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[LV] Fix cost misaligned when gather/scatter w/ addr is uniform. #157387

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Merged
merged 8 commits into from
Sep 10, 2025
Merged

[LV] Fix cost misaligned when gather/scatter w/ addr is uniform. #157387

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8d7aea3
[LV] Fix cost misaligned when gather/scatter w/ addr is uniform.
ElvisWang123 Sep 8, 2025
70936c0
!fixup, using LV formatting.
ElvisWang123 Sep 8, 2025
3b3cc6e
!fixup, remove custom types.
ElvisWang123 Sep 8, 2025
b57e641
Refine test case and drop tbaa.
ElvisWang123 Sep 9, 2025
1fcac6d
!fixup, address comments.
ElvisWang123 Sep 9, 2025
f62c348
Drop unneed var.
ElvisWang123 Sep 9, 2025
7b7b486
Update comment.
ElvisWang123 Sep 10, 2025
f1a6c9b
Merge branch 'main' into lv-skip-miscompared-assertion-gather/scatter
ElvisWang123 Sep 10, 2025
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10 changes: 10 additions & 0 deletions llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -6905,6 +6905,16 @@ static bool planContainsAdditionalSimplifications(VPlan &Plan,
if (isa<VPPartialReductionRecipe>(&R))
return true;

// The VPlan-based cost model can analyze if recipes are scalar
// recursively, but legacy cost model cannot.
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@lukel97 lukel97 Sep 9, 2025

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Suggested change
// recursively, but legacy cost model cannot.
// recursively, but the legacy cost model cannot.

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@fhahn fhahn Sep 10, 2025

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Still pending.

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@ElvisWang123 ElvisWang123 Sep 10, 2025

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Ooops, missed that. Fixed, thanks!

if (auto *WidenMemR = dyn_cast<VPWidenMemoryRecipe>(&R)) {
auto *AddrI = dyn_cast<Instruction>(
getLoadStorePointerOperand(&WidenMemR->getIngredient()));
if (AddrI && vputils::isSingleScalar(WidenMemR->getAddr()) !=
CostCtx.isLegacyUniformAfterVectorization(AddrI, VF))
return true;
}

/// If a VPlan transform folded a recipe to one producing a single-scalar,
/// but the original instruction wasn't uniform-after-vectorization in the
/// legacy cost model, the legacy cost overestimates the actual cost.
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72 changes: 72 additions & 0 deletions llvm/test/Transforms/LoopVectorize/RISCV/gather-scatter-cost.ll
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Expand Up @@ -184,3 +184,75 @@ loop:
exit:
ret void
}

