[llvm] [InstCombine] Transform (fcmp + fadd + sel) into (fcmp + sel + fadd) (PR #106492)
Matt Arsenault via llvm-commits
llvm-commits at lists.llvm.org
Thu Aug 29 01:10:36 PDT 2024
================
@@ -3668,6 +3668,51 @@ static bool hasAffectedValue(Value *V, SmallPtrSetImpl<Value *> &Affected,
return false;
}
+static Value *foldSelectAddConstant(SelectInst &SI,
+ InstCombiner::BuilderTy &Builder) {
+ Value *Cmp;
+ Instruction *FAdd;
+ ConstantFP *C;
+
+ // select((fcmp OGT/OLT, X, 0), (fadd X, C), C) => fadd((select (fcmp OGT/OLT,
+ // X, 0), X, 0), C)
+
+ // This transformation enables the possibility of transforming fcmp + sel into
+ // a fmax/fmin.
+
+ // OneUse check for `Cmp` is necessary because it makes sure that other
+ // InstCombine folds don't undo this transformation and cause an infinite
+ // loop.
+ if (match(&SI, m_Select(m_OneUse(m_Value(Cmp)), m_OneUse(m_Instruction(FAdd)),
+ m_ConstantFP(C))) ||
+ match(&SI, m_Select(m_OneUse(m_Value(Cmp)), m_ConstantFP(C),
----------------
arsenm wrote:
The conditions are a bit off. You need to know the constant isn't a nan (it doesn't even really need to be a constant, you just need to know it's not nan, which you can use isKnownNeverNaN for).
Broken: https://alive2.llvm.org/ce/z/65RLiq
Fixed: https://alive2.llvm.org/ce/z/nPXs8M
https://github.com/llvm/llvm-project/pull/106492
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