[llvm] [VPlan] Make simplifyRecipe more like InstCombine (PR #212968)

[Luke Lau via llvm-commits]

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@@ -1658,7 +1613,16 @@ void VPlanTransforms::simplifyRecipes(VPlan &Plan) {
   for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(RPOT)) {
     for (VPRecipeBase &R : make_early_inc_range(*VPBB))
       if (auto *Def = dyn_cast<VPSingleDefRecipe>(&R))
-        simplifyRecipe(Def);
+        if (VPValue *New = simplifyRecipe(Def)) {
+          if (New != Def) {
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lukel97 wrote:

We only want to RAUW if we created a new recipe to replace it. Otherwise if we've modified the recipe in place it falls through to the `else if (vputils::isDeadRecipe(R))` case below

https://github.com/llvm/llvm-project/pull/212968