[FrontEnd] Allow overriding the default C/C++ -std via CMake vars

Provide two new CMake cache variables -- CLANG_DEFAULT_STD_C
and CLANG_DEFAULT_STD_CXX -- that can be used to override the default
C/ObjC and C++/ObjC++ standards appropriately. They can be set to one of
the identifiers from LangStandards.def, or left unset (the default) to
respect the current platform default.

This option is mostly intended for compiler vendors that may wish
to adjust the defaults their compilers are using. For example, Gentoo
planned to use it to set clang and gcc to matching standards, so that
we could maintain as much compatibility between different compilers
as possible.

The code relies on explicit identifiers rather than the string aliases
for simplicity. This saves us from the necessity of parsing aliases at
build-time or adding additional processing at runtime. For the latter
case, it also adds trivial value check -- if incorrect value is passed,
the code simply fails to compile through referencing an undefined
constant.

If the variable is used to redefine the default standard, the explicit
value overrides the special case for PS4. It is done this way mostly
following other kinds of variables where 'platform defaults' are
redefined.

Differential Revision: https://reviews.llvm.org/D34365

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@326836 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/CMakeLists.txt b/CMakeLists.txt
index a2fcaec9c394e674bcee9e3fe4d9f32c7b60cbdb..3bf3cfdf3346086be1ec94b1b0d21d8e3cbe26f5 100644 (file)
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -212,6 +212,12 @@ set(ENABLE_LINKER_BUILD_ID OFF CACHE BOOL "pass --build-id to ld")
 set(ENABLE_X86_RELAX_RELOCATIONS OFF CACHE BOOL
     "enable x86 relax relocations by default")
 
+# TODO: verify the values against LangStandards.def?
+set(CLANG_DEFAULT_STD_C "" CACHE STRING
+  "Default standard to use for C/ObjC code (IDENT from LangStandards.def, empty for platform default)")
+set(CLANG_DEFAULT_STD_CXX "" CACHE STRING
+  "Default standard to use for C++/ObjC++ code (IDENT from LangStandards.def, empty for platform default)")
+
 set(CLANG_DEFAULT_LINKER "" CACHE STRING
   "Default linker to use (linker name or absolute path, empty for platform default)")
 

diff --git a/include/clang/Config/config.h.cmake b/include/clang/Config/config.h.cmake
index 5f420195e85cc22e5ec73c98c86478fd9bad80db..5822619a3715eed6293a563f925ae5a8666557f5 100644 (file)
--- a/include/clang/Config/config.h.cmake
+++ b/include/clang/Config/config.h.cmake
@@ -11,6 +11,12 @@
 /* Default linker to use. */
 #define CLANG_DEFAULT_LINKER "${CLANG_DEFAULT_LINKER}"
 
+/* Default C/ObjC standard to use. */
+#cmakedefine CLANG_DEFAULT_STD_C LangStandard::lang_${CLANG_DEFAULT_STD_C}
+
+/* Default C++/ObjC++ standard to use. */
+#cmakedefine CLANG_DEFAULT_STD_CXX LangStandard::lang_${CLANG_DEFAULT_STD_CXX}
+
 /* Default C++ stdlib to use. */
 #define CLANG_DEFAULT_CXX_STDLIB "${CLANG_DEFAULT_CXX_STDLIB}"
 

diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index 23f3c8fbbdc7d155bea3cd615cf7725270f8e981..ff8db474e180b649bd8f99d4177a46251a894259 100644 (file)
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -1809,18 +1809,30 @@ void CompilerInvocation::setLangDefaults(LangOptions &Opts, InputKind IK,
       break;
     case InputKind::Asm:
     case InputKind::C:
+#if defined(CLANG_DEFAULT_STD_C)
+      LangStd = CLANG_DEFAULT_STD_C;
+#else
       // The PS4 uses C99 as the default C standard.
       if (T.isPS4())
         LangStd = LangStandard::lang_gnu99;
       else
         LangStd = LangStandard::lang_gnu11;
+#endif
       break;
     case InputKind::ObjC:
+#if defined(CLANG_DEFAULT_STD_C)
+      LangStd = CLANG_DEFAULT_STD_C;
+#else
       LangStd = LangStandard::lang_gnu11;
+#endif
       break;
     case InputKind::CXX:
     case InputKind::ObjCXX:
+#if defined(CLANG_DEFAULT_STD_CXX)
+      LangStd = CLANG_DEFAULT_STD_CXX;
+#else
       LangStd = LangStandard::lang_gnucxx14;
+#endif
       break;
     case InputKind::RenderScript:
       LangStd = LangStandard::lang_c99;