[llvm] VPlan: prepare to recursively simplify recipes (PR #105699)

[Ramkumar Ramachandra 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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artagnon wrote:

> How can the pattern introduce a single new recipe? If we return the recipe X && (Y || Z), how will a pattern like X && true or X && false suffice? In other words, how can we ensure that Y || Z is re-queued for simplification? If we return the recipe Y || Z, that recipe might be simplfied, but then how does the root recipe involving X get re-queued for simplification?

I checked, and we do indeed need to return both the root recipe and sub-recipe.

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