[llvm] [InstCombine] Fold `fmul X, -0.0` into `copysign(0.0, -X)` (PR #85772)

[Yingwei Zheng via llvm-commits]

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@@ -814,8 +814,19 @@ Instruction *InstCombinerImpl::visitFMul(BinaryOperator &I) {
   if (match(Op1, m_SpecificFP(-1.0)))
     return UnaryOperator::CreateFNegFMF(Op0, &I);
 
-  // With no-nans: X * 0.0 --> copysign(0.0, X)
-  if (I.hasNoNaNs() && match(Op1, m_PosZeroFP())) {
+  // With no-nans/no-infs:
+  // X * 0.0 --> copysign(0.0, X)
+  // X * -0.0 --> copysign(0.0, -X)
+  const APFloat *FPC;
+  if (match(Op1, m_APFloatAllowUndef(FPC)) && FPC->isZero() &&
+      ((I.hasNoInfs() &&
+        isKnownNeverNaN(Op0, /*Depth=*/0, SQ.getWithInstruction(&I))) ||
+       isKnownNeverNaN(&I, /*Depth=*/0, SQ.getWithInstruction(&I)))) {
+    if (FPC->isNegative())
+      Op0 = Builder.CreateFNegFMF(Op0, &I);
+    Op1 = Constant::replaceUndefsWith(
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dtcxzyw wrote:

Alive2: https://alive2.llvm.org/ce/z/GNc4gb


https://github.com/llvm/llvm-project/pull/85772