[llvm] [VPlan] Fix convoluted logic in simpl ext-last-lane (PR #196355)

[Ramkumar Ramachandra via llvm-commits]

https://github.com/artagnon updated https://github.com/llvm/llvm-project/pull/196355

>From b33d56474d4f10cb7eae3d4a28635632c7709c21 Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <artagnon at tenstorrent.com>
Date: Thu, 7 May 2026 16:46:38 +0100
Subject: [PATCH] [VPlan] Fix convoluted logic in simpl ext-last-lane

When performing a replacement, we need to check Def's users, not the
users under the extract-last-lane. Also, the transformation does not
depend on the Plan being unrolled.
---
 .../Transforms/Vectorize/VPlanTransforms.cpp  | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index bcdb91a54e305..cdd67fe3946df 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -1669,6 +1669,13 @@ static void simplifyRecipe(VPSingleDefRecipe *Def, VPTypeAnalysis &TypeInfo) {
           BuildVector->getOperand(BuildVector->getNumOperands() - 1));
       return;
     }
+
+    if (match(A, m_Broadcast(m_VPValue(X))))
+      return Def->replaceAllUsesWith(X);
+
+    if (vputils::isSingleScalar(A))
+      return Def->replaceAllUsesWith(A);
+
     if (Plan->hasScalarVFOnly())
       return Def->replaceAllUsesWith(A);
   }
@@ -1791,18 +1798,6 @@ static void simplifyRecipe(VPSingleDefRecipe *Def, VPTypeAnalysis &TypeInfo) {
     return;
   }
 
-  if (match(Def, m_ExtractLastLane(m_Broadcast(m_VPValue(A))))) {
-    Def->replaceAllUsesWith(A);
-    return;
-  }
-
-  if (match(Def, m_ExtractLastLane(m_VPValue(A))) &&
-      vputils::isSingleScalar(A) && all_of(A->users(), [Def, A](VPUser *U) {
-        return U->usesScalars(A) || Def == U;
-      })) {
-    return Def->replaceAllUsesWith(A);
-  }
-
   if (Plan->getConcreteUF() == 1 && match(Def, m_ExtractLastPart(m_VPValue(A))))
     return Def->replaceAllUsesWith(A);
 }