BB) {
|
|
ConstantInt *VVal = SI->findCaseDest(BB);
|
|
assert(VVal && "Should have a unique destination value");
|
|
ICI->setOperand(0, VVal);
|
|
|
|
if (Value *V = SimplifyInstruction(ICI, DL)) {
|
|
ICI->replaceAllUsesWith(V);
|
|
ICI->eraseFromParent();
|
|
}
|
|
// BB is now empty, so it is likely to simplify away.
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
}
|
|
|
|
// Ok, the block is reachable from the default dest. If the constant we're
|
|
// comparing exists in one of the other edges, then we can constant fold ICI
|
|
// and zap it.
|
|
if (SI->findCaseValue(Cst) != SI->case_default()) {
|
|
Value *V;
|
|
if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
|
|
V = ConstantInt::getFalse(BB->getContext());
|
|
else
|
|
V = ConstantInt::getTrue(BB->getContext());
|
|
|
|
ICI->replaceAllUsesWith(V);
|
|
ICI->eraseFromParent();
|
|
// BB is now empty, so it is likely to simplify away.
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
}
|
|
|
|
// The use of the icmp has to be in the 'end' block, by the only PHI node in
|
|
// the block.
|
|
BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
|
|
PHINode *PHIUse = dyn_cast<PHINode>(ICI->user_back());
|
|
if (PHIUse == nullptr || PHIUse != &SuccBlock->front() ||
|
|
isa<PHINode>(++BasicBlock::iterator(PHIUse)))
|
|
return false;
|
|
|
|
// If the icmp is a SETEQ, then the default dest gets false, the new edge gets
|
|
// true in the PHI.
|
|
Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
|
|
Constant *NewCst = ConstantInt::getFalse(BB->getContext());
|
|
|
|
if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
|
|
std::swap(DefaultCst, NewCst);
|
|
|
|
// Replace ICI (which is used by the PHI for the default value) with true or
|
|
// false depending on if it is EQ or NE.
|
|
ICI->replaceAllUsesWith(DefaultCst);
|
|
ICI->eraseFromParent();
|
|
|
|
// Okay, the switch goes to this block on a default value. Add an edge from
|
|
// the switch to the merge point on the compared value.
|
|
BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
|
|
BB->getParent(), BB);
|
|
SmallVector<uint64_t, 8> Weights;
|
|
bool HasWeights = HasBranchWeights(SI);
|
|
if (HasWeights) {
|
|
GetBranchWeights(SI, Weights);
|
|
if (Weights.size() == 1 + SI->getNumCases()) {
|
|
// Split weight for default case to case for "Cst".
|
|
Weights[0] = (Weights[0]+1) >> 1;
|
|
Weights.push_back(Weights[0]);
|
|
|
|
SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
|
|
SI->setMetadata(LLVMContext::MD_prof,
|
|
MDBuilder(SI->getContext()).
|
|
createBranchWeights(MDWeights));
|
|
}
|
|
}
|
|
SI->addCase(Cst, NewBB);
|
|
|
|
// NewBB branches to the phi block, add the uncond branch and the phi entry.
|
|
Builder.SetInsertPoint(NewBB);
|
|
Builder.SetCurrentDebugLocation(SI->getDebugLoc());
|
|
Builder.CreateBr(SuccBlock);
|
|
PHIUse->addIncoming(NewCst, NewBB);
|
|
return true;
|
|
}
|
|
|
|
/// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
|
|
/// Check to see if it is branching on an or/and chain of icmp instructions, and
|
|
/// fold it into a switch instruction if so.
|
|
static bool SimplifyBranchOnICmpChain(BranchInst *BI, IRBuilder<> &Builder,
|
|
const DataLayout &DL) {
|
|
Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
|
|
if (!Cond) return false;
|
|
|
|
// Change br (X == 0 | X == 1), T, F into a switch instruction.
|
|
// If this is a bunch of seteq's or'd together, or if it's a bunch of
|
|
// 'setne's and'ed together, collect them.
|
|
|
|
// Try to gather values from a chain of and/or to be turned into a switch
|
|
ConstantComparesGatherer ConstantCompare(Cond, DL);
|
|
// Unpack the result
|
|
SmallVectorImpl<ConstantInt*> &Values = ConstantCompare.Vals;
|
|
Value *CompVal = ConstantCompare.CompValue;
|
|
unsigned UsedICmps = ConstantCompare.UsedICmps;
|
|
Value *ExtraCase = ConstantCompare.Extra;
|
|
|
|
// If we didn't have a multiply compared value, fail.
|
|
if (!CompVal) return false;
|
|
|
|
// Avoid turning single icmps into a switch.
|
|
if (UsedICmps <= 1)
|
|
return false;
|
|
|
|
bool TrueWhenEqual = (Cond->getOpcode() == Instruction::Or);
|
|
|
|
// There might be duplicate constants in the list, which the switch
|
|
// instruction can't handle, remove them now.
|
|
array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
|
|
Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
|
|
|
|
// If Extra was used, we require at least two switch values to do the
|
|
// transformation. A switch with one value is just an cond branch.
|
|
if (ExtraCase && Values.size() < 2) return false;
|
|
|
|
// TODO: Preserve branch weight metadata, similarly to how
|
|
// FoldValueComparisonIntoPredecessors preserves it.
|
|
|
|
// Figure out which block is which destination.
|
|
BasicBlock *DefaultBB = BI->getSuccessor(1);
|
|
BasicBlock *EdgeBB = BI->getSuccessor(0);
|
|
if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
|
|
|
|
BasicBlock *BB = BI->getParent();
|
|
|
|
DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
|
|
<< " cases into SWITCH. BB is:\n" << *BB);
|
|
|
|
// If there are any extra values that couldn't be folded into the switch
|
|
// then we evaluate them with an explicit branch first. Split the block
|
|
// right before the condbr to handle it.
|
|
if (ExtraCase) {
|
|
BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
|
|
// Remove the uncond branch added to the old block.
|
|
TerminatorInst *OldTI = BB->getTerminator();
|
|
Builder.SetInsertPoint(OldTI);
|
|
|
|
if (TrueWhenEqual)
|
|
Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB);
|
|
else
|
|
Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB);
|
|
|
|
OldTI->eraseFromParent();
|
|
|
|
// If there are PHI nodes in EdgeBB, then we need to add a new entry to them
|
|
// for the edge we just added.
|
|
AddPredecessorToBlock(EdgeBB, BB, NewBB);
|
|
|
|
DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
|
|
<< "\nEXTRABB = " << *BB);
|
|
BB = NewBB;
|
|
}
|
|
|
|
Builder.SetInsertPoint(BI);
|
|
// Convert pointer to int before we switch.
|
|
if (CompVal->getType()->isPointerTy()) {
|
|
CompVal = Builder.CreatePtrToInt(
|
|
CompVal, DL.getIntPtrType(CompVal->getType()), "magicptr");
|
|
}
|
|
|
|
// Create the new switch instruction now.
|
|
SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size());
|
|
|
|
// Add all of the 'cases' to the switch instruction.
|
|
for (unsigned i = 0, e = Values.size(); i != e; ++i)
|
|
New->addCase(Values[i], EdgeBB);
|
|
|
|
// We added edges from PI to the EdgeBB. As such, if there were any
|
|
// PHI nodes in EdgeBB, they need entries to be added corresponding to
|
|
// the number of edges added.
|
|
for (BasicBlock::iterator BBI = EdgeBB->begin();
|
|
isa<PHINode>(BBI); ++BBI) {
|
|
PHINode *PN = cast<PHINode>(BBI);
|
|
Value *InVal = PN->getIncomingValueForBlock(BB);
|
|
for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
|
|
PN->addIncoming(InVal, BB);
|
|
}
|
|
|
|
// Erase the old branch instruction.
|
|
EraseTerminatorInstAndDCECond(BI);
|
|
|
|
DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
|
|
return true;
|
|
}
|
|
|
|
bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
|
|
// If this is a trivial landing pad that just continues unwinding the caught
|
|
// exception then zap the landing pad, turning its invokes into calls.
|
|
BasicBlock *BB = RI->getParent();
|
|
LandingPadInst *LPInst = dyn_cast<LandingPadInst>(BB->getFirstNonPHI());
|
|
if (RI->getValue() != LPInst)
|
|
// Not a landing pad, or the resume is not unwinding the exception that
|
|
// caused control to branch here.
|
|
return false;
|
|
|
|
// Check that there are no other instructions except for debug intrinsics.
|
|
BasicBlock::iterator I = LPInst, E = RI;
|
|
while (++I != E)
|
|
if (!isa<DbgInfoIntrinsic>(I))
|
|
return false;
|
|
|
|
// Turn all invokes that unwind here into calls and delete the basic block.
|
|
for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
|
|
InvokeInst *II = cast<InvokeInst>((*PI++)->getTerminator());
|
|
SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
|
|
// Insert a call instruction before the invoke.
|
|
CallInst *Call = CallInst::Create(II->getCalledValue(), Args, "", II);
|
|
Call->takeName(II);
|
|
Call->setCallingConv(II->getCallingConv());
|
|
Call->setAttributes(II->getAttributes());
|
|
Call->setDebugLoc(II->getDebugLoc());
|
|
|
|
// Anything that used the value produced by the invoke instruction now uses
|
|
// the value produced by the call instruction. Note that we do this even
|
|
// for void functions and calls with no uses so that the callgraph edge is
|
|
// updated.
|
|
II->replaceAllUsesWith(Call);
|
|
BB->removePredecessor(II->getParent());
|
|
|
|
// Insert a branch to the normal destination right before the invoke.
|
|
BranchInst::Create(II->getNormalDest(), II);
|
|
|
|
// Finally, delete the invoke instruction!
|
|
II->eraseFromParent();
|
|
}
|
|
|
|
// The landingpad is now unreachable. Zap it.
|
|
BB->eraseFromParent();
|
|
return true;
|
|
}
|
|
|
|
bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
|
|
BasicBlock *BB = RI->getParent();
|
|
if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
|
|
|
|
// Find predecessors that end with branches.
|
|
SmallVector<BasicBlock*, 8> UncondBranchPreds;
|
|
SmallVector<BranchInst*, 8> CondBranchPreds;
|
|
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
|
|
BasicBlock *P = *PI;
|
|
TerminatorInst *PTI = P->getTerminator();
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
|
|
if (BI->isUnconditional())
|
|
UncondBranchPreds.push_back(P);
|
|
else
|
|
CondBranchPreds.push_back(BI);
|
|
}
|
|
}
|
|
|
|
// If we found some, do the transformation!
|
|
if (!UncondBranchPreds.empty() && DupRet) {
|
|
while (!UncondBranchPreds.empty()) {
|
|
BasicBlock *Pred = UncondBranchPreds.pop_back_val();
|
|
DEBUG(dbgs() << "FOLDING: " << *BB
|
|
<< "INTO UNCOND BRANCH PRED: " << *Pred);
|
|
(void)FoldReturnIntoUncondBranch(RI, BB, Pred);
|
|
}
|
|
|
|
// If we eliminated all predecessors of the block, delete the block now.
