[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) {
+        VPlan *Plan = R.getParent()->getPlan();
+        ArrayRef<VPValue *> Ops{I->op_begin(), I->op_end()};
+        if (Value *V = Folder.tryToConstantFold(R, I->getOpcode(), Ops))
+          R.getVPSingleValue()->replaceAllUsesWith(Plan->getOrAddLiveIn(V));
+      });
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fhahn wrote:

Better to move constant folding up to happen first, to not spend time applying other simplifications that would already be constant folded?

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