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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112332 91177308-0d34-0410-b5e6-96231b3b80d8
114 lines
3.1 KiB
C++
114 lines
3.1 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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using namespace llvm;
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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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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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if (CI->isZero()) {
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S->replaceAllUsesWith(S->getOperand(2));
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S->eraseFromParent();
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} else if (CI->isOne()) {
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S->replaceAllUsesWith(S->getOperand(1));
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S->eraseFromParent();
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} else {
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assert(0 && "Select on constant is neither 0 nor 1?");
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}
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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; i < P->getNumIncomingValues(); ++i) {
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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 || C == P->getIncomingValue(i)) 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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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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