mirror of
https://github.com/c64scene-ar/llvm-6502.git
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134057 91177308-0d34-0410-b5e6-96231b3b80d8
2782 lines
106 KiB
C++
2782 lines
106 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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#define DEBUG_TYPE "simplifycfg"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Constants.h"
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#include "llvm/Instructions.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/Type.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/GlobalVariable.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/ConstantRange.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/IRBuilder.h"
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#include "llvm/Support/NoFolder.h"
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#include "llvm/Support/raw_ostream.h"
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#include <algorithm>
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#include <set>
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#include <map>
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using namespace llvm;
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static cl::opt<unsigned>
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PHINodeFoldingThreshold("phi-node-folding-threshold", cl::Hidden, cl::init(1),
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cl::desc("Control the amount of phi node folding to perform (default = 1)"));
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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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STATISTIC(NumSpeculations, "Number of speculative executed instructions");
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namespace {
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class SimplifyCFGOpt {
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const TargetData *const TD;
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Value *isValueEqualityComparison(TerminatorInst *TI);
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BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
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std::vector<std::pair<ConstantInt*, BasicBlock*> > &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 SimplifyUnwind(UnwindInst *UI, 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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explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {}
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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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/// 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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/// GetIfCondition - Given a basic block (BB) with two predecessors (and at
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/// least one PHI node in it), check to see if the merge at this block is due
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/// to an "if condition". If so, return the boolean condition that determines
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/// which entry into BB will be taken. Also, return by references the block
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/// that will be entered from if the condition is true, and the block that will
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/// be entered if the condition is false.
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///
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/// This does no checking to see if the true/false blocks have large or unsavory
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/// instructions in them.
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static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
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BasicBlock *&IfFalse) {
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PHINode *SomePHI = cast<PHINode>(BB->begin());
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assert(SomePHI->getNumIncomingValues() == 2 &&
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"Function can only handle blocks with 2 predecessors!");
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BasicBlock *Pred1 = SomePHI->getIncomingBlock(0);
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BasicBlock *Pred2 = SomePHI->getIncomingBlock(1);
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// We can only handle branches. Other control flow will be lowered to
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// branches if possible anyway.
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BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
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BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
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if (Pred1Br == 0 || Pred2Br == 0)
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return 0;
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// Eliminate code duplication by ensuring that Pred1Br is conditional if
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// either are.
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if (Pred2Br->isConditional()) {
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// If both branches are conditional, we don't have an "if statement". In
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// reality, we could transform this case, but since the condition will be
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// required anyway, we stand no chance of eliminating it, so the xform is
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// probably not profitable.
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if (Pred1Br->isConditional())
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return 0;
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std::swap(Pred1, Pred2);
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std::swap(Pred1Br, Pred2Br);
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}
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if (Pred1Br->isConditional()) {
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// The only thing we have to watch out for here is to make sure that Pred2
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// doesn't have incoming edges from other blocks. If it does, the condition
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// doesn't dominate BB.
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if (Pred2->getSinglePredecessor() == 0)
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return 0;
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// If we found a conditional branch predecessor, make sure that it branches
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// to BB and Pred2Br. If it doesn't, this isn't an "if statement".
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if (Pred1Br->getSuccessor(0) == BB &&
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Pred1Br->getSuccessor(1) == Pred2) {
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IfTrue = Pred1;
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IfFalse = Pred2;
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} else if (Pred1Br->getSuccessor(0) == Pred2 &&
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Pred1Br->getSuccessor(1) == BB) {
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IfTrue = Pred2;
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IfFalse = Pred1;
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} else {
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// We know that one arm of the conditional goes to BB, so the other must
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// go somewhere unrelated, and this must not be an "if statement".
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return 0;
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}
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return Pred1Br->getCondition();
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}
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// Ok, if we got here, both predecessors end with an unconditional branch to
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// BB. Don't panic! If both blocks only have a single (identical)
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// predecessor, and THAT is a conditional branch, then we're all ok!
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BasicBlock *CommonPred = Pred1->getSinglePredecessor();
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if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor())
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return 0;
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// Otherwise, if this is a conditional branch, then we can use it!
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BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
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if (BI == 0) return 0;
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assert(BI->isConditional() && "Two successors but not conditional?");
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if (BI->getSuccessor(0) == Pred1) {
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IfTrue = Pred1;
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IfFalse = Pred2;
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} else {
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IfTrue = Pred2;
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IfFalse = Pred1;
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}
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return BI->getCondition();
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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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SmallPtrSet<Instruction*, 4> *AggressiveInsts,
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unsigned &CostRemaining) {
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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 == 0 || 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 == 0) 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 (!I->isSafeToSpeculativelyExecute())
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return false;
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unsigned Cost = 0;
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switch (I->getOpcode()) {
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default: return false; // Cannot hoist this out safely.
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case Instruction::Load:
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// We have to check to make sure there are no instructions before the
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// load in its basic block, as we are going to hoist the load out to its
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// predecessor.
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if (PBB->getFirstNonPHIOrDbg() != I)
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return false;
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Cost = 1;
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break;
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case Instruction::GetElementPtr:
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// GEPs are cheap if all indices are constant.
