diff options
Diffstat (limited to 'lib/verify.h')
| -rw-r--r-- | lib/verify.h | 45 |
1 files changed, 8 insertions, 37 deletions
diff --git a/lib/verify.h b/lib/verify.h index ca2a1540736..fa1ed717d0e 100644 --- a/lib/verify.h +++ b/lib/verify.h @@ -246,13 +246,6 @@ template <int w> /* @assert.h omit start@ */ -#if defined __has_builtin -/* <https://clang.llvm.org/docs/LanguageExtensions.html#builtin-functions> */ -# define _GL_HAS_BUILTIN_ASSUME __has_builtin (__builtin_assume) -#else -# define _GL_HAS_BUILTIN_ASSUME 0 -#endif - #if 3 < __GNUC__ + (3 < __GNUC_MINOR__ + (4 <= __GNUC_PATCHLEVEL__)) # define _GL_HAS_BUILTIN_TRAP 1 #elif defined __has_builtin @@ -312,36 +305,14 @@ template <int w> Although assuming R can help a compiler generate better code or diagnostics, performance can suffer if R uses hard-to-optimize - features such as function calls not inlined by the compiler. */ - -/* Use __builtin_assume in preference to __builtin_unreachable, because - in clang versions 8.0.x and older, the definition based on - __builtin_assume has an effect on optimizations, whereas the definition - based on __builtin_unreachable does not. (GCC so far has only - __builtin_unreachable.) */ -#if _GL_HAS_BUILTIN_ASSUME -/* Use __builtin_constant_p to help clang's data-flow analysis for the case - assume (0). - Use a temporary variable, to avoid a clang warning - "the argument to '__builtin_assume' has side effects that will be discarded" - if R contains invocations of functions not marked as 'const'. - The type of the temporary variable can't be __typeof__ (R), because that - does not work on bit field expressions. Use '_Bool' or 'bool' as type - instead. */ -# if defined __cplusplus -# define assume(R) \ - (__builtin_constant_p (R) && !(R) \ - ? (void) __builtin_unreachable () \ - : (void) ({ bool _gl_verify_temp = (R); \ - __builtin_assume (_gl_verify_temp); })) -# else -# define assume(R) \ - (__builtin_constant_p (R) && !(R) \ - ? (void) __builtin_unreachable () \ - : (void) ({ _Bool _gl_verify_temp = (R); \ - __builtin_assume (_gl_verify_temp); })) -# endif -#elif _GL_HAS_BUILTIN_UNREACHABLE + features such as function calls not inlined by the compiler. + + Avoid Clang's __builtin_assume, as it breaks GNU Emacs master + as of 2020-08-23T21:09:49Z!eggert@cs.ucla.edu; see + <https://bugs.gnu.org/43152#71>. It's not known whether this breakage + is a Clang bug or an Emacs bug; play it safe for now. */ + +#if _GL_HAS_BUILTIN_UNREACHABLE # define assume(R) ((R) ? (void) 0 : __builtin_unreachable ()) #elif 1200 <= _MSC_VER # define assume(R) __assume (R) |