rsmith updated this revision to Diff 144415.
rsmith added a comment.
Added release notes.
Repository:
rC Clang
https://reviews.llvm.org/D46218
Files:
docs/ReleaseNotes.rst
lib/AST/RecordLayoutBuilder.cpp
test/CodeGenCXX/alignment.cpp
test/SemaCXX/class-layout.cpp
Index: test/SemaCXX/class-layout.cpp
===================================================================
--- test/SemaCXX/class-layout.cpp
+++ test/SemaCXX/class-layout.cpp
@@ -1,5 +1,6 @@
// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -std=c++98 -Wno-inaccessible-base
// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base -fclang-abi-compat=6 -DCLANG_ABI_COMPAT=6
// expected-no-diagnostics
#define SA(n, p) int a##n[(p) ? 1 : -1]
@@ -570,3 +571,19 @@
SA(0, sizeof(might_use_tail_padding) == 80);
}
} // namespace PR16537
+
+namespace PR37275 {
+ struct X { char c; };
+
+ struct A { int n; };
+ _Static_assert(_Alignof(A) == _Alignof(int), "");
+
+ struct __attribute__((packed)) B : X, A {};
+#if defined(CLANG_ABI_COMPAT) && CLANG_ABI_COMPAT <= 6
+ _Static_assert(_Alignof(B) == 1, "");
+ _Static_assert(__builtin_offsetof(B, n) == 1, "");
+#else
+ _Static_assert(_Alignof(B) == _Alignof(int), "");
+ _Static_assert(__builtin_offsetof(B, n) == 4, "");
+#endif
+}
Index: test/CodeGenCXX/alignment.cpp
===================================================================
--- test/CodeGenCXX/alignment.cpp
+++ test/CodeGenCXX/alignment.cpp
@@ -1,4 +1,5 @@
-// RUN: %clang_cc1 %s -emit-llvm -o - -triple=x86_64-apple-darwin10 | FileCheck %s
+// RUN: %clang_cc1 %s -emit-llvm -o - -triple=x86_64-apple-darwin10 | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-NOCOMPAT
+// RUN: %clang_cc1 %s -emit-llvm -o - -triple=x86_64-apple-darwin10 -fclang-abi-compat=6.0 | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-V6COMPAT
extern int int_source();
extern void int_sink(int x);
@@ -54,19 +55,22 @@
// CHECK: [[B_P:%.*]] = bitcast i8* [[T1]] to [[B]]*
// CHECK: [[FIELD_P:%.*]] = bitcast [[B]]* [[B_P]] to i8*
// CHECK: [[TRUNC:%.*]] = trunc i32 [[CALL]] to i8
- // CHECK: [[OLD_VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2
+ // CHECK-V6COMPAT: [[OLD_VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2
+ // CHECK-NOCOMPAT: [[OLD_VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 4
// CHECK: [[T0:%.*]] = and i8 [[TRUNC]], 3
// CHECK: [[T1:%.*]] = and i8 [[OLD_VALUE]], -4
// CHECK: [[T2:%.*]] = or i8 [[T1]], [[T0]]
- // CHECK: store i8 [[T2]], i8* [[FIELD_P]], align 2
+ // CHECK-V6COMPAT: store i8 [[T2]], i8* [[FIELD_P]], align 2
+ // CHECK-NOCOMPAT: store i8 [[T2]], i8* [[FIELD_P]], align 4
c.onebit = int_source();
// CHECK: [[C_P:%.*]] = load [[C]]*, [[C]]**
// CHECK: [[T0:%.*]] = bitcast [[C]]* [[C_P]] to i8*
// CHECK: [[T1:%.*]] = getelementptr inbounds i8, i8* [[T0]], i64 8
// CHECK: [[B_P:%.*]] = bitcast i8* [[T1]] to [[B]]*
// CHECK: [[FIELD_P:%.*]] = bitcast [[B]]* [[B_P]] to i8*
- // CHECK: [[VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2
+ // CHECK-V6COMPAT: [[VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2
+ // CHECK-NOCOMPAT: [[VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 4
// CHECK: [[T0:%.*]] = shl i8 [[VALUE]], 6
// CHECK: [[T1:%.*]] = ashr i8 [[T0]], 6
// CHECK: [[T2:%.*]] = sext i8 [[T1]] to i32
@@ -83,19 +87,22 @@
// CHECK: [[B_P:%.*]] = bitcast i8* [[T1]] to [[B]]*
// CHECK: [[FIELD_P:%.*]] = bitcast [[B]]* [[B_P]] to i8*
// CHECK: [[TRUNC:%.*]] = trunc i32 [[CALL]] to i8
- // CHECK: [[OLD_VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2
+ // CHECK-V6COMPAT: [[OLD_VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2
+ // CHECK-NOCOMPAT: [[OLD_VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 4
// CHECK: [[T0:%.*]] = and i8 [[TRUNC]], 3
// CHECK: [[T1:%.*]] = and i8 [[OLD_VALUE]], -4
// CHECK: [[T2:%.*]] = or i8 [[T1]], [[T0]]
- // CHECK: store i8 [[T2]], i8* [[FIELD_P]], align 2
+ // CHECK-V6COMPAT: store i8 [[T2]], i8* [[FIELD_P]], align 2
+ // CHECK-NOCOMPAT: store i8 [[T2]], i8* [[FIELD_P]], align 4
c->onebit = int_source();
// CHECK: [[C_P:%.*]] = load [[C:%.*]]*, [[C]]**
// CHECK: [[T0:%.*]] = bitcast [[C]]* [[C_P]] to i8*
// CHECK: [[T1:%.*]] = getelementptr inbounds i8, i8* [[T0]], i64 8
// CHECK: [[B_P:%.*]] = bitcast i8* [[T1]] to [[B:%.*]]*
// CHECK: [[FIELD_P:%.*]] = bitcast [[B]]* [[B_P]] to i8*
- // CHECK: [[VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2
+ // CHECK-V6COMPAT: [[VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2
+ // CHECK-NOCOMPAT: [[VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 4
// CHECK: [[T0:%.*]] = shl i8 [[VALUE]], 6
// CHECK: [[T1:%.*]] = ashr i8 [[T0]], 6
// CHECK: [[T2:%.*]] = sext i8 [[T1]] to i32
@@ -107,27 +114,31 @@
// in an alignment-2 variable.