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if (!cast<GetElementPtrInst>(I)->hasAllConstantIndices())
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return false;
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Cost = 1;
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break;
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case Instruction::Add:
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case Instruction::Sub:
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case Instruction::And:
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case Instruction::Or:
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case Instruction::Xor:
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case Instruction::Shl:
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case Instruction::LShr:
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case Instruction::AShr:
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case Instruction::ICmp:
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case Instruction::Trunc:
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case Instruction::ZExt:
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case Instruction::SExt:
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Cost = 1;
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break; // These are all cheap and non-trapping instructions.
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case Instruction::Select:
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Cost = 2;
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break;
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}
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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))
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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 TargetData *TD) {
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// Normal constant int.
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ConstantInt *CI = dyn_cast<ConstantInt>(V);
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if (CI || !TD || !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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const IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
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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 0;
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}
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/// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
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/// collection of icmp eq/ne instructions that compare a value against a
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/// constant, return the value being compared, and stick the constant into the
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/// Values vector.
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static Value *
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GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
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const TargetData *TD, bool isEQ, unsigned &UsedICmps) {
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Instruction *I = dyn_cast<Instruction>(V);
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if (I == 0) return 0;
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// If this is an icmp against a constant, handle this as one of the cases.
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if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
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if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
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if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
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UsedICmps++;
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Vals.push_back(C);
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return I->getOperand(0);
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}
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// If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
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// the set.
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ConstantRange Span =
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ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue());
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// If this is an and/!= check then we want to optimize "x ugt 2" into
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// x != 0 && x != 1.
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if (!isEQ)
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Span = Span.inverse();
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// If there are a ton of values, we don't want to make a ginormous switch.
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if (Span.getSetSize().ugt(8) || Span.isEmptySet() ||
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// We don't handle wrapped sets yet.
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Span.isWrappedSet())
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return 0;
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for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
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Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
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UsedICmps++;
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return I->getOperand(0);
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}
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return 0;
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}
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// Otherwise, we can only handle an | or &, depending on isEQ.
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if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
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return 0;
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unsigned NumValsBeforeLHS = Vals.size();
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unsigned UsedICmpsBeforeLHS = UsedICmps;
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if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
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isEQ, UsedICmps)) {
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unsigned NumVals = Vals.size();
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unsigned UsedICmpsBeforeRHS = UsedICmps;
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if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
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isEQ, UsedICmps)) {
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if (LHS == RHS)
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return LHS;
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Vals.resize(NumVals);
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UsedICmps = UsedICmpsBeforeRHS;
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}
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// The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
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// set it and return success.
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if (Extra == 0 || Extra == I->getOperand(1)) {
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Extra = I->getOperand(1);
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return LHS;
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}
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Vals.resize(NumValsBeforeLHS);
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UsedICmps = UsedICmpsBeforeLHS;
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return 0;
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}
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// If the LHS can't be folded in, but Extra is available and RHS can, try to
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// use LHS as Extra.
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if (Extra == 0 || Extra == I->getOperand(0)) {
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Value *OldExtra = Extra;
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Extra = I->getOperand(0);
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if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
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isEQ, UsedICmps))
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return RHS;
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assert(Vals.size() == NumValsBeforeLHS);
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Extra = OldExtra;
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}
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return 0;
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}
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static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
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Instruction* Cond = 0;
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if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
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Cond = dyn_cast<Instruction>(SI->getCondition());
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} else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
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if (BI->isConditional())
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Cond = dyn_cast<Instruction>(BI->getCondition());
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} else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
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Cond = dyn_cast<Instruction>(IBI->getAddress());
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}
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TI->eraseFromParent();
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if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
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}
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/// isValueEqualityComparison - Return true if the specified terminator checks
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/// to see if a value is equal to constant integer value.
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Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
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Value *CV = 0;
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if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
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// Do not permit merging of large switch instructions into their
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// predecessors unless there is only one predecessor.
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if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
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pred_end(SI->getParent())) <= 128)
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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->getPredicate() == ICmpInst::ICMP_EQ ||
|
|
ICI->getPredicate() == ICmpInst::ICMP_NE) &&
|
|
GetConstantInt(ICI->getOperand(1), TD))
|
|
CV = ICI->getOperand(0);
|
|
|
|
// Unwrap any lossless ptrtoint cast.
|
|
if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
|
|
if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
|
|
CV = PTII->getOperand(0);
|
|
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<std::pair<ConstantInt*,
|
|
BasicBlock*> > &Cases) {
|
|
if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
|
|
Cases.reserve(SI->getNumCases());
|
|
for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
|
|
Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
|
|
return SI->getDefaultDest();
|
|
}
|
|
|
|
BranchInst *BI = cast<BranchInst>(TI);
|
|
ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
|
|
Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD),
|
|
BI->getSuccessor(ICI->getPredicate() ==
|
|
ICmpInst::ICMP_NE)));
|
|
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<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
|
|
for (unsigned i = 0, e = Cases.size(); i != e; ++i)
|
|
if (Cases[i].second == BB) {
|
|
Cases.erase(Cases.begin()+i);
|
|
--i; --e;
|
|
}
|
|
}
|
|
|
|
/// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
|
|
/// well.
