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1180 lines
46 KiB
C++
1180 lines
46 KiB
C++
//===- JumpThreading.cpp - Thread control through conditional blocks ------===//
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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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// This file implements the Jump Threading pass.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "jump-threading"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/LLVMContext.h"
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#include "llvm/Pass.h"
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#include "llvm/Analysis/ConstantFolding.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Transforms/Utils/SSAUpdater.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/ADT/DenseMap.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/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallSet.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace llvm;
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STATISTIC(NumThreads, "Number of jumps threaded");
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STATISTIC(NumFolds, "Number of terminators folded");
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STATISTIC(NumDupes, "Number of branch blocks duplicated to eliminate phi");
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static cl::opt<unsigned>
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Threshold("jump-threading-threshold",
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cl::desc("Max block size to duplicate for jump threading"),
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cl::init(6), cl::Hidden);
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namespace {
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/// This pass performs 'jump threading', which looks at blocks that have
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/// multiple predecessors and multiple successors. If one or more of the
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/// predecessors of the block can be proven to always jump to one of the
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/// successors, we forward the edge from the predecessor to the successor by
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/// duplicating the contents of this block.
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///
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/// An example of when this can occur is code like this:
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///
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/// if () { ...
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/// X = 4;
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/// }
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/// if (X < 3) {
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///
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/// In this case, the unconditional branch at the end of the first if can be
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/// revectored to the false side of the second if.
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///
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class JumpThreading : public FunctionPass {
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TargetData *TD;
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#ifdef NDEBUG
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SmallPtrSet<BasicBlock*, 16> LoopHeaders;
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#else
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SmallSet<AssertingVH<BasicBlock>, 16> LoopHeaders;
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#endif
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public:
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static char ID; // Pass identification
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JumpThreading() : FunctionPass(&ID) {}
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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}
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bool runOnFunction(Function &F);
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void FindLoopHeaders(Function &F);
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bool ProcessBlock(BasicBlock *BB);
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bool ThreadEdge(BasicBlock *BB, BasicBlock *PredBB, BasicBlock *SuccBB);
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bool DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB,
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BasicBlock *PredBB);
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BasicBlock *FactorCommonPHIPreds(PHINode *PN, Value *Val);
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bool ProcessBranchOnDuplicateCond(BasicBlock *PredBB, BasicBlock *DestBB);
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bool ProcessSwitchOnDuplicateCond(BasicBlock *PredBB, BasicBlock *DestBB);
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bool ProcessJumpOnPHI(PHINode *PN);
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bool ProcessBranchOnLogical(Value *V, BasicBlock *BB, bool isAnd);
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bool ProcessBranchOnCompare(CmpInst *Cmp, BasicBlock *BB);
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bool SimplifyPartiallyRedundantLoad(LoadInst *LI);
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};
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}
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char JumpThreading::ID = 0;
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static RegisterPass<JumpThreading>
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X("jump-threading", "Jump Threading");
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// Public interface to the Jump Threading pass
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FunctionPass *llvm::createJumpThreadingPass() { return new JumpThreading(); }
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/// runOnFunction - Top level algorithm.
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///
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bool JumpThreading::runOnFunction(Function &F) {
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DEBUG(errs() << "Jump threading on function '" << F.getName() << "'\n");
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TD = getAnalysisIfAvailable<TargetData>();
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FindLoopHeaders(F);
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bool AnotherIteration = true, EverChanged = false;
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while (AnotherIteration) {
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AnotherIteration = false;
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bool Changed = false;
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for (Function::iterator I = F.begin(), E = F.end(); I != E;) {
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BasicBlock *BB = I;
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while (ProcessBlock(BB))
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Changed = true;
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++I;
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// If the block is trivially dead, zap it. This eliminates the successor
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// edges which simplifies the CFG.
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if (pred_begin(BB) == pred_end(BB) &&
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BB != &BB->getParent()->getEntryBlock()) {
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DEBUG(errs() << " JT: Deleting dead block '" << BB->getName()
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<< "' with terminator: " << *BB->getTerminator() << '\n');
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LoopHeaders.erase(BB);
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DeleteDeadBlock(BB);
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Changed = true;
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}
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}
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AnotherIteration = Changed;
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EverChanged |= Changed;
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}
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LoopHeaders.clear();
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return EverChanged;
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}
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/// getJumpThreadDuplicationCost - Return the cost of duplicating this block to
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/// thread across it.
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static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB) {
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/// Ignore PHI nodes, these will be flattened when duplication happens.
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BasicBlock::const_iterator I = BB->getFirstNonPHI();
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// Sum up the cost of each instruction until we get to the terminator. Don't
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// include the terminator because the copy won't include it.
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unsigned Size = 0;
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for (; !isa<TerminatorInst>(I); ++I) {
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// Debugger intrinsics don't incur code size.
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if (isa<DbgInfoIntrinsic>(I)) continue;
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// If this is a pointer->pointer bitcast, it is free.
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if (isa<BitCastInst>(I) && isa<PointerType>(I->getType()))
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continue;
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// All other instructions count for at least one unit.
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++Size;
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// Calls are more expensive. If they are non-intrinsic calls, we model them
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// as having cost of 4. If they are a non-vector intrinsic, we model them
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// as having cost of 2 total, and if they are a vector intrinsic, we model
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// them as having cost 1.
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if (const CallInst *CI = dyn_cast<CallInst>(I)) {
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if (!isa<IntrinsicInst>(CI))
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Size += 3;
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else if (!isa<VectorType>(CI->getType()))
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Size += 1;
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}
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}
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// Threading through a switch statement is particularly profitable. If this
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// block ends in a switch, decrease its cost to make it more likely to happen.
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if (isa<SwitchInst>(I))
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Size = Size > 6 ? Size-6 : 0;
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return Size;
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}
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/// FindLoopHeaders - We do not want jump threading to turn proper loop
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/// structures into irreducible loops. Doing this breaks up the loop nesting
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/// hierarchy and pessimizes later transformations. To prevent this from
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/// happening, we first have to find the loop headers. Here we approximate this
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/// by finding targets of backedges in the CFG.
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///
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/// Note that there definitely are cases when we want to allow threading of
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/// edges across a loop header. For example, threading a jump from outside the
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/// loop (the preheader) to an exit block of the loop is definitely profitable.
