[InstCombine] add FMF guard to builder in fptrunc transform; NFC
This makes no difference currently because we don't apply FMF
to FP casts, but that may change.
This could also be a place to add a fold for select with fptrunc,
so it will make that patch easier/smaller.
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 2171c81..53bcaeb 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -1622,6 +1622,11 @@
Value *X;
Instruction *Op = dyn_cast<Instruction>(FPT.getOperand(0));
if (Op && Op->hasOneUse()) {
+ // FIXME: The FMF should propagate from the fptrunc, not the source op.
+ IRBuilder<>::FastMathFlagGuard FMFG(Builder);
+ if (isa<FPMathOperator>(Op))
+ Builder.setFastMathFlags(Op->getFastMathFlags());
+
if (match(Op, m_FNeg(m_Value(X)))) {
Value *InnerTrunc = Builder.CreateFPTrunc(X, Ty);