|
|
static bool
|
|
ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
|
|
std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
|
|
std::vector<std::pair<ConstantInt*, BasicBlock*> > *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].first;
|
|
for (unsigned i = 0, e = V2->size(); i != e; ++i)
|
|
if (TheVal == (*V2)[i].first)
|
|
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].first == (*V2)[i2].first)
|
|
return true;
|
|
if ((*V1)[i1].first < (*V2)[i2].first)
|
|
++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.
|
|
|
|
// Find out information about when control will move from Pred to TI's block.
|
|
std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
|
|
BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
|
|
PredCases);
|
|
EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
|
|
|
|
// Find information about how control leaves this block.
|
|
std::vector<std::pair<ConstantInt*, BasicBlock*> > 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].second->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].first);
|
|
|
|
DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
|
|
<< "Through successor TI: " << *TI);
|
|
|
|
for (unsigned i = SI->getNumCases()-1; i != 0; --i)
|
|
if (DeadCases.count(SI->getCaseValue(i))) {
|
|
SI->getSuccessor(i)->removePredecessor(TI->getParent());
|
|
SI->removeCase(i);
|
|
}
|
|
|
|
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 = 0;
|
|
BasicBlock *TIBB = TI->getParent();
|
|
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
|
|
if (PredCases[i].second == TIBB) {
|
|
if (TIV != 0)
|
|
return false; // Cannot handle multiple values coming to this block.
|
|
TIV = PredCases[i].first;
|
|
}
|
|
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 = 0;
|
|
for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
|
|
if (ThisCases[i].first == TIV) {
|
|
TheRealDest = ThisCases[i].second;
|
|
break;
|
|
}
|
|
|
|
// If not handled by any explicit cases, it is handled by the default case.
|
|
if (TheRealDest == 0) 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 = 0;
|
|
|
|
// 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(const void *P1, const void *P2) {
|
|
const ConstantInt *LHS = *(const ConstantInt**)P1;
|
|
const ConstantInt *RHS = *(const ConstantInt**)P2;
|
|
if (LHS->getValue().ult(RHS->getValue()))
|
|
return 1;
|
|
if (LHS->getValue() == RHS->getValue())
|
|
return 0;
|
|
return -1;
|
|
}
|
|
|
|
/// 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<std::pair<ConstantInt*, BasicBlock*> > BBCases;
|
|
BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
|
|
|
|
std::vector<std::pair<ConstantInt*, BasicBlock*> > 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;
|
|
|
|
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].second != BB)
|
|
PTIHandled.insert(PredCases[i].first);
|
|
else {
|
|
// The default destination is BB, we don't need explicit targets.
|
|
std::swap(PredCases[i], PredCases.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);
|
|
}
|
|
for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
|
|
if (!PTIHandled.count(BBCases[i].first) &&
|
|
BBCases[i].second != BBDefault) {
|
|
PredCases.push_back(BBCases[i]);
|
|
NewSuccessors.push_back(BBCases[i].second);
|
|
}
|
|
|
|
} 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;
|
|
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
|
|
if (PredCases[i].second == BB) {
|
|
PTIHandled.insert(PredCases[i].first);
|
|
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].first)) {
|
|
// If this is one we are capable of getting...
|
|
PredCases.push_back(BBCases[i]);
|
|
NewSuccessors.push_back(BBCases[i].second);
|
|
PTIHandled.erase(BBCases[i].first);// 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) {
|
|
PredCases.push_back(std::make_pair(*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()) {
|
|
assert(TD && "Cannot switch on pointer without TargetData");
|
|
CV = Builder.CreatePtrToInt(CV, TD->getIntPtrType(CV->getContext()),
|
|
"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].first, PredCases[i].second);
|
|
|
|
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 = 0;
|
|
for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
|
|
if (NewSI->getSuccessor(i) == BB) {
|
|
if (InfLoopBlock == 0) {
|
|
// 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;
|
|
}
|
|
|
|
/// 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) {
|
|
// 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;
|
|
|
|
// If we get here, we can hoist at least one instruction.
|
|
BasicBlock *BIParent = BI->getParent();
|
|
|
|
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;
|
|
|
|
// 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);
|
|
I2->eraseFromParent();
|
|
|
|
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 true;
|
|
|
|
// 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 == 0)
|
|
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;
|
|
}
|
|
|
|
/// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
|
|
/// and an BB2 and the only successor of BB1 is BB2, hoist simple code
|
|
/// (for now, restricted to a single instruction that's side effect free) from
|
|
/// the BB1 into the branch block to speculatively execute it.
|
|
static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
|
|
// Only speculatively execution a single instruction (not counting the
|
|
// terminator) for now.
|
|
Instruction *HInst = NULL;
|
|
Instruction *Term = BB1->getTerminator();
|
|
for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
|
|
BBI != BBE; ++BBI) {
|
|
Instruction *I = BBI;
|
|
// Skip debug info.