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/// It is also almost always profitable to thread backedges from within the loop
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/// to exit blocks, and is often profitable to thread backedges to other blocks
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/// within the loop (forming a nested loop). This simple analysis is not rich
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/// enough to track all of these properties and keep it up-to-date as the CFG
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/// mutates, so we don't allow any of these transformations.
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///
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void JumpThreading::FindLoopHeaders(Function &F) {
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SmallVector<std::pair<const BasicBlock*,const BasicBlock*>, 32> Edges;
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FindFunctionBackedges(F, Edges);
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for (unsigned i = 0, e = Edges.size(); i != e; ++i)
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LoopHeaders.insert(const_cast<BasicBlock*>(Edges[i].second));
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}
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/// FactorCommonPHIPreds - If there are multiple preds with the same incoming
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/// value for the PHI, factor them together so we get one block to thread for
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/// the whole group.
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/// This is important for things like "phi i1 [true, true, false, true, x]"
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/// where we only need to clone the block for the true blocks once.
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///
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BasicBlock *JumpThreading::FactorCommonPHIPreds(PHINode *PN, Value *Val) {
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SmallVector<BasicBlock*, 16> CommonPreds;
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for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
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if (PN->getIncomingValue(i) == Val)
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CommonPreds.push_back(PN->getIncomingBlock(i));
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if (CommonPreds.size() == 1)
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return CommonPreds[0];
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DEBUG(errs() << " Factoring out " << CommonPreds.size()
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<< " common predecessors.\n");
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return SplitBlockPredecessors(PN->getParent(),
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&CommonPreds[0], CommonPreds.size(),
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".thr_comm", this);
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}
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/// GetBestDestForBranchOnUndef - If we determine that the specified block ends
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/// in an undefined jump, decide which block is best to revector to.
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///
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/// Since we can pick an arbitrary destination, we pick the successor with the
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/// fewest predecessors. This should reduce the in-degree of the others.
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///
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static unsigned GetBestDestForJumpOnUndef(BasicBlock *BB) {
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TerminatorInst *BBTerm = BB->getTerminator();
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unsigned MinSucc = 0;
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BasicBlock *TestBB = BBTerm->getSuccessor(MinSucc);
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// Compute the successor with the minimum number of predecessors.
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unsigned MinNumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB));
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for (unsigned i = 1, e = BBTerm->getNumSuccessors(); i != e; ++i) {
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TestBB = BBTerm->getSuccessor(i);
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unsigned NumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB));
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if (NumPreds < MinNumPreds)
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MinSucc = i;
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}
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return MinSucc;
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}
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/// ProcessBlock - If there are any predecessors whose control can be threaded
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/// through to a successor, transform them now.
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bool JumpThreading::ProcessBlock(BasicBlock *BB) {
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// If this block has a single predecessor, and if that pred has a single
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// successor, merge the blocks. This encourages recursive jump threading
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// because now the condition in this block can be threaded through
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// predecessors of our predecessor block.
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if (BasicBlock *SinglePred = BB->getSinglePredecessor())
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if (SinglePred->getTerminator()->getNumSuccessors() == 1 &&
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SinglePred != BB) {
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// If SinglePred was a loop header, BB becomes one.
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if (LoopHeaders.erase(SinglePred))
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LoopHeaders.insert(BB);
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// Remember if SinglePred was the entry block of the function. If so, we
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// will need to move BB back to the entry position.
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bool isEntry = SinglePred == &SinglePred->getParent()->getEntryBlock();
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MergeBasicBlockIntoOnlyPred(BB);
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if (isEntry && BB != &BB->getParent()->getEntryBlock())
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BB->moveBefore(&BB->getParent()->getEntryBlock());
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return true;
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}
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// See if this block ends with a branch or switch. If so, see if the
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// condition is a phi node. If so, and if an entry of the phi node is a
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// constant, we can thread the block.
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Value *Condition;
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if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
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// Can't thread an unconditional jump.
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if (BI->isUnconditional()) return false;
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Condition = BI->getCondition();
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} else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator()))
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Condition = SI->getCondition();
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else
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return false; // Must be an invoke.
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// If the terminator of this block is branching on a constant, simplify the
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// terminator to an unconditional branch. This can occur due to threading in
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// other blocks.
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if (isa<ConstantInt>(Condition)) {
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DEBUG(errs() << " In block '" << BB->getName()
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<< "' folding terminator: " << *BB->getTerminator() << '\n');
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++NumFolds;
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ConstantFoldTerminator(BB);
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return true;
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}
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// If the terminator is branching on an undef, we can pick any of the
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// successors to branch to. Let GetBestDestForJumpOnUndef decide.
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if (isa<UndefValue>(Condition)) {
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unsigned BestSucc = GetBestDestForJumpOnUndef(BB);
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// Fold the branch/switch.
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TerminatorInst *BBTerm = BB->getTerminator();
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for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i) {
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if (i == BestSucc) continue;
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BBTerm->getSuccessor(i)->removePredecessor(BB);
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}
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DEBUG(errs() << " In block '" << BB->getName()
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<< "' folding undef terminator: " << *BBTerm << '\n');
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BranchInst::Create(BBTerm->getSuccessor(BestSucc), BBTerm);
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BBTerm->eraseFromParent();
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return true;
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}
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Instruction *CondInst = dyn_cast<Instruction>(Condition);
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// If the condition is an instruction defined in another block, see if a
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// predecessor has the same condition:
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// br COND, BBX, BBY
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// BBX:
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// br COND, BBZ, BBW
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if (!Condition->hasOneUse() && // Multiple uses.
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(CondInst == 0 || CondInst->getParent() != BB)) { // Non-local definition.
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pred_iterator PI = pred_begin(BB), E = pred_end(BB);
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if (isa<BranchInst>(BB->getTerminator())) {
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for (; PI != E; ++PI)
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if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
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if (PBI->isConditional() && PBI->getCondition() == Condition &&
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ProcessBranchOnDuplicateCond(*PI, BB))
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return true;
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} else {
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assert(isa<SwitchInst>(BB->getTerminator()) && "Unknown jump terminator");
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for (; PI != E; ++PI)
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if (SwitchInst *PSI = dyn_cast<SwitchInst>((*PI)->getTerminator()))
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if (PSI->getCondition() == Condition &&
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ProcessSwitchOnDuplicateCond(*PI, BB))
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return true;
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}
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}
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// All the rest of our checks depend on the condition being an instruction.
