[clang] [clang] Implement gcc_struct attribute (PR #71148)
Dan Klishch via cfe-commits
cfe-commits at lists.llvm.org
Thu Nov 2 23:24:37 PDT 2023
https://github.com/DanShaders updated https://github.com/llvm/llvm-project/pull/71148
>From da5f4a4081c4917317549075f5d0916ebb26d0e9 Mon Sep 17 00:00:00 2001
From: Dan Klishch <danilklishch at gmail.com>
Date: Thu, 2 Nov 2023 23:49:54 -0400
Subject: [PATCH] [clang] Implement gcc_struct attribute
This implements gcc_struct attribute with the behavior similar to one in
GCC.
In particular, when C++ ABI is not "Microsoft" (i. e. when
ItaniumRecordLayoutBuilder is used), [[gcc_struct]] will locally cancel
the effect of -mms-bitfields on a record. If -mms-bitfields is not
supplied and is not a default behavior on a target, [[gcc_struct]] will
be a no-op. This hopefully should provide compatibility with MinGW
binaries.
On the other hand, if C++ ABI is "Microsoft" and a record is annotated
with [[gcc_struct]], we do not have any compatibility concerns, so I
decided not to complicate MicrosoftRecordLayoutBuilder and just to fully
switch record layout to GenericItanium.
Note that -mno-ms-bitfields is no longer always a no-op. On
`x86_64-pc-windows-msvc`, specifying only it should yield the same
results as annotating all the records with [[gcc_struct]]. This makes it
impossible to use usual argument parsing for `-m{no-,}ms-bitfield` in a
driver since MSBitfields now has a default value, which non-trivially
depends on other supplied flags.
Changes related to ms_struct hopefully should not cause any observable
differences, thus the patch itself is fully backwards-compatible.
---
clang/include/clang/Basic/Attr.td | 7 ++++
clang/include/clang/Basic/LangOptions.def | 1 -
clang/include/clang/Basic/LangOptions.h | 2 +
clang/include/clang/Basic/TargetInfo.h | 4 ++
clang/include/clang/Driver/Options.td | 4 +-
clang/lib/AST/Decl.cpp | 9 +++-
clang/lib/AST/RecordLayoutBuilder.cpp | 13 +++---
clang/lib/CodeGen/CGRecordLayoutBuilder.cpp | 8 ++--
clang/lib/Driver/ToolChains/Clang.cpp | 10 +++--
clang/lib/Frontend/CompilerInvocation.cpp | 12 ++++++
clang/lib/Sema/SemaDecl.cpp | 4 +-
clang/lib/Sema/SemaDeclCXX.cpp | 9 +++-
.../CodeGenCXX/ms-bitfield-class-layout.cpp | 41 +++++++++++++++++++
.../test/CodeGenCXX/ms_struct-gcc_struct.cpp | 29 +++++++++++++
clang/test/Driver/ms-bitfields.c | 11 +++--
15 files changed, 138 insertions(+), 26 deletions(-)
create mode 100644 clang/test/CodeGenCXX/ms-bitfield-class-layout.cpp
create mode 100644 clang/test/CodeGenCXX/ms_struct-gcc_struct.cpp
diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
index 60b549999c155e5..34ec6c22481837e 100644
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -3635,6 +3635,13 @@ def MSStruct : InheritableAttr {
let SimpleHandler = 1;
}
+def GCCStruct : InheritableAttr {
+ let Spellings = [GCC<"gcc_struct">];
+ let Subjects = SubjectList<[Record]>;
+ let Documentation = [Undocumented];
+ let SimpleHandler = 1;
+}
+
def DLLExport : InheritableAttr, TargetSpecificAttr<TargetHasDLLImportExport> {
let Spellings = [Declspec<"dllexport">, GCC<"dllexport">];
let Subjects = SubjectList<[Function, Var, CXXRecord, ObjCInterface]>;
diff --git a/clang/include/clang/Basic/LangOptions.def b/clang/include/clang/Basic/LangOptions.def
index c0ea4ecb9806a5b..afbb3c724a8d193 100644
