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//===- 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/Function.h"
#include "llvm/Instructions.h"
#include "llvm/Pass.h"
#include "llvm/Analysis/LazyValueInfo.h"
#include "llvm/Support/CFG.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/ADT/DepthFirstIterator.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) { }
bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<LazyValueInfo>();
}
};
}
char CorrelatedValuePropagation::ID = 0;
INITIALIZE_PASS(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;
S->replaceAllUsesWith(S->getOperand(CI->isOne() ? 1 : 2));
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 *ConstVal = P->hasConstantValue()) {
P->replaceAllUsesWith(ConstVal);
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;
// Perform a depth-first walk of the CFG so that we don't waste time
// optimizing unreachable blocks.
for (df_iterator<BasicBlock*> FI = df_begin(&F.getEntryBlock()),
FE = df_end(&F.getEntryBlock()); 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;
}
}
// Propagating correlated values might leave cruft around.
// Try to clean it up before we continue.
if (BBChanged)
SimplifyInstructionsInBlock(*FI);
FnChanged |= BBChanged;
}
return FnChanged;
}
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