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Add fast math inst combine X*log2(Y*0.5)-->X*log2(Y)-X

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reviewed by Michael Ilseman <milseman@apple.com>



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169025 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Pedro Artigas 2012-11-30 19:09:41 +00:00
parent cb4953089b
commit 84030dcb3f
1 changed files with 77 additions and 0 deletions
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77
lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
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@ -284,6 +284,83 @@ Instruction *InstCombiner::visitFMul(BinaryOperator &I) {
if (Value *Op1v = dyn_castFNegVal(Op1))
return BinaryOperator::CreateFMul(Op0v, Op1v);
// Under unsafe algebra do:
// X * log2(0.5*Y) = X*log2(Y) - X
if (I.hasUnsafeAlgebra()) {
Value *OpX = NULL;
Value *OpY = NULL;
IntrinsicInst *Log2;
if (Op0->hasOneUse()) {
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Op0)) {
if (II->getIntrinsicID() == Intrinsic::log2 &&
II->hasUnsafeAlgebra())
{
Log2 = II;
Value *OpLog2Of = II->getArgOperand(0);
if (OpLog2Of->hasOneUse()) {
if (Instruction *I = dyn_cast<Instruction>(OpLog2Of)) {
if (I->getOpcode() == Instruction::FMul &&
I->hasUnsafeAlgebra())
{
ConstantFP *CFP = dyn_cast<ConstantFP>(I->getOperand(0));
if (CFP && CFP->isExactlyValue(0.5)) {
OpY = I->getOperand(1);
OpX = Op1;
} else {
CFP = dyn_cast<ConstantFP>(I->getOperand(1));
if (CFP && CFP->isExactlyValue(0.5)) {
OpY = I->getOperand(0);
OpX = Op1;
}
}
}
}
}
}
}
}
if (Op1->hasOneUse()) {
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Op1)) {
if (II->getIntrinsicID() == Intrinsic::log2 &&
II->hasUnsafeAlgebra())
{
Log2 = II;
Value *OpLog2Of = II->getArgOperand(0);
if (OpLog2Of->hasOneUse()) {
if (Instruction *I = dyn_cast<Instruction>(OpLog2Of)) {
if (I->getOpcode() == Instruction::FMul &&
I->hasUnsafeAlgebra())
{
ConstantFP *CFP = dyn_cast<ConstantFP>(I->getOperand(0));
if (CFP && CFP->isExactlyValue(0.5)) {
OpY = I->getOperand(1);
OpX = Op0;
} else {
CFP = dyn_cast<ConstantFP>(I->getOperand(1));
if (CFP && CFP->isExactlyValue(0.5)) {
OpY = I->getOperand(0);
OpX = Op0;
}
}
}
}
}
}
}
}
// if pattern detected emit alternate sequence
if (OpX && OpY) {
Log2->setArgOperand(0, OpY);
Value *FMulVal = Builder->CreateFMul(OpX, Log2);
Instruction *FMul = dyn_cast<Instruction>(FMulVal);
assert(FMul && "Must be instruction as Log2 is instruction");
FMul->copyFastMathFlags(Log2);
Instruction *FSub = BinaryOperator::CreateFSub(FMulVal, OpX);
FSub->copyFastMathFlags(Log2);
return FSub;
}
}
return Changed ? &I : 0;
}