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if (CondInst == 0)
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return false;
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// See if this is a phi node in the current block.
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if (PHINode *PN = dyn_cast<PHINode>(CondInst))
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if (PN->getParent() == BB)
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return ProcessJumpOnPHI(PN);
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// If this is a conditional branch whose condition is and/or of a phi, try to
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// simplify it.
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if ((CondInst->getOpcode() == Instruction::And ||
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CondInst->getOpcode() == Instruction::Or) &&
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isa<BranchInst>(BB->getTerminator()) &&
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ProcessBranchOnLogical(CondInst, BB,
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CondInst->getOpcode() == Instruction::And))
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return true;
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if (CmpInst *CondCmp = dyn_cast<CmpInst>(CondInst)) {
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if (isa<PHINode>(CondCmp->getOperand(0))) {
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// If we have "br (phi != 42)" and the phi node has any constant values
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// as operands, we can thread through this block.
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//
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// If we have "br (cmp phi, x)" and the phi node contains x such that the
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// comparison uniquely identifies the branch target, we can thread
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// through this block.
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if (ProcessBranchOnCompare(CondCmp, BB))
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return true;
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}
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// If we have a comparison, loop over the predecessors to see if there is
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// a condition with the same value.
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pred_iterator PI = pred_begin(BB), E = pred_end(BB);
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for (; PI != E; ++PI)
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if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
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if (PBI->isConditional() && *PI != BB) {
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if (CmpInst *CI = dyn_cast<CmpInst>(PBI->getCondition())) {
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if (CI->getOperand(0) == CondCmp->getOperand(0) &&
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CI->getOperand(1) == CondCmp->getOperand(1) &&
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CI->getPredicate() == CondCmp->getPredicate()) {
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// TODO: Could handle things like (x != 4) --> (x == 17)
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if (ProcessBranchOnDuplicateCond(*PI, BB))
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return true;
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}
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}
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}
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}
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// Check for some cases that are worth simplifying. Right now we want to look
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// for loads that are used by a switch or by the condition for the branch. If
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// we see one, check to see if it's partially redundant. If so, insert a PHI
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// which can then be used to thread the values.
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//
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// This is particularly important because reg2mem inserts loads and stores all
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// over the place, and this blocks jump threading if we don't zap them.
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Value *SimplifyValue = CondInst;
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if (CmpInst *CondCmp = dyn_cast<CmpInst>(SimplifyValue))
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if (isa<Constant>(CondCmp->getOperand(1)))
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SimplifyValue = CondCmp->getOperand(0);
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if (LoadInst *LI = dyn_cast<LoadInst>(SimplifyValue))
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if (SimplifyPartiallyRedundantLoad(LI))
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return true;
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// TODO: If we have: "br (X > 0)" and we have a predecessor where we know
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// "(X == 4)" thread through this block.
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return false;
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}
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/// ProcessBranchOnDuplicateCond - We found a block and a predecessor of that
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/// block that jump on exactly the same condition. This means that we almost
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/// always know the direction of the edge in the DESTBB:
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/// PREDBB:
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/// br COND, DESTBB, BBY
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/// DESTBB:
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/// br COND, BBZ, BBW
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///
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/// If DESTBB has multiple predecessors, we can't just constant fold the branch
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/// in DESTBB, we have to thread over it.
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bool JumpThreading::ProcessBranchOnDuplicateCond(BasicBlock *PredBB,
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BasicBlock *BB) {
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BranchInst *PredBI = cast<BranchInst>(PredBB->getTerminator());
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// If both successors of PredBB go to DESTBB, we don't know anything. We can
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// fold the branch to an unconditional one, which allows other recursive
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// simplifications.
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bool BranchDir;
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if (PredBI->getSuccessor(1) != BB)
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BranchDir = true;
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else if (PredBI->getSuccessor(0) != BB)
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BranchDir = false;
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else {
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DEBUG(errs() << " In block '" << PredBB->getName()
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<< "' folding terminator: " << *PredBB->getTerminator() << '\n');
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++NumFolds;
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ConstantFoldTerminator(PredBB);
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return true;
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}
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BranchInst *DestBI = cast<BranchInst>(BB->getTerminator());
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// If the dest block has one predecessor, just fix the branch condition to a
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// constant and fold it.
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if (BB->getSinglePredecessor()) {
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DEBUG(errs() << " In block '" << BB->getName()
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<< "' folding condition to '" << BranchDir << "': "
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<< *BB->getTerminator() << '\n');
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++NumFolds;
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Value *OldCond = DestBI->getCondition();
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DestBI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
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BranchDir));
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ConstantFoldTerminator(BB);
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RecursivelyDeleteTriviallyDeadInstructions(OldCond);
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return true;
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}
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|
|
// Next, figure out which successor we are threading to.
|
|
BasicBlock *SuccBB = DestBI->getSuccessor(!BranchDir);
|
|
|
|
// Ok, try to thread it!
|
|
return ThreadEdge(BB, PredBB, SuccBB);
|
|
}
|
|
|
|
/// ProcessSwitchOnDuplicateCond - We found a block and a predecessor of that
|
|
/// block that switch on exactly the same condition. This means that we almost
|
|
/// always know the direction of the edge in the DESTBB:
|
|
/// PREDBB:
|
|
/// switch COND [... DESTBB, BBY ... ]
|
|
/// DESTBB:
|
|
/// switch COND [... BBZ, BBW ]
|
|
///
|
|
/// Optimizing switches like this is very important, because simplifycfg builds
|
|
/// switches out of repeated 'if' conditions.
|
|
bool JumpThreading::ProcessSwitchOnDuplicateCond(BasicBlock *PredBB,
|
|
BasicBlock *DestBB) {
|
|
// Can't thread edge to self.
|
|
if (PredBB == DestBB)
|
|
return false;
|
|
|
|
SwitchInst *PredSI = cast<SwitchInst>(PredBB->getTerminator());
|
|
SwitchInst *DestSI = cast<SwitchInst>(DestBB->getTerminator());
|
|
|
|
// There are a variety of optimizations that we can potentially do on these
|
|
// blocks: we order them from most to least preferable.
|
|
|
|
// If DESTBB *just* contains the switch, then we can forward edges from PREDBB
|
|
// directly to their destination. This does not introduce *any* code size
|
|
// growth. Skip debug info first.