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -148,7 +148,6 @@ LANGOPT(ExternCNoUnwind , 1, 0, "Assume extern C functions don't unwind")
LANGOPT(TraditionalCPP , 1, 0, "traditional CPP emulation")
LANGOPT(RTTI , 1, 1, "run-time type information")
LANGOPT(RTTIData , 1, 1, "emit run-time type information data")
-LANGOPT(MSBitfields , 1, 0, "Microsoft-compatible structure layout")
LANGOPT(MSVolatile , 1, 0, "Microsoft-compatible volatile loads and stores")
LANGOPT(Freestanding, 1, 0, "freestanding implementation")
LANGOPT(NoBuiltin , 1, 0, "disable builtin functions")
diff --git a/clang/include/clang/Basic/LangOptions.h b/clang/include/clang/Basic/LangOptions.h
index 20a8ada60e0fe51..07eae8dad61813c 100644
--- a/clang/include/clang/Basic/LangOptions.h
+++ b/clang/include/clang/Basic/LangOptions.h
@@ -502,6 +502,8 @@ class LangOptions : public LangOptionsBase {
// received as a result of a standard operator new (-fcheck-new)
bool CheckNew = false;
+ std::optional<bool> MSBitfields;
+
LangOptions();
/// Set language defaults for the given input language and
diff --git a/clang/include/clang/Basic/TargetInfo.h b/clang/include/clang/Basic/TargetInfo.h
index b3c5cbfb319f01f..6865b6e23bc9628 100644
--- a/clang/include/clang/Basic/TargetInfo.h
+++ b/clang/include/clang/Basic/TargetInfo.h
@@ -1724,6 +1724,10 @@ class TargetInfo : public TransferrableTargetInfo,
/// Whether to support HIP image/texture API's.
virtual bool hasHIPImageSupport() const { return true; }
+ virtual bool defaultsToMsStruct() const {
+ return getCXXABI().isMicrosoft() || getTriple().isWindowsGNUEnvironment();
+ }
+
protected:
/// Copy type and layout related info.
void copyAuxTarget(const TargetInfo *Aux);
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 9c0dcaa8b3f6276..d29214ed3cb13db 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -4381,8 +4381,7 @@ def : Joined<["-"], "mmacosx-version-min=">,
Group<m_Group>, Alias<mmacos_version_min_EQ>;
def mms_bitfields : Flag<["-"], "mms-bitfields">, Group<m_Group>,
Visibility<[ClangOption, CC1Option]>,
- HelpText<"Set the default structure layout to be compatible with the Microsoft compiler standard">,
- MarshallingInfoFlag<LangOpts<"MSBitfields">>;
+ HelpText<"Set the default structure layout to be compatible with the Microsoft compiler standard">;
def moutline : Flag<["-"], "moutline">, Group<f_clang_Group>,
Visibility<[ClangOption, CC1Option]>,
HelpText<"Enable function outlining (AArch64 only)">;
@@ -4390,6 +4389,7 @@ def mno_outline : Flag<["-"], "mno-outline">, Group<f_clang_Group>,
Visibility<[ClangOption, CC1Option]>,
HelpText<"Disable function outlining (AArch64 only)">;
def mno_ms_bitfields : Flag<["-"], "mno-ms-bitfields">, Group<m_Group>,
+ Visibility<[ClangOption, CC1Option]>,
HelpText<"Do not set the default structure layout to be compatible with the Microsoft compiler standard">;
def mskip_rax_setup : Flag<["-"], "mskip-rax-setup">, Group<m_Group>,
Visibility<[ClangOption, CC1Option]>,
diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index e8062b680fbc3ab..dbb122160eff445 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -5021,7 +5021,7 @@ void RecordDecl::completeDefinition() {
ASTContext &Ctx = getASTContext();
// Layouts are dumped when computed, so if we are dumping for all complete
- // types, we need to force usage to get types that wouldn't be used elsewhere.