|
|
if (isa<DbgInfoIntrinsic>(I)) continue;
|
|
if (I == Term) break;
|
|
|
|
if (HInst)
|
|
return false;
|
|
HInst = I;
|
|
}
|
|
if (!HInst)
|
|
return false;
|
|
|
|
// Be conservative for now. FP select instruction can often be expensive.
|
|
Value *BrCond = BI->getCondition();
|
|
if (isa<FCmpInst>(BrCond))
|
|
return false;
|
|
|
|
// If BB1 is actually on the false edge of the conditional branch, remember
|
|
// to swap the select operands later.
|
|
bool Invert = false;
|
|
if (BB1 != BI->getSuccessor(0)) {
|
|
assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
|
|
Invert = true;
|
|
}
|
|
|
|
// Turn
|
|
// BB:
|
|
// %t1 = icmp
|
|
// br i1 %t1, label %BB1, label %BB2
|
|
// BB1:
|
|
// %t3 = add %t2, c
|
|
// br label BB2
|
|
// BB2:
|
|
// =>
|
|
// BB:
|
|
// %t1 = icmp
|
|
// %t4 = add %t2, c
|
|
// %t3 = select i1 %t1, %t2, %t3
|
|
switch (HInst->getOpcode()) {
|
|
default: return false; // Not safe / profitable to hoist.
|
|
case Instruction::Add:
|
|
case Instruction::Sub:
|
|
// Not worth doing for vector ops.
|
|
if (HInst->getType()->isVectorTy())
|
|
return false;
|
|
break;
|
|
case Instruction::And:
|
|
case Instruction::Or:
|
|
case Instruction::Xor:
|
|
case Instruction::Shl:
|
|
case Instruction::LShr:
|
|
case Instruction::AShr:
|
|
// Don't mess with vector operations.
|
|
if (HInst->getType()->isVectorTy())
|
|
return false;
|
|
break; // These are all cheap and non-trapping instructions.
|
|
}
|
|
|
|
// If the instruction is obviously dead, don't try to predicate it.
|
|
if (HInst->use_empty()) {
|
|
HInst->eraseFromParent();
|
|
return true;
|
|
}
|
|
|
|
// Can we speculatively execute the instruction? And what is the value
|
|
// if the condition is false? Consider the phi uses, if the incoming value
|
|
// from the "if" block are all the same V, then V is the value of the
|
|
// select if the condition is false.
|
|
BasicBlock *BIParent = BI->getParent();
|
|
SmallVector<PHINode*, 4> PHIUses;
|
|
Value *FalseV = NULL;
|
|
|
|
BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
|
|
for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
|
|
UI != E; ++UI) {
|
|
// Ignore any user that is not a PHI node in BB2. These can only occur in
|
|
// unreachable blocks, because they would not be dominated by the instr.
|
|
PHINode *PN = dyn_cast<PHINode>(*UI);
|
|
if (!PN || PN->getParent() != BB2)
|
|
return false;
|
|
PHIUses.push_back(PN);
|
|
|
|
Value *PHIV = PN->getIncomingValueForBlock(BIParent);
|
|
if (!FalseV)
|
|
FalseV = PHIV;
|
|
else if (FalseV != PHIV)
|
|
return false; // Inconsistent value when condition is false.
|
|
}
|
|
|
|
assert(FalseV && "Must have at least one user, and it must be a PHI");
|
|
|
|
// Do not hoist the instruction if any of its operands are defined but not
|
|
// used in this BB. The transformation will prevent the operand from
|
|
// being sunk into the use block.
|
|
for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
|
|
i != e; ++i) {
|
|
Instruction *OpI = dyn_cast<Instruction>(*i);
|
|
if (OpI && OpI->getParent() == BIParent &&
|
|
!OpI->isUsedInBasicBlock(BIParent))
|
|
return false;
|
|
}
|
|
|
|
// If we get here, we can hoist the instruction. Try to place it
|
|
// before the icmp instruction preceding the conditional branch.
|
|
BasicBlock::iterator InsertPos = BI;
|
|
if (InsertPos != BIParent->begin())
|
|
--InsertPos;
|
|
// Skip debug info between condition and branch.
|
|
while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
|
|
--InsertPos;
|
|
if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
|
|
SmallPtrSet<Instruction *, 4> BB1Insns;
|
|
for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
|
|
BB1I != BB1E; ++BB1I)
|
|
BB1Insns.insert(BB1I);
|
|
for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
|
|
UI != UE; ++UI) {
|
|
Instruction *Use = cast<Instruction>(*UI);
|
|
if (!BB1Insns.count(Use)) continue;
|
|
|
|
// If BrCond uses the instruction that place it just before
|
|
// branch instruction.
|
|
InsertPos = BI;
|
|
break;
|
|
}
|
|
} else
|
|
InsertPos = BI;
|
|
BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
|
|
|
|
// Create a select whose true value is the speculatively executed value and
|
|
// false value is the previously determined FalseV.
