[clang] [clang] Add /Zc:__STDC__ flag to clang-cl (PR #68690)
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Sat Mar 9 17:50:15 PST 2024
https://github.com/xbjfk updated https://github.com/llvm/llvm-project/pull/68690
>From adfced08cd4c150b02345629e1bd9c5bc4681f09 Mon Sep 17 00:00:00 2001
From: Reagan Bohan <xbjfk.github at gmail.com>
Date: Sun, 10 Mar 2024 01:49:37 +0000
Subject: [PATCH] [clang] Add /Zc:__STDC__ flag to clang-cl
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.
---
clang/docs/ReleaseNotes.rst | 3 +++
clang/include/clang/Basic/LangOptions.def | 1 +
clang/include/clang/Driver/Options.td | 7 +++++++
clang/lib/Driver/ToolChains/Clang.cpp | 9 ++++++++-
clang/lib/Frontend/InitPreprocessor.cpp | 3 ++-
clang/test/Driver/cl-zc.cpp | 9 +++++++++
clang/test/Driver/ms-define-stdc.c | 11 +++++++++++
7 files changed, 41 insertions(+), 2 deletions(-)
create mode 100644 clang/test/Driver/ms-define-stdc.c
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 3b89d5a8720785..fde603a6245247 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -177,6 +177,9 @@ New Compiler Flags
- ``-Wmissing-designated-field-initializers``, grouped under ``-Wmissing-field-initializers``.
This diagnostic can be disabled to make ``-Wmissing-field-initializers`` behave
like it did before Clang 18.x. Fixes (`#56628 <https://github.com/llvm/llvm-project/issues/68933>`_)
+- ``-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 472fd9f093a718..121db13277b474 100644
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -291,6 +291,7 @@ LANGOPT(HIPStdParInterposeAlloc, 1, 0, "Replace allocations / deallocations with
LANGOPT(OpenACC , 1, 0, "OpenACC Enabled")
+LANGOPT(MSVCEnableStdcMacro , 1, 0, "Define __STDC__ with '-fms-compatability'")
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 aca8c9b0d5487a..7a24f26530c60f 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -2934,6 +2934,10 @@ 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]>,
+ 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">,
@@ -8172,6 +8176,9 @@ 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 cc568b9a715bbe..f9e2cb043f7b5d 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -6888,8 +6888,12 @@ 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))
@@ -8065,6 +8069,9 @@ void Clang::AddClangCLArgs(const ArgList &Args, types::ID InputType,
CmdArgs.push_back("-fno-wchar");
}
+ if (!types::isCXX(InputType) && Args.hasArg(options::OPT_fms_define_stdc))
+ CmdArgs.push_back("-fms-define-stdc");
+
if (Args.hasArg(options::OPT__SLASH_kernel)) {
llvm::Triple::ArchType Arch = getToolChain().getArch();
std::vector<std::string> Values =
diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index 48ad92063bd461..f3315a1d9a8b74 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -433,7 +433,8 @@ 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/cl-zc.cpp b/clang/test/Driver/cl-zc.cpp
index c7cf5b1b6525be..16df6799d5efaa 100644
--- a/clang/test/Driver/cl-zc.cpp
+++ b/clang/test/Driver/cl-zc.cpp
@@ -123,6 +123,15 @@
// CHECK-CHAR8_T_: "-fno-char8_t"
+// 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
// These never warn, but don't have an effect yet.
diff --git a/clang/test/Driver/ms-define-stdc.c b/clang/test/Driver/ms-define-stdc.c
new file mode 100644
index 00000000000000..d5e873d21a76b5
--- /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'
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