|
|
if (pred_empty(BB))
|
|
// We know there are no successors, so just nuke the block.
|
|
BB->eraseFromParent();
|
|
|
|
return true;
|
|
}
|
|
|
|
// Check out all of the conditional branches going to this return
|
|
// instruction. If any of them just select between returns, change the
|
|
// branch itself into a select/return pair.
|
|
while (!CondBranchPreds.empty()) {
|
|
BranchInst *BI = CondBranchPreds.pop_back_val();
|
|
|
|
// Check to see if the non-BB successor is also a return block.
|
|
if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
|
|
isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
|
|
SimplifyCondBranchToTwoReturns(BI, Builder))
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
|
|
BasicBlock *BB = UI->getParent();
|
|
|
|
bool Changed = false;
|
|
|
|
// If there are any instructions immediately before the unreachable that can
|
|
// be removed, do so.
|
|
while (UI != BB->begin()) {
|
|
BasicBlock::iterator BBI = UI;
|
|
--BBI;
|
|
// Do not delete instructions that can have side effects which might cause
|
|
// the unreachable to not be reachable; specifically, calls and volatile
|
|
// operations may have this effect.
|
|
if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
|
|
|
|
if (BBI->mayHaveSideEffects()) {
|
|
if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
|
|
if (SI->isVolatile())
|
|
break;
|
|
} else if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
|
|
if (LI->isVolatile())
|
|
break;
|
|
} else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(BBI)) {
|
|
if (RMWI->isVolatile())
|
|
break;
|
|
} else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) {
|
|
if (CXI->isVolatile())
|
|
break;
|
|
} else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) &&
|
|
!isa<LandingPadInst>(BBI)) {
|
|
break;
|
|
}
|
|
// Note that deleting LandingPad's here is in fact okay, although it
|
|
// involves a bit of subtle reasoning. If this inst is a LandingPad,
|
|
// all the predecessors of this block will be the unwind edges of Invokes,
|
|
// and we can therefore guarantee this block will be erased.
|
|
}
|
|
|
|
// Delete this instruction (any uses are guaranteed to be dead)
|
|
if (!BBI->use_empty())
|
|
BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
|
|
BBI->eraseFromParent();
|
|
Changed = true;
|
|
}
|
|
|
|
// If the unreachable instruction is the first in the block, take a gander
|
|
// at all of the predecessors of this instruction, and simplify them.
|
|
if (&BB->front() != UI) return Changed;
|
|
|
|
SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
|
|
for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
|
|
TerminatorInst *TI = Preds[i]->getTerminator();
|
|
IRBuilder<> Builder(TI);
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
|
|
if (BI->isUnconditional()) {
|
|
if (BI->getSuccessor(0) == BB) {
|
|
new UnreachableInst(TI->getContext(), TI);
|
|
TI->eraseFromParent();
|
|
Changed = true;
|
|
}
|
|
} else {
|
|
if (BI->getSuccessor(0) == BB) {
|
|
Builder.CreateBr(BI->getSuccessor(1));
|
|
EraseTerminatorInstAndDCECond(BI);
|
|
} else if (BI->getSuccessor(1) == BB) {
|
|
Builder.CreateBr(BI->getSuccessor(0));
|
|
EraseTerminatorInstAndDCECond(BI);
|
|
Changed = true;
|
|
}
|
|
}
|
|
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
|
|
for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
|
|
i != e; ++i)
|
|
if (i.getCaseSuccessor() == BB) {
|
|
BB->removePredecessor(SI->getParent());
|
|
SI->removeCase(i);
|
|
--i; --e;
|
|
Changed = true;
|
|
}
|
|
} else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
|
|
if (II->getUnwindDest() == BB) {
|
|
// Convert the invoke to a call instruction. This would be a good
|
|
// place to note that the call does not throw though.
|
|
BranchInst *BI = Builder.CreateBr(II->getNormalDest());
|
|
II->removeFromParent(); // Take out of symbol table
|
|
|
|
// Insert the call now...
|
|
SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
|
|
Builder.SetInsertPoint(BI);
|
|
CallInst *CI = Builder.CreateCall(II->getCalledValue(),
|
|
Args, II->getName());
|
|
CI->setCallingConv(II->getCallingConv());
|
|
CI->setAttributes(II->getAttributes());
|
|
// If the invoke produced a value, the call does now instead.
|
|
II->replaceAllUsesWith(CI);
|
|
delete II;
|
|
Changed = true;
|
|
}
|
|
}
|
|
}
|
|
|
|
// If this block is now dead, remove it.
|
|
if (pred_empty(BB) &&
|
|
BB != &BB->getParent()->getEntryBlock()) {
|
|
// We know there are no successors, so just nuke the block.
|
|
BB->eraseFromParent();
|
|
return true;
|
|
}
|
|
|
|
return Changed;
|
|
}
|
|
|
|
static bool CasesAreContiguous(SmallVectorImpl<ConstantInt *> &Cases) {
|
|
assert(Cases.size() >= 1);
|
|
|
|
array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
|
|
for (size_t I = 1, E = Cases.size(); I != E; ++I) {
|
|
if (Cases[I - 1]->getValue() != Cases[I]->getValue() + 1)
|
|
return false;
|
|
}
|
|
return true;
|
|
}
|
|
|
|
/// Turn a switch with two reachable destinations into an integer range
|
|
/// comparison and branch.
|
|
static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
|
|
assert(SI->getNumCases() > 1 && "Degenerate switch?");
|
|
|
|
bool HasDefault =
|
|
!isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
|
|
|
|
// Partition the cases into two sets with different destinations.
|
|
BasicBlock *DestA = HasDefault ? SI->getDefaultDest() : nullptr;
|
|
BasicBlock *DestB = nullptr;
|
|
SmallVector <ConstantInt *, 16> CasesA;
|
|
SmallVector <ConstantInt *, 16> CasesB;
|
|
|
|
for (SwitchInst::CaseIt I : SI->cases()) {
|
|
BasicBlock *Dest = I.getCaseSuccessor();
|
|
if (!DestA) DestA = Dest;
|
|
if (Dest == DestA) {
|
|
CasesA.push_back(I.getCaseValue());
|
|
continue;
|
|
}
|
|
if (!DestB) DestB = Dest;
|
|
if (Dest == DestB) {
|
|
CasesB.push_back(I.getCaseValue());
|
|
continue;
|
|
}
|
|
return false; // More than two destinations.
|
|
}
|
|
|
|
assert(DestA && DestB && "Single-destination switch should have been folded.");
|
|
assert(DestA != DestB);
|
|
assert(DestB != SI->getDefaultDest());
|
|
assert(!CasesB.empty() && "There must be non-default cases.");
|
|
assert(!CasesA.empty() || HasDefault);
|
|
|
|
// Figure out if one of the sets of cases form a contiguous range.
|
|
SmallVectorImpl<ConstantInt *> *ContiguousCases = nullptr;
|
|
BasicBlock *ContiguousDest = nullptr;
|
|
BasicBlock *OtherDest = nullptr;
|
|
if (!CasesA.empty() && CasesAreContiguous(CasesA)) {
|
|
ContiguousCases = &CasesA;
|
|
ContiguousDest = DestA;
|
|
OtherDest = DestB;
|
|
} else if (CasesAreContiguous(CasesB)) {
|
|
ContiguousCases = &CasesB;
|
|
ContiguousDest = DestB;
|
|
OtherDest = DestA;
|
|
} else
|
|
return false;
|
|
|
|
// Start building the compare and branch.
|
|
|
|
Constant *Offset = ConstantExpr::getNeg(ContiguousCases->back());
|
|
Constant *NumCases = ConstantInt::get(Offset->getType(), ContiguousCases->size());
|
|
|
|
Value *Sub = SI->getCondition();
|
|
if (!Offset->isNullValue())
|
|
Sub = Builder.CreateAdd(Sub, Offset, Sub->getName() + ".off");
|
|
|
|
Value *Cmp;
|
|
// If NumCases overflowed, then all possible values jump to the successor.
|
|
if (NumCases->isNullValue() && !ContiguousCases->empty())
|
|
Cmp = ConstantInt::getTrue(SI->getContext());
|
|
else
|
|
Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
|
|
BranchInst *NewBI = Builder.CreateCondBr(Cmp, ContiguousDest, OtherDest);
|
|
|
|
// Update weight for the newly-created conditional branch.
|
|
if (HasBranchWeights(SI)) {
|
|
SmallVector<uint64_t, 8> Weights;
|
|
GetBranchWeights(SI, Weights);
|
|
if (Weights.size() == 1 + SI->getNumCases()) {
|
|
uint64_t TrueWeight = 0;
|
|
uint64_t FalseWeight = 0;
|
|
for (size_t I = 0, E = Weights.size(); I != E; ++I) {
|
|
if (SI->getSuccessor(I) == ContiguousDest)
|
|
TrueWeight += Weights[I];
|
|
else
|
|
FalseWeight += Weights[I];
|
|
}
|
|
while (TrueWeight > UINT32_MAX || FalseWeight > UINT32_MAX) {
|
|
TrueWeight /= 2;
|
|
FalseWeight /= 2;
|
|
}
|
|
NewBI->setMetadata(LLVMContext::MD_prof,
|
|
MDBuilder(SI->getContext()).createBranchWeights(
|
|
(uint32_t)TrueWeight, (uint32_t)FalseWeight));
|
|
}
|
|
}
|
|
|
|
// Prune obsolete incoming values off the successors' PHI nodes.
|
|
for (auto BBI = ContiguousDest->begin(); isa<PHINode>(BBI); ++BBI) {
|
|
unsigned PreviousEdges = ContiguousCases->size();
|
|
if (ContiguousDest == SI->getDefaultDest()) ++PreviousEdges;
|
|
for (unsigned I = 0, E = PreviousEdges - 1; I != E; ++I)
|
|
cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
|
|
}
|
|
for (auto BBI = OtherDest->begin(); isa<PHINode>(BBI); ++BBI) {
|
|
unsigned PreviousEdges = SI->getNumCases() - ContiguousCases->size();
|
|
if (OtherDest == SI->getDefaultDest()) ++PreviousEdges;
|
|
for (unsigned I = 0, E = PreviousEdges - 1; I != E; ++I)
|
|
cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
|
|
}
|
|
|
|
// Drop the switch.
|
|
SI->eraseFromParent();
|
|
|
|
return true;
|
|
}
|
|
|
|
/// EliminateDeadSwitchCases - Compute masked bits for the condition of a switch
|
|
/// and use it to remove dead cases.