+ // types, we need to force usage to pet types that wouldn't be used elsewhere.
if (Ctx.getLangOpts().DumpRecordLayoutsComplete)
(void)Ctx.getASTRecordLayout(this);
}
@@ -5030,7 +5030,12 @@ void RecordDecl::completeDefinition() {
/// This which can be turned on with an attribute, pragma, or the
/// -mms-bitfields command-line option.
bool RecordDecl::isMsStruct(const ASTContext &C) const {
- return hasAttr<MSStructAttr>() || C.getLangOpts().MSBitfields == 1;
+ if (hasAttr<MSStructAttr>())
+ return true;
+ if (hasAttr<GCCStructAttr>())
+ return false;
+ return C.getLangOpts().MSBitfields.value_or(
+ C.getTargetInfo().defaultsToMsStruct());
}
void RecordDecl::reorderDecls(const SmallVectorImpl<Decl *> &Decls) {
diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
index 5d4f930fca50e2b..f38c6432a9992a6 100644
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -2447,8 +2447,9 @@ static bool mustSkipTailPadding(TargetCXXABI ABI, const CXXRecordDecl *RD) {
llvm_unreachable("bad tail-padding use kind");
}
-static bool isMsLayout(const ASTContext &Context) {
- return Context.getTargetInfo().getCXXABI().isMicrosoft();
+static bool isMsLayout(const ASTContext &Context, const RecordDecl *RD) {
+ return Context.getTargetInfo().getCXXABI().isMicrosoft() &&
+ RD->isMsStruct(Context);
}
// This section contains an implementation of struct layout that is, up to the
@@ -3341,7 +3342,7 @@ ASTContext::getASTRecordLayout(const RecordDecl *D) const {
const ASTRecordLayout *NewEntry = nullptr;
- if (isMsLayout(*this)) {
+ if (isMsLayout(*this, D)) {
if (const auto *RD = dyn_cast<CXXRecordDecl>(D)) {
EmptySubobjectMap EmptySubobjects(*this, RD);
MicrosoftRecordLayoutBuilder Builder(*this, &EmptySubobjects);
@@ -3617,7 +3618,7 @@ static void DumpRecordLayout(raw_ostream &OS, const RecordDecl *RD,
bool HasOwnVBPtr = Layout.hasOwnVBPtr();
// Vtable pointer.
- if (CXXRD->isDynamicClass() && !PrimaryBase && !isMsLayout(C)) {
+ if (CXXRD->isDynamicClass() && !PrimaryBase && !isMsLayout(C, RD)) {
PrintOffset(OS, Offset, IndentLevel);
OS << '(' << *RD << " vtable pointer)\n";
} else if (HasOwnVFPtr) {
@@ -3717,7 +3718,7 @@ static void DumpRecordLayout(raw_ostream &OS, const RecordDecl *RD,
PrintIndentNoOffset(OS, IndentLevel - 1);
OS << "[sizeof=" << Layout.getSize().getQuantity();
- if (CXXRD && !isMsLayout(C))
+ if (CXXRD && !isMsLayout(C, RD))
OS << ", dsize=" << Layout.getDataSize().getQuantity();
OS << ", align=" << Layout.getAlignment().getQuantity();
if (C.getTargetInfo().defaultsToAIXPowerAlignment())
@@ -3756,7 +3757,7 @@ void ASTContext::DumpRecordLayout(const RecordDecl *RD, raw_ostream &OS,
OS << "\nLayout: ";
OS << "<ASTRecordLayout\n";
OS << " Size:" << toBits(Info.getSize()) << "\n";
- if (!isMsLayout(*this))
+ if (!isMsLayout(*this, RD))
OS << " DataSize:" << toBits(Info.getDataSize()) << "\n";
OS << " Alignment:" << toBits(Info.getAlignment()) << "\n";
if (Target->defaultsToAIXPowerAlignment())
diff --git a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
index cbfa79e10bfefcc..88a766adfe82a1c 100644
--- a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
+++ b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
@@ -104,10 +104,7 @@ struct CGRecordLowering {
/// fields of the same formal type. We want to emit a layout with
/// these discrete storage units instead of combining them into a
/// continuous run.
- bool isDiscreteBitFieldABI() {
- return Context.getTargetInfo().getCXXABI().isMicrosoft() ||
- D->isMsStruct(Context);
- }
+ bool isDiscreteBitFieldABI() { return D->isMsStruct(Context); }
/// Helper function to check if we are targeting AAPCS.
bool isAAPCS() const {
@@ -122,7 +119,8 @@ struct CGRecordLowering {
///
/// Note specifically that the ms_struct attribute doesn't change this.
bool isOverlappingVBaseABI() {
- return !Context.getTargetInfo().getCXXABI().isMicrosoft();
+ return !Context.getTargetInfo().getCXXABI().isMicrosoft() ||
+ !D->isMsStruct(Context);
}
/// Wraps llvm::Type::getIntNTy with some implicit arguments.
