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Merged
merged 9 commits into from
Jul 17, 2025
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[clang][CodeGen] Fix metadata when vectorization is disabled by pragma #135163

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79186af
[clang][CodeGen] Fix metadata when vectorization is disabled by pragma
kasuga-fj Apr 4, 2025
aed6f10
Fix OpenMP test
kasuga-fj Apr 11, 2025
98bee49
Fix behavior when scalable is specified
kasuga-fj Apr 11, 2025
0e60403
Update the docs
kasuga-fj Apr 11, 2025
16b6d51
Fix the comment, thanks!
kasuga-fj Apr 15, 2025
375dc8f
Merge branch 'main' into bugfix/metadata-vectorize-disable
kasuga-fj Jul 15, 2025
6d68a79
Undo document changes
kasuga-fj Jul 15, 2025
32a6d9c
Address review comments
kasuga-fj Jul 15, 2025
2989929
Remove unrelated change
kasuga-fj Jul 15, 2025
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7 changes: 3 additions & 4 deletions clang/lib/CodeGen/CGLoopInfo.cpp
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Expand Up @@ -200,7 +200,8 @@ LoopInfo::createLoopVectorizeMetadata(const LoopAttributes &Attrs,
LLVMContext &Ctx = Header->getContext();

std::optional<bool> Enabled;
if (Attrs.VectorizeEnable == LoopAttributes::Disable)
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@kasuga-fj kasuga-fj Apr 10, 2025

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Perhaps this condition has never been met.

if (Attrs.VectorizeEnable == LoopAttributes::Disable ||
Attrs.VectorizeWidth == 1)
Enabled = false;
else if (Attrs.VectorizeEnable != LoopAttributes::Unspecified ||
Attrs.VectorizePredicateEnable != LoopAttributes::Unspecified ||
Expand Down Expand Up @@ -643,9 +644,7 @@ void LoopInfoStack::push(BasicBlock *Header, clang::ASTContext &Ctx,
case LoopHintAttr::Disable:
switch (Option) {
case LoopHintAttr::Vectorize:
// Disable vectorization by specifying a width of 1.
setVectorizeWidth(1);
setVectorizeScalable(LoopAttributes::Unspecified);
setVectorizeEnable(false);
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@Meinersbur Meinersbur Jul 14, 2025

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Doesn't this also disable interleaving?

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@kasuga-fj kasuga-fj Jul 15, 2025

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Yes, I haven’t fixed it yet… For now, I’ve added WIP to the PR title.

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@kasuga-fj kasuga-fj Jul 15, 2025

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Fixed

break;
case LoopHintAttr::Interleave:
// Disable interleaving by speciyfing a count of 1.
Expand Down
12 changes: 6 additions & 6 deletions clang/test/CodeGenCXX/pragma-loop-pr27643.cpp
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Expand Up @@ -40,14 +40,14 @@ void loop4(int *List, int Length) {
List[i] = i * 2;
}

// CHECK: ![[LOOP1]] = distinct !{![[LOOP1]], [[MP:![0-9]+]], ![[VEC_WIDTH_1:.*]], ![[FIXED_WIDTH:.*]], ![[VEC_ENABLE:.*]]}
// CHECK: ![[VEC_WIDTH_1]] = !{!"llvm.loop.vectorize.width", i32 1}
// CHECK: ![[FIXED_WIDTH]] = !{!"llvm.loop.vectorize.scalable.enable", i1 false}
// CHECK: ![[VEC_ENABLE]] = !{!"llvm.loop.vectorize.enable", i1 true}
// CHECK: ![[LOOP1]] = distinct !{![[LOOP1]], [[MP:![0-9]+]], ![[VEC_DISABLE:[0-9]+]]}
// CHECK: ![[VEC_DISABLE]] = !{!"llvm.loop.vectorize.enable", i1 false}

// CHECK: ![[LOOP2]] = distinct !{![[LOOP2]], [[MP]], ![[VEC_WIDTH_2:.*]], ![[FIXED_WIDTH:.*]], ![[VEC_ENABLE]]}
// CHECK: ![[LOOP2]] = distinct !{![[LOOP2]], [[MP]], ![[VEC_WIDTH_2:.*]], ![[FIXED_WIDTH:[0-9]+]], ![[VEC_ENABLE:[0-9]+]]}
// CHECK: ![[VEC_WIDTH_2]] = !{!"llvm.loop.vectorize.width", i32 2}
// CHECK: ![[FIXED_WIDTH]] = !{!"llvm.loop.vectorize.scalable.enable", i1 false}
// CHECK: ![[VEC_ENABLE]] = !{!"llvm.loop.vectorize.enable", i1 true}

