This revision was automatically updated to reflect the committed changes. Closed by commit rL331620: Non-zero-length bit-fields make a class non-empty. (authored by rsmith, committed by ). Herald added a subscriber: llvm-commits.
Changed prior to commit: https://reviews.llvm.org/D45174?vs=140654&id=145428#toc Repository: rL LLVM https://reviews.llvm.org/D45174 Files: cfe/trunk/docs/ReleaseNotes.rst cfe/trunk/lib/AST/DeclCXX.cpp cfe/trunk/test/Layout/ms-x86-pack-and-align.cpp cfe/trunk/test/Layout/v6-empty.cpp cfe/trunk/test/SemaCXX/type-traits.cpp
Index: cfe/trunk/docs/ReleaseNotes.rst =================================================================== --- cfe/trunk/docs/ReleaseNotes.rst +++ cfe/trunk/docs/ReleaseNotes.rst @@ -84,6 +84,15 @@ Clang 7 and earlier versions. The old behavior can be restored by setting ``-fclang-abi-compat`` to ``6`` or earlier. +- Clang implements the proposed resolution of LWG issue 2358, along with the + `corresponding change to the Itanium C++ ABI + <https://github.com/itanium-cxx-abi/cxx-abi/pull/51>`_, which make classes + containing only unnamed non-zero-length bit-fields be considered non-empty. + This is an ABI break compared to prior Clang releases, but makes Clang + generate code that is ABI-compatible with other compilers. The old + behavior can be restored by setting ``-fclang-abi-compat`` to ``6`` or + lower. + - ... New Compiler Flags Index: cfe/trunk/test/Layout/ms-x86-pack-and-align.cpp =================================================================== --- cfe/trunk/test/Layout/ms-x86-pack-and-align.cpp +++ cfe/trunk/test/Layout/ms-x86-pack-and-align.cpp @@ -188,12 +188,12 @@ __declspec(align(32)) char : 1; }; // CHECK: *** Dumping AST Record Layout -// CHECK-NEXT: 0 | struct YA (empty) +// CHECK-NEXT: 0 | struct YA // CHECK-NEXT:0:0-0 | char // CHECK-NEXT: | [sizeof=32, align=32 // CHECK-NEXT: | nvsize=32, nvalign=32] // CHECK-X64: *** Dumping AST Record Layout -// CHECK-X64-NEXT: 0 | struct YA (empty) +// CHECK-X64-NEXT: 0 | struct YA // CHECK-X64-NEXT:0:0-0 | char // CHECK-X64-NEXT: | [sizeof=32, align=32 // CHECK-X64-NEXT: | nvsize=32, nvalign=32] @@ -206,14 +206,14 @@ // CHECK: *** Dumping AST Record Layout // CHECK-NEXT: 0 | struct YB // CHECK-NEXT: 0 | char a -// CHECK-NEXT: 1 | struct YA b (empty) +// CHECK-NEXT: 1 | struct YA b // CHECK-NEXT:1:0-0 | char // CHECK-NEXT: | [sizeof=33, align=1 // CHECK-NEXT: | nvsize=33, nvalign=1] // CHECK-X64: *** Dumping AST Record Layout // CHECK-X64-NEXT: 0 | struct YB // CHECK-X64-NEXT: 0 | char a -// CHECK-X64-NEXT: 1 | struct YA b (empty) +// CHECK-X64-NEXT: 1 | struct YA b // CHECK-X64-NEXT:1:0-0 | char // CHECK-X64-NEXT: | [sizeof=33, align=1 // CHECK-X64-NEXT: | nvsize=33, nvalign=1] @@ -223,12 +223,12 @@ __declspec(align(32)) char : 1; }; // CHECK: *** Dumping AST Record Layout -// CHECK-NEXT: 0 | struct YC (empty) +// CHECK-NEXT: 0 | struct YC // CHECK-NEXT:0:0-0 | char // CHECK-NEXT: | [sizeof=32, align=32 // CHECK-NEXT: | nvsize=32, nvalign=32] // CHECK-X64: *** Dumping AST Record Layout -// CHECK-X64-NEXT: 0 | struct YC (empty) +// CHECK-X64-NEXT: 0 | struct YC // CHECK-X64-NEXT: 0:0-0 | char // CHECK-X64-NEXT: | [sizeof=8, align=32 // CHECK-X64-NEXT: | nvsize=8, nvalign=32] @@ -241,14 +241,14 @@ // CHECK: *** Dumping AST Record Layout // CHECK-NEXT: 0 | struct YD // CHECK-NEXT: 0 | char a -// CHECK-NEXT: 1 | struct YC b (empty) +// CHECK-NEXT: 1 | struct YC b // CHECK-NEXT:1:0-0 | char // CHECK-NEXT: | [sizeof=33, align=1 // CHECK-NEXT: | nvsize=33, nvalign=1] // CHECK-X64: *** Dumping AST Record Layout // CHECK-X64-NEXT: 0 | struct YD // CHECK-X64-NEXT: 0 | char a -// CHECK-X64-NEXT: 1 | struct YC b (empty) +// CHECK-X64-NEXT: 1 | struct YC b // CHECK-X64-NEXT:1:0-0 | char // CHECK-X64-NEXT: | [sizeof=9, align=1 // CHECK-X64-NEXT: | nvsize=9, nvalign=1] @@ -258,12 +258,12 @@ __declspec(align(32)) char : 1; }; // CHECK: *** Dumping AST Record Layout -// CHECK-NEXT: 0 | struct YE (empty) +// CHECK-NEXT: 0 | struct YE // CHECK-NEXT: 0:0-0 | char // CHECK-NEXT: | [sizeof=4, align=32 // CHECK-NEXT: | nvsize=4, nvalign=32] // CHECK-X64: *** Dumping AST Record Layout -// CHECK-X64-NEXT: 0 | struct YE (empty) +// CHECK-X64-NEXT: 0 | struct YE // CHECK-X64-NEXT: 0:0-0 | char // CHECK-X64-NEXT: | [sizeof=4, align=32 // CHECK-X64-NEXT: | nvsize=4, nvalign=32] @@ -276,14 +276,14 @@ // CHECK: *** Dumping AST Record Layout // CHECK-NEXT: 0 | struct YF // CHECK-NEXT: 0 | char a -// CHECK-NEXT: 1 | struct YE b (empty) +// CHECK-NEXT: 1 | struct YE b // CHECK-NEXT:1:0-0 | char // CHECK-NEXT: | [sizeof=5, align=1 // CHECK-NEXT: | nvsize=5, nvalign=1] // CHECK-X64: *** Dumping AST Record Layout // CHECK-X64-NEXT: 0 | struct YF // CHECK-X64-NEXT: 0 | char a -// CHECK-X64-NEXT: 1 | struct YE b (empty) +// CHECK-X64-NEXT: 1 | struct YE b // CHECK-X64-NEXT:1:0-0 | char // CHECK-X64-NEXT: | [sizeof=5, align=1 // CHECK-X64-NEXT: | nvsize=5, nvalign=1] Index: cfe/trunk/test/Layout/v6-empty.cpp =================================================================== --- cfe/trunk/test/Layout/v6-empty.cpp +++ cfe/trunk/test/Layout/v6-empty.cpp @@ -0,0 +1,20 @@ +// RUN: %clang_cc1 -fsyntax-only -fclang-abi-compat=6 -triple x86_64-linux-gnu -fdump-record-layouts %s | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-V6 +// RUN: %clang_cc1 -fsyntax-only -fclang-abi-compat=7 -triple x86_64-linux-gnu -fdump-record-layouts %s | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-V7 + +// In Clang 6 and before, we determined that Nonempty was empty, so we +// applied EBO to it. +struct Nonempty { int : 4; }; +struct A : Nonempty { int n; }; +int k = sizeof(A); + +// CHECK:*** Dumping AST Record Layout +// CHECK: 0 | struct A +// CHECK-V6-NEXT: 0 | struct Nonempty (base) (empty) +// CHECK-V7-NEXT: 0 | struct Nonempty (base){{$}} +// CHECK-NEXT: 0:0-3 | int +// CHECK-V6-NEXT: 0 | int n +// CHECK-V7-NEXT: 4 | int n +// CHECK-V6-NEXT: | [sizeof=4, dsize=4, align=4, +// CHECK-V6-NEXT: | nvsize=4, nvalign=4] +// CHECK-V7-NEXT: | [sizeof=8, dsize=8, align=4, +// CHECK-V7-NEXT: | nvsize=8, nvalign=4] Index: cfe/trunk/test/SemaCXX/type-traits.cpp =================================================================== --- cfe/trunk/test/SemaCXX/type-traits.cpp +++ cfe/trunk/test/SemaCXX/type-traits.cpp @@ -262,6 +262,7 @@ typedef Empty EmptyAr[10]; struct Bit0 { int : 0; }; struct Bit0Cons { int : 0; Bit0Cons(); }; +struct AnonBitOnly { int : 3; }; struct BitOnly { int x : 3; }; struct DerivesVirt : virtual POD {}; @@ -287,6 +288,7 @@ { int arr[F(__is_empty(EmptyAr))]; } { int arr[F(__is_empty(HasRef))]; } { int arr[F(__is_empty(HasVirt))]; } + { int arr[F(__is_empty(AnonBitOnly))]; } { int arr[F(__is_empty(BitOnly))]; } { int arr[F(__is_empty(void))]; } { int arr[F(__is_empty(IntArNB))]; } Index: cfe/trunk/lib/AST/DeclCXX.cpp =================================================================== --- cfe/trunk/lib/AST/DeclCXX.cpp +++ cfe/trunk/lib/AST/DeclCXX.cpp @@ -856,10 +856,10 @@ return; } - ASTContext &Context = getASTContext(); - // Handle non-static data members. if (const auto *Field = dyn_cast<FieldDecl>(D)) { + ASTContext &Context = getASTContext(); + // C++2a [class]p7: // A standard-layout class is a class that: // [...] @@ -872,8 +872,16 @@ // A declaration for a bit-field that omits the identifier declares an // unnamed bit-field. Unnamed bit-fields are not members and cannot be // initialized. - if (Field->isUnnamedBitfield()) + if (Field->isUnnamedBitfield()) { + // C++ [meta.unary.prop]p4: [LWG2358] + // T is a class type [...] with [...] no unnamed bit-fields of non-zero + // length + if (data().Empty && !Field->isZeroLengthBitField(Context) && + Context.getLangOpts().getClangABICompat() > + LangOptions::ClangABI::Ver6) + data().Empty = false; return; + } // C++11 [class]p7: // A standard-layout class is a class that: @@ -1220,12 +1228,8 @@ } // C++14 [meta.unary.prop]p4: - // T is a class type [...] with [...] no non-static data members other - // than bit-fields of length 0... - if (data().Empty) { - if (!Field->isZeroLengthBitField(Context)) - data().Empty = false; - } + // T is a class type [...] with [...] no non-static data members + data().Empty = false; } // Handle using declarations of conversion functions.
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