[llvm] VPlan: introduce worklist in simplifyRecipes (PR #105699)

[via llvm-commits]

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@@ -1009,8 +1015,16 @@ static void simplifyRecipes(VPlan &Plan, LLVMContext &Ctx) {
       Plan.getEntry());
   VPTypeAnalysis TypeInfo(Plan.getCanonicalIV()->getScalarType(), Ctx);
   for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(RPOT)) {
-    for (VPRecipeBase &R : make_early_inc_range(*VPBB)) {
-      simplifyRecipe(R, TypeInfo);
+    // Populate a Worklist, as simplifyRecipe might return a new recipe that we
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ayalz wrote:

Currently, it seems something like the following change
```
    for (VPRecipeBase &R : make_early_inc_range(*VPBB)) {
      VPRecipeBase *NewR = simplifyRecipe(R, TypeInfo);
      while (NewR)
        NewR = simplifyRecipe(*NewR, TypeInfo);
    }
```
would suffice, as simplifyRecipe() currently creates at most one new recipe, and the order in which recipes are simplified does not matter (right?). If/when simplifying a recipe R may create multiple new recipes, as long as only one NewR will replace all of R's uses, it may suffice to return NewR, and perhaps call recursivelySimplifyRecipes(NewR), similar to recursivelyDeleteDeadRecipes().

https://github.com/llvm/llvm-project/pull/105699