|
|
BasicBlock::iterator BBI = DestBB->begin();
|
|
while (isa<DbgInfoIntrinsic>(BBI))
|
|
BBI++;
|
|
|
|
// FIXME: Thread if it just contains a PHI.
|
|
if (isa<SwitchInst>(BBI)) {
|
|
bool MadeChange = false;
|
|
// Ignore the default edge for now.
|
|
for (unsigned i = 1, e = DestSI->getNumSuccessors(); i != e; ++i) {
|
|
ConstantInt *DestVal = DestSI->getCaseValue(i);
|
|
BasicBlock *DestSucc = DestSI->getSuccessor(i);
|
|
|
|
// Okay, DestSI has a case for 'DestVal' that goes to 'DestSucc'. See if
|
|
// PredSI has an explicit case for it. If so, forward. If it is covered
|
|
// by the default case, we can't update PredSI.
|
|
unsigned PredCase = PredSI->findCaseValue(DestVal);
|
|
if (PredCase == 0) continue;
|
|
|
|
// If PredSI doesn't go to DestBB on this value, then it won't reach the
|
|
// case on this condition.
|
|
if (PredSI->getSuccessor(PredCase) != DestBB &&
|
|
DestSI->getSuccessor(i) != DestBB)
|
|
continue;
|
|
|
|
// Otherwise, we're safe to make the change. Make sure that the edge from
|
|
// DestSI to DestSucc is not critical and has no PHI nodes.
|
|
DEBUG(errs() << "FORWARDING EDGE " << *DestVal << " FROM: " << *PredSI);
|
|
DEBUG(errs() << "THROUGH: " << *DestSI);
|
|
|
|
// If the destination has PHI nodes, just split the edge for updating
|
|
// simplicity.
|
|
if (isa<PHINode>(DestSucc->begin()) && !DestSucc->getSinglePredecessor()){
|
|
SplitCriticalEdge(DestSI, i, this);
|
|
DestSucc = DestSI->getSuccessor(i);
|
|
}
|
|
FoldSingleEntryPHINodes(DestSucc);
|
|
PredSI->setSuccessor(PredCase, DestSucc);
|
|
MadeChange = true;
|
|
}
|
|
|
|
if (MadeChange)
|
|
return true;
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
|
|
/// SimplifyPartiallyRedundantLoad - If LI is an obviously partially redundant
|
|
/// load instruction, eliminate it by replacing it with a PHI node. This is an
|
|
/// important optimization that encourages jump threading, and needs to be run
|
|
/// interlaced with other jump threading tasks.
|
|
bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) {
|
|
// Don't hack volatile loads.
|
|
if (LI->isVolatile()) return false;
|
|
|
|
// If the load is defined in a block with exactly one predecessor, it can't be
|
|
// partially redundant.
|
|
BasicBlock *LoadBB = LI->getParent();
|
|
if (LoadBB->getSinglePredecessor())
|
|
return false;
|
|
|
|
Value *LoadedPtr = LI->getOperand(0);
|
|
|
|
// If the loaded operand is defined in the LoadBB, it can't be available.
|
|
// FIXME: Could do PHI translation, that would be fun :)
|
|
if (Instruction *PtrOp = dyn_cast<Instruction>(LoadedPtr))
|
|
if (PtrOp->getParent() == LoadBB)
|
|
return false;
|
|
|
|
// Scan a few instructions up from the load, to see if it is obviously live at
|
|
// the entry to its block.
|
|
BasicBlock::iterator BBIt = LI;
|
|
|
|
if (Value *AvailableVal = FindAvailableLoadedValue(LoadedPtr, LoadBB,
|
|
BBIt, 6)) {
|
|
// If the value if the load is locally available within the block, just use
|
|
// it. This frequently occurs for reg2mem'd allocas.
|
|
//cerr << "LOAD ELIMINATED:\n" << *BBIt << *LI << "\n";
|
|
|
|
// If the returned value is the load itself, replace with an undef. This can
|
|
// only happen in dead loops.
|
|
if (AvailableVal == LI) AvailableVal = UndefValue::get(LI->getType());
|
|
LI->replaceAllUsesWith(AvailableVal);
|
|
LI->eraseFromParent();
|
|
return true;
|
|
}
|
|
|
|
// Otherwise, if we scanned the whole block and got to the top of the block,
|
|
// we know the block is locally transparent to the load. If not, something
|
|
// might clobber its value.
|
|
if (BBIt != LoadBB->begin())
|
|
return false;
|
|
|
|
|
|
SmallPtrSet<BasicBlock*, 8> PredsScanned;
|
|
typedef SmallVector<std::pair<BasicBlock*, Value*>, 8> AvailablePredsTy;
|
|
AvailablePredsTy AvailablePreds;
|
|
BasicBlock *OneUnavailablePred = 0;
|
|
|
|
// If we got here, the loaded value is transparent through to the start of the
|
|
// block. Check to see if it is available in any of the predecessor blocks.
|
|
for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB);
|
|
PI != PE; ++PI) {
|
|
BasicBlock *PredBB = *PI;
|
|
|
|
// If we already scanned this predecessor, skip it.
|
|
if (!PredsScanned.insert(PredBB))
|
|
continue;
|
|
|
|
// Scan the predecessor to see if the value is available in the pred.
|
|
BBIt = PredBB->end();
|
|
Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt, 6);
|
|
if (!PredAvailable) {
|
|
OneUnavailablePred = PredBB;
|
|
continue;
|
|
}
|
|
|
|
// If so, this load is partially redundant. Remember this info so that we
|
|
// can create a PHI node.
|
|
AvailablePreds.push_back(std::make_pair(PredBB, PredAvailable));
|
|
}
|
|
|
|
// If the loaded value isn't available in any predecessor, it isn't partially
|
|
// redundant.
|
|
if (AvailablePreds.empty()) return false;
|
|
|
|
// Okay, the loaded value is available in at least one (and maybe all!)
|
|
// predecessors. If the value is unavailable in more than one unique
|
|
// predecessor, we want to insert a merge block for those common predecessors.
|
|
// This ensures that we only have to insert one reload, thus not increasing
|
|
// code size.
|
|
BasicBlock *UnavailablePred = 0;
|
|
|
|
// If there is exactly one predecessor where the value is unavailable, the
|
|
// already computed 'OneUnavailablePred' block is it. If it ends in an
|
|
// unconditional branch, we know that it isn't a critical edge.