// CHECK: ![[LOOP3]] = distinct !{![[LOOP3]], [[MP]], ![[VEC_WIDTH_1]], ![[FIXED_WIDTH]]}
// CHECK: ![[LOOP3]] = distinct !{![[LOOP3]], [[MP]], ![[VEC_DISABLE]]}

// CHECK: ![[LOOP4]] = distinct !{![[LOOP4]], [[MP]], ![[VEC_WIDTH_2]], ![[FIXED_WIDTH]], ![[VEC_ENABLE]]}
22 changes: 11 additions & 11 deletions clang/test/CodeGenCXX/pragma-loop-predicate.cpp
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Expand Up @@ -37,8 +37,8 @@ void test3(int *List, int Length) {
List[i] = i * 2;
}

// Check that disabling vectorization means a vectorization width of 1, and
// also that vectorization_predicate isn't enabled.
// Check that vectorize is disabled, and also that vectorization_predicate is
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@david-arm david-arm Apr 15, 2025

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nit: The loop doesn't have a vectorize_predicate pragma so I think this should just be // Check that vectorization is disabled

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@kasuga-fj kasuga-fj Apr 15, 2025

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You are right, thanks!

// ignored.
void test4(int *List, int Length) {
// CHECK-LABEL: @{{.*}}test4{{.*}}(
// CHECK: br label {{.*}}, !llvm.loop ![[LOOP4:.*]]
Expand All @@ -48,7 +48,7 @@ void test4(int *List, int Length) {
List[i] = i * 2;
}

// Check that vectorize and vectorize_predicate are disabled.
// Check that vectorize is disabled and vectorize_predicate is ignored.
void test5(int *List, int Length) {
// CHECK-LABEL: @{{.*}}test5{{.*}}(
// CHECK: br label {{.*}}, !llvm.loop ![[LOOP5:.*]]
Expand Down Expand Up @@ -114,16 +114,16 @@ void test9(int *List, int Length) {
// CHECK-NEXT: ![[LOOP3]] = distinct !{![[LOOP3]], [[MP]], [[GEN6]], [[GEN3]]}

// CHECK-NEXT: ![[LOOP4]] = distinct !{![[LOOP4]], [[MP]], [[GEN10:![0-9]+]]}
// CHECK-NEXT: [[GEN10]] = !{!"llvm.loop.vectorize.width", i32 1}
// CHECK-NEXT: [[GEN10]] = !{!"llvm.loop.vectorize.enable", i1 false}

// CHECK-NEXT: ![[LOOP5]] = distinct !{![[LOOP5]], [[MP]], [[GEN6]], [[GEN10]]}
// CHECK-NEXT: ![[LOOP5]] = distinct !{![[LOOP5]], [[MP]], [[GEN10]]}

// CHECK-NEXT: ![[LOOP6]] = distinct !{![[LOOP6]], [[MP]], [[GEN8]], [[GEN10]], [[GEN11:![0-9]+]]}
// CHECK-NEXT: [[GEN11]] = !{!"llvm.loop.vectorize.scalable.enable", i1 false}
// CHECK-NEXT: ![[LOOP6]] = distinct !{![[LOOP6]], [[MP]], [[GEN10]]}

// CHECK-NEXT: ![[LOOP7]] = distinct !{![[LOOP7]], [[MP]], [[GEN8]], [[GEN12:![0-9]+]], [[GEN11]], [[GEN3]]}
// CHECK-NEXT: [[GEN12]] = !{!"llvm.loop.vectorize.width", i32 4}
// CHECK-NEXT: ![[LOOP7]] = distinct !{![[LOOP7]], [[MP]], [[GEN8]], [[GEN11:![0-9]+]], [[GEN12:![0-9]+]], [[GEN3]]}
// CHECK-NEXT: [[GEN11]] = !{!"llvm.loop.vectorize.width", i32 4}
// CHECK-NEXT: [[GEN12]] = !{!"llvm.loop.vectorize.scalable.enable", i1 false}

// CHECK-NEXT: ![[LOOP8]] = distinct !{![[LOOP8]], [[MP]], [[GEN6]], [[GEN10]], [[GEN11]]}
// CHECK-NEXT: ![[LOOP8]] = distinct !{![[LOOP8]], [[MP]], [[GEN10]]}