|
|
static bool EliminateDeadSwitchCases(SwitchInst *SI, AssumptionCache *AC,
|
|
const DataLayout &DL) {
|
|
Value *Cond = SI->getCondition();
|
|
unsigned Bits = Cond->getType()->getIntegerBitWidth();
|
|
APInt KnownZero(Bits, 0), KnownOne(Bits, 0);
|
|
computeKnownBits(Cond, KnownZero, KnownOne, DL, 0, AC, SI);
|
|
|
|
// Gather dead cases.
|
|
SmallVector<ConstantInt*, 8> DeadCases;
|
|
for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) {
|
|
if ((I.getCaseValue()->getValue() & KnownZero) != 0 ||
|
|
(I.getCaseValue()->getValue() & KnownOne) != KnownOne) {
|
|
DeadCases.push_back(I.getCaseValue());
|
|
DEBUG(dbgs() << "SimplifyCFG: switch case '"
|
|
<< I.getCaseValue() << "' is dead.\n");
|
|
}
|
|
}
|
|
|
|
SmallVector<uint64_t, 8> Weights;
|
|
bool HasWeight = HasBranchWeights(SI);
|
|
if (HasWeight) {
|
|
GetBranchWeights(SI, Weights);
|
|
HasWeight = (Weights.size() == 1 + SI->getNumCases());
|
|
}
|
|
|
|
// Remove dead cases from the switch.
|
|
for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) {
|
|
SwitchInst::CaseIt Case = SI->findCaseValue(DeadCases[I]);
|
|
assert(Case != SI->case_default() &&
|
|
"Case was not found. Probably mistake in DeadCases forming.");
|
|
if (HasWeight) {
|
|
std::swap(Weights[Case.getCaseIndex()+1], Weights.back());
|
|
Weights.pop_back();
|
|
}
|
|
|
|
// Prune unused values from PHI nodes.
|
|
Case.getCaseSuccessor()->removePredecessor(SI->getParent());
|
|
SI->removeCase(Case);
|
|
}
|
|
if (HasWeight && Weights.size() >= 2) {
|
|
SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
|
|
SI->setMetadata(LLVMContext::MD_prof,
|
|
MDBuilder(SI->getParent()->getContext()).
|
|
createBranchWeights(MDWeights));
|
|
}
|
|
|
|
return !DeadCases.empty();
|
|
}
|
|
|
|
/// FindPHIForConditionForwarding - If BB would be eligible for simplification
|
|
/// by TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated
|
|
/// by an unconditional branch), look at the phi node for BB in the successor
|
|
/// block and see if the incoming value is equal to CaseValue. If so, return
|
|
/// the phi node, and set PhiIndex to BB's index in the phi node.
|
|
static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue,
|
|
BasicBlock *BB,
|
|
int *PhiIndex) {
|
|
if (BB->getFirstNonPHIOrDbg() != BB->getTerminator())
|
|
return nullptr; // BB must be empty to be a candidate for simplification.
|
|
if (!BB->getSinglePredecessor())
|
|
return nullptr; // BB must be dominated by the switch.
|
|
|
|
BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator());
|
|
if (!Branch || !Branch->isUnconditional())
|
|
return nullptr; // Terminator must be unconditional branch.
|
|
|
|
BasicBlock *Succ = Branch->getSuccessor(0);
|
|
|
|
BasicBlock::iterator I = Succ->begin();
|
|
while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
|
|
int Idx = PHI->getBasicBlockIndex(BB);
|
|
assert(Idx >= 0 && "PHI has no entry for predecessor?");
|
|
|
|
Value *InValue = PHI->getIncomingValue(Idx);
|
|
if (InValue != CaseValue) continue;
|
|
|
|
*PhiIndex = Idx;
|
|
return PHI;
|
|
}
|
|
|
|
return nullptr;
|
|
}
|
|
|
|
/// ForwardSwitchConditionToPHI - Try to forward the condition of a switch
|
|
/// instruction to a phi node dominated by the switch, if that would mean that
|
|
/// some of the destination blocks of the switch can be folded away.
|
|
/// Returns true if a change is made.
|
|
static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
|
|
typedef DenseMap<PHINode*, SmallVector<int,4> > ForwardingNodesMap;
|
|
ForwardingNodesMap ForwardingNodes;
|
|
|
|
for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) {
|
|
ConstantInt *CaseValue = I.getCaseValue();
|
|
BasicBlock *CaseDest = I.getCaseSuccessor();
|
|
|
|
int PhiIndex;
|
|
PHINode *PHI = FindPHIForConditionForwarding(CaseValue, CaseDest,
|
|
&PhiIndex);
|
|
if (!PHI) continue;
|
|
|
|
ForwardingNodes[PHI].push_back(PhiIndex);
|
|
}
|
|
|
|
bool Changed = false;
|
|
|
|
for (ForwardingNodesMap::iterator I = ForwardingNodes.begin(),
|
|
E = ForwardingNodes.end(); I != E; ++I) {
|
|
PHINode *Phi = I->first;
|
|
SmallVectorImpl<int> &Indexes = I->second;
|
|
|
|
if (Indexes.size() < 2) continue;
|
|
|
|
for (size_t I = 0, E = Indexes.size(); I != E; ++I)
|
|
Phi->setIncomingValue(Indexes[I], SI->getCondition());
|
|
Changed = true;
|
|
}
|
|
|
|
return Changed;
|
|
}
|
|
|
|
/// ValidLookupTableConstant - Return true if the backend will be able to handle
|
|
/// initializing an array of constants like C.
|
|
static bool ValidLookupTableConstant(Constant *C) {
|
|
if (C->isThreadDependent())
|
|
return false;
|
|
if (C->isDLLImportDependent())
|
|
return false;
|
|
|
|
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C))
|
|
return CE->isGEPWithNoNotionalOverIndexing();
|
|
|
|
return isa<ConstantFP>(C) ||
|
|
isa<ConstantInt>(C) ||
|
|
isa<ConstantPointerNull>(C) ||
|
|
isa<GlobalValue>(C) ||
|
|
isa<UndefValue>(C);
|
|
}
|
|
|
|
/// LookupConstant - If V is a Constant, return it. Otherwise, try to look up
|
|
/// its constant value in ConstantPool, returning 0 if it's not there.
|
|
static Constant *LookupConstant(Value *V,
|
|
const SmallDenseMap<Value*, Constant*>& ConstantPool) {
|
|
if (Constant *C = dyn_cast<Constant>(V))
|
|
return C;
|
|
return ConstantPool.lookup(V);
|
|
}
|
|
|
|
/// ConstantFold - Try to fold instruction I into a constant. This works for
|
|
/// simple instructions such as binary operations where both operands are
|
|
/// constant or can be replaced by constants from the ConstantPool. Returns the
|
|
/// resulting constant on success, 0 otherwise.
|
|
static Constant *
|
|
ConstantFold(Instruction *I, const DataLayout &DL,
|
|
const SmallDenseMap<Value *, Constant *> &ConstantPool) {
|
|
if (SelectInst *Select = dyn_cast<SelectInst>(I)) {
|
|
Constant *A = LookupConstant(Select->getCondition(), ConstantPool);
|
|
if (!A)
|
|
return nullptr;
|
|
if (A->isAllOnesValue())
|
|
return LookupConstant(Select->getTrueValue(), ConstantPool);
|
|
if (A->isNullValue())
|
|
return LookupConstant(Select->getFalseValue(), ConstantPool);
|
|
return nullptr;
|
|
}
|
|
|
|
SmallVector<Constant *, 4> COps;
|
|
for (unsigned N = 0, E = I->getNumOperands(); N != E; ++N) {
|
|
if (Constant *A = LookupConstant(I->getOperand(N), ConstantPool))
|
|
COps.push_back(A);
|
|
else
|
|
return nullptr;
|
|
}
|
|
|
|
if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
|
|
return ConstantFoldCompareInstOperands(Cmp->getPredicate(), COps[0],
|
|
COps[1], DL);
|
|
}
|
|
|
|
return ConstantFoldInstOperands(I->getOpcode(), I->getType(), COps, DL);
|
|
}
|
|
|
|
/// GetCaseResults - Try to determine the resulting constant values in phi nodes
|
|
/// at the common destination basic block, *CommonDest, for one of the case
|
|
/// destionations CaseDest corresponding to value CaseVal (0 for the default
|
|
/// case), of a switch instruction SI.
|
|
static bool
|
|
GetCaseResults(SwitchInst *SI, ConstantInt *CaseVal, BasicBlock *CaseDest,
|
|
BasicBlock **CommonDest,
|
|
SmallVectorImpl<std::pair<PHINode *, Constant *>> &Res,
|
|
const DataLayout &DL) {
|
|
// The block from which we enter the common destination.
|
|
BasicBlock *Pred = SI->getParent();
|
|
|
|
// If CaseDest is empty except for some side-effect free instructions through
|
|
// which we can constant-propagate the CaseVal, continue to its successor.
|
|
SmallDenseMap<Value*, Constant*> ConstantPool;
|
|
ConstantPool.insert(std::make_pair(SI->getCondition(), CaseVal));
|
|
for (BasicBlock::iterator I = CaseDest->begin(), E = CaseDest->end(); I != E;
|
|
++I) {
|
|
if (TerminatorInst *T = dyn_cast<TerminatorInst>(I)) {
|
|
// If the terminator is a simple branch, continue to the next block.
|
|
if (T->getNumSuccessors() != 1)
|
|
return false;
|
|
Pred = CaseDest;
|
|
CaseDest = T->getSuccessor(0);
|
|
} else if (isa<DbgInfoIntrinsic>(I)) {
|
|
// Skip debug intrinsic.
|
|
continue;
|
|
} else if (Constant *C = ConstantFold(I, DL, ConstantPool)) {
|
|
// Instruction is side-effect free and constant.
|
|
|
|
// If the instruction has uses outside this block or a phi node slot for
|
|
// the block, it is not safe to bypass the instruction since it would then
|
|
// no longer dominate all its uses.
|
|
for (auto &Use : I->uses()) {
|
|
User *User = Use.getUser();
|
|
if (Instruction *I = dyn_cast<Instruction>(User))
|
|
if (I->getParent() == CaseDest)
|
|
continue;
|
|
if (PHINode *Phi = dyn_cast<PHINode>(User))
|
|
if (Phi->getIncomingBlock(Use) == CaseDest)
|
|
continue;
|
|
return false;
|
|
}
|
|
|
|
ConstantPool.insert(std::make_pair(I, C));
|
|
} else {
|
|
break;
|
|
}
|
|
}
|
|
|
|
// If we did not have a CommonDest before, use the current one.
|
|
if (!*CommonDest)
|
|
*CommonDest = CaseDest;
|
|
// If the destination isn't the common one, abort.
|
|
if (CaseDest != *CommonDest)
|
|
return false;
|
|
|
|
// Get the values for this case from phi nodes in the destination block.
|
|
BasicBlock::iterator I = (*CommonDest)->begin();
|
|
while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
|
|
int Idx = PHI->getBasicBlockIndex(Pred);
|
|
if (Idx == -1)
|
|
continue;
|
|
|
|
Constant *ConstVal = LookupConstant(PHI->getIncomingValue(Idx),
|
|
ConstantPool);
|
|
if (!ConstVal)
|
|
return false;
|
|
|
|
// Be conservative about which kinds of constants we support.