|
|
IRBuilder<true, NoFolder> Builder(BI);
|
|
SelectInst *SI;
|
|
if (Invert)
|
|
SI = cast<SelectInst>
|
|
(Builder.CreateSelect(BrCond, FalseV, HInst,
|
|
FalseV->getName() + "." + HInst->getName()));
|
|
else
|
|
SI = cast<SelectInst>
|
|
(Builder.CreateSelect(BrCond, HInst, FalseV,
|
|
HInst->getName() + "." + FalseV->getName()));
|
|
|
|
// Make the PHI node use the select for all incoming values for "then" and
|
|
// "if" blocks.
|
|
for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
|
|
PHINode *PN = PHIUses[i];
|
|
for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
|
|
if (PN->getIncomingBlock(j) == BB1 || PN->getIncomingBlock(j) == BIParent)
|
|
PN->setIncomingValue(j, SI);
|
|
}
|
|
|
|
++NumSpeculations;
|
|
return true;
|
|
}
|
|
|
|
/// 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 (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
|
|
UI != E; ++UI) {
|
|
Instruction *U = cast<Instruction>(*UI);
|
|
if (U->getParent() != BB || isa<PHINode>(U)) 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 TargetData *TD) {
|
|
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;
|
|
|
|
// 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 == 0 || !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, TD)) {
|
|
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, TD) | 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 TargetData *TD) {
|
|
// 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;
|
|
|
|
for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
|
|
PHINode *PN = cast<PHINode>(II++);
|
|
if (Value *V = SimplifyInstruction(PN, TD)) {
|
|
PN->replaceAllUsesWith(V);
|
|
PN->eraseFromParent();
|
|
continue;
|
|
}
|
|
|
|
if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
|
|
MaxCostVal0) ||
|
|
!DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
|
|
MaxCostVal1))
|
|
return false;
|
|
}
|
|
|
|
// If we folded the 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 == 0) 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 = 0;
|
|
BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
|
|
BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
|
|
if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
|
|
IfBlock1 = 0;
|
|
} 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 = 0;
|
|
} 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;
|
|
}
|
|
|
|
/// 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) {
|
|
BasicBlock *BB = BI->getParent();
|
|
|
|
Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
|
|
if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
|
|
Cond->getParent() != BB || !Cond->hasOneUse())
|
|
return false;
|
|
|
|
// Only allow this if the condition is a simple instruction that can be
|
|
// executed unconditionally. It must be in the same block as the branch, and
|
|
// must be at the front of the block.
|
|
BasicBlock::iterator FrontIt = BB->front();
|
|
|
|
// Ignore dbg intrinsics.
|
|
while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
|
|
|
|
// Allow a single instruction to be hoisted in addition to the compare
|
|
// that feeds the branch. We later ensure that any values that _it_ uses
|
|
// were also live in the predecessor, so that we don't unnecessarily create
|
|
// register pressure or inhibit out-of-order execution.
|
|
Instruction *BonusInst = 0;
|
|
if (&*FrontIt != Cond &&
|
|
FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
|
|
FrontIt->isSafeToSpeculativelyExecute()) {
|
|
BonusInst = &*FrontIt;
|
|
++FrontIt;
|
|
|
|
// Ignore dbg intrinsics.
|
|
while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
|
|
}
|
|
|
|
// Only a single bonus inst is allowed.
|
|
if (&*FrontIt != Cond)
|
|
return false;
|
|
|
|
// Make sure the instruction after the condition is the cond branch.
|
|
BasicBlock::iterator CondIt = Cond; ++CondIt;
|
|
|
|
// Ingore dbg intrinsics.
|
|
while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt;
|
|
|
|
if (&*CondIt != BI)
|
|
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->getSuccessor(1);
|
|
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.
|
|
if (PBI == 0 || PBI->isUnconditional() || !SafeToMergeTerminators(BI, PBI))
|
|
continue;
|
|
|
|
// Determine if the two branches share a common destination.
|
|
Instruction::BinaryOps Opc;
|
|
bool InvertPredCond = false;
|
|
|
|
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;
|
|
|
|
// Ensure that any values used in the bonus instruction are also used
|
|
// by the terminator of the predecessor. This means that those values
|
|
// must already have been resolved, so we won't be inhibiting the
|
|
// out-of-order core by speculating them earlier.
|
|
if (BonusInst) {
|
|
// Collect the values used by the bonus inst
|
|
SmallPtrSet<Value*, 4> UsedValues;
|
|
for (Instruction::op_iterator OI = BonusInst->op_begin(),
|
|
OE = BonusInst->op_end(); OI != OE; ++OI) {
|
|
Value* V = *OI;
|
|
if (!isa<Constant>(V))
|
|
UsedValues.insert(V);
|
|
}
|
|
|
|
SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
|
|
Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
|
|
|
|
// Walk up to four levels back up the use-def chain of the predecessor's
|
|
// terminator to see if all those values were used. The choice of four
|
|
// levels is arbitrary, to provide a compile-time-cost bound.
