[llvm] [SLP]Buildvector for alternate instructions with non-profitable gather operands. (PR #84978)

[Valery Dmitriev via llvm-commits]

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@@ -6074,6 +6194,14 @@ BoUpSLP::TreeEntry::EntryState BoUpSLP::getScalarsVectorizationState(
       LLVM_DEBUG(dbgs() << "SLP: ShuffleVector are not vectorized.\n");
       return TreeEntry::NeedToGather;
     }
+    if (!areAltOperandsProfitable(S, VL)) {
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valerydmit wrote:

Hi Alexey. Can you please put this under an option (let it be true by default)?
Here is the problem: sometime we create LIT tests deliberately short and force to go through via just making slp-threshold very low. We merely need SLP vectorizer to execute specific path even though it could be unprofitable in a test case scenario. But since this new staff does not check cost threshold at all, we observe changing some tests behavior and they no longer serve their purpose. Having the option we could fix that.


https://github.com/llvm/llvm-project/pull/84978