[InstCombine] fold fneg into constant operand of fmul/fdiv
This accounts for the missing IR fold noted in D50195. We don't need any fast-math to enable the negation transform.
FP negation can always be folded into an fmul/fdiv constant to eliminate the fneg.
I've limited this to one-use to ensure that we are eliminating an instruction rather than replacing fneg by a
potentially expensive fdiv or fmul.
Differential Revision: https://reviews.llvm.org/D50417
llvm-svn: 339248
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 8305458..052cb4a 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1847,13 +1847,27 @@
if (I.hasNoSignedZeros() && match(Op0, m_PosZeroFP()))
return BinaryOperator::CreateFNegFMF(Op1, &I);
+ Value *X, *Y;
+ Constant *C;
+
+ // Fold negation into constant operand. This is limited with one-use because
+ // fneg is assumed better for analysis and cheaper in codegen than fmul/fdiv.
+ // -(X * C) --> X * (-C)
+ if (match(&I, m_FNeg(m_OneUse(m_FMul(m_Value(X), m_Constant(C))))))
+ return BinaryOperator::CreateFMulFMF(X, ConstantExpr::getFNeg(C), &I);
+ // -(X / C) --> X / (-C)
+ if (match(&I, m_FNeg(m_OneUse(m_FDiv(m_Value(X), m_Constant(C))))))
+ return BinaryOperator::CreateFDivFMF(X, ConstantExpr::getFNeg(C), &I);
+ // -(C / X) --> (-C) / X
+ if (match(&I, m_FNeg(m_OneUse(m_FDiv(m_Constant(C), m_Value(X))))))
+ return BinaryOperator::CreateFDivFMF(ConstantExpr::getFNeg(C), X, &I);
+
// If Op0 is not -0.0 or we can ignore -0.0: Z - (X - Y) --> Z + (Y - X)
// Canonicalize to fadd to make analysis easier.
// This can also help codegen because fadd is commutative.
// Note that if this fsub was really an fneg, the fadd with -0.0 will get
// killed later. We still limit that particular transform with 'hasOneUse'
// because an fneg is assumed better/cheaper than a generic fsub.
- Value *X, *Y;
if (I.hasNoSignedZeros() || CannotBeNegativeZero(Op0, SQ.TLI)) {
if (match(Op1, m_OneUse(m_FSub(m_Value(X), m_Value(Y))))) {
Value *NewSub = Builder.CreateFSubFMF(Y, X, &I);
@@ -1869,7 +1883,6 @@
// X - C --> X + (-C)
// But don't transform constant expressions because there's an inverse fold
// for X + (-Y) --> X - Y.
- Constant *C;
if (match(Op1, m_Constant(C)) && !isa<ConstantExpr>(Op1))
return BinaryOperator::CreateFAddFMF(Op0, ConstantExpr::getFNeg(C), &I);