cd3ebfe293
The layout_version attribute is pretty straightforward: use the layout
rules from version XYZ of MSVC when used like
struct __declspec(layout_version(XYZ)) S {};
The empty_bases attribute is more interesting. It tries to get the C++
empty base optimization to fire more often by tweaking the MSVC ABI
rules in subtle ways:
1. Disable the leading and trailing zero-sized object flags if a class
is marked __declspec(empty_bases) and is empty.
This means that given:
struct __declspec(empty_bases) A {};
struct __declspec(empty_bases) B {};
struct C : A, B {};
'C' will have size 1 and nvsize 0 despite not being annotated
__declspec(empty_bases).
2. When laying out virtual or non-virtual bases, disable the injection
of padding between classes if the most derived class is marked
__declspec(empty_bases).
This means that given:
struct A {};
struct B {};
struct __declspec(empty_bases) C : A, B {};
'C' will have size 1 and nvsize 0.
3. When calculating the offset of a non-virtual base, choose offset zero
if the most derived class is marked __declspec(empty_bases) and the
base is empty _and_ has an nvsize of 0.
Because of the ABI rules, this does not mean that empty bases
reliably get placed at offset 0!
For example:
struct A {};
struct B {};
struct __declspec(empty_bases) C : A, B { virtual ~C(); };
'C' will be pointer sized to account for the vfptr at offset 0.
'A' and 'B' will _not_ be at offset 0 despite being empty!
Instead, they will be located right after the vfptr.
This occurs due to the interaction betweeen non-virtual base layout
and virtual function pointer injection: injection occurs after the
nv-bases and shifts them down by the size of a pointer.
llvm-svn: 270457
267 lines
8.5 KiB
C++
267 lines
8.5 KiB
C++
// RUN: %clang_cc1 -fno-rtti -emit-llvm-only -triple i686-pc-win32 -fms-extensions -fdump-record-layouts -fsyntax-only %s 2>/dev/null \
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// RUN: | FileCheck %s
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// RUN: %clang_cc1 -fno-rtti -emit-llvm-only -triple x86_64-pc-win32 -fms-extensions -fdump-record-layouts -fsyntax-only %s 2>/dev/null \
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// RUN: | FileCheck %s
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namespace test1 {
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struct A {
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int a;
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};
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struct B {
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int b;
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};
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struct C {};
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struct __declspec(align(16)) D {};
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struct __declspec(empty_bases) X : A, D, B, C {
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};
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test1::A
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// CHECK-NEXT: 0 | int a
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// CHECK-NEXT: | [sizeof=4, align=4,
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// CHECK-NEXT: | nvsize=4, nvalign=4]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test1::D (empty)
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// CHECK-NEXT: | [sizeof=16, align=16,
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// CHECK-NEXT: | nvsize=0, nvalign=16]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test1::B
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// CHECK-NEXT: 0 | int b
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// CHECK-NEXT: | [sizeof=4, align=4,
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// CHECK-NEXT: | nvsize=4, nvalign=4]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test1::C (empty)
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// CHECK-NEXT: | [sizeof=1, align=1,
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// CHECK-NEXT: | nvsize=0, nvalign=1]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test1::X
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// CHECK-NEXT: 0 | struct test1::A (base)
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// CHECK-NEXT: 0 | int a
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// CHECK-NEXT: 0 | struct test1::D (base) (empty)
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// CHECK-NEXT: 0 | struct test1::C (base) (empty)
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// CHECK-NEXT: 4 | struct test1::B (base)
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// CHECK-NEXT: 4 | int b
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// CHECK-NEXT: | [sizeof=16, align=16,
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// CHECK-NEXT: | nvsize=16, nvalign=16]
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int _ = sizeof(X);
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}
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namespace test2 {
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struct A {
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int a;
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};
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struct __declspec(empty_bases) B {};
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struct C : A {
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B b;
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};
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struct D {};
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struct E {
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int e;
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};
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struct F : D, E {};
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struct G : C, F {};
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int _ = sizeof(G);
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test2::A
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// CHECK-NEXT: 0 | int a
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// CHECK-NEXT: | [sizeof=4, align=4,
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// CHECK-NEXT: | nvsize=4, nvalign=4]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test2::B (empty)
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// CHECK-NEXT: | [sizeof=1, align=1,
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// CHECK-NEXT: | nvsize=0, nvalign=1]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test2::C
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// CHECK-NEXT: 0 | struct test2::A (base)
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// CHECK-NEXT: 0 | int a
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// CHECK-NEXT: 4 | struct test2::B b (empty)
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// CHECK-NEXT: | [sizeof=8, align=4,
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// CHECK-NEXT: | nvsize=8, nvalign=4]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test2::D (empty)
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// CHECK-NEXT: | [sizeof=1, align=1,
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// CHECK-NEXT: | nvsize=0, nvalign=1]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test2::E
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// CHECK-NEXT: 0 | int e
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// CHECK-NEXT: | [sizeof=4, align=4,
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// CHECK-NEXT: | nvsize=4, nvalign=4]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test2::F
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// CHECK-NEXT: 0 | struct test2::D (base) (empty)
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// CHECK-NEXT: 0 | struct test2::E (base)
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// CHECK-NEXT: 0 | int e
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// CHECK-NEXT: | [sizeof=4, align=4,
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// CHECK-NEXT: | nvsize=4, nvalign=4]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test2::G
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// CHECK-NEXT: 0 | struct test2::C (base)
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// CHECK-NEXT: 0 | struct test2::A (base)
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// CHECK-NEXT: 0 | int a
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// CHECK-NEXT: 4 | struct test2::B b (empty)
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// CHECK-NEXT: 8 | struct test2::F (base)
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// CHECK-NEXT: 8 | struct test2::D (base) (empty)
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// CHECK-NEXT: 8 | struct test2::E (base)
