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Turn a phi of many loads into a phi of the address and a single load of the

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result.  This can significantly shrink code and exposes identities more
aggressively.

llvm-svn: 31344
This commit is contained in:
Chris Lattner 2006-11-01 07:13:54 +00:00
parent 790d5c7697
commit 61ea2af8fe
1 changed files with 30 additions and 41 deletions
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71
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -6833,6 +6833,19 @@ Instruction *InstCombiner::FoldPHIArgBinOpIntoPHI(PHINode &PN) {
NewLHS, NewRHS);
}
/// isSafeToSinkLoad - Return true if we know that it is safe sink the load out
/// of the block that defines it. This means that it must be obvious the value
/// of the load is not changed from the point of the load to the end of the
/// block it is in.
static bool isSafeToSinkLoad(LoadInst *L) {
BasicBlock::iterator BBI = L, E = L->getParent()->end();
for (++BBI; BBI != E; ++BBI)
if (BBI->mayWriteToMemory())
return false;
return true;
}
// FoldPHIArgOpIntoPHI - If all operands to a PHI node are the same "unary"
// operator and they all are only used by the PHI, PHI together their
@ -6846,6 +6859,7 @@ Instruction *InstCombiner::FoldPHIArgOpIntoPHI(PHINode &PN) {
// code size and simplifying code.
Constant *ConstantOp = 0;
const Type *CastSrcTy = 0;
bool isVolatile = false;
if (isa<CastInst>(FirstInst)) {
CastSrcTy = FirstInst->getOperand(0)->getType();
} else if (isa<BinaryOperator>(FirstInst) || isa<ShiftInst>(FirstInst)) {
@ -6854,6 +6868,13 @@ Instruction *InstCombiner::FoldPHIArgOpIntoPHI(PHINode &PN) {
ConstantOp = dyn_cast<Constant>(FirstInst->getOperand(1));
if (ConstantOp == 0)
return FoldPHIArgBinOpIntoPHI(PN);
} else if (LoadInst *LI = dyn_cast<LoadInst>(FirstInst)) {
isVolatile = LI->isVolatile();
// We can't sink the load if the loaded value could be modified between the
// load and the PHI.
if (LI->getParent() != PN.getIncomingBlock(0) ||
!isSafeToSinkLoad(LI))
return 0;
} else {
return 0; // Cannot fold this operation.
}
@ -6867,6 +6888,13 @@ Instruction *InstCombiner::FoldPHIArgOpIntoPHI(PHINode &PN) {
if (CastSrcTy) {
if (I->getOperand(0)->getType() != CastSrcTy)
return 0; // Cast operation must match.
} else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
// We can't sink the load if the loaded value could be modified between the
// load and the PHI.
if (LI->isVolatile() != isVolatile ||
LI->getParent() != PN.getIncomingBlock(i) ||
!isSafeToSinkLoad(LI))
return 0;
} else if (I->getOperand(1) != ConstantOp) {
return 0;
}
@ -6903,6 +6931,8 @@ Instruction *InstCombiner::FoldPHIArgOpIntoPHI(PHINode &PN) {
// Insert and return the new operation.
if (isa<CastInst>(FirstInst))
return new CastInst(PhiVal, PN.getType());
else if (LoadInst *LI = dyn_cast<LoadInst>(FirstInst))
return new LoadInst(PhiVal, "", isVolatile);
else if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(FirstInst))
return BinaryOperator::create(BinOp->getOpcode(), PhiVal, ConstantOp);
else
@ -7537,47 +7567,6 @@ Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
LI.setOperand(0, SI->getOperand(1));
return &LI;
}
} else if (PHINode *PN = dyn_cast<PHINode>(Op)) {
// load (phi (&V1, &V2, &V3)) --> phi(load &V1, load &V2, load &V3)
bool Safe = PN->getParent() == LI.getParent();
// Scan all of the instructions between the PHI and the load to make
// sure there are no instructions that might possibly alter the value
// loaded from the PHI.
if (Safe) {
BasicBlock::iterator I = &LI;
for (--I; !isa<PHINode>(I); --I)
if (isa<StoreInst>(I) || isa<CallInst>(I)) {
Safe = false;
break;
}
}
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e && Safe; ++i)
if (!isSafeToLoadUnconditionally(PN->getIncomingValue(i),
PN->getIncomingBlock(i)->getTerminator()))
Safe = false;
if (Safe) {
// Create the PHI.
PHINode *NewPN = new PHINode(LI.getType(), PN->getName());
InsertNewInstBefore(NewPN, *PN);
std::map<BasicBlock*,Value*> LoadMap; // Don't insert duplicate loads
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
BasicBlock *BB = PN->getIncomingBlock(i);
Value *&TheLoad = LoadMap[BB];
if (TheLoad == 0) {
Value *InVal = PN->getIncomingValue(i);
TheLoad = InsertNewInstBefore(new LoadInst(InVal,
InVal->getName()+".val"),
*BB->getTerminator());
}
NewPN->addIncoming(TheLoad, BB);
}
return ReplaceInstUsesWith(LI, NewPN);
}
}
}
return 0;