// CHECK-NEXT: ![[LOOP9]] = distinct !{![[LOOP9]], [[MP]], [[GEN6]], [[GEN12]], [[GEN11]], [[GEN3]]}
// CHECK-NEXT: ![[LOOP9]] = distinct !{![[LOOP9]], [[MP]], [[GEN6]], [[GEN11]], [[GEN12]], [[GEN3]]}
4 changes: 2 additions & 2 deletions clang/test/CodeGenCXX/pragma-loop-safety.cpp
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Expand Up @@ -53,6 +53,6 @@ void interleave_test(int *List, int Length) {
// CHECK: ![[INTERLEAVE_1]] = !{!"llvm.loop.interleave.count", i32 1}
// CHECK: ![[INTENABLE_1]] = !{!"llvm.loop.vectorize.enable", i1 true}
// CHECK: ![[ACCESS_GROUP_8]] = distinct !{}
// CHECK: ![[LOOP2_HINTS]] = distinct !{![[LOOP2_HINTS]], [[MP]], ![[PARALLEL_ACCESSES_11:[0-9]+]], ![[UNROLL_DISABLE]], ![[WIDTH_1:[0-9]+]], ![[INTENABLE_1]]}
// CHECK: ![[LOOP2_HINTS]] = distinct !{![[LOOP2_HINTS]], [[MP]], ![[PARALLEL_ACCESSES_11:[0-9]+]], ![[UNROLL_DISABLE]], ![[VECTORIZE_DISABLED:[0-9]+]]}
// CHECK: ![[PARALLEL_ACCESSES_11]] = !{!"llvm.loop.parallel_accesses", ![[ACCESS_GROUP_8]]}
// CHECK: ![[WIDTH_1]] = !{!"llvm.loop.vectorize.width", i32 1}
// CHECK: ![[VECTORIZE_DISABLED]] = !{!"llvm.loop.vectorize.enable", i1 false}
29 changes: 25 additions & 4 deletions clang/test/CodeGenCXX/pragma-loop.cpp
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Expand Up @@ -194,7 +194,7 @@ void for_test_scalable(int *List, int Length) {
}
}

// Verify for loop is performing scalable vectorization
// Verify for loop is NOT performing vectorization because the width is 1
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@david-arm david-arm Apr 10, 2025

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This isn't true because VF=vscale x 1 vectorize_width(1, scalable) is a valid vectorisation factor and RISC-V targets in particular make use of this. The value of vscale at runtime could be > 1, and so you're still processing > 1 element.

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@kasuga-fj kasuga-fj Apr 10, 2025

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You are right, I misunderstood the condition, thanks.

So what if the width is 1 and fixed/scalable is not explicitly specified? Should vectorization run? If taking the intent of the original implementation, then it appears to not vectorize the loop.

llvm-project/clang/lib/CodeGen/CGLoopInfo.cpp

Lines 646 to 648 in a03b225

// Disable vectorization by specifying a width of 1.
setVectorizeWidth(1);
setVectorizeScalable(LoopAttributes::Unspecified);

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@lukel97 lukel97 Apr 10, 2025

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If taking the intent of the original implementation, then it appears to not vectorize the loop.

Yeah I think that makes sense, i.e. we should disable vectorization if (Attrs.VectorizeEnable == LoopAttributes::Disable || (Attrs.VectorizeWidth == 1 && Attrs.VectorizeScalable != LoopAttributes:: Enable)).

We should probably also update this bit in the docs to be explicit about it:

Specifying a non-scalable width/count of 1 disables the optimization, and is equivalent to vectorize(disable) or interleave(disable).

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@kasuga-fj kasuga-fj Apr 11, 2025

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Fixed both code and docs. Thanks.

void for_test_scalable_1(int *List, int Length) {
#pragma clang loop vectorize_width(1, scalable) interleave_count(4) unroll(disable) distribute(disable)
for (int i = 0; i < Length; i++) {
Expand All @@ -203,6 +203,24 @@ void for_test_scalable_1(int *List, int Length) {
}
}

// Verify for loop is performing scalable vectorization
void for_test_scalable_2(int *List, int Length) {
#pragma clang loop vectorize_width(2, scalable) interleave_count(4) unroll(disable) distribute(disable)
for (int i = 0; i < Length; i++) {
// CHECK: br label {{.*}}, !llvm.loop ![[LOOP_20:.*]]
List[i] = i * 2;
}
}

// Verify unroll attributes are directly attached to the loop metadata
void for_test_vectorize_disable_unroll(int *List, int Length) {
#pragma clang loop vectorize(disable) unroll_count(8)
for (int i = 0; i < Length; i++) {
// CHECK: br label {{.*}}, !llvm.loop ![[LOOP_21:.*]]
List[i] = i * 2;
}
}

// CHECK-DAG: ![[MP:[0-9]+]] = !{!"llvm.loop.mustprogress"}

// CHECK-DAG: ![[UNROLL_DISABLE:[0-9]+]] = !{!"llvm.loop.unroll.disable"}
Expand All @@ -220,9 +238,9 @@ void for_test_scalable_1(int *List, int Length) {
// CHECK-DAG: ![[INTERLEAVE_16:[0-9]+]] = !{!"llvm.loop.interleave.count", i32 16}