|
|
if (!ValidLookupTableConstant(ConstVal))
|
|
return false;
|
|
|
|
Res.push_back(std::make_pair(PHI, ConstVal));
|
|
}
|
|
|
|
return Res.size() > 0;
|
|
}
|
|
|
|
// MapCaseToResult - Helper function used to
|
|
// add CaseVal to the list of cases that generate Result.
|
|
static void MapCaseToResult(ConstantInt *CaseVal,
|
|
SwitchCaseResultVectorTy &UniqueResults,
|
|
Constant *Result) {
|
|
for (auto &I : UniqueResults) {
|
|
if (I.first == Result) {
|
|
I.second.push_back(CaseVal);
|
|
return;
|
|
}
|
|
}
|
|
UniqueResults.push_back(std::make_pair(Result,
|
|
SmallVector<ConstantInt*, 4>(1, CaseVal)));
|
|
}
|
|
|
|
// InitializeUniqueCases - Helper function that initializes a map containing
|
|
// results for the PHI node of the common destination block for a switch
|
|
// instruction. Returns false if multiple PHI nodes have been found or if
|
|
// there is not a common destination block for the switch.
|
|
static bool InitializeUniqueCases(SwitchInst *SI, PHINode *&PHI,
|
|
BasicBlock *&CommonDest,
|
|
SwitchCaseResultVectorTy &UniqueResults,
|
|
Constant *&DefaultResult,
|
|
const DataLayout &DL) {
|
|
for (auto &I : SI->cases()) {
|
|
ConstantInt *CaseVal = I.getCaseValue();
|
|
|
|
// Resulting value at phi nodes for this case value.
|
|
SwitchCaseResultsTy Results;
|
|
if (!GetCaseResults(SI, CaseVal, I.getCaseSuccessor(), &CommonDest, Results,
|
|
DL))
|
|
return false;
|
|
|
|
// Only one value per case is permitted
|
|
if (Results.size() > 1)
|
|
return false;
|
|
MapCaseToResult(CaseVal, UniqueResults, Results.begin()->second);
|
|
|
|
// Check the PHI consistency.
|
|
if (!PHI)
|
|
PHI = Results[0].first;
|
|
else if (PHI != Results[0].first)
|
|
return false;
|
|
}
|
|
// Find the default result value.
|
|
SmallVector<std::pair<PHINode *, Constant *>, 1> DefaultResults;
|
|
BasicBlock *DefaultDest = SI->getDefaultDest();
|
|
GetCaseResults(SI, nullptr, SI->getDefaultDest(), &CommonDest, DefaultResults,
|
|
DL);
|
|
// If the default value is not found abort unless the default destination
|
|
// is unreachable.
|
|
DefaultResult =
|
|
DefaultResults.size() == 1 ? DefaultResults.begin()->second : nullptr;
|
|
if ((!DefaultResult &&
|
|
!isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg())))
|
|
return false;
|
|
|
|
return true;
|
|
}
|
|
|
|
// ConvertTwoCaseSwitch - Helper function that checks if it is possible to
|
|
// transform a switch with only two cases (or two cases + default)
|
|
// that produces a result into a value select.
|
|
// Example:
|
|
// switch (a) {
|
|
// case 10: %0 = icmp eq i32 %a, 10
|
|
// return 10; %1 = select i1 %0, i32 10, i32 4
|
|
// case 20: ----> %2 = icmp eq i32 %a, 20
|
|
// return 2; %3 = select i1 %2, i32 2, i32 %1
|
|
// default:
|
|
// return 4;
|
|
// }
|
|
static Value *
|
|
ConvertTwoCaseSwitch(const SwitchCaseResultVectorTy &ResultVector,
|
|
Constant *DefaultResult, Value *Condition,
|
|
IRBuilder<> &Builder) {
|
|
assert(ResultVector.size() == 2 &&
|
|
"We should have exactly two unique results at this point");
|
|
// If we are selecting between only two cases transform into a simple
|
|
// select or a two-way select if default is possible.
|
|
if (ResultVector[0].second.size() == 1 &&
|
|
ResultVector[1].second.size() == 1) {
|
|
ConstantInt *const FirstCase = ResultVector[0].second[0];
|
|
ConstantInt *const SecondCase = ResultVector[1].second[0];
|
|
|
|
bool DefaultCanTrigger = DefaultResult;
|
|
Value *SelectValue = ResultVector[1].first;
|
|
if (DefaultCanTrigger) {
|
|
Value *const ValueCompare =
|
|
Builder.CreateICmpEQ(Condition, SecondCase, "switch.selectcmp");
|
|
SelectValue = Builder.CreateSelect(ValueCompare, ResultVector[1].first,
|
|
DefaultResult, "switch.select");
|
|
}
|
|
Value *const ValueCompare =
|
|
Builder.CreateICmpEQ(Condition, FirstCase, "switch.selectcmp");
|
|
return Builder.CreateSelect(ValueCompare, ResultVector[0].first, SelectValue,
|
|
"switch.select");
|
|
}
|
|
|
|
return nullptr;
|
|
}
|
|
|
|
// RemoveSwitchAfterSelectConversion - Helper function to cleanup a switch
|
|
// instruction that has been converted into a select, fixing up PHI nodes and
|
|
// basic blocks.
|
|
static void RemoveSwitchAfterSelectConversion(SwitchInst *SI, PHINode *PHI,
|
|
Value *SelectValue,
|
|
IRBuilder<> &Builder) {
|
|
BasicBlock *SelectBB = SI->getParent();
|
|
while (PHI->getBasicBlockIndex(SelectBB) >= 0)
|
|
PHI->removeIncomingValue(SelectBB);
|
|
PHI->addIncoming(SelectValue, SelectBB);
|
|
|
|
Builder.CreateBr(PHI->getParent());
|
|
|
|
// Remove the switch.
|
|
for (unsigned i = 0, e = SI->getNumSuccessors(); i < e; ++i) {
|
|
BasicBlock *Succ = SI->getSuccessor(i);
|
|
|
|
if (Succ == PHI->getParent())
|
|
continue;
|
|
Succ->removePredecessor(SelectBB);
|
|
}
|
|
SI->eraseFromParent();
|
|
}
|
|
|
|
/// SwitchToSelect - If the switch is only used to initialize one or more
|
|
/// phi nodes in a common successor block with only two different
|
|
/// constant values, replace the switch with select.
|
|
static bool SwitchToSelect(SwitchInst *SI, IRBuilder<> &Builder,
|
|
AssumptionCache *AC, const DataLayout &DL) {
|
|
Value *const Cond = SI->getCondition();
|
|
PHINode *PHI = nullptr;
|
|
BasicBlock *CommonDest = nullptr;
|
|
Constant *DefaultResult;
|
|
SwitchCaseResultVectorTy UniqueResults;
|
|
// Collect all the cases that will deliver the same value from the switch.
|
|
if (!InitializeUniqueCases(SI, PHI, CommonDest, UniqueResults, DefaultResult,
|
|
DL))
|
|
return false;
|
|
// Selects choose between maximum two values.
|
|
if (UniqueResults.size() != 2)
|
|
return false;
|
|
assert(PHI != nullptr && "PHI for value select not found");
|
|
|
|
Builder.SetInsertPoint(SI);
|
|
Value *SelectValue = ConvertTwoCaseSwitch(
|
|
UniqueResults,
|
|
DefaultResult, Cond, Builder);
|
|
if (SelectValue) {
|
|
RemoveSwitchAfterSelectConversion(SI, PHI, SelectValue, Builder);
|
|
return true;
|
|
}
|
|
// The switch couldn't be converted into a select.
|
|
return false;
|
|
}
|
|
|
|
namespace {
|
|
/// SwitchLookupTable - This class represents a lookup table that can be used
|
|
/// to replace a switch.
|
|
class SwitchLookupTable {
|
|
public:
|
|
/// SwitchLookupTable - Create a lookup table to use as a switch replacement
|
|
/// with the contents of Values, using DefaultValue to fill any holes in the
|
|
/// table.
|
|
SwitchLookupTable(
|
|
Module &M, uint64_t TableSize, ConstantInt *Offset,
|
|
const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values,
|
|
Constant *DefaultValue, const DataLayout &DL);
|
|
|
|
/// BuildLookup - Build instructions with Builder to retrieve the value at
|
|
/// the position given by Index in the lookup table.
|
|
Value *BuildLookup(Value *Index, IRBuilder<> &Builder);
|
|
|
|
/// WouldFitInRegister - Return true if a table with TableSize elements of
|
|
/// type ElementType would fit in a target-legal register.
|
|
static bool WouldFitInRegister(const DataLayout &DL, uint64_t TableSize,
|
|
const Type *ElementType);
|
|
|
|
private:
|
|
// Depending on the contents of the table, it can be represented in
|
|
// different ways.
|
|
enum {
|
|
// For tables where each element contains the same value, we just have to
|
|
// store that single value and return it for each lookup.
|
|
SingleValueKind,
|
|
|
|
// For tables where there is a linear relationship between table index
|
|
// and values. We calculate the result with a simple multiplication
|
|
// and addition instead of a table lookup.
|
|
LinearMapKind,
|
|
|
|
// For small tables with integer elements, we can pack them into a bitmap
|
|
// that fits into a target-legal register. Values are retrieved by
|
|
// shift and mask operations.
|
|
BitMapKind,
|
|
|
|
// The table is stored as an array of values. Values are retrieved by load
|
|
// instructions from the table.
|
|
ArrayKind
|
|
} Kind;
|
|
|
|
// For SingleValueKind, this is the single value.
|
|
Constant *SingleValue;
|
|
|
|
// For BitMapKind, this is the bitmap.
|
|
ConstantInt *BitMap;
|
|
IntegerType *BitMapElementTy;
|
|
|
|
// For LinearMapKind, these are the constants used to derive the value.
|
|
ConstantInt *LinearOffset;
|
|
ConstantInt *LinearMultiplier;
|
|
|
|
// For ArrayKind, this is the array.
|
|
GlobalVariable *Array;
|
|
};
|
|
}
|
|
|
|
SwitchLookupTable::SwitchLookupTable(
|
|
Module &M, uint64_t TableSize, ConstantInt *Offset,
|
|
const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values,
|
|
Constant *DefaultValue, const DataLayout &DL)
|
|
: SingleValue(nullptr), BitMap(nullptr), BitMapElementTy(nullptr),
|
|
LinearOffset(nullptr), LinearMultiplier(nullptr), Array(nullptr) {
|
|
assert(Values.size() && "Can't build lookup table without values!");
|
|
assert(TableSize >= Values.size() && "Can't fit values in table!");
|
|
|
|
// If all values in the table are equal, this is that value.
