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Change FoldPHIArgBinOpIntoPHI to decline folding if it would introduce two

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phis, similar to the FoldPHIArgGEPIntoPHI change.

Also, delete some comments that don't reflect the code.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@82053 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2009-09-16 16:50:24 +00:00
parent 46fb0dee03
commit 9ad29207db
1 changed files with 13 additions and 7 deletions
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20
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -10313,8 +10313,8 @@ Instruction *InstCombiner::transformCallThroughTrampoline(CallSite CS) {
return CS.getInstruction();
}
/// FoldPHIArgBinOpIntoPHI - If we have something like phi [add (a,b), add(c,d)]
/// and if a/b/c/d and the add's all have a single use, turn this into two phi's
/// FoldPHIArgBinOpIntoPHI - If we have something like phi [add (a,b), add(a,c)]
/// and if a/b/c and the add's all have a single use, turn this into a phi
/// and a single binop.
Instruction *InstCombiner::FoldPHIArgBinOpIntoPHI(PHINode &PN) {
Instruction *FirstInst = cast<Instruction>(PN.getIncomingValue(0));
@ -10326,8 +10326,7 @@ Instruction *InstCombiner::FoldPHIArgBinOpIntoPHI(PHINode &PN) {
const Type *LHSType = LHSVal->getType();
const Type *RHSType = RHSVal->getType();
// Scan to see if all operands are the same opcode, all have one use, and all
// kill their operands (i.e. the operands have one use).
// Scan to see if all operands are the same opcode, and all have one use.
for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) {
Instruction *I = dyn_cast<Instruction>(PN.getIncomingValue(i));
if (!I || I->getOpcode() != Opc || !I->hasOneUse() ||
@ -10347,6 +10346,13 @@ Instruction *InstCombiner::FoldPHIArgBinOpIntoPHI(PHINode &PN) {
if (I->getOperand(0) != LHSVal) LHSVal = 0;
if (I->getOperand(1) != RHSVal) RHSVal = 0;
}
// If both LHS and RHS would need a PHI, don't do this transformation,
// because it would increase the number of PHIs entering the block,
// which leads to higher register pressure. This is especially
// bad when the PHIs are in the header of a loop.
if (!LHSVal && !RHSVal)
return 0;
// Otherwise, this is safe to transform!
@ -10403,11 +10409,11 @@ Instruction *InstCombiner::FoldPHIArgGEPIntoPHI(PHINode &PN) {
bool AllBasePointersAreAllocas = true;
// We don't want to replace this phi if the replacement would require
// more than one phi.
// more than one phi, which leads to higher register pressure. This is
// especially bad when the PHIs are in the header of a loop.
bool NeededPhi = false;
// Scan to see if all operands are the same opcode, all have one use, and all
// kill their operands (i.e. the operands have one use).
// Scan to see if all operands are the same opcode, and all have one use.
for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) {
GetElementPtrInst *GEP= dyn_cast<GetElementPtrInst>(PN.getIncomingValue(i));
if (!GEP || !GEP->hasOneUse() || GEP->getType() != FirstInst->getType() ||