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//===- ValuePropagation.cpp - Propagate information derived control flow --===//
//
// 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 Value Propagation pass.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "value-propagation"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Function.h"
#include "llvm/Instructions.h"
#include "llvm/Pass.h"
#include "llvm/Analysis/LazyValueInfo.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");
namespace {
class ValuePropagation : public FunctionPass {
LazyValueInfo *LVI;
bool processSelect(SelectInst *SI);
bool processPHI(PHINode *P);
public:
static char ID;
ValuePropagation(): FunctionPass(ID) { }
bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<LazyValueInfo>();
}
};
}
char ValuePropagation::ID = 0;
INITIALIZE_PASS(ValuePropagation, "value-propagation",
"Value Propagation", false, false);
// Public interface to the Value Propagation pass
Pass *llvm::createValuePropagationPass() {
return new ValuePropagation();
}
bool ValuePropagation::processSelect(SelectInst *S) {
Constant *C = LVI->getConstant(S->getOperand(0), S->getParent());
if (!C) return false;
ConstantInt *CI = dyn_cast<ConstantInt>(C);
if (!CI) return false;
if (CI->isZero()) {
S->replaceAllUsesWith(S->getOperand(2));
S->eraseFromParent();
} else if (CI->isOne()) {
S->replaceAllUsesWith(S->getOperand(1));
S->eraseFromParent();
} else {
assert(0 && "Select on constant is neither 0 nor 1?");
}
++NumSelects;
return true;
}
bool ValuePropagation::processPHI(PHINode *P) {
bool changed = false;
BasicBlock *BB = P->getParent();
for (unsigned i = 0; i < P->getNumIncomingValues(); ++i) {
Constant *C = LVI->getConstantOnEdge(P->getIncomingValue(i),
P->getIncomingBlock(i),
BB);
if (!C || C == P->getIncomingValue(i)) continue;
P->setIncomingValue(i, C);
changed = true;
}
if (Value *ConstVal = P->hasConstantValue()) {
P->replaceAllUsesWith(ConstVal);
P->eraseFromParent();
changed = true;
}
++NumPhis;
return changed;
}
bool ValuePropagation::runOnFunction(Function &F) {
LVI = &getAnalysis<LazyValueInfo>();
bool changed = false;
for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ) {
Instruction *II = BI++;
if (SelectInst *SI = dyn_cast<SelectInst>(II))
changed |= processSelect(SI);
else if (PHINode *P = dyn_cast<PHINode>(II))
changed |= processPHI(P);
}
if (changed)
for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
SimplifyInstructionsInBlock(FI);
return changed;
}
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