[llvm] [VPlan] Recognize disjoint 'or' in getSCEVExprForVPValue (PR #218405)

[Mel Chen via llvm-commits]

https://github.com/Mel-Chen created https://github.com/llvm/llvm-project/pull/218405

Handle disjoint 'or' instructions as 'add nuw nsw' in getSCEVExprForVPValue to detect more strided access patterns.

>From ea8340a0122a2248b702f70c288e079b30e571d2 Mon Sep 17 00:00:00 2001
From: Mel Chen <mel.chen at sifive.com>
Date: Mon, 24 Aug 2026 06:00:58 -0700
Subject: [PATCH] support disjoint or

---
 llvm/lib/Transforms/Vectorize/VPlanUtils.cpp      |  5 +++++
 .../LoopVectorize/RISCV/strided-accesses.ll       | 15 +++++----------
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/VPlanUtils.cpp b/llvm/lib/Transforms/Vectorize/VPlanUtils.cpp
index e6b267493d987..fcb858e3b1641 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanUtils.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanUtils.cpp
@@ -164,6 +164,11 @@ const SCEV *vputils::getSCEVExprForVPValue(const VPValue *V,
     return CreateSCEV({LHSVal, RHSVal}, [&](ArrayRef<SCEVUse> Ops) {
       return SE.getAddExpr(Ops[0], Ops[1], SCEV::FlagAnyWrap, 0);
     });
+  if (match(V, m_BinaryOr(m_VPValue(LHSVal), m_VPValue(RHSVal))))
+    if (cast<VPRecipeWithIRFlags>(V->getDefiningRecipe())->isDisjoint())
+      return CreateSCEV({LHSVal, RHSVal}, [&](ArrayRef<SCEVUse> Ops) {
+        return SE.getAddExpr(Ops[0], Ops[1], SCEV::FlagNSW | SCEV::FlagNUW, 0);
+      });
   if (match(V, m_Sub(m_VPValue(LHSVal), m_VPValue(RHSVal))))
     return CreateSCEV({LHSVal, RHSVal}, [&](ArrayRef<SCEVUse> Ops) {
       return SE.getMinusSCEV(Ops[0], Ops[1], SCEV::FlagAnyWrap, 0);
diff --git a/llvm/test/Transforms/LoopVectorize/RISCV/strided-accesses.ll b/llvm/test/Transforms/LoopVectorize/RISCV/strided-accesses.ll
index 300d28be48054..714953ce460ed 100644
--- a/llvm/test/Transforms/LoopVectorize/RISCV/strided-accesses.ll
+++ b/llvm/test/Transforms/LoopVectorize/RISCV/strided-accesses.ll
@@ -1754,25 +1754,20 @@ define void @or_disjoint_stride(ptr noalias %in, ptr noalias %out) {
 ; CHECK-NEXT:  [[ENTRY:.*:]]
 ; CHECK-NEXT:    br label %[[VECTOR_PH:.*]]
 ; CHECK:       [[VECTOR_PH]]:
-; CHECK-NEXT:    [[TMP0:%.*]] = call <vscale x 4 x i64> @llvm.stepvector.nxv4i64()
+; CHECK-NEXT:    [[TMP0:%.*]] = getelementptr nuw i8, ptr [[IN]], i64 4
 ; CHECK-NEXT:    br label %[[VECTOR_BODY:.*]]
 ; CHECK:       [[VECTOR_BODY]]:
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[CURRENT_ITERATION_NEXT:%.*]], %[[VECTOR_BODY]] ]
-; CHECK-NEXT:    [[VEC_IND:%.*]] = phi <vscale x 4 x i64> [ [[TMP0]], %[[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], %[[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[AVL:%.*]] = phi i64 [ 1024, %[[VECTOR_PH]] ], [ [[AVL_NEXT:%.*]], %[[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @llvm.experimental.get.vector.length.i64(i64 [[AVL]], i32 4, i1 true)
-; CHECK-NEXT:    [[TMP6:%.*]] = zext i32 [[TMP1]] to i64
-; CHECK-NEXT:    [[BROADCAST_SPLATINSERT:%.*]] = insertelement <vscale x 4 x i64> poison, i64 [[TMP6]], i64 0
-; CHECK-NEXT:    [[BROADCAST_SPLAT:%.*]] = shufflevector <vscale x 4 x i64> [[BROADCAST_SPLATINSERT]], <vscale x 4 x i64> poison, <vscale x 4 x i32> zeroinitializer
-; CHECK-NEXT:    [[TMP3:%.*]] = shl nuw nsw <vscale x 4 x i64> [[VEC_IND]], splat (i64 1)
-; CHECK-NEXT:    [[TMP8:%.*]] = or disjoint <vscale x 4 x i64> [[TMP3]], splat (i64 1)
-; CHECK-NEXT:    [[WIDE_GEP:%.*]] = getelementptr nusw i32, ptr [[IN]], <vscale x 4 x i64> [[TMP8]]
-; CHECK-NEXT:    [[TMP4:%.*]] = call <vscale x 4 x i32> @llvm.vp.gather.nxv4i32.nxv4p0(<vscale x 4 x ptr> align 4 [[WIDE_GEP]], <vscale x 4 x i1> splat (i1 true), i32 [[TMP1]])
+; CHECK-NEXT:    [[TMP2:%.*]] = shl nuw i64 [[INDEX]], 3
+; CHECK-NEXT:    [[TMP3:%.*]] = getelementptr nuw i8, ptr [[TMP0]], i64 [[TMP2]]
+; CHECK-NEXT:    [[TMP4:%.*]] = call <vscale x 4 x i32> @llvm.experimental.vp.strided.load.nxv4i32.p0.i64(ptr align 4 [[TMP3]], i64 8, <vscale x 4 x i1> splat (i1 true), i32 [[TMP1]])
 ; CHECK-NEXT:    [[TMP5:%.*]] = getelementptr nusw i32, ptr [[OUT]], i64 [[INDEX]]
 ; CHECK-NEXT:    call void @llvm.vp.store.nxv4i32.p0(<vscale x 4 x i32> [[TMP4]], ptr align 4 [[TMP5]], <vscale x 4 x i1> splat (i1 true), i32 [[TMP1]])
+; CHECK-NEXT:    [[TMP6:%.*]] = zext i32 [[TMP1]] to i64
 ; CHECK-NEXT:    [[CURRENT_ITERATION_NEXT]] = add nuw i64 [[TMP6]], [[INDEX]]
 ; CHECK-NEXT:    [[AVL_NEXT]] = sub nuw i64 [[AVL]], [[TMP6]]
-; CHECK-NEXT:    [[VEC_IND_NEXT]] = add nuw <vscale x 4 x i64> [[VEC_IND]], [[BROADCAST_SPLAT]]
 ; CHECK-NEXT:    [[TMP7:%.*]] = icmp eq i64 [[AVL_NEXT]], 0
 ; CHECK-NEXT:    br i1 [[TMP7]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], {{!llvm.loop ![0-9]+}}
 ; CHECK:       [[MIDDLE_BLOCK]]: