[NFC][InstCombine] Add FIXME for one-use check on constant negation transforms.
llvm-svn: 361197
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 421d49f..2d608e7 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1830,6 +1830,8 @@
// 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)
+ // FIXME: It's arguable whether these should be m_OneUse or not. The current
+ // belief is that the FNeg allows for better reassociation opportunities.
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)