[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:

Why is this needed? This effectively disables cost checking for any plans with blends? If the blend gets simplified away, the regular checks should already catch this?

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