[llvm] [VPlan] Simplify VPBlendRecipes to select instructions (PR #133993)

[Florian Hahn via llvm-commits]

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@@ -7047,6 +7047,13 @@ static bool planContainsAdditionalSimplifications(VPlan &Plan,
       if (isa<VPPartialReductionRecipe>(&R))
         return true;
 
+      // VPBlendRecipes are converted to selects and may have been simplified.
+      using namespace VPlanPatternMatch;
+      if (match(&R, m_VPInstruction<Instruction::Select>(
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fhahn wrote:

Argh I see, so we create multiple selects with the same underlying instruction and this is causing the issue.

As lowering blends to selects becomes mandatory, it would probably be better to do it in convertToConcreteRecipes, at least to start with, removing the cost-model issue?

https://github.com/llvm/llvm-project/pull/133993