|
|
while (!Worklist.empty()) {
|
|
std::pair<Value*, unsigned> Pair = Worklist.back();
|
|
Worklist.pop_back();
|
|
|
|
if (Pair.second >= 4) continue;
|
|
UsedValues.erase(Pair.first);
|
|
if (UsedValues.empty()) break;
|
|
|
|
if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
|
|
for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
|
|
OI != OE; ++OI)
|
|
Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
|
|
}
|
|
}
|
|
|
|
if (!UsedValues.empty()) return false;
|
|
}
|
|
|
|
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);
|
|
BasicBlock *OldTrue = PBI->getSuccessor(0);
|
|
BasicBlock *OldFalse = PBI->getSuccessor(1);
|
|
PBI->setSuccessor(0, OldFalse);
|
|
PBI->setSuccessor(1, OldTrue);
|
|
}
|
|
|
|
// If we have a bonus inst, clone it into the predecessor block.
|
|
Instruction *NewBonus = 0;
|
|
if (BonusInst) {
|
|
NewBonus = BonusInst->clone();
|
|
PredBlock->getInstList().insert(PBI, NewBonus);
|
|
NewBonus->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();
|
|
if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
|
|
PredBlock->getInstList().insert(PBI, New);
|
|
New->takeName(Cond);
|
|
Cond->setName(New->getName()+".old");
|
|
|
|
Instruction *NewCond =
|
|
cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(),
|
|
New, "or.cond"));
|
|
PBI->setCondition(NewCond);
|
|
if (PBI->getSuccessor(0) == BB) {
|
|
AddPredecessorToBlock(TrueDest, PredBlock, BB);
|
|
PBI->setSuccessor(0, TrueDest);
|
|
}
|
|
if (PBI->getSuccessor(1) == BB) {
|
|
AddPredecessorToBlock(FalseDest, PredBlock, BB);
|
|
PBI->setSuccessor(1, FalseDest);
|
|
}
|
|
|
|
// 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 is 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.
|
|
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;
|
|
|
|
// 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);
|
|
|
|
// 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){
|
|
// 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 : 0;
|
|
|
|
// 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 = 0;
|
|
else if (Succ == KeepEdge2)
|
|
KeepEdge2 = 0;
|
|
else
|
|
Succ->removePredecessor(OldTerm->getParent());
|
|
}
|
|
|
|
IRBuilder<> Builder(OldTerm);
|
|
Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
|
|
|
|
// Insert an appropriate new terminator.
|
|
if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
|
|
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.
|
|
Builder.CreateCondBr(Cond, TrueBB, FalseBB);
|
|
} 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 == 0)
|
|
// 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->getSuccessor(SI->findCaseValue(TrueVal));
|
|
BasicBlock *FalseBB = SI->getSuccessor(SI->findCaseValue(FalseVal));
|
|
|
|
// Perform the actual simplification.
|
|
return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB);
|
|
}
|
|
|
|
// 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);
|
|
}
|
|
|
|
/// 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,
|
|
const TargetData *TD,
|
|
IRBuilder<> &Builder) {
|
|
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 == 0 || !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, TD)) {
|
|
ICI->replaceAllUsesWith(V);
|
|
ICI->eraseFromParent();
|
|
}
|
|
// BB is now empty, so it is likely to simplify away.
|
|
return SimplifyCFG(BB) | 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) != 0) {
|
|
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) | 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->use_back());
|
|
if (PHIUse == 0 || 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);
|
|
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, const TargetData *TD,
|
|
IRBuilder<> &Builder) {
|
|
Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
|
|
if (Cond == 0) 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.
|
|
Value *CompVal = 0;
|
|
std::vector<ConstantInt*> Values;
|
|
bool TrueWhenEqual = true;
|
|
Value *ExtraCase = 0;
|
|
unsigned UsedICmps = 0;
|
|
|
|
if (Cond->getOpcode() == Instruction::Or) {
|
|
CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true,
|
|
UsedICmps);
|
|
} else if (Cond->getOpcode() == Instruction::And) {
|
|
CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false,
|
|
UsedICmps);
|
|
TrueWhenEqual = false;
|
|
}
|
|
|
|
// If we didn't have a multiply compared value, fail.
|
|
if (CompVal == 0) return false;
|
|
|
|
// Avoid turning single icmps into a switch.
|
|
if (UsedICmps <= 1)
|
|
return false;
|
|
|
|
// 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;
|
|
|
|
// 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()) {
|
|
assert(TD && "Cannot switch on pointer without TargetData");
|
|
CompVal = Builder.CreatePtrToInt(CompVal,
|
|
TD->getIntPtrType(CompVal->getContext()),
|
|
"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::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_begin(BB) == pred_end(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::SimplifyUnwind(UnwindInst *UI, IRBuilder<> &Builder) {
|
|
// Check to see if the first instruction in this block is just an unwind.
|
|
// If so, replace any invoke instructions which use this as an exception
|
|
// destination with call instructions.
|
|
BasicBlock *BB = UI->getParent();
|
|
if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
|
|
|
|
bool Changed = false;
|
|
SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
|
|
while (!Preds.empty()) {
|
|
BasicBlock *Pred = Preds.back();
|
|
InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator());
|
|
if (II && II->getUnwindDest() == BB) {
|
|
// Insert a new branch instruction before the invoke, because this
|
|
// is now a fall through.