|
|
SingleValue = Values.begin()->second;
|
|
|
|
Type *ValueType = Values.begin()->second->getType();
|
|
|
|
// Build up the table contents.
|
|
SmallVector<Constant*, 64> TableContents(TableSize);
|
|
for (size_t I = 0, E = Values.size(); I != E; ++I) {
|
|
ConstantInt *CaseVal = Values[I].first;
|
|
Constant *CaseRes = Values[I].second;
|
|
assert(CaseRes->getType() == ValueType);
|
|
|
|
uint64_t Idx = (CaseVal->getValue() - Offset->getValue())
|
|
.getLimitedValue();
|
|
TableContents[Idx] = CaseRes;
|
|
|
|
if (CaseRes != SingleValue)
|
|
SingleValue = nullptr;
|
|
}
|
|
|
|
// Fill in any holes in the table with the default result.
|
|
if (Values.size() < TableSize) {
|
|
assert(DefaultValue &&
|
|
"Need a default value to fill the lookup table holes.");
|
|
assert(DefaultValue->getType() == ValueType);
|
|
for (uint64_t I = 0; I < TableSize; ++I) {
|
|
if (!TableContents[I])
|
|
TableContents[I] = DefaultValue;
|
|
}
|
|
|
|
if (DefaultValue != SingleValue)
|
|
SingleValue = nullptr;
|
|
}
|
|
|
|
// If each element in the table contains the same value, we only need to store
|
|
// that single value.
|
|
if (SingleValue) {
|
|
Kind = SingleValueKind;
|
|
return;
|
|
}
|
|
|
|
// Check if we can derive the value with a linear transformation from the
|
|
// table index.
|
|
if (isa<IntegerType>(ValueType)) {
|
|
bool LinearMappingPossible = true;
|
|
APInt PrevVal;
|
|
APInt DistToPrev;
|
|
assert(TableSize >= 2 && "Should be a SingleValue table.");
|
|
// Check if there is the same distance between two consecutive values.
|
|
for (uint64_t I = 0; I < TableSize; ++I) {
|
|
ConstantInt *ConstVal = dyn_cast<ConstantInt>(TableContents[I]);
|
|
if (!ConstVal) {
|
|
// This is an undef. We could deal with it, but undefs in lookup tables
|
|
// are very seldom. It's probably not worth the additional complexity.
|
|
LinearMappingPossible = false;
|
|
break;
|
|
}
|
|
APInt Val = ConstVal->getValue();
|
|
if (I != 0) {
|
|
APInt Dist = Val - PrevVal;
|
|
if (I == 1) {
|
|
DistToPrev = Dist;
|
|
} else if (Dist != DistToPrev) {
|
|
LinearMappingPossible = false;
|
|
break;
|
|
}
|
|
}
|
|
PrevVal = Val;
|
|
}
|
|
if (LinearMappingPossible) {
|
|
LinearOffset = cast<ConstantInt>(TableContents[0]);
|
|
LinearMultiplier = ConstantInt::get(M.getContext(), DistToPrev);
|
|
Kind = LinearMapKind;
|
|
++NumLinearMaps;
|
|
return;
|
|
}
|
|
}
|
|
|
|
// If the type is integer and the table fits in a register, build a bitmap.
|
|
if (WouldFitInRegister(DL, TableSize, ValueType)) {
|
|
IntegerType *IT = cast<IntegerType>(ValueType);
|
|
APInt TableInt(TableSize * IT->getBitWidth(), 0);
|
|
for (uint64_t I = TableSize; I > 0; --I) {
|
|
TableInt <<= IT->getBitWidth();
|
|
// Insert values into the bitmap. Undef values are set to zero.
|
|
if (!isa<UndefValue>(TableContents[I - 1])) {
|
|
ConstantInt *Val = cast<ConstantInt>(TableContents[I - 1]);
|
|
TableInt |= Val->getValue().zext(TableInt.getBitWidth());
|
|
}
|
|
}
|
|
BitMap = ConstantInt::get(M.getContext(), TableInt);
|
|
BitMapElementTy = IT;
|
|
Kind = BitMapKind;
|
|
++NumBitMaps;
|
|
return;
|
|
}
|
|
|
|
// Store the table in an array.
|
|
ArrayType *ArrayTy = ArrayType::get(ValueType, TableSize);
|
|
Constant *Initializer = ConstantArray::get(ArrayTy, TableContents);
|
|
|
|
Array = new GlobalVariable(M, ArrayTy, /*constant=*/ true,
|
|
GlobalVariable::PrivateLinkage,
|
|
Initializer,
|
|
"switch.table");
|
|
Array->setUnnamedAddr(true);
|
|
Kind = ArrayKind;
|
|
}
|
|
|
|
Value *SwitchLookupTable::BuildLookup(Value *Index, IRBuilder<> &Builder) {
|
|
switch (Kind) {
|
|
case SingleValueKind:
|
|
return SingleValue;
|
|
case LinearMapKind: {
|
|
// Derive the result value from the input value.
|
|
Value *Result = Builder.CreateIntCast(Index, LinearMultiplier->getType(),
|
|
false, "switch.idx.cast");
|
|
if (!LinearMultiplier->isOne())
|
|
Result = Builder.CreateMul(Result, LinearMultiplier, "switch.idx.mult");
|
|
if (!LinearOffset->isZero())
|
|
Result = Builder.CreateAdd(Result, LinearOffset, "switch.offset");
|
|
return Result;
|
|
}
|
|
case BitMapKind: {
|
|
// Type of the bitmap (e.g. i59).
|
|
IntegerType *MapTy = BitMap->getType();
|
|
|
|
// Cast Index to the same type as the bitmap.
|
|
// Note: The Index is <= the number of elements in the table, so
|
|
// truncating it to the width of the bitmask is safe.
|
|
Value *ShiftAmt = Builder.CreateZExtOrTrunc(Index, MapTy, "switch.cast");
|
|
|
|
// Multiply the shift amount by the element width.
|
|
ShiftAmt = Builder.CreateMul(ShiftAmt,
|
|
ConstantInt::get(MapTy, BitMapElementTy->getBitWidth()),
|
|
"switch.shiftamt");
|
|
|
|
// Shift down.
|
|
Value *DownShifted = Builder.CreateLShr(BitMap, ShiftAmt,
|
|
"switch.downshift");
|
|
// Mask off.
|
|
return Builder.CreateTrunc(DownShifted, BitMapElementTy,
|
|
"switch.masked");
|
|
}
|
|
case ArrayKind: {
|
|
// Make sure the table index will not overflow when treated as signed.
|
|
IntegerType *IT = cast<IntegerType>(Index->getType());
|
|
uint64_t TableSize = Array->getInitializer()->getType()
|
|
->getArrayNumElements();
|
|
if (TableSize > (1ULL << (IT->getBitWidth() - 1)))
|
|
Index = Builder.CreateZExt(Index,
|
|
IntegerType::get(IT->getContext(),
|
|
IT->getBitWidth() + 1),
|
|
"switch.tableidx.zext");
|
|
|
|
Value *GEPIndices[] = { Builder.getInt32(0), Index };
|
|
Value *GEP = Builder.CreateInBoundsGEP(Array->getValueType(), Array,
|
|
GEPIndices, "switch.gep");
|
|
return Builder.CreateLoad(GEP, "switch.load");
|
|
}
|
|
}
|
|
llvm_unreachable("Unknown lookup table kind!");
|
|
}
|
|
|
|
bool SwitchLookupTable::WouldFitInRegister(const DataLayout &DL,
|
|
uint64_t TableSize,
|
|
const Type *ElementType) {
|
|
const IntegerType *IT = dyn_cast<IntegerType>(ElementType);
|
|
if (!IT)
|
|
return false;
|
|
// FIXME: If the type is wider than it needs to be, e.g. i8 but all values
|
|
// are <= 15, we could try to narrow the type.
|
|
|
|
// Avoid overflow, fitsInLegalInteger uses unsigned int for the width.
|
|
if (TableSize >= UINT_MAX/IT->getBitWidth())
|
|
return false;
|
|
return DL.fitsInLegalInteger(TableSize * IT->getBitWidth());
|
|
}
|
|
|
|
/// ShouldBuildLookupTable - Determine whether a lookup table should be built
|
|
/// for this switch, based on the number of cases, size of the table and the
|
|
/// types of the results.
|
|
static bool
|
|
ShouldBuildLookupTable(SwitchInst *SI, uint64_t TableSize,
|
|
const TargetTransformInfo &TTI, const DataLayout &DL,
|
|
const SmallDenseMap<PHINode *, Type *> &ResultTypes) {
|
|
if (SI->getNumCases() > TableSize || TableSize >= UINT64_MAX / 10)
|
|
return false; // TableSize overflowed, or mul below might overflow.
|
|
|
|
bool AllTablesFitInRegister = true;
|
|
bool HasIllegalType = false;
|
|
for (const auto &I : ResultTypes) {
|
|
Type *Ty = I.second;
|
|
|
|
// Saturate this flag to true.
|
|
HasIllegalType = HasIllegalType || !TTI.isTypeLegal(Ty);
|
|
|
|
// Saturate this flag to false.
|
|
AllTablesFitInRegister = AllTablesFitInRegister &&
|
|
SwitchLookupTable::WouldFitInRegister(DL, TableSize, Ty);
|
|
|
|
// If both flags saturate, we're done. NOTE: This *only* works with
|
|
// saturating flags, and all flags have to saturate first due to the
|
|
// non-deterministic behavior of iterating over a dense map.
|
|
if (HasIllegalType && !AllTablesFitInRegister)
|
|
break;
|
|
}
|
|
|
|
// If each table would fit in a register, we should build it anyway.
|
|
if (AllTablesFitInRegister)
|
|
return true;
|
|
|
|
// Don't build a table that doesn't fit in-register if it has illegal types.
|
|
if (HasIllegalType)
|
|
return false;
|
|
|
|
// The table density should be at least 40%. This is the same criterion as for
|
|
// jump tables, see SelectionDAGBuilder::handleJTSwitchCase.
|
|
// FIXME: Find the best cut-off.
|
|
return SI->getNumCases() * 10 >= TableSize * 4;
|
|
}
|
|
|
|
/// Try to reuse the switch table index compare. Following pattern:
|
|
/// \code
|
|
/// if (idx < tablesize)
|
|
/// r = table[idx]; // table does not contain default_value
|
|
/// else
|
|
/// r = default_value;
|
|
/// if (r != default_value)
|
|
/// ...
|
|
/// \endcode
|
|
/// Is optimized to:
|
|
/// \code
|
|
/// cond = idx < tablesize;
|
|
/// if (cond)
|
|
/// r = table[idx];
|
|
/// else
|
|
/// r = default_value;
|
|
/// if (cond)
|
|
/// ...
|
|
/// \endcode
|
|
/// Jump threading will then eliminate the second if(cond).
