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[CodeGen] Treat all vector fields as mayalias 

Because it is common to treat vector types as an array of their elements, or
even some other type that's not the element type, and thus index into them, we
can't use struct-path TBAA for these accesses. Even though we already treat all
vector types as equivalent to 'char', we were using field-offset information
for them with TBAA, and this renders undefined the intra-value indexing we
intend to allow. Note that, although 'char' is universally aliasing, with path
TBAA, we can still differentiate between access to s.a and s.b in
  struct { char a, b; } s;. We can't use this capability as-is for vector types.

Fixes PR33967.

llvm-svn: 312447
This commit is contained in:
Hal Finkel 2017-09-03 17:18:25 +00:00
parent 7954a221f3
commit c9fac9e151
2 changed files with 22 additions and 2 deletions
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4
clang/lib/CodeGen/CGExpr.cpp
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@ -3665,8 +3665,9 @@ LValue CodeGenFunction::EmitLValueForField(LValue base,
getFieldAlignmentSource(BaseInfo.getAlignmentSource());
LValueBaseInfo FieldBaseInfo(fieldAlignSource, BaseInfo.getMayAlias());
QualType type = field->getType();
const RecordDecl *rec = field->getParent();
if (rec->isUnion() || rec->hasAttr<MayAliasAttr>())
if (rec->isUnion() || rec->hasAttr<MayAliasAttr>() || type->isVectorType())
FieldBaseInfo.setMayAlias(true);
bool mayAlias = FieldBaseInfo.getMayAlias();
@ -3691,7 +3692,6 @@ LValue CodeGenFunction::EmitLValueForField(LValue base,
return LValue::MakeBitfield(Addr, Info, fieldType, FieldBaseInfo);
}
QualType type = field->getType();
Address addr = base.getAddress();
unsigned cvr = base.getVRQualifiers();
bool TBAAPath = CGM.getCodeGenOpts().StructPathTBAA;

20
clang/test/CodeGen/tbaa-vec.cpp Normal file
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@ -0,0 +1,20 @@
// RUN: %clang_cc1 -triple x86_64-apple-darwin -O1 -disable-llvm-passes %s -emit-llvm -o - | FileCheck %s
// Test TBAA metadata generated by front-end (vector types are always treated as mayalias).
typedef float __m128 __attribute__ ((__vector_size__ (16)));
struct A {
__m128 a, b;
};
void foo(A *a, __m128 v) {
// CHECK-LABEL: define void @_Z3fooP1ADv4_f
a->a = v;
// CHECK: store <4 x float> %v, <4 x float>* %{{.*}}, align 16, !tbaa [[TAG_char:!.*]]
// CHECK: store <4 x float> %{{.*}}, <4 x float>* %{{.*}}, align 16, !tbaa [[TAG_char]]
}
// CHECK: [[TYPE_char:!.*]] = !{!"omnipotent char", [[TAG_cxx_tbaa:!.*]],
// CHECK: [[TAG_cxx_tbaa]] = !{!"Simple C++ TBAA"}
// CHECK: [[TAG_char]] = !{[[TYPE_char]], [[TYPE_char]], i64 0}