[llvm] [VPlan] Run initial recipe simplification on VPlan0. (PR #176828)

[Florian Hahn via llvm-commits]

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@@ -8122,6 +8122,8 @@ void LoopVectorizationPlanner::buildVPlansWithVPRecipes(ElementCount MinVF,
       Legal->getReductionVars(), Legal->getFixedOrderRecurrences(),
       CM.getInLoopReductions(), Hints.allowReordering());
 
+  VPlanTransforms::simplifyRecipes(*VPlan0);
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fhahn wrote:

The issue is not really predication, but that we will fail to create VPWidenRecipes for the transformed VPInstructions without underlying value. This means we may miss out on some transformations that only work for VPWidenRecipes.

I think in general we may have to revisit this independent of the patch. We currently replace a VPWidenRecipe with a VPInstruction without underlying value, but now we skip the VPInstruction during cost computation, which is not right.

https://github.com/llvm/llvm-project/pull/176828