|
|
if (PredsScanned.size() == AvailablePreds.size()+1 &&
|
|
OneUnavailablePred->getTerminator()->getNumSuccessors() == 1) {
|
|
UnavailablePred = OneUnavailablePred;
|
|
} else if (PredsScanned.size() != AvailablePreds.size()) {
|
|
// Otherwise, we had multiple unavailable predecessors or we had a critical
|
|
// edge from the one.
|
|
SmallVector<BasicBlock*, 8> PredsToSplit;
|
|
SmallPtrSet<BasicBlock*, 8> AvailablePredSet;
|
|
|
|
for (unsigned i = 0, e = AvailablePreds.size(); i != e; ++i)
|
|
AvailablePredSet.insert(AvailablePreds[i].first);
|
|
|
|
// Add all the unavailable predecessors to the PredsToSplit list.
|
|
for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB);
|
|
PI != PE; ++PI)
|
|
if (!AvailablePredSet.count(*PI))
|
|
PredsToSplit.push_back(*PI);
|
|
|
|
// Split them out to their own block.
|
|
UnavailablePred =
|
|
SplitBlockPredecessors(LoadBB, &PredsToSplit[0], PredsToSplit.size(),
|
|
"thread-split", this);
|
|
}
|
|
|
|
// If the value isn't available in all predecessors, then there will be
|
|
// exactly one where it isn't available. Insert a load on that edge and add
|
|
// it to the AvailablePreds list.
|
|
if (UnavailablePred) {
|
|
assert(UnavailablePred->getTerminator()->getNumSuccessors() == 1 &&
|
|
"Can't handle critical edge here!");
|
|
Value *NewVal = new LoadInst(LoadedPtr, LI->getName()+".pr",
|
|
UnavailablePred->getTerminator());
|
|
AvailablePreds.push_back(std::make_pair(UnavailablePred, NewVal));
|
|
}
|
|
|
|
// Now we know that each predecessor of this block has a value in
|
|
// AvailablePreds, sort them for efficient access as we're walking the preds.
|
|
array_pod_sort(AvailablePreds.begin(), AvailablePreds.end());
|
|
|
|
// Create a PHI node at the start of the block for the PRE'd load value.
|
|
PHINode *PN = PHINode::Create(LI->getType(), "", LoadBB->begin());
|
|
PN->takeName(LI);
|
|
|
|
// Insert new entries into the PHI for each predecessor. A single block may
|
|
// have multiple entries here.
|
|
for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); PI != E;
|
|
++PI) {
|
|
AvailablePredsTy::iterator I =
|
|
std::lower_bound(AvailablePreds.begin(), AvailablePreds.end(),
|
|
std::make_pair(*PI, (Value*)0));
|
|
|
|
assert(I != AvailablePreds.end() && I->first == *PI &&
|
|
"Didn't find entry for predecessor!");
|
|
|
|
PN->addIncoming(I->second, I->first);
|
|
}
|
|
|
|
//cerr << "PRE: " << *LI << *PN << "\n";
|
|
|
|
LI->replaceAllUsesWith(PN);
|
|
LI->eraseFromParent();
|
|
|
|
return true;
|
|
}
|
|
|
|
|
|
/// ProcessJumpOnPHI - We have a conditional branch or switch on a PHI node in
|
|
/// the current block. See if there are any simplifications we can do based on
|
|
/// inputs to the phi node.
|
|
///
|
|
bool JumpThreading::ProcessJumpOnPHI(PHINode *PN) {
|
|
BasicBlock *BB = PN->getParent();
|
|
|
|
// See if the phi node has any constant integer or undef values. If so, we
|
|
// can determine where the corresponding predecessor will branch.
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
Value *PredVal = PN->getIncomingValue(i);
|
|
|
|
// Check to see if this input is a constant integer. If so, the direction
|
|
// of the branch is predictable.
|
|
if (ConstantInt *CI = dyn_cast<ConstantInt>(PredVal)) {
|
|
// Merge any common predecessors that will act the same.
|
|
BasicBlock *PredBB = FactorCommonPHIPreds(PN, CI);
|
|
|
|
BasicBlock *SuccBB;
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()))
|
|
SuccBB = BI->getSuccessor(CI->isZero());
|
|
else {
|
|
SwitchInst *SI = cast<SwitchInst>(BB->getTerminator());
|
|
SuccBB = SI->getSuccessor(SI->findCaseValue(CI));
|
|
}
|
|
|
|
// Ok, try to thread it!
|
|
return ThreadEdge(BB, PredBB, SuccBB);
|
|
}
|
|
|
|
// If the input is an undef, then it doesn't matter which way it will go.
|
|
// Pick an arbitrary dest and thread the edge.
|
|
if (UndefValue *UV = dyn_cast<UndefValue>(PredVal)) {
|
|
// Merge any common predecessors that will act the same.
|
|
BasicBlock *PredBB = FactorCommonPHIPreds(PN, UV);
|
|
BasicBlock *SuccBB =
|
|
BB->getTerminator()->getSuccessor(GetBestDestForJumpOnUndef(BB));
|
|
|
|
// Ok, try to thread it!
|
|
return ThreadEdge(BB, PredBB, SuccBB);
|
|
}
|
|
}
|
|
|
|
// If the incoming values are all variables, we don't know the destination of
|
|
// any predecessors. However, if any of the predecessor blocks end in an
|
|
// unconditional branch, we can *duplicate* the jump into that block in order
|
|
// to further encourage jump threading and to eliminate cases where we have
|
|
// branch on a phi of an icmp (branch on icmp is much better).
|
|
|
|
// We don't want to do this tranformation for switches, because we don't
|
|
// really want to duplicate a switch.
|
|
if (isa<SwitchInst>(BB->getTerminator()))
|
|
return false;
|
|
|
|
// Look for unconditional branch predecessors.
