[llvm] [VPlan] First step towards VPlan cost modeling (LegacyCM in CostCtx) (PR #92555)

[via llvm-commits]

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@@ -910,6 +910,10 @@ static void simplifyRecipe(VPRecipeBase &R, VPTypeAnalysis &TypeInfo) {
                                  : Instruction::ZExt;
         auto *VPC =
             new VPWidenCastRecipe(Instruction::CastOps(ExtOpcode), A, TruncTy);
+        if (auto *UnderlyingExt = R.getOperand(0)->getUnderlyingValue()) {
+          // UnderlyingExt has distinct return type, used to retain legacy cost.
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ayalz wrote:

If the original Trunc is set as underlying, the result type would match that of the recipe, but the cost of original Ext is more accurate for this recipe, being an Ext?

https://github.com/llvm/llvm-project/pull/92555