|
|
static void reuseTableCompare(User *PhiUser, BasicBlock *PhiBlock,
|
|
BranchInst *RangeCheckBranch, Constant *DefaultValue,
|
|
const SmallVectorImpl<std::pair<ConstantInt*, Constant*> >& Values) {
|
|
|
|
ICmpInst *CmpInst = dyn_cast<ICmpInst>(PhiUser);
|
|
if (!CmpInst)
|
|
return;
|
|
|
|
// We require that the compare is in the same block as the phi so that jump
|
|
// threading can do its work afterwards.
|
|
if (CmpInst->getParent() != PhiBlock)
|
|
return;
|
|
|
|
Constant *CmpOp1 = dyn_cast<Constant>(CmpInst->getOperand(1));
|
|
if (!CmpOp1)
|
|
return;
|
|
|
|
Value *RangeCmp = RangeCheckBranch->getCondition();
|
|
Constant *TrueConst = ConstantInt::getTrue(RangeCmp->getType());
|
|
Constant *FalseConst = ConstantInt::getFalse(RangeCmp->getType());
|
|
|
|
// Check if the compare with the default value is constant true or false.
|
|
Constant *DefaultConst = ConstantExpr::getICmp(CmpInst->getPredicate(),
|
|
DefaultValue, CmpOp1, true);
|
|
if (DefaultConst != TrueConst && DefaultConst != FalseConst)
|
|
return;
|
|
|
|
// Check if the compare with the case values is distinct from the default
|
|
// compare result.
|
|
for (auto ValuePair : Values) {
|
|
Constant *CaseConst = ConstantExpr::getICmp(CmpInst->getPredicate(),
|
|
ValuePair.second, CmpOp1, true);
|
|
if (!CaseConst || CaseConst == DefaultConst)
|
|
return;
|
|
assert((CaseConst == TrueConst || CaseConst == FalseConst) &&
|
|
"Expect true or false as compare result.");
|
|
}
|
|
|
|
// Check if the branch instruction dominates the phi node. It's a simple
|
|
// dominance check, but sufficient for our needs.
|
|
// Although this check is invariant in the calling loops, it's better to do it
|
|
// at this late stage. Practically we do it at most once for a switch.
|
|
BasicBlock *BranchBlock = RangeCheckBranch->getParent();
|
|
for (auto PI = pred_begin(PhiBlock), E = pred_end(PhiBlock); PI != E; ++PI) {
|
|
BasicBlock *Pred = *PI;
|
|
if (Pred != BranchBlock && Pred->getUniquePredecessor() != BranchBlock)
|
|
return;
|
|
}
|
|
|
|
if (DefaultConst == FalseConst) {
|
|
// The compare yields the same result. We can replace it.
|
|
CmpInst->replaceAllUsesWith(RangeCmp);
|
|
++NumTableCmpReuses;
|
|
} else {
|
|
// The compare yields the same result, just inverted. We can replace it.
|
|
Value *InvertedTableCmp = BinaryOperator::CreateXor(RangeCmp,
|
|
ConstantInt::get(RangeCmp->getType(), 1), "inverted.cmp",
|
|
RangeCheckBranch);
|
|
CmpInst->replaceAllUsesWith(InvertedTableCmp);
|
|
++NumTableCmpReuses;
|
|
}
|
|
}
|
|
|
|
/// SwitchToLookupTable - If the switch is only used to initialize one or more
|
|
/// phi nodes in a common successor block with different constant values,
|
|
/// replace the switch with lookup tables.
|
|
static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
|
|
const DataLayout &DL,
|
|
const TargetTransformInfo &TTI) {
|
|
assert(SI->getNumCases() > 1 && "Degenerate switch?");
|
|
|
|
// Only build lookup table when we have a target that supports it.
|
|
if (!TTI.shouldBuildLookupTables())
|
|
return false;
|
|
|
|
// FIXME: If the switch is too sparse for a lookup table, perhaps we could
|
|
// split off a dense part and build a lookup table for that.
|
|
|
|
// FIXME: This creates arrays of GEPs to constant strings, which means each
|
|
// GEP needs a runtime relocation in PIC code. We should just build one big
|
|
// string and lookup indices into that.
|
|
|
|
// Ignore switches with less than three cases. Lookup tables will not make them
|
|
// faster, so we don't analyze them.
|
|
if (SI->getNumCases() < 3)
|
|
return false;
|
|
|
|
// Figure out the corresponding result for each case value and phi node in the
|
|
// common destination, as well as the the min and max case values.
|
|
assert(SI->case_begin() != SI->case_end());
|
|
SwitchInst::CaseIt CI = SI->case_begin();
|
|
ConstantInt *MinCaseVal = CI.getCaseValue();
|
|
ConstantInt *MaxCaseVal = CI.getCaseValue();
|
|
|
|
BasicBlock *CommonDest = nullptr;
|
|
typedef SmallVector<std::pair<ConstantInt*, Constant*>, 4> ResultListTy;
|
|
SmallDenseMap<PHINode*, ResultListTy> ResultLists;
|
|
SmallDenseMap<PHINode*, Constant*> DefaultResults;
|
|
SmallDenseMap<PHINode*, Type*> ResultTypes;
|
|
SmallVector<PHINode*, 4> PHIs;
|
|
|
|
for (SwitchInst::CaseIt E = SI->case_end(); CI != E; ++CI) {
|
|
ConstantInt *CaseVal = CI.getCaseValue();
|
|
if (CaseVal->getValue().slt(MinCaseVal->getValue()))
|
|
MinCaseVal = CaseVal;
|
|
if (CaseVal->getValue().sgt(MaxCaseVal->getValue()))
|
|
MaxCaseVal = CaseVal;
|
|
|
|
// Resulting value at phi nodes for this case value.
|
|
typedef SmallVector<std::pair<PHINode*, Constant*>, 4> ResultsTy;
|
|
ResultsTy Results;
|
|
if (!GetCaseResults(SI, CaseVal, CI.getCaseSuccessor(), &CommonDest,
|
|
Results, DL))
|
|
return false;
|
|
|
|
// Append the result from this case to the list for each phi.
|
|
for (const auto &I : Results) {
|
|
PHINode *PHI = I.first;
|
|
Constant *Value = I.second;
|
|
if (!ResultLists.count(PHI))
|
|
PHIs.push_back(PHI);
|
|
ResultLists[PHI].push_back(std::make_pair(CaseVal, Value));
|
|
}
|
|
}
|
|
|
|
// Keep track of the result types.
|
|
for (PHINode *PHI : PHIs) {
|
|
ResultTypes[PHI] = ResultLists[PHI][0].second->getType();
|
|
}
|
|
|
|
uint64_t NumResults = ResultLists[PHIs[0]].size();
|
|
APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue();
|
|
uint64_t TableSize = RangeSpread.getLimitedValue() + 1;
|
|
bool TableHasHoles = (NumResults < TableSize);
|
|
|
|
// If the table has holes, we need a constant result for the default case
|
|
// or a bitmask that fits in a register.
|
|
SmallVector<std::pair<PHINode*, Constant*>, 4> DefaultResultsList;
|
|
bool HasDefaultResults = GetCaseResults(SI, nullptr, SI->getDefaultDest(),
|
|
&CommonDest, DefaultResultsList, DL);
|
|
|
|
bool NeedMask = (TableHasHoles && !HasDefaultResults);
|
|
if (NeedMask) {
|
|
// As an extra penalty for the validity test we require more cases.
|
|
if (SI->getNumCases() < 4) // FIXME: Find best threshold value (benchmark).
|
|
return false;
|
|
if (!DL.fitsInLegalInteger(TableSize))
|
|
return false;
|
|
}
|
|
|
|
for (const auto &I : DefaultResultsList) {
|
|
PHINode *PHI = I.first;
|
|
Constant *Result = I.second;
|
|
DefaultResults[PHI] = Result;
|
|
}
|
|
|
|
if (!ShouldBuildLookupTable(SI, TableSize, TTI, DL, ResultTypes))
|
|
return false;
|
|
|
|
// Create the BB that does the lookups.
|
|
Module &Mod = *CommonDest->getParent()->getParent();
|
|
BasicBlock *LookupBB = BasicBlock::Create(Mod.getContext(),
|
|
"switch.lookup",
|
|
CommonDest->getParent(),
|
|
CommonDest);
|
|
|
|
// Compute the table index value.
|
|
Builder.SetInsertPoint(SI);
|
|
Value *TableIndex = Builder.CreateSub(SI->getCondition(), MinCaseVal,
|
|
"switch.tableidx");
|
|
|
|
// Compute the maximum table size representable by the integer type we are
|
|
// switching upon.
|
|
unsigned CaseSize = MinCaseVal->getType()->getPrimitiveSizeInBits();
|
|
uint64_t MaxTableSize = CaseSize > 63 ? UINT64_MAX : 1ULL << CaseSize;
|
|
assert(MaxTableSize >= TableSize &&
|
|
"It is impossible for a switch to have more entries than the max "
|
|
"representable value of its input integer type's size.");
|
|
|
|
// If the default destination is unreachable, or if the lookup table covers
|
|
// all values of the conditional variable, branch directly to the lookup table
|
|
// BB. Otherwise, check that the condition is within the case range.
|
|
const bool DefaultIsReachable =
|
|
!isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
|
|
const bool GeneratingCoveredLookupTable = (MaxTableSize == TableSize);
|
|
BranchInst *RangeCheckBranch = nullptr;
|
|
|
|
if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
|
|
Builder.CreateBr(LookupBB);
|
|
// Note: We call removeProdecessor later since we need to be able to get the
|
|
// PHI value for the default case in case we're using a bit mask.
|
|
} else {
|
|
Value *Cmp = Builder.CreateICmpULT(TableIndex, ConstantInt::get(
|
|
MinCaseVal->getType(), TableSize));
|
|
RangeCheckBranch = Builder.CreateCondBr(Cmp, LookupBB, SI->getDefaultDest());
|
|
}
|
|
|
|
// Populate the BB that does the lookups.
|
|
Builder.SetInsertPoint(LookupBB);
|
|
|
|
if (NeedMask) {
|
|
// Before doing the lookup we do the hole check.
|
|
// The LookupBB is therefore re-purposed to do the hole check
|
|
// and we create a new LookupBB.
|
|
BasicBlock *MaskBB = LookupBB;
|
|
MaskBB->setName("switch.hole_check");
|
|
LookupBB = BasicBlock::Create(Mod.getContext(),
|
|
"switch.lookup",
|
|
CommonDest->getParent(),
|
|
CommonDest);
|
|
|
|
// Make the mask's bitwidth at least 8bit and a power-of-2 to avoid
|
|
// unnecessary illegal types.
|
|
uint64_t TableSizePowOf2 = NextPowerOf2(std::max(7ULL, TableSize - 1ULL));
|
|
APInt MaskInt(TableSizePowOf2, 0);
|
|
APInt One(TableSizePowOf2, 1);
|
|
// Build bitmask; fill in a 1 bit for every case.