|
|
Builder.SetInsertPoint(II);
|
|
BranchInst *BI = Builder.CreateBr(II->getNormalDest());
|
|
Pred->getInstList().remove(II); // 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.begin(), Args.end(),
|
|
II->getName());
|
|
CI->setCallingConv(II->getCallingConv());
|
|
CI->setAttributes(II->getAttributes());
|
|
// If the invoke produced a value, the Call now does instead.
|
|
II->replaceAllUsesWith(CI);
|
|
delete II;
|
|
Changed = true;
|
|
}
|
|
|
|
Preds.pop_back();
|
|
}
|
|
|
|
// If this block is now dead (and isn't the entry block), remove it.
|
|
if (pred_begin(BB) == pred_end(BB) &&
|
|
BB != &BB->getParent()->getEntryBlock()) {
|
|
// We know there are no successors, so just nuke the block.
|
|
BB->eraseFromParent();
|
|
return true;
|
|
}
|
|
|
|
return Changed;
|
|
}
|
|
|
|
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, like calls
|
|
// (which may never return) and volatile loads and stores.
|
|
if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
|
|
|
|
if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
|
|
if (SI->isVolatile())
|
|
break;
|
|
|
|
if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
|
|
if (LI->isVolatile())
|
|
break;
|
|
|
|
// 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 (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
|
|
if (SI->getSuccessor(i) == BB) {
|
|
BB->removePredecessor(SI->getParent());
|
|
SI->removeCase(i);
|
|
--i; --e;
|
|
Changed = true;
|
|
}
|
|
// If the default value is unreachable, figure out the most popular
|
|
// destination and make it the default.
|
|
if (SI->getSuccessor(0) == BB) {
|
|
std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity;
|
|
for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) {
|
|
std::pair<unsigned, unsigned>& entry =
|
|
Popularity[SI->getSuccessor(i)];
|
|
if (entry.first == 0) {
|
|
entry.first = 1;
|
|
entry.second = i;
|
|
} else {
|
|
entry.first++;
|
|
}
|
|
}
|
|
|
|
// Find the most popular block.
|
|
unsigned MaxPop = 0;
|
|
unsigned MaxIndex = 0;
|
|
BasicBlock *MaxBlock = 0;
|
|
for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator
|
|
I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
|
|
if (I->second.first > MaxPop ||
|
|
(I->second.first == MaxPop && MaxIndex > I->second.second)) {
|
|
MaxPop = I->second.first;
|
|
MaxIndex = I->second.second;
|
|
MaxBlock = I->first;
|
|
}
|
|
}
|
|
if (MaxBlock) {
|
|
// Make this the new default, allowing us to delete any explicit
|
|
// edges to it.
|
|
SI->setSuccessor(0, MaxBlock);
|
|
Changed = true;
|
|
|
|
// If MaxBlock has phinodes in it, remove MaxPop-1 entries from
|
|
// it.
|
|
if (isa<PHINode>(MaxBlock->begin()))
|
|
for (unsigned i = 0; i != MaxPop-1; ++i)
|
|
MaxBlock->removePredecessor(SI->getParent());
|
|
|
|
for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
|
|
if (SI->getSuccessor(i) == MaxBlock) {
|
|
SI->removeCase(i);
|
|
--i; --e;
|
|
}
|
|
}
|
|
}
|
|
} 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.begin(), Args.end(),
|
|
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_begin(BB) == pred_end(BB) &&
|
|
BB != &BB->getParent()->getEntryBlock()) {
|
|
// We know there are no successors, so just nuke the block.
|
|
BB->eraseFromParent();
|
|
return true;
|
|
}
|
|
|
|
return Changed;
|
|
}
|
|
|
|
/// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a
|
|
/// integer range comparison into a sub, an icmp and a branch.
|
|
static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
|
|
assert(SI->getNumCases() > 2 && "Degenerate switch?");
|
|
|
|
// Make sure all cases point to the same destination and gather the values.
|
|
SmallVector<ConstantInt *, 16> Cases;
|
|
Cases.push_back(SI->getCaseValue(1));
|
|
for (unsigned I = 2, E = SI->getNumCases(); I != E; ++I) {
|
|
if (SI->getSuccessor(I-1) != SI->getSuccessor(I))
|
|
return false;
|
|
Cases.push_back(SI->getCaseValue(I));
|
|
}
|
|
assert(Cases.size() == SI->getNumCases()-1 && "Not all cases gathered");
|
|
|
|
// Sort the case values, then check if they form a range we can transform.
|
|
array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
|
|
for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
|
|
if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
|
|
return false;
|
|
}
|
|
|
|
Constant *Offset = ConstantExpr::getNeg(Cases.back());
|
|
Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases()-1);
|
|
|
|
Value *Sub = SI->getCondition();
|
|
if (!Offset->isNullValue())
|
|
Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off");
|
|
Value *Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
|
|
Builder.CreateCondBr(Cmp, SI->getSuccessor(1), SI->getDefaultDest());
|
|
|
|
// Prune obsolete incoming values off the successor's PHI nodes.