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
BasicBlock *PredBB = PN->getIncomingBlock(i);
|
|
if (BranchInst *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator()))
|
|
if (PredBr->isUnconditional() &&
|
|
// Try to duplicate BB into PredBB.
|
|
DuplicateCondBranchOnPHIIntoPred(BB, PredBB))
|
|
return true;
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
|
|
/// ProcessJumpOnLogicalPHI - PN's basic block contains a conditional branch
|
|
/// whose condition is an AND/OR where one side is PN. If PN has constant
|
|
/// operands that permit us to evaluate the condition for some operand, thread
|
|
/// through the block. For example with:
|
|
/// br (and X, phi(Y, Z, false))
|
|
/// the predecessor corresponding to the 'false' will always jump to the false
|
|
/// destination of the branch.
|
|
///
|
|
bool JumpThreading::ProcessBranchOnLogical(Value *V, BasicBlock *BB,
|
|
bool isAnd) {
|
|
// If this is a binary operator tree of the same AND/OR opcode, check the
|
|
// LHS/RHS.
|
|
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(V))
|
|
if ((isAnd && BO->getOpcode() == Instruction::And) ||
|
|
(!isAnd && BO->getOpcode() == Instruction::Or)) {
|
|
if (ProcessBranchOnLogical(BO->getOperand(0), BB, isAnd))
|
|
return true;
|
|
if (ProcessBranchOnLogical(BO->getOperand(1), BB, isAnd))
|
|
return true;
|
|
}
|
|
|
|
// If this isn't a PHI node, we can't handle it.
|
|
PHINode *PN = dyn_cast<PHINode>(V);
|
|
if (!PN || PN->getParent() != BB) return false;
|
|
|
|
// We can only do the simplification for phi nodes of 'false' with AND or
|
|
// 'true' with OR. See if we have any entries in the phi for this.
|
|
unsigned PredNo = ~0U;
|
|
ConstantInt *PredCst = ConstantInt::get(Type::getInt1Ty(BB->getContext()),
|
|
!isAnd);
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
if (PN->getIncomingValue(i) == PredCst) {
|
|
PredNo = i;
|
|
break;
|
|
}
|
|
}
|
|
|
|
// If no match, bail out.
|
|
if (PredNo == ~0U)
|
|
return false;
|
|
|
|
// If so, we can actually do this threading. Merge any common predecessors
|
|
// that will act the same.
|
|
BasicBlock *PredBB = FactorCommonPHIPreds(PN, PredCst);
|
|
|
|
// Next, figure out which successor we are threading to. If this was an AND,
|
|
// the constant must be FALSE, and we must be targeting the 'false' block.
|
|
// If this is an OR, the constant must be TRUE, and we must be targeting the
|
|
// 'true' block.
|
|
BasicBlock *SuccBB = BB->getTerminator()->getSuccessor(isAnd);
|
|
|
|
// Ok, try to thread it!
|
|
return ThreadEdge(BB, PredBB, SuccBB);
|
|
}
|
|
|
|
/// GetResultOfComparison - Given an icmp/fcmp predicate and the left and right
|
|
/// hand sides of the compare instruction, try to determine the result. If the
|
|
/// result can not be determined, a null pointer is returned.
|
|
static Constant *GetResultOfComparison(CmpInst::Predicate pred,
|
|
Value *LHS, Value *RHS,
|
|
LLVMContext &Context) {
|
|
if (Constant *CLHS = dyn_cast<Constant>(LHS))
|
|
if (Constant *CRHS = dyn_cast<Constant>(RHS))
|
|
return ConstantExpr::getCompare(pred, CLHS, CRHS);
|
|
|
|
if (LHS == RHS)
|
|
if (isa<IntegerType>(LHS->getType()) || isa<PointerType>(LHS->getType()))
|
|
return ICmpInst::isTrueWhenEqual(pred) ?
|
|
ConstantInt::getTrue(Context) : ConstantInt::getFalse(Context);
|
|
|
|
return 0;
|
|
}
|
|
|
|
/// ProcessBranchOnCompare - We found a branch on a comparison between a phi
|
|
/// node and a value. If we can identify when the comparison is true between
|
|
/// the phi inputs and the value, we can fold the compare for that edge and
|
|
/// thread through it.
|
|
bool JumpThreading::ProcessBranchOnCompare(CmpInst *Cmp, BasicBlock *BB) {
|
|
PHINode *PN = cast<PHINode>(Cmp->getOperand(0));
|
|
Value *RHS = Cmp->getOperand(1);
|
|
|
|
// If the phi isn't in the current block, an incoming edge to this block
|
|
// doesn't control the destination.
|
|
if (PN->getParent() != BB)
|
|
return false;
|
|
|
|
// We can do this simplification if any comparisons fold to true or false.
|
|
// See if any do.
|
|
Value *PredVal = 0;
|
|
bool TrueDirection = false;
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
PredVal = PN->getIncomingValue(i);
|
|
|
|
Constant *Res = GetResultOfComparison(Cmp->getPredicate(), PredVal,
|
|
RHS, Cmp->getContext());
|
|
if (!Res) {
|
|
PredVal = 0;
|
|
continue;
|
|
}
|
|
|
|
// If this folded to a constant expr, we can't do anything.
|
|
if (ConstantInt *ResC = dyn_cast<ConstantInt>(Res)) {
|
|
TrueDirection = ResC->getZExtValue();
|
|
break;
|
|
}
|
|
// If this folded to undef, just go the false way.
|
|
if (isa<UndefValue>(Res)) {
|
|
TrueDirection = false;
|
|
break;
|
|
}
|
|
|
|
// Otherwise, we can't fold this input.
|
|
PredVal = 0;
|
|
}
|
|
|
|
// If no match, bail out.
|
|
if (PredVal == 0)
|
|
return false;
|
|
|
|
// If so, we can actually do this threading. Merge any common predecessors
|
|
// that will act the same.
|
|
BasicBlock *PredBB = FactorCommonPHIPreds(PN, PredVal);
|
|
|
|
// Next, get our successor.
|
|
BasicBlock *SuccBB = BB->getTerminator()->getSuccessor(!TrueDirection);
|
|
|
|
// Ok, try to thread it!
|
|
return ThreadEdge(BB, PredBB, SuccBB);
|
|
}
|
|
|
|
|
|
/// AddPHINodeEntriesForMappedBlock - We're adding 'NewPred' as a new
|
|
/// predecessor to the PHIBB block. If it has PHI nodes, add entries for
|
|
/// NewPred using the entries from OldPred (suitably mapped).
