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

[Ramkumar Ramachandra via llvm-commits]

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

>From dd3cbcab91c6eeb13d7fd29d5f228ae1cbf40e71 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 +++
 .../Transforms/LoopVectorize/X86/pr109581-unused-blend.ll    | 5 +----
 .../X86/replicate-recipe-with-only-first-lane-used.ll        | 5 +----
 llvm/test/Transforms/LoopVectorize/pr37248.ll                | 5 +----
 4 files changed, 6 insertions(+), 12 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index bcdb91a54e305..64589032f7fcf 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -1704,6 +1704,9 @@ 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/X86/pr109581-unused-blend.ll b/llvm/test/Transforms/LoopVectorize/X86/pr109581-unused-blend.ll
index a5692ae9fef0d..0323a6771949d 100644
--- a/llvm/test/Transforms/LoopVectorize/X86/pr109581-unused-blend.ll
+++ b/llvm/test/Transforms/LoopVectorize/X86/pr109581-unused-blend.ll
@@ -12,12 +12,9 @@ define i32 @unused_blend_after_unrolling(ptr %p, i32 %a, i1 %c.1, i16 %x, i16 %y
 ; CHECK-NEXT:    [[C:%.*]] = icmp eq i32 [[A]], 0
 ; CHECK-NEXT:    br label %[[VECTOR_PH:.*]]
 ; CHECK:       [[VECTOR_PH]]:
-; CHECK-NEXT:    [[BROADCAST_SPLATINSERT:%.*]] = insertelement <4 x i1> poison, i1 [[C_1]], i64 0
-; CHECK-NEXT:    [[BROADCAST_SPLAT:%.*]] = shufflevector <4 x i1> [[BROADCAST_SPLATINSERT]], <4 x i1> poison, <4 x i32> zeroinitializer
 ; CHECK-NEXT:    [[BROADCAST_SPLATINSERT16:%.*]] = insertelement <4 x i1> poison, i1 [[C]], i64 0
 ; CHECK-NEXT:    [[BROADCAST_SPLAT17:%.*]] = shufflevector <4 x i1> [[BROADCAST_SPLATINSERT16]], <4 x i1> poison, <4 x i32> zeroinitializer
-; CHECK-NEXT:    [[TMP0:%.*]] = extractelement <4 x i1> [[BROADCAST_SPLAT]], i64 0
-; CHECK-NEXT:    [[TMP2:%.*]] = xor i1 [[TMP0]], true
+; CHECK-NEXT:    [[TMP2:%.*]] = xor i1 [[C_1]], true
 ; CHECK-NEXT:    [[TMP22:%.*]] = xor <4 x i1> [[BROADCAST_SPLAT17]], splat (i1 true)
 ; CHECK-NEXT:    br label %[[VECTOR_BODY:.*]]
 ; CHECK:       [[VECTOR_BODY]]:
diff --git a/llvm/test/Transforms/LoopVectorize/X86/replicate-recipe-with-only-first-lane-used.ll b/llvm/test/Transforms/LoopVectorize/X86/replicate-recipe-with-only-first-lane-used.ll
index adb5453d0404a..485dc0e16952a 100644
--- a/llvm/test/Transforms/LoopVectorize/X86/replicate-recipe-with-only-first-lane-used.ll
+++ b/llvm/test/Transforms/LoopVectorize/X86/replicate-recipe-with-only-first-lane-used.ll
@@ -71,10 +71,7 @@ define void @replicate_udiv_with_only_first_lane_used2(i32 %x, ptr %dst, i64 %d)
 ; CHECK-NEXT:    [[C:%.*]] = icmp eq i32 [[X]], 10
 ; CHECK-NEXT:    br label %[[VECTOR_PH:.*]]
 ; CHECK:       [[VECTOR_PH]]:
-; CHECK-NEXT:    [[BROADCAST_SPLATINSERT:%.*]] = insertelement <4 x i1> poison, i1 [[C]], i64 0
-; CHECK-NEXT:    [[BROADCAST_SPLAT:%.*]] = shufflevector <4 x i1> [[BROADCAST_SPLATINSERT]], <4 x i1> poison, <4 x i32> zeroinitializer
-; CHECK-NEXT:    [[TMP0:%.*]] = extractelement <4 x i1> [[BROADCAST_SPLAT]], i64 0
-; CHECK-NEXT:    [[TMP1:%.*]] = xor i1 [[TMP0]], true
+; CHECK-NEXT:    [[TMP1:%.*]] = xor i1 [[C]], true
 ; CHECK-NEXT:    br label %[[VECTOR_BODY:.*]]
 ; CHECK:       [[VECTOR_BODY]]:
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[PRED_UDIV_CONTINUE14:.*]] ]
diff --git a/llvm/test/Transforms/LoopVectorize/pr37248.ll b/llvm/test/Transforms/LoopVectorize/pr37248.ll
index 03e3d1f222399..c2e26c5d66877 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:.*]] ]