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 79f7fba22570746..2602d1f6bedee9f 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -5645,9 +5645,13 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
if (KernelOrKext && RawTriple.isOSDarwin())
CmdArgs.push_back("-fforbid-guard-variables");
- if (Args.hasFlag(options::OPT_mms_bitfields, options::OPT_mno_ms_bitfields,
- Triple.isWindowsGNUEnvironment())) {
- CmdArgs.push_back("-mms-bitfields");
+ if (Args.hasArg(options::OPT_mms_bitfields) ||
+ Args.hasArg(options::OPT_mno_ms_bitfields)) {
+ if (Args.hasFlag(options::OPT_mms_bitfields, options::OPT_mno_ms_bitfields,
+ false))
+ CmdArgs.push_back("-mms-bitfields");
+ else
+ CmdArgs.push_back("-mno-ms-bitfields");
}
if (Triple.isWindowsGNUEnvironment()) {
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 637c6a35af6532b..a0576441c5d24a7 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -3619,6 +3619,13 @@ void CompilerInvocationBase::GenerateLangArgs(const LangOptions &Opts,
GenerateArg(Consumer, OPT_fcxx_abi_EQ,
TargetCXXABI::getSpelling(*Opts.CXXABI));
+ if (Opts.MSBitfields.has_value()) {
+ if (Opts.MSBitfields.value())
+ GenerateArg(Consumer, OPT_mms_bitfields);
+ else
+ GenerateArg(Consumer, OPT_mno_ms_bitfields);
+ }
+
if (Opts.RelativeCXXABIVTables)
GenerateArg(Consumer, OPT_fexperimental_relative_cxx_abi_vtables);
else
@@ -4153,6 +4160,11 @@ bool CompilerInvocation::ParseLangArgs(LangOptions &Opts, ArgList &Args,
options::OPT_fno_experimental_relative_cxx_abi_vtables,
TargetCXXABI::usesRelativeVTables(T));
+ if (Args.hasArg(options::OPT_mms_bitfields) ||
+ Args.hasArg(options::OPT_mno_ms_bitfields))
+ Opts.MSBitfields = Args.hasFlag(options::OPT_mms_bitfields,
+ options::OPT_mno_ms_bitfields, false);
+
// RTTI is on by default.
bool HasRTTI = Args.hasFlag(options::OPT_frtti, options::OPT_fno_rtti, true);
Opts.OmitVTableRTTI =
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index b4affa7277f6b2b..698b30f5de40434 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -18188,9 +18188,7 @@ ExprResult Sema::VerifyBitField(SourceLocation FieldLoc,
// ABI.
bool CStdConstraintViolation =
BitfieldIsOverwide && !getLangOpts().CPlusPlus;
- bool MSBitfieldViolation =
- Value.ugt(TypeStorageSize) &&
- (IsMsStruct || Context.getTargetInfo().getCXXABI().isMicrosoft());
+ bool MSBitfieldViolation = Value.ugt(TypeStorageSize) && IsMsStruct;
if (CStdConstraintViolation || MSBitfieldViolation) {
unsigned DiagWidth =
CStdConstraintViolation ? TypeWidth : TypeStorageSize;
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index be79defbbfac6f1..9d42157534eda47 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -7265,7 +7265,14 @@ void Sema::CheckCompletedCXXClass(Scope *S, CXXRecordDecl *Record) {
// 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 &&
+ // We do not support ABI compatibility mode in the other direction,
+ // however. Whenever we encounter type with gcc_struct attribute on a
+ // target with Microsoft C++ ABI, we switch layout completely to
+ // Itanium. Therefore, record ABI would be fully compatible and there
+ // is no point in emitting the diagnostic.