// CHECK-LABEL: @_ZN5test01dEv
void d() {
- // CHECK: [[C_P:%.*]] = alloca [[C:%.*]], align 2
+ // CHECK-V6COMPAT: [[C_P:%.*]] = alloca [[C:%.*]], align 2
+ // CHECK-NOCOMPAT: [[C_P:%.*]] = alloca [[C:%.*]], align 4
C c;
// CHECK: [[CALL:%.*]] = call i32 @_Z10int_sourcev()
// CHECK: [[T0:%.*]] = bitcast [[C]]* [[C_P]] to i8*
// CHECK: [[T1:%.*]] = getelementptr inbounds i8, i8* [[T0]], i64 8
// CHECK: [[B_P:%.*]] = bitcast i8* [[T1]] to [[B]]*
// CHECK: [[FIELD_P:%.*]] = bitcast [[B]]* [[B_P]] to i8*
// CHECK: [[TRUNC:%.*]] = trunc i32 [[CALL]] to i8
- // CHECK: [[OLD_VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2
+ // CHECK-V6COMPAT: [[OLD_VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2
+ // CHECK-NOCOMPAT: [[OLD_VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 4
// CHECK: [[T0:%.*]] = and i8 [[TRUNC]], 3
// CHECK: [[T1:%.*]] = and i8 [[OLD_VALUE]], -4
// CHECK: [[T2:%.*]] = or i8 [[T1]], [[T0]]
- // CHECK: store i8 [[T2]], i8* [[FIELD_P]], align 2
+ // CHECK-V6COMPAT: store i8 [[T2]], i8* [[FIELD_P]], align 2
+ // CHECK-NOCOMPAT: store i8 [[T2]], i8* [[FIELD_P]], align 4
c.onebit = int_source();
// CHECK: [[T0:%.*]] = bitcast [[C]]* [[C_P]] to i8*
// CHECK: [[T1:%.*]] = getelementptr inbounds i8, i8* [[T0]], i64 8
// CHECK: [[B_P:%.*]] = bitcast i8* [[T1]] to [[B:%.*]]*
// CHECK: [[FIELD_P:%.*]] = bitcast [[B]]* [[B_P]] to i8*
- // CHECK: [[VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2
+ // CHECK-V6COMPAT: [[VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 2
+ // CHECK-NOCOMPAT: [[VALUE:%.*]] = load i8, i8* [[FIELD_P]], align 4
// CHECK: [[T0:%.*]] = shl i8 [[VALUE]], 6
// CHECK: [[T1:%.*]] = ashr i8 [[T0]], 6
// CHECK: [[T2:%.*]] = sext i8 [[T1]] to i32
Index: lib/AST/RecordLayoutBuilder.cpp
===================================================================
--- lib/AST/RecordLayoutBuilder.cpp
+++ lib/AST/RecordLayoutBuilder.cpp
@@ -967,7 +967,7 @@
void ItaniumRecordLayoutBuilder::EnsureVTablePointerAlignment(
CharUnits UnpackedBaseAlign) {
- CharUnits BaseAlign = (Packed) ? CharUnits::One() : UnpackedBaseAlign;
+ CharUnits BaseAlign = Packed ? CharUnits::One() : UnpackedBaseAlign;
// The maximum field alignment overrides base align.
if (!MaxFieldAlignment.isZero()) {
@@ -1175,9 +1175,14 @@
HasExternalLayout = External.getExternalVBaseOffset(Base->Class, Offset);
}
+ // Clang <= 6 incorrectly applied the 'packed' attribute to base classes.
+ // Per GCC's documentation, it only applies to non-static data members.
CharUnits UnpackedBaseAlign = Layout.getNonVirtualAlignment();
- CharUnits BaseAlign = (Packed) ? CharUnits::One() : UnpackedBaseAlign;
-
+ CharUnits BaseAlign = (Packed && Context.getLangOpts().getClangABICompat() <=
+ LangOptions::ClangABI::Ver6)
+ ? CharUnits::One()
+ : UnpackedBaseAlign;
+
// If we have an empty base class, try to place it at offset 0.
if (Base->Class->isEmpty() &&
(!HasExternalLayout || Offset == CharUnits::Zero()) &&
Index: docs/ReleaseNotes.rst
===================================================================
--- docs/ReleaseNotes.rst
+++ docs/ReleaseNotes.rst
@@ -78,6 +78,12 @@
standard-layout if all base classes and the first data member (or bit-field)
can be laid out at offset zero.
+- Clang's handling of the GCC ``packed`` class attribute in C++ has been fixed
+ to apply only to non-static data members and not to base classes. This fixes
+ an ABI difference between Clang and GCC, but creates an ABI difference between
+ Clang 7 and earlier versions. The old behavior can be restored by setting
+ ``-fclang-abi-compat`` to ``6`` or earlier.
+
- ...
New Compiler Flags
_______________________________________________
cfe-commits mailing list
cfe-commits@lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