define void @store_to_addr_generated_from_invariant_addr(ptr noalias %p0, ptr noalias %p1, ptr noalias %p2, ptr %p3, i64 %N) {
; CHECK-LABEL: @store_to_addr_generated_from_invariant_addr(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[TMP0:%.*]] = add i64 [[N:%.*]], 1
; CHECK-NEXT: br i1 false, label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
; CHECK: vector.ph:
; CHECK-NEXT: [[BROADCAST_SPLATINSERT2:%.*]] = insertelement <vscale x 2 x ptr> poison, ptr [[P0:%.*]], i64 0
; CHECK-NEXT: [[BROADCAST_SPLAT1:%.*]] = shufflevector <vscale x 2 x ptr> [[BROADCAST_SPLATINSERT2]], <vscale x 2 x ptr> poison, <vscale x 2 x i32> zeroinitializer
; CHECK-NEXT: [[TMP1:%.*]] = call <vscale x 2 x i64> @llvm.stepvector.nxv2i64()
; CHECK-NEXT: [[TMP2:%.*]] = mul <vscale x 2 x i64> [[TMP1]], splat (i64 1)
; CHECK-NEXT: [[INDUCTION:%.*]] = add <vscale x 2 x i64> zeroinitializer, [[TMP2]]
; CHECK-NEXT: br label [[VECTOR_BODY:%.*]]
; CHECK: vector.body:
; CHECK-NEXT: [[VEC_IND:%.*]] = phi <vscale x 2 x i64> [ [[INDUCTION]], [[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], [[VECTOR_BODY]] ]
; CHECK-NEXT: [[AVL:%.*]] = phi i64 [ [[TMP0]], [[VECTOR_PH]] ], [ [[AVL_NEXT:%.*]], [[VECTOR_BODY]] ]
; CHECK-NEXT: [[TMP3:%.*]] = call i32 @llvm.experimental.get.vector.length.i64(i64 [[AVL]], i32 2, i1 true)
; CHECK-NEXT: [[TMP4:%.*]] = zext i32 [[TMP3]] to i64
; CHECK-NEXT: [[BROADCAST_SPLATINSERT:%.*]] = insertelement <vscale x 2 x i64> poison, i64 [[TMP4]], i64 0
; CHECK-NEXT: [[BROADCAST_SPLAT:%.*]] = shufflevector <vscale x 2 x i64> [[BROADCAST_SPLATINSERT]], <vscale x 2 x i64> poison, <vscale x 2 x i32> zeroinitializer
; CHECK-NEXT: [[TMP5:%.*]] = getelementptr i32, ptr [[P1:%.*]], <vscale x 2 x i64> [[VEC_IND]]
; CHECK-NEXT: call void @llvm.vp.scatter.nxv2p0.nxv2p0(<vscale x 2 x ptr> [[BROADCAST_SPLAT1]], <vscale x 2 x ptr> align 8 [[TMP5]], <vscale x 2 x i1> splat (i1 true), i32 [[TMP3]])
; CHECK-NEXT: [[TMP6:%.*]] = load i64, ptr [[P2:%.*]], align 4
; CHECK-NEXT: [[BROADCAST_SPLATINSERT1:%.*]] = insertelement <vscale x 2 x i64> poison, i64 [[TMP6]], i64 0
; CHECK-NEXT: [[BROADCAST_SPLAT2:%.*]] = shufflevector <vscale x 2 x i64> [[BROADCAST_SPLATINSERT1]], <vscale x 2 x i64> poison, <vscale x 2 x i32> zeroinitializer
; CHECK-NEXT: [[TMP7:%.*]] = getelementptr i8, ptr [[P3:%.*]], <vscale x 2 x i64> [[BROADCAST_SPLAT2]]
; CHECK-NEXT: call void @llvm.vp.scatter.nxv2i32.nxv2p0(<vscale x 2 x i32> zeroinitializer, <vscale x 2 x ptr> align 4 [[TMP7]], <vscale x 2 x i1> splat (i1 true), i32 [[TMP3]])
; CHECK-NEXT: call void @llvm.vp.scatter.nxv2i32.nxv2p0(<vscale x 2 x i32> zeroinitializer, <vscale x 2 x ptr> align 4 [[TMP7]], <vscale x 2 x i1> splat (i1 true), i32 [[TMP3]])
; CHECK-NEXT: call void @llvm.vp.scatter.nxv2i8.nxv2p0(<vscale x 2 x i8> zeroinitializer, <vscale x 2 x ptr> align 1 [[TMP7]], <vscale x 2 x i1> splat (i1 true), i32 [[TMP3]])
; CHECK-NEXT: [[TMP8:%.*]] = zext i32 [[TMP3]] to i64
; CHECK-NEXT: [[AVL_NEXT]] = sub nuw i64 [[AVL]], [[TMP8]]
; CHECK-NEXT: [[VEC_IND_NEXT]] = add <vscale x 2 x i64> [[VEC_IND]], [[BROADCAST_SPLAT]]
; CHECK-NEXT: [[TMP9:%.*]] = icmp eq i64 [[AVL_NEXT]], 0
; CHECK-NEXT: br i1 [[TMP9]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP12:![0-9]+]]
; CHECK: middle.block:
; CHECK-NEXT: br label [[EXIT:%.*]]
; CHECK: scalar.ph:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i64 [ 0, [[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
; CHECK-NEXT: [[ARRAYIDX11:%.*]] = getelementptr i32, ptr [[P1]], i64 [[IV]]
; CHECK-NEXT: store ptr [[P0]], ptr [[ARRAYIDX11]], align 8
; CHECK-NEXT: [[TMP10:%.*]] = load i64, ptr [[P2]], align 4
; CHECK-NEXT: [[BITS_TO_GO:%.*]] = getelementptr i8, ptr [[P3]], i64 [[TMP10]]
; CHECK-NEXT: store i32 0, ptr [[BITS_TO_GO]], align 4
; CHECK-NEXT: store i32 0, ptr [[BITS_TO_GO]], align 4
; CHECK-NEXT: store i8 0, ptr [[BITS_TO_GO]], align 1
; CHECK-NEXT: [[IV_NEXT]] = add i64 [[IV]], 1
; CHECK-NEXT: [[EXITCOND_NOT:%.*]] = icmp eq i64 [[IV]], [[N]]
; CHECK-NEXT: br i1 [[EXITCOND_NOT]], label [[EXIT]], label [[LOOP]], !llvm.loop [[LOOP13:![0-9]+]]
; CHECK: exit:
; CHECK-NEXT: ret void
;
entry:
br label %loop

loop:
%iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
%arrayidx11 = getelementptr i32, ptr %p1, i64 %iv
store ptr %p0, ptr %arrayidx11, align 8
%0 = load i64, ptr %p2, align 4
%bits_to_go = getelementptr i8, ptr %p3, i64 %0
store i32 0, ptr %bits_to_go, align 4
store i32 0, ptr %bits_to_go, align 4
store i8 0, ptr %bits_to_go, align 1
%iv.next = add i64 %iv, 1
%exitcond.not = icmp eq i64 %iv, %N
br i1 %exitcond.not, label %exit, label %loop

exit:
ret void
}