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[VectorCombine] Don't vectorize scalar load under asan/hwasan/memtag/tsan 

Similar to the tsan suppression in
`Utils/VNCoercion.cpp:getLoadLoadClobberFullWidthSize` (rL175034; load widening used by GVN),
the D81766 optimization should be suppressed under tsan due to potential
spurious data race reports:

  struct A {
    int i;
    const short s; // the load cannot be vectorized because
    int modify;    // it overlaps with bytes being concurrently modified
    long pad1, pad2;
  };
  // __tsan_read16 does not know that some bytes are undef and accessing is safe

Similarly, under asan, users can mark memory regions with
`__asan_poison_memory_region`. A widened load can lead to a spurious
use-after-poison error. hwasan/memtag should be similarly suppressed.

`mustSuppressSpeculation` suppresses asan/hwasan/tsan but not memtag, so
we need to exclude memtag in `vectorizeLoadInsert`.

Note, memtag suppression can be relaxed if the load is aligned to the
its granule (usually 16), but that is out of scope of this patch.

Reviewed By: spatel, vitalybuka

Differential Revision: https://reviews.llvm.org/D87538
This commit is contained in:
Fangrui Song 2020-09-14 15:11:55 -07:00
parent 127faae752
commit 4452cc4086
2 changed files with 79 additions and 1 deletions
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7
llvm/lib/Transforms/Vectorize/VectorCombine.cpp
View File

@ -98,7 +98,12 @@ bool VectorCombine::vectorizeLoadInsert(Instruction &I) {
return false;
auto *Load = dyn_cast<LoadInst>(Scalar);
Type *ScalarTy = Scalar->getType();
if (!Load || !Load->isSimple())
// Do not vectorize scalar load (widening) if atomic/volatile or under
// asan/hwasan/memtag/tsan. The widened load may load data from dirty regions
// or create data races non-existent in the source.
if (!Load || !Load->isSimple() ||
Load->getFunction()->hasFnAttribute(Attribute::SanitizeMemTag) ||
mustSuppressSpeculation(*Load))
return false;
auto *Ty = dyn_cast<FixedVectorType>(I.getType());
if (!Ty)

73
llvm/test/Transforms/VectorCombine/X86/load.ll
View File

@ -292,6 +292,66 @@ define <8 x i16> @gep10_load_i16_insert_v8i16(<8 x i16>* align 16 dereferenceabl
ret <8 x i16> %r
}
; Negative test - disable under asan because widened load can cause spurious
; use-after-poison issues when __asan_poison_memory_region is used.
define <8 x i16> @gep10_load_i16_insert_v8i16_asan(<8 x i16>* align 16 dereferenceable(32) %p) sanitize_address {
; CHECK-LABEL: @gep10_load_i16_insert_v8i16_asan(
; CHECK-NEXT: [[GEP:%.*]] = getelementptr inbounds <8 x i16>, <8 x i16>* [[P:%.*]], i64 1, i64 0
; CHECK-NEXT: [[S:%.*]] = load i16, i16* [[GEP]], align 16
; CHECK-NEXT: [[R:%.*]] = insertelement <8 x i16> undef, i16 [[S]], i64 0
; CHECK-NEXT: ret <8 x i16> [[R]]
;
%gep = getelementptr inbounds <8 x i16>, <8 x i16>* %p, i64 1, i64 0
%s = load i16, i16* %gep, align 16
%r = insertelement <8 x i16> undef, i16 %s, i64 0
ret <8 x i16> %r
}
; hwasan and memtag should be similarly suppressed.
define <8 x i16> @gep10_load_i16_insert_v8i16_hwasan(<8 x i16>* align 16 dereferenceable(32) %p) sanitize_hwaddress {
; CHECK-LABEL: @gep10_load_i16_insert_v8i16_hwasan(
; CHECK-NEXT: [[GEP:%.*]] = getelementptr inbounds <8 x i16>, <8 x i16>* [[P:%.*]], i64 1, i64 0
; CHECK-NEXT: [[S:%.*]] = load i16, i16* [[GEP]], align 16
; CHECK-NEXT: [[R:%.*]] = insertelement <8 x i16> undef, i16 [[S]], i64 0
; CHECK-NEXT: ret <8 x i16> [[R]]
;
%gep = getelementptr inbounds <8 x i16>, <8 x i16>* %p, i64 1, i64 0
%s = load i16, i16* %gep, align 16
%r = insertelement <8 x i16> undef, i16 %s, i64 0
ret <8 x i16> %r
}
define <8 x i16> @gep10_load_i16_insert_v8i16_memtag(<8 x i16>* align 16 dereferenceable(32) %p) sanitize_memtag {
; CHECK-LABEL: @gep10_load_i16_insert_v8i16_memtag(
; CHECK-NEXT: [[GEP:%.*]] = getelementptr inbounds <8 x i16>, <8 x i16>* [[P:%.*]], i64 1, i64 0
; CHECK-NEXT: [[S:%.*]] = load i16, i16* [[GEP]], align 16
; CHECK-NEXT: [[R:%.*]] = insertelement <8 x i16> undef, i16 [[S]], i64 0
; CHECK-NEXT: ret <8 x i16> [[R]]
;
%gep = getelementptr inbounds <8 x i16>, <8 x i16>* %p, i64 1, i64 0
%s = load i16, i16* %gep, align 16
%r = insertelement <8 x i16> undef, i16 %s, i64 0
ret <8 x i16> %r
}
; Negative test - disable under tsan because widened load may overlap bytes
; being concurrently modified. tsan does not know that some bytes are undef.
define <8 x i16> @gep10_load_i16_insert_v8i16_tsan(<8 x i16>* align 16 dereferenceable(32) %p) sanitize_thread {
; CHECK-LABEL: @gep10_load_i16_insert_v8i16_tsan(
; CHECK-NEXT: [[GEP:%.*]] = getelementptr inbounds <8 x i16>, <8 x i16>* [[P:%.*]], i64 1, i64 0
; CHECK-NEXT: [[S:%.*]] = load i16, i16* [[GEP]], align 16
; CHECK-NEXT: [[R:%.*]] = insertelement <8 x i16> undef, i16 [[S]], i64 0
; CHECK-NEXT: ret <8 x i16> [[R]]
;
%gep = getelementptr inbounds <8 x i16>, <8 x i16>* %p, i64 1, i64 0
%s = load i16, i16* %gep, align 16
%r = insertelement <8 x i16> undef, i16 %s, i64 0
ret <8 x i16> %r
}
; Negative test - can't safely load the offset vector, but could load+shuffle.
define <8 x i16> @gep10_load_i16_insert_v8i16_deref(<8 x i16>* align 16 dereferenceable(31) %p) {
@ -393,3 +453,16 @@ define <2 x float> @load_f32_insert_v2f32(float* align 16 dereferenceable(16) %p
%r = insertelement <2 x float> undef, float %s, i32 0
ret <2 x float> %r
}
; Negative test - suppress load widening for asan/hwasan/memtag/tsan.
define <2 x float> @load_f32_insert_v2f32_asan(float* align 16 dereferenceable(16) %p) sanitize_address {
; CHECK-LABEL: @load_f32_insert_v2f32_asan(
; CHECK-NEXT: [[S:%.*]] = load float, float* [[P:%.*]], align 4
; CHECK-NEXT: [[R:%.*]] = insertelement <2 x float> undef, float [[S]], i32 0
; CHECK-NEXT: ret <2 x float> [[R]]
;
%s = load float, float* %p, align 4
%r = insertelement <2 x float> undef, float %s, i32 0
ret <2 x float> %r
}