// CHECK-DAG: ![[VECTORIZE_ENABLE:[0-9]+]] = !{!"llvm.loop.vectorize.enable", i1 true}
// CHECK-DAG: ![[VECTORIZE_DISABLE:[0-9]+]] = !{!"llvm.loop.vectorize.enable", i1 false}
// CHECK-DAG: ![[FIXED_VEC:[0-9]+]] = !{!"llvm.loop.vectorize.scalable.enable", i1 false}
// CHECK-DAG: ![[SCALABLE_VEC:[0-9]+]] = !{!"llvm.loop.vectorize.scalable.enable", i1 true}
// CHECK-DAG: ![[WIDTH_1:[0-9]+]] = !{!"llvm.loop.vectorize.width", i32 1}
// CHECK-DAG: ![[WIDTH_2:[0-9]+]] = !{!"llvm.loop.vectorize.width", i32 2}
// CHECK-DAG: ![[WIDTH_5:[0-9]+]] = !{!"llvm.loop.vectorize.width", i32 5}
// CHECK-DAG: ![[WIDTH_6:[0-9]+]] = !{!"llvm.loop.vectorize.width", i32 6}
Expand All @@ -241,7 +259,7 @@ void for_test_scalable_1(int *List, int Length) {

// CHECK-DAG: ![[LOOP_4]] = distinct !{![[LOOP_4]], ![[WIDTH_2]], ![[FIXED_VEC]], ![[INTERLEAVE_2]], ![[VECTORIZE_ENABLE]]}

// CHECK-DAG: ![[LOOP_5]] = distinct !{![[LOOP_5]], ![[MP]], ![[UNROLL_DISABLE]], ![[DISTRIBUTE_DISABLE]], ![[WIDTH_1]]}
// CHECK-DAG: ![[LOOP_5]] = distinct !{![[LOOP_5]], ![[MP]], ![[UNROLL_DISABLE]], ![[DISTRIBUTE_DISABLE]], ![[VECTORIZE_DISABLE]]}

// CHECK-DAG: ![[LOOP_6]] = distinct !{![[LOOP_6]], ![[MP]], ![[WIDTH_2]], ![[FIXED_VEC]], ![[INTERLEAVE_2]], ![[VECTORIZE_ENABLE]], ![[FOLLOWUP_VECTOR_3]]}

Expand Down Expand Up @@ -269,4 +287,7 @@ void for_test_scalable_1(int *List, int Length) {

// CHECK-DAG: ![[LOOP_17]] = distinct !{![[LOOP_17]], ![[MP]], ![[UNROLL_DISABLE]], ![[DISTRIBUTE_DISABLE]], ![[FIXED_VEC]], ![[INTERLEAVE_4]], ![[VECTORIZE_ENABLE]]}
// CHECK-DAG: ![[LOOP_18]] = distinct !{![[LOOP_18]], ![[MP]], ![[UNROLL_DISABLE]], ![[DISTRIBUTE_DISABLE]], ![[SCALABLE_VEC]], ![[INTERLEAVE_4]], ![[VECTORIZE_ENABLE]]}
// CHECK-DAG: ![[LOOP_19]] = distinct !{![[LOOP_19]], ![[MP]], ![[UNROLL_DISABLE]], ![[DISTRIBUTE_DISABLE]], ![[WIDTH_1]], ![[SCALABLE_VEC]], ![[INTERLEAVE_4]], ![[VECTORIZE_ENABLE]]}
// CHECK-DAG: ![[LOOP_19]] = distinct !{![[LOOP_19]], ![[MP]], ![[UNROLL_DISABLE]], ![[DISTRIBUTE_DISABLE]], ![[VECTORIZE_DISABLE]]}
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@david-arm david-arm Apr 10, 2025

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Again, I think this is broken. We should still be vectorising with VF=vscale x 1

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@kasuga-fj kasuga-fj Apr 11, 2025

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Undid this, thanks.

// CHECK-DAG: ![[LOOP_20]] = distinct !{![[LOOP_20]], ![[MP]], ![[UNROLL_DISABLE]], ![[DISTRIBUTE_DISABLE]], ![[WIDTH_2]], ![[SCALABLE_VEC]], ![[INTERLEAVE_4]], ![[VECTORIZE_ENABLE]]}

// CHECK-DAG: ![[LOOP_21]] = distinct !{![[LOOP_21]], ![[MP]], ![[VECTORIZE_DISABLE]], ![[UNROLL_8]]}
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