|
|
static void AddPHINodeEntriesForMappedBlock(BasicBlock *PHIBB,
|
|
BasicBlock *OldPred,
|
|
BasicBlock *NewPred,
|
|
DenseMap<Instruction*, Value*> &ValueMap) {
|
|
for (BasicBlock::iterator PNI = PHIBB->begin();
|
|
PHINode *PN = dyn_cast<PHINode>(PNI); ++PNI) {
|
|
// Ok, we have a PHI node. Figure out what the incoming value was for the
|
|
// DestBlock.
|
|
Value *IV = PN->getIncomingValueForBlock(OldPred);
|
|
|
|
// Remap the value if necessary.
|
|
if (Instruction *Inst = dyn_cast<Instruction>(IV)) {
|
|
DenseMap<Instruction*, Value*>::iterator I = ValueMap.find(Inst);
|
|
if (I != ValueMap.end())
|
|
IV = I->second;
|
|
}
|
|
|
|
PN->addIncoming(IV, NewPred);
|
|
}
|
|
}
|
|
|
|
/// ThreadEdge - We have decided that it is safe and profitable to thread an
|
|
/// edge from PredBB to SuccBB across BB. Transform the IR to reflect this
|
|
/// change.
|
|
bool JumpThreading::ThreadEdge(BasicBlock *BB, BasicBlock *PredBB,
|
|
BasicBlock *SuccBB) {
|
|
// If threading to the same block as we come from, we would infinite loop.
|
|
if (SuccBB == BB) {
|
|
DEBUG(errs() << " Not threading across BB '" << BB->getName()
|
|
<< "' - would thread to self!\n");
|
|
return false;
|
|
}
|
|
|
|
// If threading this would thread across a loop header, don't thread the edge.
|
|
// See the comments above FindLoopHeaders for justifications and caveats.
|
|
if (LoopHeaders.count(BB)) {
|
|
DEBUG(errs() << " Not threading from '" << PredBB->getName()
|
|
<< "' across loop header BB '" << BB->getName()
|
|
<< "' to dest BB '" << SuccBB->getName()
|
|
<< "' - it might create an irreducible loop!\n");
|
|
return false;
|
|
}
|
|
|
|
unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB);
|
|
if (JumpThreadCost > Threshold) {
|
|
DEBUG(errs() << " Not threading BB '" << BB->getName()
|
|
<< "' - Cost is too high: " << JumpThreadCost << "\n");
|
|
return false;
|
|
}
|
|
|
|
// And finally, do it!
|
|
DEBUG(errs() << " Threading edge from '" << PredBB->getName() << "' to '"
|
|
<< SuccBB->getName() << "' with cost: " << JumpThreadCost
|
|
<< ", across block:\n "
|
|
<< *BB << "\n");
|
|
|
|
// We are going to have to map operands from the original BB block to the new
|
|
// copy of the block 'NewBB'. If there are PHI nodes in BB, evaluate them to
|
|
// account for entry from PredBB.
|
|
DenseMap<Instruction*, Value*> ValueMapping;
|
|
|
|
BasicBlock *NewBB = BasicBlock::Create(BB->getContext(),
|
|
BB->getName()+".thread",
|
|
BB->getParent(), BB);
|
|
NewBB->moveAfter(PredBB);
|
|
|
|
BasicBlock::iterator BI = BB->begin();
|
|
for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
|
|
ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
|
|
|
|
// Clone the non-phi instructions of BB into NewBB, keeping track of the
|
|
// mapping and using it to remap operands in the cloned instructions.
|
|
for (; !isa<TerminatorInst>(BI); ++BI) {
|
|
Instruction *New = BI->clone();
|
|
New->setName(BI->getName());
|
|
NewBB->getInstList().push_back(New);
|
|
ValueMapping[BI] = New;
|
|
|
|
// Remap operands to patch up intra-block references.
|
|
for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
|
|
if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) {
|
|
DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst);
|
|
if (I != ValueMapping.end())
|
|
New->setOperand(i, I->second);
|
|
}
|
|
}
|
|
|
|
// We didn't copy the terminator from BB over to NewBB, because there is now
|
|
// an unconditional jump to SuccBB. Insert the unconditional jump.
|
|
BranchInst::Create(SuccBB, NewBB);
|
|
|
|
// Check to see if SuccBB has PHI nodes. If so, we need to add entries to the
|
|
// PHI nodes for NewBB now.
|
|
AddPHINodeEntriesForMappedBlock(SuccBB, BB, NewBB, ValueMapping);
|
|
|
|
// If there were values defined in BB that are used outside the block, then we
|
|
// now have to update all uses of the value to use either the original value,
|
|
// the cloned value, or some PHI derived value. This can require arbitrary
|
|
// PHI insertion, of which we are prepared to do, clean these up now.
|
|
SSAUpdater SSAUpdate;
|
|
SmallVector<Use*, 16> UsesToRename;
|
|
for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
|
|
// Scan all uses of this instruction to see if it is used outside of its
|
|
// block, and if so, record them in UsesToRename.
|
|
for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
|
|
++UI) {
|
|
Instruction *User = cast<Instruction>(*UI);
|
|
if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
|
|
if (UserPN->getIncomingBlock(UI) == BB)
|
|
continue;
|
|
} else if (User->getParent() == BB)
|
|
continue;
|
|
|
|
UsesToRename.push_back(&UI.getUse());
|
|
}
|
|
|
|
// If there are no uses outside the block, we're done with this instruction.
|
|
if (UsesToRename.empty())
|
|
continue;
|
|
|
|
DEBUG(errs() << "JT: Renaming non-local uses of: " << *I << "\n");
|
|
|
|
// We found a use of I outside of BB. Rename all uses of I that are outside
|
|
// its block to be uses of the appropriate PHI node etc. See ValuesInBlocks
|
|
// with the two values we know.
|
|
SSAUpdate.Initialize(I);
|
|
SSAUpdate.AddAvailableValue(BB, I);
|
|
SSAUpdate.AddAvailableValue(NewBB, ValueMapping[I]);
|
|
|
|
while (!UsesToRename.empty())
|
|
SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
|
|
DEBUG(errs() << "\n");
|
|
}
|
|
|
|
|
|
// Ok, NewBB is good to go. Update the terminator of PredBB to jump to
|
|
// NewBB instead of BB. This eliminates predecessors from BB, which requires
|
|
// us to simplify any PHI nodes in BB.
