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[InstCombine] add helper for x/pow(); NFC 

We at least want to add powi to this list, so
split it off into a switch to reduce code duplication.
This commit is contained in:
Sanjay Patel 2021-02-24 15:31:59 -05:00
parent 80f329bcd0
commit 868d43fbd6
1 changed files with 35 additions and 22 deletions
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57
llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
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@ -1274,6 +1274,37 @@ static Instruction *foldFDivConstantDividend(BinaryOperator &I) {
return BinaryOperator::CreateFDivFMF(NewC, X, &I);
}
/// Negate the exponent of pow/exp to fold division-by-pow() into multiply.
static Instruction *foldFDivPowDivisor(BinaryOperator &I,
InstCombiner::BuilderTy &Builder) {
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
auto *II = dyn_cast<IntrinsicInst>(Op1);
if (!II || !II->hasOneUse() || !I.hasAllowReassoc() ||
!I.hasAllowReciprocal())
return nullptr;
// Z / pow(X, Y) --> Z * pow(X, -Y)
// Z / exp{2}(Y) --> Z * exp{2}(-Y)
// In the general case, this creates an extra instruction, but fmul allows
// for better canonicalization and optimization than fdiv.
Intrinsic::ID IID = II->getIntrinsicID();
SmallVector<Value *> Args;
switch (IID) {
case Intrinsic::pow:
Args.push_back(II->getArgOperand(0));
Args.push_back(Builder.CreateFNegFMF(II->getArgOperand(1), &I));
break;
case Intrinsic::exp:
case Intrinsic::exp2:
Args.push_back(Builder.CreateFNegFMF(II->getArgOperand(0), &I));
break;
default:
return nullptr;
}
Value *Pow = Builder.CreateIntrinsic(IID, I.getType(), Args, &I);
return BinaryOperator::CreateFMulFMF(Op0, Pow, &I);
}
Instruction *InstCombinerImpl::visitFDiv(BinaryOperator &I) {
if (Value *V = SimplifyFDivInst(I.getOperand(0), I.getOperand(1),
I.getFastMathFlags(),
@ -1325,28 +1356,6 @@ Instruction *InstCombinerImpl::visitFDiv(BinaryOperator &I) {
// replaced by a multiplication.
if (match(Op1, m_FDiv(m_SpecificFP(1.0), m_Value(Y))))
return BinaryOperator::CreateFMulFMF(Y, Op0, &I);
// Negate the exponent of pow/exp to fold division-by-pow() into multiply:
// Z / pow(X, Y) --> Z * pow(X, -Y)
// Z / exp{2}(Y) --> Z * exp{2}(-Y)
// In the general case, this creates an extra instruction, but fmul allows
// for better canonicalization and optimization than fdiv.
if (match(Op1,
m_OneUse(m_Intrinsic<Intrinsic::pow>(m_Value(X), m_Value(Y))))) {
Value *NegY = Builder.CreateFNegFMF(Y, &I);
Value *Pow = Builder.CreateBinaryIntrinsic(Intrinsic::pow, X, NegY, &I);
return BinaryOperator::CreateFMulFMF(Op0, Pow, &I);
}
if (match(Op1, m_OneUse(m_Intrinsic<Intrinsic::exp>(m_Value(Y))))) {
Value *NegY = Builder.CreateFNegFMF(Y, &I);
Value *Pow = Builder.CreateUnaryIntrinsic(Intrinsic::exp, NegY, &I);
return BinaryOperator::CreateFMulFMF(Op0, Pow, &I);
}
if (match(Op1, m_OneUse(m_Intrinsic<Intrinsic::exp2>(m_Value(Y))))) {
Value *NegY = Builder.CreateFNegFMF(Y, &I);
Value *Pow = Builder.CreateUnaryIntrinsic(Intrinsic::exp2, NegY, &I);
return BinaryOperator::CreateFMulFMF(Op0, Pow, &I);
}
}
if (I.hasAllowReassoc() && Op0->hasOneUse() && Op1->hasOneUse()) {
@ -1394,6 +1403,10 @@ Instruction *InstCombinerImpl::visitFDiv(BinaryOperator &I) {
Intrinsic::copysign, ConstantFP::get(I.getType(), 1.0), X, &I);
return replaceInstUsesWith(I, V);
}
if (Instruction *Mul = foldFDivPowDivisor(I, Builder))
return Mul;
return nullptr;
}