[clang] [MinGW] Set a predefined __GXX_TYPEINFO_EQUALITY_INLINE=0 for…

[mstorsjo]

… MinGW targets

libstdc++ requires this define to match what is predefined in GCC for the ABI of this platform; GCC hardcodes this define for all mingw configurations in gcc/config/i386/cygming.h.

(It also defines __GXX_MERGED_TYPEINFO_NAMES=0, but that happens to match the defaults in libstdc++ headers, so there's no similar need to define it in Clang.)

This fixes a Clang/libstdc++ interop issue discussed at https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110572.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Martin Storsjö (mstorsjo)

Changes

… MinGW targets

libstdc++ requires this define to match what is predefined in GCC for the ABI of this platform; GCC hardcodes this define for all mingw configurations in gcc/config/i386/cygming.h.

(It also defines __GXX_MERGED_TYPEINFO_NAMES=0, but that happens to match the defaults in libstdc++ headers, so there's no similar need to define it in Clang.)

This fixes a Clang/libstdc++ interop issue discussed at https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110572.

---

Full diff: https://github.com/llvm/llvm-project/pull/96062.diff

2 Files Affected:

• (modified) clang/lib/Frontend/InitPreprocessor.cpp (+6)
• (modified) clang/test/Preprocessor/predefined-win-macros.c (+10)

diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index e8c8a5175f8f4..2d20b56966186 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -926,6 +926,12 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
   if (LangOpts.GNUCVersion && LangOpts.CPlusPlus11)
     Builder.defineMacro("__GXX_EXPERIMENTAL_CXX0X__");
 
+  if (TI.getTriple().isWindowsGNUEnvironment() && LangOpts.CPlusPlus) {
+    // Set ABI defining macros for libstdc++ for MinGW, where the
+    // default in libstdc++ differs from the defaults for this target.
+    Builder.defineMacro("__GXX_TYPEINFO_EQUALITY_INLINE", "0");
+  }
+
   if (LangOpts.ObjC) {
     if (LangOpts.ObjCRuntime.isNonFragile()) {
       Builder.defineMacro("__OBJC2__");
diff --git a/clang/test/Preprocessor/predefined-win-macros.c b/clang/test/Preprocessor/predefined-win-macros.c
index 14e2f584bd093..12e705875b123 100644
--- a/clang/test/Preprocessor/predefined-win-macros.c
+++ b/clang/test/Preprocessor/predefined-win-macros.c
@@ -163,3 +163,13 @@
 // CHECK-ARM64EC-MINGW: #define __arm64ec__ 1
 // CHECK-ARM64EC-MINGW: #define __x86_64 1
 // CHECK-ARM64EC-MINGW: #define __x86_64__ 1
+
+// RUN: %clang_cc1 -triple x86_64-windows-gnu %s -E -dM -o - \
+// RUN:   | FileCheck -match-full-lines %s --check-prefix=CHECK-MINGW-C
+
+// CHECK-MINGW-C-NOT: #define __GXX_TYPEINFO_EQUALITY_INLINE
+
+// RUN: %clang_cc1 -triple x86_64-windows-gnu -x c++ %s -E -dM -o - \
+// RUN:   | FileCheck -match-full-lines %s --check-prefix=CHECK-MINGW-CXX
+
+// CHECK-MINGW-CXX: #define __GXX_TYPEINFO_EQUALITY_INLINE 0

[mstorsjo]

CC @jwakely

[MaskRay]

The CPlusPlus condition should probably be removed.

% x86_64-w64-mingw32-gcc -dM -xc -E /dev/null | grep TYPEINFO
#define __GXX_TYPEINFO_EQUALITY_INLINE 0
#define __GXX_MERGED_TYPEINFO_NAMES 0

[mstorsjo]

Ok, done. Yeah while it doesn't serve much purpose in non-c++ mode, it doesn't hurt either and simplifies things a little bit.

[silverqx]

Do you already know in which Clang versions this will be fixed? Also thx for fixing this 👍

[mstorsjo]

Do you already know in which Clang versions this will be fixed? Also thx for fixing this 👍

The fix will be in the upcoming 19.x which is going to release candidates in August and might be released in September/October. (Although, downstreams may pick it up and backport the patch to earlier releases - msys2 does this if the fix is relevant to them.)

[silverqx]

Thx