|
|
const ResultListTy &ResultList = ResultLists[PHIs[0]];
|
|
for (size_t I = 0, E = ResultList.size(); I != E; ++I) {
|
|
uint64_t Idx = (ResultList[I].first->getValue() -
|
|
MinCaseVal->getValue()).getLimitedValue();
|
|
MaskInt |= One << Idx;
|
|
}
|
|
ConstantInt *TableMask = ConstantInt::get(Mod.getContext(), MaskInt);
|
|
|
|
// Get the TableIndex'th bit of the bitmask.
|
|
// If this bit is 0 (meaning hole) jump to the default destination,
|
|
// else continue with table lookup.
|
|
IntegerType *MapTy = TableMask->getType();
|
|
Value *MaskIndex = Builder.CreateZExtOrTrunc(TableIndex, MapTy,
|
|
"switch.maskindex");
|
|
Value *Shifted = Builder.CreateLShr(TableMask, MaskIndex,
|
|
"switch.shifted");
|
|
Value *LoBit = Builder.CreateTrunc(Shifted,
|
|
Type::getInt1Ty(Mod.getContext()),
|
|
"switch.lobit");
|
|
Builder.CreateCondBr(LoBit, LookupBB, SI->getDefaultDest());
|
|
|
|
Builder.SetInsertPoint(LookupBB);
|
|
AddPredecessorToBlock(SI->getDefaultDest(), MaskBB, SI->getParent());
|
|
}
|
|
|
|
if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
|
|
// We cached PHINodes in PHIs, to avoid accessing deleted PHINodes later,
|
|
// do not delete PHINodes here.
|
|
SI->getDefaultDest()->removePredecessor(SI->getParent(),
|
|
/*DontDeleteUselessPHIs=*/true);
|
|
}
|
|
|
|
bool ReturnedEarly = false;
|
|
for (size_t I = 0, E = PHIs.size(); I != E; ++I) {
|
|
PHINode *PHI = PHIs[I];
|
|
const ResultListTy &ResultList = ResultLists[PHI];
|
|
|
|
// If using a bitmask, use any value to fill the lookup table holes.
|
|
Constant *DV = NeedMask ? ResultLists[PHI][0].second : DefaultResults[PHI];
|
|
SwitchLookupTable Table(Mod, TableSize, MinCaseVal, ResultList, DV, DL);
|
|
|
|
Value *Result = Table.BuildLookup(TableIndex, Builder);
|
|
|
|
// If the result is used to return immediately from the function, we want to
|
|
// do that right here.
|
|
if (PHI->hasOneUse() && isa<ReturnInst>(*PHI->user_begin()) &&
|
|
PHI->user_back() == CommonDest->getFirstNonPHIOrDbg()) {
|
|
Builder.CreateRet(Result);
|
|
ReturnedEarly = true;
|
|
break;
|
|
}
|
|
|
|
// Do a small peephole optimization: re-use the switch table compare if
|
|
// possible.
|
|
if (!TableHasHoles && HasDefaultResults && RangeCheckBranch) {
|
|
BasicBlock *PhiBlock = PHI->getParent();
|
|
// Search for compare instructions which use the phi.
|
|
for (auto *User : PHI->users()) {
|
|
reuseTableCompare(User, PhiBlock, RangeCheckBranch, DV, ResultList);
|
|
}
|
|
}
|
|
|
|
PHI->addIncoming(Result, LookupBB);
|
|
}
|
|
|
|
if (!ReturnedEarly)
|
|
Builder.CreateBr(CommonDest);
|
|
|
|
// Remove the switch.
|
|
for (unsigned i = 0, e = SI->getNumSuccessors(); i < e; ++i) {
|
|
BasicBlock *Succ = SI->getSuccessor(i);
|
|
|
|
if (Succ == SI->getDefaultDest())
|
|
continue;
|
|
Succ->removePredecessor(SI->getParent());
|
|
}
|
|
SI->eraseFromParent();
|
|
|
|
++NumLookupTables;
|
|
if (NeedMask)
|
|
++NumLookupTablesHoles;
|
|
return true;
|
|
}
|
|
|
|
bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
|
|
BasicBlock *BB = SI->getParent();
|
|
|
|
if (isValueEqualityComparison(SI)) {
|
|
// If we only have one predecessor, and if it is a branch on this value,
|
|
// see if that predecessor totally determines the outcome of this switch.
|
|
if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
|
|
if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder))
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
|
|
Value *Cond = SI->getCondition();
|
|
if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
|
|
if (SimplifySwitchOnSelect(SI, Select))
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
|
|
// If the block only contains the switch, see if we can fold the block
|
|
// away into any preds.
|
|
BasicBlock::iterator BBI = BB->begin();
|
|
// Ignore dbg intrinsics.
|
|
while (isa<DbgInfoIntrinsic>(BBI))
|
|
++BBI;
|
|
if (SI == &*BBI)
|
|
if (FoldValueComparisonIntoPredecessors(SI, Builder))
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
}
|
|
|
|
// Try to transform the switch into an icmp and a branch.
|
|
if (TurnSwitchRangeIntoICmp(SI, Builder))
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
|
|
// Remove unreachable cases.
|
|
if (EliminateDeadSwitchCases(SI, AC, DL))
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
|
|
if (SwitchToSelect(SI, Builder, AC, DL))
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
|
|
if (ForwardSwitchConditionToPHI(SI))
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
|
|
if (SwitchToLookupTable(SI, Builder, DL, TTI))
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
|
|
return false;
|
|
}
|
|
|
|
bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
|
|
BasicBlock *BB = IBI->getParent();
|
|
bool Changed = false;
|
|
|
|
// Eliminate redundant destinations.
|
|
SmallPtrSet<Value *, 8> Succs;
|
|
for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
|
|
BasicBlock *Dest = IBI->getDestination(i);
|
|
if (!Dest->hasAddressTaken() || !Succs.insert(Dest).second) {
|
|
Dest->removePredecessor(BB);
|
|
IBI->removeDestination(i);
|
|
--i; --e;
|
|
Changed = true;
|
|
}
|
|
}
|
|
|
|
if (IBI->getNumDestinations() == 0) {
|
|
// If the indirectbr has no successors, change it to unreachable.
|
|
new UnreachableInst(IBI->getContext(), IBI);
|
|
EraseTerminatorInstAndDCECond(IBI);
|
|
return true;
|
|
}
|
|
|
|
if (IBI->getNumDestinations() == 1) {
|
|
// If the indirectbr has one successor, change it to a direct branch.
|
|
BranchInst::Create(IBI->getDestination(0), IBI);
|
|
EraseTerminatorInstAndDCECond(IBI);
|
|
return true;
|
|
}
|
|
|
|
if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
|
|
if (SimplifyIndirectBrOnSelect(IBI, SI))
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
}
|
|
return Changed;
|
|
}
|
|
|
|
/// Given an block with only a single landing pad and a unconditional branch
|
|
/// try to find another basic block which this one can be merged with. This
|
|
/// handles cases where we have multiple invokes with unique landing pads, but
|
|
/// a shared handler.
|
|
///
|
|
/// We specifically choose to not worry about merging non-empty blocks
|
|
/// here. That is a PRE/scheduling problem and is best solved elsewhere. In
|
|
/// practice, the optimizer produces empty landing pad blocks quite frequently
|
|
/// when dealing with exception dense code. (see: instcombine, gvn, if-else
|
|
/// sinking in this file)
|
|
///
|
|
/// This is primarily a code size optimization. We need to avoid performing
|
|
/// any transform which might inhibit optimization (such as our ability to
|
|
/// specialize a particular handler via tail commoning). We do this by not
|
|
/// merging any blocks which require us to introduce a phi. Since the same
|
|
/// values are flowing through both blocks, we don't loose any ability to
|
|
/// specialize. If anything, we make such specialization more likely.
|
|
///
|
|
/// TODO - This transformation could remove entries from a phi in the target
|
|
/// block when the inputs in the phi are the same for the two blocks being
|
|
/// merged. In some cases, this could result in removal of the PHI entirely.
|
|
static bool TryToMergeLandingPad(LandingPadInst *LPad, BranchInst *BI,
|
|
BasicBlock *BB) {
|
|
auto Succ = BB->getUniqueSuccessor();
|
|
assert(Succ);
|
|
// If there's a phi in the successor block, we'd likely have to introduce
|
|
// a phi into the merged landing pad block.
|
|
if (isa<PHINode>(*Succ->begin()))
|
|
return false;
|
|
|
|
for (BasicBlock *OtherPred : predecessors(Succ)) {
|
|
if (BB == OtherPred)
|
|
continue;
|
|
BasicBlock::iterator I = OtherPred->begin();
|
|
LandingPadInst *LPad2 = dyn_cast<LandingPadInst>(I);
|
|
if (!LPad2 || !LPad2->isIdenticalTo(LPad))
|
|
continue;
|
|
for (++I; isa<DbgInfoIntrinsic>(I); ++I) {}
|
|
BranchInst *BI2 = dyn_cast<BranchInst>(I);
|
|
if (!BI2 || !BI2->isIdenticalTo(BI))
|
|
continue;
|
|
|
|
// We've found an identical block. Update our predeccessors to take that
|
|
// path instead and make ourselves dead.
|
|
SmallSet<BasicBlock *, 16> Preds;
|
|
Preds.insert(pred_begin(BB), pred_end(BB));
|
|
for (BasicBlock *Pred : Preds) {
|
|
InvokeInst *II = cast<InvokeInst>(Pred->getTerminator());
|
|
assert(II->getNormalDest() != BB &&
|
|
II->getUnwindDest() == BB && "unexpected successor");
|
|
II->setUnwindDest(OtherPred);
|
|
}
|
|
|
|
// The debug info in OtherPred doesn't cover the merged control flow that
|
|
// used to go through BB. We need to delete it or update it.
|
|
for (auto I = OtherPred->begin(), E = OtherPred->end();
|
|
I != E;) {
|
|
Instruction &Inst = *I; I++;
|
|
if (isa<DbgInfoIntrinsic>(Inst))
|
|
Inst.eraseFromParent();
|
|
}
|
|
|
|
SmallSet<BasicBlock *, 16> Succs;
|
|
Succs.insert(succ_begin(BB), succ_end(BB));
|
|
for (BasicBlock *Succ : Succs) {
|
|
Succ->removePredecessor(BB);
|
|
}
|
|
|
|
IRBuilder<> Builder(BI);
|
|
Builder.CreateUnreachable();
|
|
BI->eraseFromParent();
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){
|
|
BasicBlock *BB = BI->getParent();
|
|
|
|
if (SinkCommon && SinkThenElseCodeToEnd(BI))
|
|
return true;
|
|
|
|
// If the Terminator is the only non-phi instruction, simplify the block.
|
|
BasicBlock::iterator I = BB->getFirstNonPHIOrDbg();
|
|
if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
|
|
TryToSimplifyUncondBranchFromEmptyBlock(BB))
|
|
return true;
|
|
|
|
// If the only instruction in the block is a seteq/setne comparison
|
|
// against a constant, try to simplify the block.
