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[clang] Don't emit warn_cxx_ms_struct when MSBitfields is enabled globally 

This diagnostic (which defaults to an error, added in
95833f33bd) was intended to clearly
point out cases where the C++ ABI won't match the Microsoft C++ ABI,
for cases when this is enabled via a pragma over a region of code.

The MSVC compatible struct layout feature can also be enabled via a
compiler option (-mms-bitfields). If enabled that way, one essentially
can't compile any C++ code unless also building with
-Wno-incompatible-ms-struct (which GCC doesn't support, and projects
developed with GCC aren't setting).

For the MinGW target, it's expected that the C++ ABI won't match
the MSVC one, if this option is used for getting the struct
layout to match MSVC.

Differential Revision: https://reviews.llvm.org/D81794
This commit is contained in:
Martin Storsjö 2020-06-13 22:29:52 +03:00
parent beeed368b6
commit 7b3fe96992
2 changed files with 15 additions and 5 deletions
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6
clang/lib/Sema/SemaDeclCXX.cpp
View File

@ -6773,7 +6773,11 @@ void Sema::CheckCompletedCXXClass(Scope *S, CXXRecordDecl *Record) {
// headers, sweeping up a bunch of types that the project doesn't
// really rely on MSVC-compatible layout for. We must therefore
// support "ms_struct except for C++ stuff" as a secondary ABI.
if (Record->isMsStruct(Context) &&
// Don't emit this diagnostic if the feature was enabled as a
// language option (as opposed to via a pragma or attribute), as
// the option -mms-bitfields otherwise essentially makes it impossible
// to build C++ code, unless this diagnostic is turned off.
if (Record->isMsStruct(Context) && !Context.getLangOpts().MSBitfields &&
(Record->isPolymorphic() || Record->getNumBases())) {
Diag(Record->getLocation(), diag::warn_cxx_ms_struct);
}

14
clang/test/SemaCXX/ms_struct.cpp
View File

@ -1,8 +1,11 @@
// RUN: %clang_cc1 -fsyntax-only -Wno-error=incompatible-ms-struct -verify -triple i686-apple-darwin9 -std=c++11 %s
// RUN: %clang_cc1 -fsyntax-only -Wno-error=incompatible-ms-struct -verify -triple armv7-apple-darwin9 -std=c++11 %s
// RUN: %clang_cc1 -fsyntax-only -DTEST_FOR_WARNING -Wno-error=incompatible-ms-struct -verify -triple i686-apple-darwin9 -std=c++11 %s
// RUN: %clang_cc1 -fsyntax-only -DTEST_FOR_WARNING -Wno-error=incompatible-ms-struct -verify -triple armv7-apple-darwin9 -std=c++11 %s
// RUN: %clang_cc1 -fsyntax-only -DTEST_FOR_ERROR -verify -triple armv7-apple-darwin9 -std=c++11 %s
// RUN: %clang_cc1 -fsyntax-only -DNO_PRAGMA -mms-bitfields -verify -triple armv7-apple-darwin9 -std=c++11 %s
#ifndef NO_PRAGMA
#pragma ms_struct on
#endif
struct A {
unsigned long a:4;
@ -12,7 +15,7 @@ struct A {
struct B : public A {
#ifdef TEST_FOR_ERROR
// expected-error@-2 {{ms_struct may not produce Microsoft-compatible layouts for classes with base classes or virtual functions}}
#else
#elif defined(TEST_FOR_WARNING)
// expected-warning@-4 {{ms_struct may not produce Microsoft-compatible layouts for classes with base classes or virtual functions}}
#endif
unsigned long c:16;
@ -27,7 +30,7 @@ static_assert(__builtin_offsetof(B, d) == 12,
struct C {
#ifdef TEST_FOR_ERROR
// expected-error@-2 {{ms_struct may not produce Microsoft-compatible layouts for classes with base classes or virtual functions}}
#else
#elif defined(TEST_FOR_WARNING)
// expected-warning@-4 {{ms_struct may not produce Microsoft-compatible layouts for classes with base classes or virtual functions}}
#endif
virtual void foo();
@ -36,3 +39,6 @@ struct C {
static_assert(__builtin_offsetof(C, n) == 8,
"long long field in ms_struct should be 8-byte aligned");
#if !defined(TEST_FOR_ERROR) && !defined(TEST_FOR_WARNING)
// expected-no-diagnostics
#endif