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[llvm] revisions to export annotation macros to avoid compiler warnings #135995

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[llvm] revisions to export annotation macros to avoid compiler warnings #135995

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7aeebfd
[llvm] use __attribute__ for export visibility macros
andrurogerz Apr 16, 2025
c57be05
[llvm] do not define LLVM_TEMPLATE_ABI for GCC builds
andrurogerz Apr 16, 2025
3d62cf0
[llvm] check for visibility attribute
andrurogerz Apr 16, 2025
74ed68f
[llvm] additional comments
andrurogerz Apr 16, 2025
294ea13
clang format
andrurogerz Apr 16, 2025
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31 changes: 23 additions & 8 deletions llvm/include/llvm/Support/Compiler.h
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Original file line number Diff line number Diff line change
Expand Up @@ -197,17 +197,32 @@
#define LLVM_EXPORT_TEMPLATE
#endif
#define LLVM_ABI_EXPORT __declspec(dllexport)
#elif defined(__ELF__) || defined(__MINGW32__) || defined(_AIX) || \
defined(__MVS__)
#define LLVM_ABI LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
#define LLVM_TEMPLATE_ABI LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
#elif (defined(__ELF__) || defined(__MINGW32__) || defined(_AIX) || \
defined(__MVS__)) && \
__has_attribute(visibililty)
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__has_attribute is a clang extension, and would generally be defined as follows:

#if !defined(__has_attribute)
#define __has_attribute(attribute) 0
#endif

This basically means that the compiler which would previously attempted to use the GNU syntax would no longer do so if it is not clang or does not implement the clang extensions (or does not enable them by default).

// Use __attribute__((visibility(""))) syntax for visibility rather than
// [[gnu::visibility("")]] because compilers are more permissive with its
// placement.
Comment on lines +203 to +205
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This is not a compilers thing IMO. This is because the C++ generalised attributes have stricter positioning requirements. The GNU attribute parsing is far more complicated due to the long history and its organic growth. That is to say, I think that this is a property of the attribute spelling itself.

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Makes sense; will revise this comment.

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fwiw, clang is happy with the [[gnu::visibility("")]] attribute in places that gcc is not, so the comment isn't exactly wrong. Point taken, though.

#define LLVM_ABI __attribute__((visibility("default")))
#if defined(__GNUC__) && !defined(__clang__)
// GCC produces warnings on visibility attributes applied to some templates.
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Ouch! Is this really limited to just GCC? What about QCC? What about ICC (or I suppose the now deprecated ICC)? What about xLC? That is, is this potentially a clang extension?

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I suppose I could just invert this and make it clang-only? I don't think it is a clang extension, I just think clang is less whiny about attributes. I've only tested with clang and gcc.

#define LLVM_TEMPLATE_ABI
#else
#define LLVM_TEMPLATE_ABI __attribute__((visibility("default")))
#endif
#define LLVM_EXPORT_TEMPLATE
#define LLVM_ABI_EXPORT __attribute__((visibility("default")))
#elif (defined(__MACH__) || defined(__WASM__) || defined(__EMSCRIPTEN__)) && \
__has_attribute(visibility)
#define LLVM_ABI __attribute__((visibility("default")))
#define LLVM_TEMPLATE_ABI
#define LLVM_EXPORT_TEMPLATE
#define LLVM_ABI_EXPORT LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
#elif defined(__MACH__) || defined(__WASM__) || defined(__EMSCRIPTEN__)
#define LLVM_ABI LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
#define LLVM_ABI_EXPORT __attribute__((visibility("default")))
#else
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This block seems like a pretty complicated way to say:

#if !defined(_WIN32)
# if __has_attribute(__visibility)
#   define LLVM_ABI __attribute__((__visibility__("default")))
#   define LLVM_ABI_EXPORT __attribute__((__visibility__("default")))
#   if defined(__clang__)
#     define LLVM_TEMPLATE_ABI __attribute__((__visibility__("default")))
#   else
#     define LLVM_TEMPLATE_ABI
#   endif
# endif
#else

#define LLVM_ABI
#define LLVM_TEMPLATE_ABI
#define LLVM_EXPORT_TEMPLATE
#define LLVM_ABI_EXPORT LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
#define LLVM_ABI_EXPORT
#endif
#else
#define LLVM_ABI
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