| //===- CorrelatedValuePropagation.cpp - Propagate CFG-derived info --------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file implements the Correlated Value Propagation pass. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #define DEBUG_TYPE "correlated-value-propagation" |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/Constants.h" |
| #include "llvm/Function.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Analysis/InstructionSimplify.h" |
| #include "llvm/Analysis/LazyValueInfo.h" |
| #include "llvm/Support/CFG.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/ADT/Statistic.h" |
| using namespace llvm; |
| |
| STATISTIC(NumPhis, "Number of phis propagated"); |
| STATISTIC(NumSelects, "Number of selects propagated"); |
| STATISTIC(NumMemAccess, "Number of memory access targets propagated"); |
| STATISTIC(NumCmps, "Number of comparisons propagated"); |
| |
| namespace { |
| class CorrelatedValuePropagation : public FunctionPass { |
| LazyValueInfo *LVI; |
| |
| bool processSelect(SelectInst *SI); |
| bool processPHI(PHINode *P); |
| bool processMemAccess(Instruction *I); |
| bool processCmp(CmpInst *C); |
| |
| public: |
| static char ID; |
| CorrelatedValuePropagation(): FunctionPass(ID) { |
| initializeCorrelatedValuePropagationPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| bool runOnFunction(Function &F); |
| |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.addRequired<LazyValueInfo>(); |
| } |
| }; |
| } |
| |
| char CorrelatedValuePropagation::ID = 0; |
| INITIALIZE_PASS_BEGIN(CorrelatedValuePropagation, "correlated-propagation", |
| "Value Propagation", false, false) |
| INITIALIZE_PASS_DEPENDENCY(LazyValueInfo) |
| INITIALIZE_PASS_END(CorrelatedValuePropagation, "correlated-propagation", |
| "Value Propagation", false, false) |
| |
| // Public interface to the Value Propagation pass |
| Pass *llvm::createCorrelatedValuePropagationPass() { |
| return new CorrelatedValuePropagation(); |
| } |
| |
| bool CorrelatedValuePropagation::processSelect(SelectInst *S) { |
| if (S->getType()->isVectorTy()) return false; |
| if (isa<Constant>(S->getOperand(0))) return false; |
| |
| Constant *C = LVI->getConstant(S->getOperand(0), S->getParent()); |
| if (!C) return false; |
| |
| ConstantInt *CI = dyn_cast<ConstantInt>(C); |
| if (!CI) return false; |
| |
| Value *ReplaceWith = S->getOperand(1); |
| Value *Other = S->getOperand(2); |
| if (!CI->isOne()) std::swap(ReplaceWith, Other); |
| if (ReplaceWith == S) ReplaceWith = UndefValue::get(S->getType()); |
| |
| S->replaceAllUsesWith(ReplaceWith); |
| S->eraseFromParent(); |
| |
| ++NumSelects; |
| |
| return true; |
| } |
| |
| bool CorrelatedValuePropagation::processPHI(PHINode *P) { |
| bool Changed = false; |
| |
| BasicBlock *BB = P->getParent(); |
| for (unsigned i = 0, e = P->getNumIncomingValues(); i < e; ++i) { |
| Value *Incoming = P->getIncomingValue(i); |
| if (isa<Constant>(Incoming)) continue; |
| |
| Constant *C = LVI->getConstantOnEdge(P->getIncomingValue(i), |
| P->getIncomingBlock(i), |
| BB); |
| if (!C) continue; |
| |
| P->setIncomingValue(i, C); |
| Changed = true; |
| } |
| |
| if (Value *V = SimplifyInstruction(P)) { |
| P->replaceAllUsesWith(V); |
| P->eraseFromParent(); |
| Changed = true; |
| } |
| |
| ++NumPhis; |
| |
| return Changed; |
| } |
| |
| bool CorrelatedValuePropagation::processMemAccess(Instruction *I) { |
| Value *Pointer = 0; |
| if (LoadInst *L = dyn_cast<LoadInst>(I)) |
| Pointer = L->getPointerOperand(); |
| else |
| Pointer = cast<StoreInst>(I)->getPointerOperand(); |
| |
| if (isa<Constant>(Pointer)) return false; |
| |
| Constant *C = LVI->getConstant(Pointer, I->getParent()); |
| if (!C) return false; |
| |
| ++NumMemAccess; |
| I->replaceUsesOfWith(Pointer, C); |
| return true; |
| } |
| |
| /// processCmp - If the value of this comparison could be determined locally, |
| /// constant propagation would already have figured it out. Instead, walk |
| /// the predecessors and statically evaluate the comparison based on information |
| /// available on that edge. If a given static evaluation is true on ALL |
| /// incoming edges, then it's true universally and we can simplify the compare. |
| bool CorrelatedValuePropagation::processCmp(CmpInst *C) { |
| Value *Op0 = C->getOperand(0); |
| if (isa<Instruction>(Op0) && |
| cast<Instruction>(Op0)->getParent() == C->getParent()) |
| return false; |
| |
| Constant *Op1 = dyn_cast<Constant>(C->getOperand(1)); |
| if (!Op1) return false; |
| |
| pred_iterator PI = pred_begin(C->getParent()), PE = pred_end(C->getParent()); |
| if (PI == PE) return false; |
| |
| LazyValueInfo::Tristate Result = LVI->getPredicateOnEdge(C->getPredicate(), |
| C->getOperand(0), Op1, *PI, C->getParent()); |
| if (Result == LazyValueInfo::Unknown) return false; |
| |
| ++PI; |
| while (PI != PE) { |
| LazyValueInfo::Tristate Res = LVI->getPredicateOnEdge(C->getPredicate(), |
| C->getOperand(0), Op1, *PI, C->getParent()); |
| if (Res != Result) return false; |
| ++PI; |
| } |
| |
| ++NumCmps; |
| |
| if (Result == LazyValueInfo::True) |
| C->replaceAllUsesWith(ConstantInt::getTrue(C->getContext())); |
| else |
| C->replaceAllUsesWith(ConstantInt::getFalse(C->getContext())); |
| |
| C->eraseFromParent(); |
| |
| return true; |
| } |
| |
| bool CorrelatedValuePropagation::runOnFunction(Function &F) { |
| LVI = &getAnalysis<LazyValueInfo>(); |
| |
| bool FnChanged = false; |
| |
| for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) { |
| bool BBChanged = false; |
| for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ) { |
| Instruction *II = BI++; |
| switch (II->getOpcode()) { |
| case Instruction::Select: |
| BBChanged |= processSelect(cast<SelectInst>(II)); |
| break; |
| case Instruction::PHI: |
| BBChanged |= processPHI(cast<PHINode>(II)); |
| break; |
| case Instruction::ICmp: |
| case Instruction::FCmp: |
| BBChanged |= processCmp(cast<CmpInst>(II)); |
| break; |
| case Instruction::Load: |
| case Instruction::Store: |
| BBChanged |= processMemAccess(II); |
| break; |
| } |
| } |
| |
| FnChanged |= BBChanged; |
| } |
| |
| return FnChanged; |
| } |