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[clang] Add /Zc:__STDC__ flag to clang-cl #68690

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Merged
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May 25, 2024
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[clang] Add /Zc:__STDC__ flag to clang-cl #68690

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4 changes: 4 additions & 0 deletions clang/docs/ReleaseNotes.rst
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Expand Up @@ -341,6 +341,10 @@ New Compiler Flags
``__attribute__((section(...)))``. This enables linker GC to collect unused
symbols without having to use a per-symbol section.

- ``-fms-define-stdc`` and its clang-cl counterpart ``/Zc:__STDC__``.
Matches MSVC behaviour by defining ``__STDC__`` to ``1`` when
MSVC compatibility mode is used. It has no effect for C++ code.

Deprecated Compiler Flags
-------------------------

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1 change: 1 addition & 0 deletions clang/include/clang/Basic/LangOptions.def
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Expand Up @@ -300,6 +300,7 @@ LANGOPT(HIPStdParInterposeAlloc, 1, 0, "Replace allocations / deallocations with

LANGOPT(OpenACC , 1, 0, "OpenACC Enabled")

LANGOPT(MSVCEnableStdcMacro , 1, 0, "Define __STDC__ with '-fms-compatibility'")
LANGOPT(SizedDeallocation , 1, 0, "sized deallocation")
LANGOPT(AlignedAllocation , 1, 0, "aligned allocation")
LANGOPT(AlignedAllocationUnavailable, 1, 0, "aligned allocation functions are unavailable")
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7 changes: 7 additions & 0 deletions clang/include/clang/Driver/Options.td
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Expand Up @@ -2981,6 +2981,10 @@ def fms_compatibility : Flag<["-"], "fms-compatibility">, Group<f_Group>,
Visibility<[ClangOption, CC1Option, CLOption]>,
HelpText<"Enable full Microsoft Visual C++ compatibility">,
MarshallingInfoFlag<LangOpts<"MSVCCompat">>;
def fms_define_stdc : Flag<["-"], "fms-define-stdc">, Group<f_Group>,
Visibility<[ClangOption, CC1Option, CLOption]>,
HelpText<"Define '__STDC__' to '1' in MSVC Compatibility mode">,
MarshallingInfoFlag<LangOpts<"MSVCEnableStdcMacro">>;
def fms_extensions : Flag<["-"], "fms-extensions">, Group<f_Group>,
Visibility<[ClangOption, CC1Option, CLOption]>,
HelpText<"Accept some non-standard constructs supported by the Microsoft compiler">,
Expand Down Expand Up @@ -8312,6 +8316,9 @@ def _SLASH_vd : CLJoined<"vd">, HelpText<"Control vtordisp placement">,
Alias<vtordisp_mode_EQ>;
def _SLASH_X : CLFlag<"X">,
HelpText<"Do not add %INCLUDE% to include search path">, Alias<nostdlibinc>;
def _SLASH_Zc___STDC__ : CLFlag<"Zc:__STDC__">,
HelpText<"Define __STDC__">,
Alias<fms_define_stdc>;
def _SLASH_Zc_sizedDealloc : CLFlag<"Zc:sizedDealloc">,
HelpText<"Enable C++14 sized global deallocation functions">,
Alias<fsized_deallocation>;
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6 changes: 5 additions & 1 deletion clang/lib/Driver/ToolChains/Clang.cpp
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Expand Up @@ -7027,8 +7027,12 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
options::OPT_fms_compatibility, options::OPT_fno_ms_compatibility,
(IsWindowsMSVC && Args.hasFlag(options::OPT_fms_extensions,
options::OPT_fno_ms_extensions, true)));
if (IsMSVCCompat)
if (IsMSVCCompat) {
CmdArgs.push_back("-fms-compatibility");
if (!types::isCXX(Input.getType()) &&
Args.hasArg(options::OPT_fms_define_stdc))
CmdArgs.push_back("-fms-define-stdc");
}

if (Triple.isWindowsMSVCEnvironment() && !D.IsCLMode() &&
Args.hasArg(options::OPT_fms_runtime_lib_EQ))
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3 changes: 2 additions & 1 deletion clang/lib/Frontend/InitPreprocessor.cpp
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Expand Up @@ -432,7 +432,8 @@ static void InitializeStandardPredefinedMacros(const TargetInfo &TI,
// [C++] Whether __STDC__ is predefined and if so, what its value is,
// are implementation-defined.
// (Removed in C++20.)
if (!LangOpts.MSVCCompat && !LangOpts.TraditionalCPP)
if ((!LangOpts.MSVCCompat || LangOpts.MSVCEnableStdcMacro) &&
!LangOpts.TraditionalCPP)
Builder.defineMacro("__STDC__");
// -- __STDC_HOSTED__
// The integer literal 1 if the implementation is a hosted
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11 changes: 11 additions & 0 deletions clang/test/Driver/ms-define-stdc.c
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@@ -0,0 +1,11 @@
// Note: %s must be preceded by --, otherwise it may be interpreted as a
// command-line option, e.g. on Mac where %s is commonly under /Users.
//
// Note: see also cl-zc.cpp

// RUN: %clang_cl /TC /dev/null /E -Xclang -dM /Zc:__STDC__- 2>&1 | FileCheck %s --check-prefix=ZCSTDCIGNORED
// ZCSTDCIGNORED-NOT: #define __STDC__ 1
// ZCSTDCIGNORED: argument unused during compilation

// RUN: not %clang -Xclang -fno-ms-define-stdc %s 2>&1 | FileCheck %s --check-prefix="NOARG"
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This tests that -fno-ms-define-stdc is not a cc1 option. We almost never do it. There could be a value to test whether the driver -fno-ms-define-stdc option is present.

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Hmmm, this test was requested by @AaronBallman - what would you do in this case?

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@MaskRay -- see #68690 (comment) as to why I think it's valuable to have this test (but if you think it's not a useful test, I don't insist on it).

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@MaskRay are you good now or do we need a change to move this forward?

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Sorry for the late reply. If you want to show the behavior of the driver option -fno-ms-define-stdc, feel free to add it when you think there is sufficient value.

For CC1 options, I believe we perform a negative test: hey, we check that the negative form is not present.
The value testing that seems low.

// NOARG: error: unknown argument: '-fno-ms-define-stdc'
9 changes: 9 additions & 0 deletions clang/test/Preprocessor/stdc-ms-extension.cpp
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@@ -0,0 +1,9 @@
// RUN: %clang_cl /TC /dev/null /E -Xclang -dM 2> /dev/null | FileCheck -match-full-lines %s --check-prefix=NOSTDC
// RUN: %clang_cl /TC /dev/null /E -Xclang -dM /Zc:__STDC__ 2> /dev/null | FileCheck -match-full-lines %s --check-prefix=YESSTDC
// __STDC__ should never be defined in C++ mode with fms-compatibility.
// RUN: %clang_cl /dev/null /E -Xclang -dM 2>&1 | FileCheck %s --check-prefix=NOSTDC
// RUN: %clang_cl /dev/null /E -Xclang -dM /Zc:__STDC__ 2>&1 | FileCheck %s --check-prefix=ZCSTDCIGNORED
// YESSTDC: #define __STDC__ 1
// NOSTDC-NOT: #define __STDC__ 1
// ZCSTDCIGNORED-NOT: #define __STDC__ 1
// ZCSTDCIGNORED: argument unused during compilation
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