[llvm] [VPlan] Simplify BCast with only-first-lane used (PR #195444)

[Ramkumar Ramachandra via llvm-commits]

https://github.com/artagnon created https://github.com/llvm/llvm-project/pull/195444

None

>From a01fb9da5bd5f0918df5e1811d7c4bc09a6c724f Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <artagnon at tenstorrent.com>
Date: Sat, 2 May 2026 12:24:33 +0100
Subject: [PATCH] [VPlan] Simplify BCast with only-first-lane used

---
 llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp | 3 +++
 llvm/test/Transforms/LoopVectorize/pr37248.ll     | 5 +----
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index 11e5b18bca871..4277757808460 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -1701,6 +1701,9 @@ static void simplifyRecipe(VPSingleDefRecipe *Def, VPTypeAnalysis &TypeInfo) {
     return;
   }
 
+  if (match(Def, m_Broadcast(m_VPValue(X))) && vputils::onlyFirstLaneUsed(Def))
+    return Def->replaceAllUsesWith(X);
+
   if (isa<VPPhi, VPWidenPHIRecipe, VPHeaderPHIRecipe>(Def)) {
     if (Def->getNumOperands() == 1) {
       Def->replaceAllUsesWith(Def->getOperand(0));
diff --git a/llvm/test/Transforms/LoopVectorize/pr37248.ll b/llvm/test/Transforms/LoopVectorize/pr37248.ll
index 60736f5f126c6..82d345846c279 100644
--- a/llvm/test/Transforms/LoopVectorize/pr37248.ll
+++ b/llvm/test/Transforms/LoopVectorize/pr37248.ll
@@ -34,11 +34,8 @@ define void @f1(ptr noalias %b, i1 %c, i32 %start) {
 ; CHECK:       [[VECTOR_PH]]:
 ; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i32 [[TMP1]], 2
 ; CHECK-NEXT:    [[N_VEC:%.*]] = sub i32 [[TMP1]], [[N_MOD_VF]]
-; CHECK-NEXT:    [[BROADCAST_SPLATINSERT:%.*]] = insertelement <2 x i1> poison, i1 [[C]], i64 0
-; CHECK-NEXT:    [[BROADCAST_SPLAT:%.*]] = shufflevector <2 x i1> [[BROADCAST_SPLATINSERT]], <2 x i1> poison, <2 x i32> zeroinitializer
 ; CHECK-NEXT:    [[TMP10:%.*]] = sub i32 [[START]], [[N_VEC]]
-; CHECK-NEXT:    [[TMP11:%.*]] = extractelement <2 x i1> [[BROADCAST_SPLAT]], i64 0
-; CHECK-NEXT:    [[TMP12:%.*]] = xor i1 [[TMP11]], true
+; CHECK-NEXT:    [[TMP12:%.*]] = xor i1 [[C]], true
 ; CHECK-NEXT:    br label %[[VECTOR_BODY:.*]]
 ; CHECK:       [[VECTOR_BODY]]:
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[PRED_STORE_CONTINUE3:.*]] ]