[InstCombine] fold fneg disguised as select+fmul (PR43497)
Extends rL373230 and solves the motivating bug (although in a narrow way):
https://bugs.llvm.org/show_bug.cgi?id=43497
llvm-svn: 373851
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index a301d9e..0b9128a 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -124,6 +124,50 @@
return ConstantVector::get(Elts);
}
+// TODO: This is a specific form of a much more general pattern.
+// We could detect a select with any binop identity constant, or we
+// could use SimplifyBinOp to see if either arm of the select reduces.
+// But that needs to be done carefully and/or while removing potential
+// reverse canonicalizations as in InstCombiner::foldSelectIntoOp().
+static Value *foldMulSelectToNegate(BinaryOperator &I,
+ InstCombiner::BuilderTy &Builder) {
+ Value *Cond, *OtherOp;
+
+ // mul (select Cond, 1, -1), OtherOp --> select Cond, OtherOp, -OtherOp
+ // mul OtherOp, (select Cond, 1, -1) --> select Cond, OtherOp, -OtherOp
+ if (match(&I, m_c_Mul(m_OneUse(m_Select(m_Value(Cond), m_One(), m_AllOnes())),
+ m_Value(OtherOp))))
+ return Builder.CreateSelect(Cond, OtherOp, Builder.CreateNeg(OtherOp));
+
+ // mul (select Cond, -1, 1), OtherOp --> select Cond, -OtherOp, OtherOp
+ // mul OtherOp, (select Cond, -1, 1) --> select Cond, -OtherOp, OtherOp
+ if (match(&I, m_c_Mul(m_OneUse(m_Select(m_Value(Cond), m_AllOnes(), m_One())),
+ m_Value(OtherOp))))
+ return Builder.CreateSelect(Cond, Builder.CreateNeg(OtherOp), OtherOp);
+
+ // fmul (select Cond, 1.0, -1.0), OtherOp --> select Cond, OtherOp, -OtherOp
+ // fmul OtherOp, (select Cond, 1.0, -1.0) --> select Cond, OtherOp, -OtherOp
+ if (match(&I, m_c_FMul(m_OneUse(m_Select(m_Value(Cond), m_SpecificFP(1.0),
+ m_SpecificFP(-1.0))),
+ m_Value(OtherOp)))) {
+ IRBuilder<>::FastMathFlagGuard FMFGuard(Builder);
+ Builder.setFastMathFlags(I.getFastMathFlags());
+ return Builder.CreateSelect(Cond, OtherOp, Builder.CreateFNeg(OtherOp));
+ }
+
+ // fmul (select Cond, -1.0, 1.0), OtherOp --> select Cond, -OtherOp, OtherOp
+ // fmul OtherOp, (select Cond, -1.0, 1.0) --> select Cond, -OtherOp, OtherOp
+ if (match(&I, m_c_FMul(m_OneUse(m_Select(m_Value(Cond), m_SpecificFP(-1.0),
+ m_SpecificFP(1.0))),
+ m_Value(OtherOp)))) {
+ IRBuilder<>::FastMathFlagGuard FMFGuard(Builder);
+ Builder.setFastMathFlags(I.getFastMathFlags());
+ return Builder.CreateSelect(Cond, Builder.CreateFNeg(OtherOp), OtherOp);
+ }
+
+ return nullptr;
+}
+
Instruction *InstCombiner::visitMul(BinaryOperator &I) {
if (Value *V = SimplifyMulInst(I.getOperand(0), I.getOperand(1),
SQ.getWithInstruction(&I)))
@@ -213,24 +257,8 @@
if (Instruction *FoldedMul = foldBinOpIntoSelectOrPhi(I))
return FoldedMul;
- // TODO: This is a specific form of a much more general pattern.
- // We could detect a select with any binop identity constant, or we
- // could use SimplifyBinOp to see if either arm of the select reduces.
- // But that needs to be done carefully and/or while removing potential
- // reverse canonicalizations as in InstCombiner::foldSelectIntoOp().
- // mul (select Cond, 1, -1), Op1 --> select Cond, Op1, -Op1
- // mul (select Cond, -1, 1), Op1 --> select Cond, -Op1, Op1
- // mul Op0, (select Cond, 1, -1) --> select Cond, Op0, -Op0
- // mul Op0, (select Cond, -1, 1) --> select Cond, -Op0, Op0
- Value *Cond;
- if (match(Op0, m_OneUse(m_Select(m_Value(Cond), m_One(), m_AllOnes()))))
- return SelectInst::Create(Cond, Op1, Builder.CreateNeg(Op1));
- if (match(Op0, m_OneUse(m_Select(m_Value(Cond), m_AllOnes(), m_One()))))
- return SelectInst::Create(Cond, Builder.CreateNeg(Op1), Op1);
- if (match(Op1, m_OneUse(m_Select(m_Value(Cond), m_One(), m_AllOnes()))))
- return SelectInst::Create(Cond, Op0, Builder.CreateNeg(Op0));
- if (match(Op1, m_OneUse(m_Select(m_Value(Cond), m_AllOnes(), m_One()))))
- return SelectInst::Create(Cond, Builder.CreateNeg(Op0), Op0);
+ if (Value *FoldedMul = foldMulSelectToNegate(I, Builder))
+ return replaceInstUsesWith(I, FoldedMul);
// Simplify mul instructions with a constant RHS.
if (isa<Constant>(Op1)) {
@@ -377,6 +405,9 @@
if (Instruction *FoldedMul = foldBinOpIntoSelectOrPhi(I))
return FoldedMul;
+ if (Value *FoldedMul = foldMulSelectToNegate(I, Builder))
+ return replaceInstUsesWith(I, FoldedMul);
+
// X * -1.0 --> -X
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
if (match(Op1, m_SpecificFP(-1.0)))