[llvm] 747cf24 - [LV] Rework legacy widen/replicate in tryToBuildVPlan (NFC) (#224569)

[via llvm-commits]

Author: Ramkumar Ramachandra
Date: 2026-09-22T17:48:43Z
New Revision: 747cf241988e83e9ab4aae88efc10d91e87a0b90

URL: https://github.com/llvm/llvm-project/commit/747cf241988e83e9ab4aae88efc10d91e87a0b90
DIFF: https://github.com/llvm/llvm-project/commit/747cf241988e83e9ab4aae88efc10d91e87a0b90.diff

LOG: [LV] Rework legacy widen/replicate in tryToBuildVPlan (NFC) (#224569)

The code has been rewritten for clarity:

- An RPOT traversal is unnecessary, and a depth-first will do.
- The list of recipes to be skipped continues to grow, and its utility
is in question. Replace it with a clean make_isa_range over
VPInstructions, and an assert.
- Clarify that tryToCreateWidenNonPhiRecipe is the routine that produces
VPWidenIntOrFpInductionRecipes.
- Clarify the necessity of the underling value.

Added: 
    

Modified: 
    llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 983eaf665839c..6e27d1e209daf 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -6645,12 +6645,6 @@ VPlanPtr LoopVectorizationPlanner::tryToBuildVPlan(VPlanPtr Plan,
   // ---------------------------------------------------------------------------
   VPRecipeBuilder RecipeBuilder(*Plan, Legal, *CM, Builder);
 
-  // Scan the body of the loop in a topological order to visit each basic block
-  // after having visited its predecessor basic blocks.
-  VPBasicBlock *HeaderVPBB = LoopRegion->getEntryBasicBlock();
-  ReversePostOrderTraversal<VPBlockShallowTraversalWrapper<VPBlockBase *>> RPOT(
-      HeaderVPBB);
-
   RUN_VPLAN_PASS(VPlanTransforms::createInLoopReductionRecipes, *Plan,
                  Range.Start);
 
@@ -6664,50 +6658,55 @@ VPlanPtr LoopVectorizationPlanner::tryToBuildVPlan(VPlanPtr Plan,
   RUN_VPLAN_PASS(VPlanTransforms::makeCallWideningDecisions, *Plan, Range,
                  RecipeBuilder, CostCtx);
 
-  // Now process all other blocks and instructions.
-  for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(RPOT)) {
-    // Convert input VPInstructions to widened recipes.
-    for (VPRecipeBase &R : make_early_inc_range(
-             make_range(VPBB->getFirstNonPhi(), VPBB->end()))) {
-      // Skip recipes that do not need transforming or have already been
-      // transformed.
-      if (isa<VPWidenCanonicalIVRecipe, VPBlendRecipe, VPReductionRecipe,
-              VPReplicateRecipe, VPWidenLoadRecipe, VPWidenStoreRecipe,
-              VPWidenCallRecipe, VPWidenIntrinsicRecipe, VPVectorPointerRecipe,
-              VPVectorEndPointerRecipe, VPHistogramRecipe>(&R) ||
-          (Instruction::isCast(cast<VPInstruction>(R).getOpcode()) &&
-           vputils::onlyFirstLaneUsed(R.getVPSingleValue())))
+  // Convert remaining VPInstructions to widen or replicate recipes.
+  // TODO: This legacy code should eventually be migrated to VPlan.
+  VPBasicBlock *HeaderVPBB = LoopRegion->getEntryBasicBlock();
+  for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(
+           vp_depth_first_shallow(HeaderVPBB))) {
+    // All types but VPInstructions are already widened and don't need extra
+    // processing. We process VPInstructions below.
+    assert(
+        all_of(
+            make_range(VPBB->getFirstNonPhi(), VPBB->end()),
+            IsaPred<VPWidenCanonicalIVRecipe, VPBlendRecipe, VPReductionRecipe,
+                    VPReplicateRecipe, VPWidenLoadRecipe, VPWidenStoreRecipe,
+                    VPWidenCallRecipe, VPWidenIntrinsicRecipe,
+                    VPVectorPointerRecipe, VPVectorEndPointerRecipe,
+                    VPHistogramRecipe, VPInstruction>) &&
+        "Unexpected recipe");
+    for (VPInstruction &VPI :
+         make_early_inc_range(make_isa_range<VPInstruction>(*VPBB))) {
+      // We represent single-scalar casts directly as VPInstructions.
+      if (Instruction::isCast(VPI.getOpcode()) &&
+          vputils::onlyFirstLaneUsed(&VPI))
         continue;
-      auto *VPI = cast<VPInstruction>(&R);
-      if (!VPI->getUnderlyingValue())
+
+      // Only VPInstrutions with an underlying value need to be processed.
+      if (!VPI.getUnderlyingValue())
         continue;
 
-      // TODO: Gradually replace uses of underlying instruction by analyses on
-      // VPlan. Migrate code relying on the underlying instruction from VPlan0
-      // to construct recipes below to not use the underlying instruction.
-      Instruction *Instr = cast<Instruction>(VPI->getUnderlyingValue());
-      Builder.setInsertPoint(VPI);
+      Builder.setInsertPoint(&VPI);
 
       VPRecipeBase *Recipe =
-          RecipeBuilder.tryToCreateWidenNonPhiRecipe(VPI, Range);
-      if (!Recipe)
-        Recipe =
-            RecipeBuilder.handleReplication(cast<VPInstruction>(VPI), Range);
+          RecipeBuilder.tryToCreateWidenNonPhiRecipe(&VPI, Range);
 
-      if (isa<VPWidenIntOrFpInductionRecipe>(Recipe) && isa<TruncInst>(Instr)) {
+      if (isa_and_nonnull<VPWidenIntOrFpInductionRecipe>(Recipe) &&
+          VPI.getOpcode() == Instruction::Trunc) {
         // Optimized a truncate to VPWidenIntOrFpInductionRecipe. It needs to be
         // moved to the phi section in the header.
         Recipe->insertBefore(*HeaderVPBB, HeaderVPBB->getFirstNonPhi());
       } else {
+        if (!Recipe)
+          Recipe = RecipeBuilder.handleReplication(&VPI, Range);
         Builder.insert(Recipe);
       }
       if (Recipe->getNumDefinedValues() == 1) {
-        VPI->replaceAllUsesWith(Recipe->getVPSingleValue());
+        VPI.replaceAllUsesWith(Recipe->getVPSingleValue());
       } else {
         assert(Recipe->getNumDefinedValues() == 0 &&
                "Unexpected multidef recipe");
       }
-      R.eraseFromParent();
+      VPI.eraseFromParent();
     }
   }