|
|
for (BasicBlock::iterator BBI = SI->getSuccessor(1)->begin();
|
|
isa<PHINode>(BBI); ++BBI) {
|
|
for (unsigned I = 0, E = SI->getNumCases()-2; I != E; ++I)
|
|
cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
|
|
}
|
|
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) {
|
|
Value *Cond = SI->getCondition();
|
|
unsigned Bits = cast<IntegerType>(Cond->getType())->getBitWidth();
|
|
APInt KnownZero(Bits, 0), KnownOne(Bits, 0);
|
|
ComputeMaskedBits(Cond, APInt::getAllOnesValue(Bits), KnownZero, KnownOne);
|
|
|
|
// Gather dead cases.
|
|
SmallVector<ConstantInt*, 8> DeadCases;
|
|
for (unsigned I = 1, E = SI->getNumCases(); I != E; ++I) {
|
|
if ((SI->getCaseValue(I)->getValue() & KnownZero) != 0 ||
|
|
(SI->getCaseValue(I)->getValue() & KnownOne) != KnownOne) {
|
|
DeadCases.push_back(SI->getCaseValue(I));
|
|
DEBUG(dbgs() << "SimplifyCFG: switch case '"
|
|
<< SI->getCaseValue(I)->getValue() << "' is dead.\n");
|
|
}
|
|
}
|
|
|
|
// Remove dead cases from the switch.
|
|
for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) {
|
|
unsigned Case = SI->findCaseValue(DeadCases[I]);
|
|
// Prune unused values from PHI nodes.
|
|
SI->getSuccessor(Case)->removePredecessor(SI->getParent());
|
|
SI->removeCase(Case);
|
|
}
|
|
|
|
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 NULL; // BB must be empty to be a candidate for simplification.
|
|
if (!BB->getSinglePredecessor())
|
|
return NULL; // BB must be dominated by the switch.
|
|
|
|
BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator());
|
|
if (!Branch || !Branch->isUnconditional())
|
|
return NULL; // 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 NULL;
|
|
}
|
|
|
|
/// 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 (unsigned I = 1; I < SI->getNumCases(); ++I) { // 0 is the default case.
|
|
ConstantInt *CaseValue = SI->getCaseValue(I);
|
|
BasicBlock *CaseDest = SI->getSuccessor(I);
|
|
|
|
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;
|
|
SmallVector<int,4> &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;
|
|
}
|
|
|
|
bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
|
|
// If this switch is too complex to want to look at, ignore it.
|
|
if (!isValueEqualityComparison(SI))
|
|
return false;
|
|
|
|
BasicBlock *BB = SI->getParent();
|
|
|
|
// 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) | true;
|
|
|
|
Value *Cond = SI->getCondition();
|
|
if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
|
|
if (SimplifySwitchOnSelect(SI, Select))
|
|
return SimplifyCFG(BB) | 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) | true;
|
|
|
|
// Try to transform the switch into an icmp and a branch.
|
|
if (TurnSwitchRangeIntoICmp(SI, Builder))
|
|
return SimplifyCFG(BB) | true;
|
|
|
|
// Remove unreachable cases.
|
|
if (EliminateDeadSwitchCases(SI))
|
|
return SimplifyCFG(BB) | true;
|
|
|
|
if (ForwardSwitchConditionToPHI(SI))
|
|
return SimplifyCFG(BB) | 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)) {
|
|
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) | true;
|
|
}
|
|
return Changed;
|
|
}
|
|
|
|
bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){
|
|
BasicBlock *BB = BI->getParent();
|
|
|
|
// If the Terminator is the only non-phi instruction, simplify the block.
|
|
BasicBlock::iterator I = BB->getFirstNonPHIOrDbgOrLifetime();
|
|
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, TD, Builder))
|
|
return 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) | 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) | 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) | true;
|
|
}
|
|
}
|
|
|
|
// Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
|
|
if (SimplifyBranchOnICmpChain(BI, TD, Builder))
|
|
return 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() != 0) {
|
|
if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
|
|
if (HoistThenElseCodeToIf(BI))
|
|
return SimplifyCFG(BB) | 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)))
|
|
return SimplifyCFG(BB) | true;
|
|
}
|
|
} else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
|
|
// 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)))
|
|
return SimplifyCFG(BB) | 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, TD))
|
|
return SimplifyCFG(BB) | true;
|
|
|
|
// If this basic block is ONLY a setcc and a branch, and if a predecessor
|
|
// branches to us and one of our successors, fold the setcc into the
|
|
// predecessor and use logical operations to pick the right destination.
|
|
if (FoldBranchToCommonDest(BI))
|
|
return SimplifyCFG(BB) | 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) | true;
|
|
|
|
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_begin(BB) == pred_end(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);
|
|
|
|
// 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, TD);
|
|
|
|
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 (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 (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
|
|
if (SimplifyUnwind(UI, Builder)) 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 TargetData *TD) {
|
|
return SimplifyCFGOpt(TD).run(BB);
|
|
}
|