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// CHECK-NEXT: 8 | int e
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// CHECK-NEXT: | [sizeof=12, align=4,
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// CHECK-NEXT: | nvsize=12, nvalign=4]
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}
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namespace test3 {
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struct A {
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int a;
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};
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struct B {};
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struct C : A {
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B b;
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};
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struct D {};
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struct E {
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int e;
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};
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struct F : D, E {};
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struct __declspec(empty_bases) G : C, F {};
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int _ = sizeof(G);
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test3::A
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// CHECK-NEXT: 0 | int a
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// CHECK-NEXT: | [sizeof=4, align=4,
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// CHECK-NEXT: | nvsize=4, nvalign=4]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test3::B (empty)
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// CHECK-NEXT: | [sizeof=1, align=1,
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// CHECK-NEXT: | nvsize=0, nvalign=1]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test3::C
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// CHECK-NEXT: 0 | struct test3::A (base)
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// CHECK-NEXT: 0 | int a
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// CHECK-NEXT: 4 | struct test3::B b (empty)
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// CHECK-NEXT: | [sizeof=8, align=4,
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// CHECK-NEXT: | nvsize=8, nvalign=4]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test3::D (empty)
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// CHECK-NEXT: | [sizeof=1, align=1,
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// CHECK-NEXT: | nvsize=0, nvalign=1]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test3::E
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// CHECK-NEXT: 0 | int e
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// CHECK-NEXT: | [sizeof=4, align=4,
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// CHECK-NEXT: | nvsize=4, nvalign=4]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test3::F
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// CHECK-NEXT: 0 | struct test3::D (base) (empty)
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// CHECK-NEXT: 0 | struct test3::E (base)
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// CHECK-NEXT: 0 | int e
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// CHECK-NEXT: | [sizeof=4, align=4,
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// CHECK-NEXT: | nvsize=4, nvalign=4]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test3::G
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// CHECK-NEXT: 0 | struct test3::C (base)
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// CHECK-NEXT: 0 | struct test3::A (base)
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// CHECK-NEXT: 0 | int a
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// CHECK-NEXT: 4 | struct test3::B b (empty)
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// CHECK-NEXT: 8 | struct test3::F (base)
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// CHECK-NEXT: 8 | struct test3::D (base) (empty)
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// CHECK-NEXT: 8 | struct test3::E (base)
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// CHECK-NEXT: 8 | int e
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// CHECK-NEXT: | [sizeof=12, align=4,
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// CHECK-NEXT: | nvsize=12, nvalign=4]
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}
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namespace test4 {
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struct A {
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int a;
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};
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struct B {};
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struct C : A {
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B b;
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};
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struct __declspec(empty_bases) D {};
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struct E {
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int e;
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};
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struct F : D, E {};
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struct G : C, F {};
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int _ = sizeof(G);
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test4::A
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// CHECK-NEXT: 0 | int a
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// CHECK-NEXT: | [sizeof=4, align=4,
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// CHECK-NEXT: | nvsize=4, nvalign=4]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test4::B (empty)
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// CHECK-NEXT: | [sizeof=1, align=1,
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// CHECK-NEXT: | nvsize=0, nvalign=1]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test4::C
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// CHECK-NEXT: 0 | struct test4::A (base)
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// CHECK-NEXT: 0 | int a
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// CHECK-NEXT: 4 | struct test4::B b (empty)
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// CHECK-NEXT: | [sizeof=8, align=4,
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// CHECK-NEXT: | nvsize=8, nvalign=4]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test4::D (empty)
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// CHECK-NEXT: | [sizeof=1, align=1,
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// CHECK-NEXT: | nvsize=0, nvalign=1]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test4::E
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// CHECK-NEXT: 0 | int e
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// CHECK-NEXT: | [sizeof=4, align=4,
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// CHECK-NEXT: | nvsize=4, nvalign=4]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test4::F
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// CHECK-NEXT: 0 | struct test4::D (base) (empty)
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// CHECK-NEXT: 0 | struct test4::E (base)
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// CHECK-NEXT: 0 | int e
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// CHECK-NEXT: | [sizeof=4, align=4,
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// CHECK-NEXT: | nvsize=4, nvalign=4]
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// CHECK: *** Dumping AST Record Layout
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// CHECK-NEXT: 0 | struct test4::G
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// CHECK-NEXT: 0 | struct test4::C (base)
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// CHECK-NEXT: 0 | struct test4::A (base)
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// CHECK-NEXT: 0 | int a
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// CHECK-NEXT: 4 | struct test4::B b (empty)
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// CHECK-NEXT: 8 | struct test4::F (base)
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// CHECK-NEXT: 8 | struct test4::D (base) (empty)
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// CHECK-NEXT: 8 | struct test4::E (base)
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// CHECK-NEXT: 8 | int e
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// CHECK-NEXT: | [sizeof=12, align=4,
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// CHECK-NEXT: | nvsize=12, nvalign=4]
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}
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