|
|
TerminatorInst *PredTerm = PredBB->getTerminator();
|
|
for (unsigned i = 0, e = PredTerm->getNumSuccessors(); i != e; ++i)
|
|
if (PredTerm->getSuccessor(i) == BB) {
|
|
BB->removePredecessor(PredBB);
|
|
PredTerm->setSuccessor(i, NewBB);
|
|
}
|
|
|
|
// At this point, the IR is fully up to date and consistent. Do a quick scan
|
|
// over the new instructions and zap any that are constants or dead. This
|
|
// frequently happens because of phi translation.
|
|
BI = NewBB->begin();
|
|
for (BasicBlock::iterator E = NewBB->end(); BI != E; ) {
|
|
Instruction *Inst = BI++;
|
|
if (Constant *C = ConstantFoldInstruction(Inst, BB->getContext(), TD)) {
|
|
Inst->replaceAllUsesWith(C);
|
|
Inst->eraseFromParent();
|
|
continue;
|
|
}
|
|
|
|
RecursivelyDeleteTriviallyDeadInstructions(Inst);
|
|
}
|
|
|
|
// Threaded an edge!
|
|
++NumThreads;
|
|
return true;
|
|
}
|
|
|
|
/// DuplicateCondBranchOnPHIIntoPred - PredBB contains an unconditional branch
|
|
/// to BB which contains an i1 PHI node and a conditional branch on that PHI.
|
|
/// If we can duplicate the contents of BB up into PredBB do so now, this
|
|
/// improves the odds that the branch will be on an analyzable instruction like
|
|
/// a compare.
|
|
bool JumpThreading::DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB,
|
|
BasicBlock *PredBB) {
|
|
// If BB is a loop header, then duplicating this block outside the loop would
|
|
// cause us to transform this into an irreducible loop, don't do this.
|
|
// See the comments above FindLoopHeaders for justifications and caveats.
|
|
if (LoopHeaders.count(BB)) {
|
|
DEBUG(errs() << " Not duplicating loop header '" << BB->getName()
|
|
<< "' into predecessor block '" << PredBB->getName()
|
|
<< "' - it might create an irreducible loop!\n");
|
|
return false;
|
|
}
|
|
|
|
unsigned DuplicationCost = getJumpThreadDuplicationCost(BB);
|
|
if (DuplicationCost > Threshold) {
|
|
DEBUG(errs() << " Not duplicating BB '" << BB->getName()
|
|
<< "' - Cost is too high: " << DuplicationCost << "\n");
|
|
return false;
|
|
}
|
|
|
|
// Okay, we decided to do this! Clone all the instructions in BB onto the end
|
|
// of PredBB.
|
|
DEBUG(errs() << " Duplicating block '" << BB->getName() << "' into end of '"
|
|
<< PredBB->getName() << "' to eliminate branch on phi. Cost: "
|
|
<< DuplicationCost << " block is:" << *BB << "\n");
|
|
|
|
// We are going to have to map operands from the original BB block into the
|
|
// PredBB block. Evaluate PHI nodes in BB.
|
|
DenseMap<Instruction*, Value*> ValueMapping;
|
|
|
|
BasicBlock::iterator BI = BB->begin();
|
|
for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
|
|
ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
|
|
|
|
BranchInst *OldPredBranch = cast<BranchInst>(PredBB->getTerminator());
|
|
|
|
// Clone the non-phi instructions of BB into PredBB, keeping track of the
|
|
// mapping and using it to remap operands in the cloned instructions.
|
|
for (; BI != BB->end(); ++BI) {
|
|
Instruction *New = BI->clone();
|
|
New->setName(BI->getName());
|
|
PredBB->getInstList().insert(OldPredBranch, New);
|
|
ValueMapping[BI] = New;
|
|
|
|
// Remap operands to patch up intra-block references.
|
|
for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
|
|
if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) {
|
|
DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst);
|
|
if (I != ValueMapping.end())
|
|
New->setOperand(i, I->second);
|
|
}
|
|
}
|
|
|
|
// Check to see if the targets of the branch had PHI nodes. If so, we need to
|
|
// add entries to the PHI nodes for branch from PredBB now.
|
|
BranchInst *BBBranch = cast<BranchInst>(BB->getTerminator());
|
|
AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(0), BB, PredBB,
|
|
ValueMapping);
|
|
AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(1), BB, PredBB,
|
|
ValueMapping);
|
|
|
|
// If there were values defined in BB that are used outside the block, then we
|
|
// now have to update all uses of the value to use either the original value,
|
|
// the cloned value, or some PHI derived value. This can require arbitrary
|
|
// PHI insertion, of which we are prepared to do, clean these up now.
|
|
SSAUpdater SSAUpdate;
|
|
SmallVector<Use*, 16> UsesToRename;
|
|
for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
|
|
// Scan all uses of this instruction to see if it is used outside of its
|
|
// block, and if so, record them in UsesToRename.
|
|
for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
|
|
++UI) {
|
|
Instruction *User = cast<Instruction>(*UI);
|
|
if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
|
|
if (UserPN->getIncomingBlock(UI) == BB)
|
|
continue;
|
|
} else if (User->getParent() == BB)
|
|
continue;
|
|
|
|
UsesToRename.push_back(&UI.getUse());
|
|
}
|
|
|
|
// If there are no uses outside the block, we're done with this instruction.
|
|
if (UsesToRename.empty())
|
|
continue;
|
|
|
|
DEBUG(errs() << "JT: Renaming non-local uses of: " << *I << "\n");
|
|
|
|
// We found a use of I outside of BB. Rename all uses of I that are outside
|
|
// its block to be uses of the appropriate PHI node etc. See ValuesInBlocks
|
|
// with the two values we know.
|
|
SSAUpdate.Initialize(I);
|
|
SSAUpdate.AddAvailableValue(BB, I);
|
|
SSAUpdate.AddAvailableValue(PredBB, ValueMapping[I]);
|
|
|
|
while (!UsesToRename.empty())
|
|
SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
|
|
DEBUG(errs() << "\n");
|
|
}
|
|
|
|
// PredBB no longer jumps to BB, remove entries in the PHI node for the edge
|
|
// that we nuked.
|
|
BB->removePredecessor(PredBB);
|
|
|
|
// Remove the unconditional branch at the end of the PredBB block.
|
|
OldPredBranch->eraseFromParent();
|
|
|
|
++NumDupes;
|
|
return true;
|
|
}
|
|
|
|
|