+ if (!Context.getLangOpts().MSBitfields.has_value() &&
+ Record->isMsStruct(Context) &&
+ !Context.getTargetInfo().defaultsToMsStruct() &&
(Record->isPolymorphic() || Record->getNumBases())) {
Diag(Record->getLocation(), diag::warn_cxx_ms_struct);
}
diff --git a/clang/test/CodeGenCXX/ms-bitfield-class-layout.cpp b/clang/test/CodeGenCXX/ms-bitfield-class-layout.cpp
new file mode 100644
index 000000000000000..6fefd3f608bd051
--- /dev/null
+++ b/clang/test/CodeGenCXX/ms-bitfield-class-layout.cpp
@@ -0,0 +1,41 @@
+// RUN: %clang_cc1 -fdump-record-layouts -Wno-incompatible-ms-struct -emit-llvm-only -triple x86_64-none-none %s -o %t.ll > %t
+// RUN: FileCheck --check-prefix=ITANIUM %s < %t
+// RUN: %clang_cc1 -fdump-record-layouts -Wno-incompatible-ms-struct -emit-llvm-only -triple x86_64-none-windows-msvc %s -o %t.ll > %t
+// RUN: FileCheck --check-prefix=MSVC %s < %t
+// RUN: %clang_cc1 -fdump-record-layouts -Wno-incompatible-ms-struct -emit-llvm-only -triple x86_64-none-windows-gnu %s -o %t.ll > %t
+// RUN: FileCheck --check-prefix=ITANIUM %s < %t
+// RUN: %clang_cc1 -fdump-record-layouts -Wno-incompatible-ms-struct -emit-llvm-only -triple x86_64-none-none -mms-bitfields %s -o %t.ll > %t
+// RUN: FileCheck --check-prefix=ITANIUM %s < %t
+// RUN: %clang_cc1 -fdump-record-layouts -Wno-incompatible-ms-struct -emit-llvm-only -triple x86_64-none-windows-msvc -mms-bitfields %s -o %t.ll > %t
+// RUN: FileCheck --check-prefix=MSVC %s < %t
+// RUN: %clang_cc1 -fdump-record-layouts -Wno-incompatible-ms-struct -emit-llvm-only -triple x86_64-none-windows-gnu -mms-bitfields %s -o %t.ll > %t
+// RUN: FileCheck --check-prefix=ITANIUM %s < %t
+// RUN: %clang_cc1 -fdump-record-layouts -Wno-incompatible-ms-struct -emit-llvm-only -triple x86_64-none-none -mno-ms-bitfields %s -o %t.ll > %t
+// RUN: FileCheck --check-prefix=ITANIUM %s < %t
+// RUN: %clang_cc1 -fdump-record-layouts -Wno-incompatible-ms-struct -emit-llvm-only -triple x86_64-none-windows-msvc -mno-ms-bitfields %s -o %t.ll > %t
+// RUN: FileCheck --check-prefix=ITANIUM-EXCEPT-FOR-S3 %s < %t
+// RUN: %clang_cc1 -fdump-record-layouts -Wno-incompatible-ms-struct -emit-llvm-only -triple x86_64-none-windows-gnu -mno-ms-bitfields %s -o %t.ll > %t
+// RUN: FileCheck --check-prefix=ITANIUM %s < %t
+
+// ITANIUM:(S1 vtable pointer)
+// ITANIUM-EXCEPT-FOR-S3:(S1 vtable pointer)
+// MSVC:(S1 vftable pointer)
+struct S1 {
+ virtual void f() {}
+};
+
+// ITANIUM:(S2 vtable pointer)
+// ITANIUM-EXCEPT-FOR-S3:(S2 vtable pointer)
+// MSVC:(S2 vtable pointer)
+struct [[gnu::gcc_struct]] S2 {
+ virtual void f() {}
+};
+
+// ITANIUM:(S3 vtable pointer)
+// ITANIUM-EXCEPT-FOR-S3:(S3 vftable pointer)
+// MSVC:(S3 vftable pointer)
+struct [[gnu::ms_struct]] S3 {
+ virtual void f() {}
+};
+
+void use(S1 s1, S2 s2, S3 s3) { s1.f(); s2.f(); s3.f(); }
diff --git a/clang/test/CodeGenCXX/ms_struct-gcc_struct.cpp b/clang/test/CodeGenCXX/ms_struct-gcc_struct.cpp
new file mode 100644
