[llvm] [VPlan] Introduce VPlanConstantFolder (PR #125365)

[Florian Hahn via llvm-commits]

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@@ -1047,15 +1049,27 @@ static void simplifyRecipe(VPRecipeBase &R, VPTypeAnalysis &TypeInfo) {
     R.setOperand(0, Y);
     return;
   }
+
+  // Constant folding.
+  VPConstantFolder Folder(DL, TypeInfo);
+  TypeSwitch<VPRecipeBase *, void>(&R)
+      .Case<VPInstruction, VPWidenRecipe, VPWidenCastRecipe, VPHistogramRecipe,
+            VPPartialReductionRecipe, VPReplicateRecipe>([&](auto *I) {
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fhahn wrote:

Not sure if it makes sense to apply constant folding to VPHistogramRecipe/VPPartialReductionRecipe, those do more than applying the opcode to the operands.

https://github.com/llvm/llvm-project/pull/125365