[llvm-branch-commits] [llvm] [AArch64] Tweak the cost-model of partial reductions to mitigate regressions from #181706 (PR #181707)

[Florian Hahn via llvm-branch-commits]

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@@ -5915,7 +5915,7 @@ InstructionCost AArch64TTIImpl::getPartialReductionCost(
   // The sub/negation cannot be folded into the operands of
   // ISD::PARTIAL_REDUCE_*MLA, so make the cost more expensive.
   if (Opcode == Instruction::Sub)
-    Cost += 8;
+    Cost *= 4;
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fhahn wrote:

Why scale by 4 and by 8 below? We usually sink the sub, right?

https://github.com/llvm/llvm-project/pull/181707