|
|
if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
|
|
if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
|
|
for (++I; isa<DbgInfoIntrinsic>(I); ++I)
|
|
;
|
|
if (I->isTerminator() &&
|
|
TryToSimplifyUncondBranchWithICmpInIt(ICI, Builder, DL, TTI,
|
|
BonusInstThreshold, AC))
|
|
return true;
|
|
}
|
|
|
|
// See if we can merge an empty landing pad block with another which is
|
|
// equivalent.
|
|
if (LandingPadInst *LPad = dyn_cast<LandingPadInst>(I)) {
|
|
for (++I; isa<DbgInfoIntrinsic>(I); ++I) {}
|
|
if (I->isTerminator() &&
|
|
TryToMergeLandingPad(LPad, BI, BB))
|
|
return true;
|
|
}
|
|
|
|
// If this basic block is ONLY a compare and a branch, and if a predecessor
|
|
// branches to us and our successor, fold the comparison into the
|
|
// predecessor and use logical operations to update the incoming value
|
|
// for PHI nodes in common successor.
|
|
if (FoldBranchToCommonDest(BI, BonusInstThreshold))
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
return false;
|
|
}
|
|
|
|
|
|
bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
|
|
BasicBlock *BB = BI->getParent();
|
|
|
|
// Conditional branch
|
|
if (isValueEqualityComparison(BI)) {
|
|
// If we only have one predecessor, and if it is a branch on this value,
|
|
// see if that predecessor totally determines the outcome of this
|
|
// switch.
|
|
if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
|
|
if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
|
|
// This block must be empty, except for the setcond inst, if it exists.
|
|
// Ignore dbg intrinsics.
|
|
BasicBlock::iterator I = BB->begin();
|
|
// Ignore dbg intrinsics.
|
|
while (isa<DbgInfoIntrinsic>(I))
|
|
++I;
|
|
if (&*I == BI) {
|
|
if (FoldValueComparisonIntoPredecessors(BI, Builder))
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
} else if (&*I == cast<Instruction>(BI->getCondition())){
|
|
++I;
|
|
// Ignore dbg intrinsics.
|
|
while (isa<DbgInfoIntrinsic>(I))
|
|
++I;
|
|
if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder))
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
}
|
|
}
|
|
|
|
// Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
|
|
if (SimplifyBranchOnICmpChain(BI, Builder, DL))
|
|
return true;
|
|
|
|
// If this basic block is ONLY a compare and a branch, and if a predecessor
|
|
// branches to us and one of our successors, fold the comparison into the
|
|
// predecessor and use logical operations to pick the right destination.
|
|
if (FoldBranchToCommonDest(BI, BonusInstThreshold))
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
|
|
// We have a conditional branch to two blocks that are only reachable
|
|
// from BI. We know that the condbr dominates the two blocks, so see if
|
|
// there is any identical code in the "then" and "else" blocks. If so, we
|
|
// can hoist it up to the branching block.
|
|
if (BI->getSuccessor(0)->getSinglePredecessor()) {
|
|
if (BI->getSuccessor(1)->getSinglePredecessor()) {
|
|
if (HoistThenElseCodeToIf(BI, TTI))
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
} else {
|
|
// If Successor #1 has multiple preds, we may be able to conditionally
|
|
// execute Successor #0 if it branches to Successor #1.
|
|
TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
|
|
if (Succ0TI->getNumSuccessors() == 1 &&
|
|
Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
|
|
if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0), TTI))
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
}
|
|
} else if (BI->getSuccessor(1)->getSinglePredecessor()) {
|
|
// If Successor #0 has multiple preds, we may be able to conditionally
|
|
// execute Successor #1 if it branches to Successor #0.
|
|
TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
|
|
if (Succ1TI->getNumSuccessors() == 1 &&
|
|
Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
|
|
if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1), TTI))
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
}
|
|
|
|
// If this is a branch on a phi node in the current block, thread control
|
|
// through this block if any PHI node entries are constants.
|
|
if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
|
|
if (PN->getParent() == BI->getParent())
|
|
if (FoldCondBranchOnPHI(BI, DL))
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
|
|
// Scan predecessor blocks for conditional branches.
|
|
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
|
|
if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
|
|
if (PBI != BI && PBI->isConditional())
|
|
if (SimplifyCondBranchToCondBranch(PBI, BI))
|
|
return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
|
|
|
|
return false;
|
|
}
|
|
|
|
/// Check if passing a value to an instruction will cause undefined behavior.
|
|
static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) {
|
|
Constant *C = dyn_cast<Constant>(V);
|
|
if (!C)
|
|
return false;
|
|
|
|
if (I->use_empty())
|
|
return false;
|
|
|
|
if (C->isNullValue()) {
|
|
// Only look at the first use, avoid hurting compile time with long uselists
|
|
User *Use = *I->user_begin();
|
|
|
|
// Now make sure that there are no instructions in between that can alter
|
|
// control flow (eg. calls)
|
|
for (BasicBlock::iterator i = ++BasicBlock::iterator(I); &*i != Use; ++i)
|
|
if (i == I->getParent()->end() || i->mayHaveSideEffects())
|
|
return false;
|
|
|
|
// Look through GEPs. A load from a GEP derived from NULL is still undefined
|
|
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use))
|
|
if (GEP->getPointerOperand() == I)
|
|
return passingValueIsAlwaysUndefined(V, GEP);
|
|
|
|
// Look through bitcasts.
|
|
if (BitCastInst *BC = dyn_cast<BitCastInst>(Use))
|
|
return passingValueIsAlwaysUndefined(V, BC);
|
|
|
|
// Load from null is undefined.
|
|
if (LoadInst *LI = dyn_cast<LoadInst>(Use))
|
|
if (!LI->isVolatile())
|
|
return LI->getPointerAddressSpace() == 0;
|
|
|
|
// Store to null is undefined.
|
|
if (StoreInst *SI = dyn_cast<StoreInst>(Use))
|
|
if (!SI->isVolatile())
|
|
return SI->getPointerAddressSpace() == 0 && SI->getPointerOperand() == I;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/// If BB has an incoming value that will always trigger undefined behavior
|
|
/// (eg. null pointer dereference), remove the branch leading here.
|
|
static bool removeUndefIntroducingPredecessor(BasicBlock *BB) {
|
|
for (BasicBlock::iterator i = BB->begin();
|
|
PHINode *PHI = dyn_cast<PHINode>(i); ++i)
|
|
for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
|
|
if (passingValueIsAlwaysUndefined(PHI->getIncomingValue(i), PHI)) {
|
|
TerminatorInst *T = PHI->getIncomingBlock(i)->getTerminator();
|
|
IRBuilder<> Builder(T);
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
|
|
BB->removePredecessor(PHI->getIncomingBlock(i));
|
|
// Turn uncoditional branches into unreachables and remove the dead
|
|
// destination from conditional branches.
|
|
if (BI->isUnconditional())
|
|
Builder.CreateUnreachable();
|
|
else
|
|
Builder.CreateBr(BI->getSuccessor(0) == BB ? BI->getSuccessor(1) :
|
|
BI->getSuccessor(0));
|
|
BI->eraseFromParent();
|
|
return true;
|
|
}
|
|
// TODO: SwitchInst.
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
bool SimplifyCFGOpt::run(BasicBlock *BB) {
|
|
bool Changed = false;
|
|
|
|
assert(BB && BB->getParent() && "Block not embedded in function!");
|
|
assert(BB->getTerminator() && "Degenerate basic block encountered!");
|
|
|
|
// Remove basic blocks that have no predecessors (except the entry block)...
|
|
// or that just have themself as a predecessor. These are unreachable.
|
|
if ((pred_empty(BB) &&
|
|
BB != &BB->getParent()->getEntryBlock()) ||
|
|
BB->getSinglePredecessor() == BB) {
|
|
DEBUG(dbgs() << "Removing BB: \n" << *BB);
|
|
DeleteDeadBlock(BB);
|
|
return true;
|
|
}
|
|
|
|
// Check to see if we can constant propagate this terminator instruction
|
|
// away...
|
|
Changed |= ConstantFoldTerminator(BB, true);
|
|
|
|
// Check for and eliminate duplicate PHI nodes in this block.
|
|
Changed |= EliminateDuplicatePHINodes(BB);
|
|
|
|
// Check for and remove branches that will always cause undefined behavior.
|
|
Changed |= removeUndefIntroducingPredecessor(BB);
|
|
|
|
// Merge basic blocks into their predecessor if there is only one distinct
|
|
// pred, and if there is only one distinct successor of the predecessor, and
|
|
// if there are no PHI nodes.
|
|
//
|
|
if (MergeBlockIntoPredecessor(BB))
|
|
return true;
|
|
|
|
IRBuilder<> Builder(BB);
|
|
|
|
// If there is a trivial two-entry PHI node in this basic block, and we can
|
|
// eliminate it, do so now.
|
|
if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
|
|
if (PN->getNumIncomingValues() == 2)
|
|
Changed |= FoldTwoEntryPHINode(PN, TTI, DL);
|
|
|
|
Builder.SetInsertPoint(BB->getTerminator());
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
|
|
if (BI->isUnconditional()) {
|
|
if (SimplifyUncondBranch(BI, Builder)) return true;
|
|
} else {
|
|
if (SimplifyCondBranch(BI, Builder)) return true;
|
|
}
|
|
} else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
|
|
if (SimplifyReturn(RI, Builder)) return true;
|
|
} else if (ResumeInst *RI = dyn_cast<ResumeInst>(BB->getTerminator())) {
|
|
if (SimplifyResume(RI, Builder)) return true;
|
|
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
|
|
if (SimplifySwitch(SI, Builder)) return true;
|
|
} else if (UnreachableInst *UI =
|
|
dyn_cast<UnreachableInst>(BB->getTerminator())) {
|
|
if (SimplifyUnreachable(UI)) return true;
|
|
} else if (IndirectBrInst *IBI =
|
|
dyn_cast<IndirectBrInst>(BB->getTerminator())) {
|
|
if (SimplifyIndirectBr(IBI)) return true;
|
|
}
|
|
|
|
return Changed;
|
|
}
|
|
|
|
/// SimplifyCFG - This function is used to do simplification of a CFG. For
|
|
/// example, it adjusts branches to branches to eliminate the extra hop, it
|
|
/// eliminates unreachable basic blocks, and does other "peephole" optimization
|
|
/// of the CFG. It returns true if a modification was made.
|
|
///
|
|
bool llvm::SimplifyCFG(BasicBlock *BB, const TargetTransformInfo &TTI,
|
|
unsigned BonusInstThreshold, AssumptionCache *AC) {
|
|
return SimplifyCFGOpt(TTI, BB->getModule()->getDataLayout(),
|
|
BonusInstThreshold, AC).run(BB);
|
|
}
|