[llvm] [SLP] Guard FMulAdd conversion to require single-use/non-reordered FMul operands (PR #189692)

[Ryan Buchner via llvm-commits]

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@@ -14351,6 +14351,22 @@ void BoUpSLP::transformNodes() {
       if (E.State != TreeEntry::Vectorize ||
           !E.getOperations().isAddSubLikeOp())
         break;
+      const TreeEntry *LHS = getOperandEntry(&E, 0);
+      const TreeEntry *RHS = getOperandEntry(&E, 1);
+      auto IsOneUseVectorFMulOperand = [](const TreeEntry *TE) {
+        return TE->State == TreeEntry::Vectorize &&
+               TE->ReorderIndices.empty() && TE->ReuseShuffleIndices.empty() &&
+               TE->getOpcode() == Instruction::FMul && !TE->isAltShuffle() &&
+               all_of(TE->Scalars, [&](Value *V) {
+                 return (TE->hasCopyableElements() &&
+                         TE->isCopyableElement(V)) ||
+                        V->hasOneUse();
+               });
+      };
+      if (!IsOneUseVectorFMulOperand(LHS) &&
+          (E.getOpcode() == Instruction::FSub ||
+           !IsOneUseVectorFMulOperand(RHS)))
+        break;
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bababuck wrote:

Should this be moved into `canConvertToFMA` so that this change is also picked up by the costing (the other user of `canConvertToFMA`)?

https://github.com/llvm/llvm-project/pull/189692