[clang] 778dbcb - [clang] Add /Zc:__STDC__ flag to clang-cl (#68690)
via cfe-commits
cfe-commits at lists.llvm.org
Fri May 24 20:48:17 PDT 2024
Author: Reagan
Date: 2024-05-24T23:48:13-04:00
New Revision: 778dbcbbb5c4e462231e812ab463b586555b6a0a
URL: https://github.com/llvm/llvm-project/commit/778dbcbbb5c4e462231e812ab463b586555b6a0a
DIFF: https://github.com/llvm/llvm-project/commit/778dbcbbb5c4e462231e812ab463b586555b6a0a.diff
LOG: [clang] Add /Zc:__STDC__ flag to clang-cl (#68690)
This commit adds the /Zc:\_\_STDC\_\_ argument from MSVC, which defines
\_\_STDC_\_.
This means, alongside stronger feature parity with MSVC, that things
that rely on \_\_STDC\_\_, such as autoconf, can work.
Link to MSVC documentation of this flag:
https://learn.microsoft.com/en-us/cpp/build/reference/zc-stdc?view=msvc-170
Added:
clang/test/Driver/ms-define-stdc.c
clang/test/Preprocessor/stdc-ms-extension.cpp
Modified:
clang/docs/ReleaseNotes.rst
clang/include/clang/Basic/LangOptions.def
clang/include/clang/Driver/Options.td
clang/lib/Driver/ToolChains/Clang.cpp
clang/lib/Frontend/InitPreprocessor.cpp
Removed:
################################################################################
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index e40b236c914d9..d023f53754cb3 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -342,6 +342,10 @@ 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
-------------------------
diff --git a/clang/include/clang/Basic/LangOptions.def b/clang/include/clang/Basic/LangOptions.def
index 09eb92d6f10d2..4061451b2150a 100644
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -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")
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 9a5bffce20460..de2f245fb29f8 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -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">,
@@ -8306,6 +8310,9 @@ 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>;
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index adb1b2ff566cb..97e451cfe2acb 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -7026,8 +7026,12 @@ 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))
diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index 68760e00003e0..e8c8a5175f8f4 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -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
diff --git a/clang/test/Driver/ms-define-stdc.c b/clang/test/Driver/ms-define-stdc.c
new file mode 100644
index 0000000000000..d5e873d21a76b
--- /dev/null
+++ b/clang/test/Driver/ms-define-stdc.c
@@ -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"
+// NOARG: error: unknown argument: '-fno-ms-define-stdc'
diff --git a/clang/test/Preprocessor/stdc-ms-extension.cpp b/clang/test/Preprocessor/stdc-ms-extension.cpp
new file mode 100644
index 0000000000000..6e9fa6055306e
--- /dev/null
+++ b/clang/test/Preprocessor/stdc-ms-extension.cpp
@@ -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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