[llvm] [VPlan] Strip WidenStore handling in narrowToSingleScalars (PR #184765)

[Ramkumar Ramachandra via llvm-commits]

https://github.com/artagnon updated https://github.com/llvm/llvm-project/pull/184765

>From 27448d198d7ae8947c23a02987e0664a7bde11de Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <artagnon at tenstorrent.com>
Date: Thu, 5 Mar 2026 10:17:19 +0000
Subject: [PATCH] [VPlan] Strip WidenStore handling in narrowToSingleScalars

Although the codepath seems to be reached in a few cases, it doesn't
seem to be making any changes: what matters is that the operands of the
WidenStore are narrowed to single-scalars maximally.
---
 .../Transforms/Vectorize/VPlanTransforms.cpp  | 38 ++-----------------
 1 file changed, 3 insertions(+), 35 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index 9944df4778774..900ea5020558a 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -1799,45 +1799,13 @@ static void narrowToSingleScalarRecipes(VPlan &Plan) {
   for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(
            vp_depth_first_shallow(Plan.getVectorLoopRegion()->getEntry()))) {
     for (VPRecipeBase &R : make_early_inc_range(reverse(*VPBB))) {
-      if (!isa<VPWidenRecipe, VPWidenGEPRecipe, VPReplicateRecipe,
-               VPWidenStoreRecipe>(&R))
+      if (!isa<VPWidenRecipe, VPWidenGEPRecipe, VPReplicateRecipe>(&R))
         continue;
       auto *RepR = dyn_cast<VPReplicateRecipe>(&R);
       if (RepR && (RepR->isSingleScalar() || RepR->isPredicated()))
         continue;
 
-      // Convert an unmasked scatter with an uniform address into
-      // extract-last-lane + scalar store.
-      // TODO: Add a profitability check comparing the cost of a scatter vs.
-      // extract + scalar store.
-      auto *WidenStoreR = dyn_cast<VPWidenStoreRecipe>(&R);
-      if (WidenStoreR && vputils::isSingleScalar(WidenStoreR->getAddr()) &&
-          !WidenStoreR->isConsecutive()) {
-        assert(!WidenStoreR->isReverse() &&
-               "Not consecutive memory recipes shouldn't be reversed");
-        VPValue *Mask = WidenStoreR->getMask();
-
-        // Only convert the scatter to a scalar store if it is unmasked.
-        // TODO: Support converting scatter masked by the header mask to scalar
-        // store.
-        if (Mask)
-          continue;
-
-        auto *Extract = new VPInstruction(VPInstruction::ExtractLastLane,
-                                          {WidenStoreR->getOperand(1)});
-        Extract->insertBefore(WidenStoreR);
-
-        // TODO: Sink the scalar store recipe to middle block if possible.
-        auto *ScalarStore = new VPReplicateRecipe(
-            &WidenStoreR->getIngredient(), {Extract, WidenStoreR->getAddr()},
-            true /*IsSingleScalar*/, nullptr /*Mask*/, {},
-            *WidenStoreR /*Metadata*/);
-        ScalarStore->insertBefore(WidenStoreR);
-        WidenStoreR->eraseFromParent();
-        continue;
-      }
-
-      auto *RepOrWidenR = dyn_cast<VPRecipeWithIRFlags>(&R);
+      auto *RepOrWidenR = cast<VPRecipeWithIRFlags>(&R);
       if (RepR && isa<StoreInst>(RepR->getUnderlyingInstr()) &&
           vputils::isSingleScalar(RepR->getOperand(1))) {
         auto *Clone = new VPReplicateRecipe(
@@ -1858,7 +1826,7 @@ static void narrowToSingleScalarRecipes(VPlan &Plan) {
       }
 
       // Skip recipes that aren't single scalars.
-      if (!RepOrWidenR || !vputils::isSingleScalar(RepOrWidenR))
+      if (!vputils::isSingleScalar(RepOrWidenR))
         continue;
 
       // Predicate to check if a user of Op introduces extra broadcasts.