[VPlan] Run recipe removal and simplification after optimizeForVFAndUF. (#125926)

Run recipe simplification and dead recipe removal after VPlan-based
unrolling and optimizeForVFAndUF, to clean up any redundant or dead
recipes introduced by them. Currently this is NFC, as it removes the
corresponding removeDeadRecipes run in optimizeForVFAndUF and no
additional simplifications kick in after unrolling yet. That is changing
with #123655.

Note that with this change, pattern-matching is now applied after
EVL-based recipes have been introduced.

Trying to match VPWidenEVLRecipe when not explicitly requested might
apply a pattern with 2 operands to one with 3 due to the extra EVL
operand and VPWidenEVLRecipe being a subclass of VPWidenRecipe.

To prevent this, update Recipe_match::match to only match
VPWidenEVLRecipe if it is in the requested recipe types (RecipeTy).

PR: #125926

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -7672,6 +7672,8 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
   VPlanTransforms::runPass(VPlanTransforms::unrollByUF, BestVPlan, BestUF,
                            OrigLoop->getHeader()->getContext());
   VPlanTransforms::optimizeForVFAndUF(BestVPlan, BestVF, BestUF, PSE);
+  VPlanTransforms::simplifyRecipes(BestVPlan, *Legal->getWidestInductionType());
+  VPlanTransforms::removeDeadRecipes(BestVPlan);
   VPlanTransforms::convertToConcreteRecipes(BestVPlan);
 
   // Perform the actual loop transformation.

llvm/lib/Transforms/Vectorize/VPlanPatternMatch.h

@@ -155,6 +155,14 @@ struct Recipe_match {
     if ((!matchRecipeAndOpcode<RecipeTys>(R) && ...))
       return false;
 
+    if (!(std::is_same_v<VPWidenEVLRecipe, RecipeTys> || ...) &&
+        isa<VPWidenEVLRecipe>(R)) {
+      // Don't match VPWidenEVLRecipe if it is not explicitly part of RecipeTys.
+      // Otherwise we might match it unexpectedly when trying to match
+      // VPWidenRecipe, of which VPWidenEVLRecipe is a subclass of.
+      return false;
+    }
+
     assert(R->getNumOperands() == std::tuple_size<Ops_t>::value &&
            "recipe with matched opcode the expected number of operands");
 

llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

@@ -964,9 +964,7 @@ static void simplifyRecipe(VPRecipeBase &R, VPTypeAnalysis &TypeInfo) {
     return R.getVPSingleValue()->replaceAllUsesWith(R.getOperand(1));
 }
 
-/// Try to simplify the recipes in \p Plan. Use \p CanonicalIVTy as type for all
-/// un-typed live-ins in VPTypeAnalysis.
-static void simplifyRecipes(VPlan &Plan, Type &CanonicalIVTy) {
+void VPlanTransforms::simplifyRecipes(VPlan &Plan, Type &CanonicalIVTy) {
   ReversePostOrderTraversal<VPBlockDeepTraversalWrapper<VPBlockBase *>> RPOT(
       Plan.getEntry());
   VPTypeAnalysis TypeInfo(&CanonicalIVTy);
@@ -1043,7 +1041,6 @@ void VPlanTransforms::optimizeForVFAndUF(VPlan &Plan, ElementCount BestVF,
   }
 
   Term->eraseFromParent();
-  VPlanTransforms::removeDeadRecipes(Plan);
 
   Plan.setVF(BestVF);
   Plan.setUF(BestUF);

llvm/lib/Transforms/Vectorize/VPlanTransforms.h

@@ -163,6 +163,10 @@ struct VPlanTransforms {
   /// Lower abstract recipes to concrete ones, that can be codegen'd.
   static void convertToConcreteRecipes(VPlan &Plan);
 
+  /// Perform instcombine-like simplifications on recipes in \p Plan. Use \p
+  /// CanonicalIVTy as type for all un-typed live-ins in VPTypeAnalysis.
+  static void simplifyRecipes(VPlan &Plan, Type &CanonicalIVTy);
+
   /// If there's a single exit block, optimize its phi recipes that use exiting
   /// IV values by feeding them precomputed end values instead, possibly taken
   /// one step backwards.