index 000000000000000..803ca59ffca584b
--- /dev/null
+++ b/clang/test/CodeGenCXX/ms_struct-gcc_struct.cpp
@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -emit-llvm-only -triple x86_64-none-none -verify=default-itanium %s
+// RUN: %clang_cc1 -emit-llvm-only -triple x86_64-none-windows-msvc -verify=default-msvc %s
+// RUN: %clang_cc1 -emit-llvm-only -triple x86_64-none-windows-gnu -verify=default-msvc %s
+// RUN: %clang_cc1 -mms-bitfields -emit-llvm-only -triple x86_64-none-none -verify=default-msvc %s
+// RUN: %clang_cc1 -mms-bitfields -emit-llvm-only -triple x86_64-none-windows-msvc -verify=default-msvc %s
+// RUN: %clang_cc1 -mms-bitfields -emit-llvm-only -triple x86_64-none-windows-gnu -verify=default-msvc %s
+// RUN: %clang_cc1 -mno-ms-bitfields -emit-llvm-only -triple x86_64-none-none -verify=default-itanium %s
+// RUN: %clang_cc1 -mno-ms-bitfields -emit-llvm-only -triple x86_64-none-windows-msvc -verify=default-itanium %s
+// RUN: %clang_cc1 -mno-ms-bitfields -emit-llvm-only -triple x86_64-none-windows-gnu -verify=default-itanium %s
+
+struct [[gnu::gcc_struct]] S1 {
+ unsigned a : 1;
+ unsigned long long b : 1;
+};
+
+struct S2 {
+ unsigned a : 1;
+ unsigned long long b : 1;
+};
+
+struct [[gnu::ms_struct]] S3 {
+ unsigned a : 1;
+ unsigned long long b : 1;
+};
+
+int a1[sizeof(S1) == 8 ? 1 : -1];
+int a2[sizeof(S2) == 8 ? 1 : -1]; // default-msvc-error {{'a2' declared as an array with a negative size}}
+int a3[sizeof(S2) == 16 ? 1 : -1]; // default-itanium-error {{'a3' declared as an array with a negative size}}
+int a4[sizeof(S3) == 16 ? 1 : -1];
diff --git a/clang/test/Driver/ms-bitfields.c b/clang/test/Driver/ms-bitfields.c
index 031ed41e2aad678..4cd3f1380e41acf 100644
--- a/clang/test/Driver/ms-bitfields.c
+++ b/clang/test/Driver/ms-bitfields.c
@@ -1,8 +1,13 @@
-// RUN: %clang -### -target x86_64-linux-gnu %s 2>&1 | FileCheck %s -check-prefix=NO-MSBITFIELDS
-// RUN: %clang -### -target x86_64-windows-gnu %s 2>&1 | FileCheck %s -check-prefix=MSBITFIELDS
+// RUN: %clang -### -target x86_64-linux-gnu %s 2>&1 | FileCheck %s -check-prefix=DEFAULT-MSBITFIELDS
+// RUN: %clang -### -target x86_64-windows-gnu %s 2>&1 | FileCheck %s -check-prefix=DEFAULT-MSBITFIELDS
+// RUN: %clang -### -target x86_64-windows-msvc %s 2>&1 | FileCheck %s -check-prefix=DEFAULT-MSBITFIELDS
+// RUN: %clang -### -mms-bitfields %s 2>&1 | FileCheck %s -check-prefix=MSBITFIELDS
+// RUN: %clang -### -mno-ms-bitfields %s 2>&1 | FileCheck %s -check-prefix=NO-MSBITFIELDS
// RUN: %clang -### -mno-ms-bitfields -mms-bitfields %s 2>&1 | FileCheck %s -check-prefix=MSBITFIELDS
// RUN: %clang -### -mms-bitfields -mno-ms-bitfields %s 2>&1 | FileCheck %s -check-prefix=NO-MSBITFIELDS
// MSBITFIELDS: -mms-bitfields
-// NO-MSBITFIELDS-NOT: -mms-bitfields
+// NO-MSBITFIELDS: -mno-ms-bitfields
+// DEFAULT-MSBITFIELDS-NOT: -mms-bitfields
+// DEFAULT-MSBITFIELDS-NOT: -mno-ms-bitfields
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