[llvm] [InstCombine] Enable FAdd simplifications when user can ignore sign bit (PR #157757)

[Nikita Popov via llvm-commits]

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@@ -2002,6 +2002,16 @@ Instruction *InstCombinerImpl::visitFAdd(BinaryOperator &I) {
   if (Instruction *FoldedFAdd = foldBinOpIntoSelectOrPhi(I))
     return FoldedFAdd;
 
+  // B = fadd A, 0
+  // Z = Op B
+  // can be transformed into
+  // Z = Op A
+  // Where Op is such that we can ignore sign of 0 in fadd
+  Value *A;
+  if (match(&I, m_c_FAdd(m_Value(A), m_AnyZeroFP())) && !I.use_empty() &&
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nikic wrote:

This needs to check for one use, otherwise you're only checking that the transform is safe for a single use, but doing it for all of them. Please also add multi use test.

https://github.com/llvm/llvm-project/pull/157757