[llvm] Add LoopVectorizer support for `llvm.vector.partial.reduce.fadd` (PR #163975)

[Gaëtan Bossu via llvm-commits]

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@@ -8301,6 +8302,9 @@ VPRecipeBuilder::tryToCreatePartialReduction(VPInstruction *Reduction,
          "all accumulators in chain must have same scale factor");
 
   auto *ReductionI = Reduction->getUnderlyingInstr();
+  if (Reduction->getOpcode() == Instruction::FAdd &&
+      !ReductionI->hasAllowReassoc())
+    return nullptr;
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gbossu wrote:

Out of curiosity: Is `contract` implied by fast-math?

https://github.com/llvm/llvm-project/pull/163975