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

[Nikita Popov via llvm-commits]

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@@ -5710,7 +5710,9 @@ simplifyFAddInst(Value *Op0, Value *Op1, FastMathFlags FMF,
   // fadd X, 0 ==> X, when we know X is not -0
   if (canIgnoreSNaN(ExBehavior, FMF))
     if (match(Op1, m_PosZeroFP()) &&
-        (FMF.noSignedZeros() || cannotBeNegativeZero(Op0, Q)))
+        (FMF.noSignedZeros() || cannotBeNegativeZero(Op0, Q) ||
+         (Q.CxtI && !Q.CxtI->use_empty() &&
+          canIgnoreSignBitOfZero(*(Q.CxtI->use_begin())))))
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nikic wrote:

You can't do use-based reasoning inside InstSimplify, this must happen in InstCombine.

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