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120 lines
3.2 KiB
C++
120 lines
3.2 KiB
C++
//===- ValuePropagation.cpp - Propagate information derived control flow --===//
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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 Value Propagation pass.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "value-propagation"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Function.h"
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#include "llvm/Instructions.h"
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#include "llvm/Pass.h"
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#include "llvm/Analysis/LazyValueInfo.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/ADT/Statistic.h"
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using namespace llvm;
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STATISTIC(NumPhis, "Number of phis propagated");
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STATISTIC(NumSelects, "Number of selects propagated");
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namespace {
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class ValuePropagation : public FunctionPass {
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LazyValueInfo *LVI;
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bool processSelect(SelectInst *SI);
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bool processPHI(PHINode *P);
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public:
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static char ID;
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ValuePropagation(): FunctionPass(ID) { }
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bool runOnFunction(Function &F);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<LazyValueInfo>();
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}
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};
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}
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char ValuePropagation::ID = 0;
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INITIALIZE_PASS(ValuePropagation, "value-propagation",
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"Value Propagation", false, false);
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// Public interface to the Value Propagation pass
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Pass *llvm::createValuePropagationPass() {
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return new ValuePropagation();
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}
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bool ValuePropagation::processSelect(SelectInst *S) {
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if (S->getType()->isVectorTy()) return false;
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Constant *C = LVI->getConstant(S->getOperand(0), S->getParent());
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if (!C) return false;
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ConstantInt *CI = dyn_cast<ConstantInt>(C);
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if (!CI) return false;
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S->replaceAllUsesWith(S->getOperand(CI->isOne() ? 1 : 2));
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S->eraseFromParent();
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++NumSelects;
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return true;
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}
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bool ValuePropagation::processPHI(PHINode *P) {
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bool Changed = false;
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BasicBlock *BB = P->getParent();
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for (unsigned i = 0, e = P->getNumIncomingValues(); i < e; ++i) {
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Value *Incoming = P->getIncomingValue(i);
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if (isa<Constant>(Incoming)) continue;
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Constant *C = LVI->getConstantOnEdge(P->getIncomingValue(i),
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P->getIncomingBlock(i),
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BB);
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if (!C) continue;
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P->setIncomingValue(i, C);
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Changed = true;
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}
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if (Value *ConstVal = P->hasConstantValue()) {
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P->replaceAllUsesWith(ConstVal);
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P->eraseFromParent();
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Changed = true;
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}
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++NumPhis;
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return Changed;
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}
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bool ValuePropagation::runOnFunction(Function &F) {
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LVI = &getAnalysis<LazyValueInfo>();
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bool Changed = false;
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for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
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for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ) {
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Instruction *II = BI++;
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if (SelectInst *SI = dyn_cast<SelectInst>(II))
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Changed |= processSelect(SI);
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else if (PHINode *P = dyn_cast<PHINode>(II))
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Changed |= processPHI(P);
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}
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if (Changed)
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for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
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SimplifyInstructionsInBlock(FI);
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return Changed;
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}
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