From: Paul Eggert <eggert@cs.ucla.edu> Date: Mon, 17 Aug 2020 21:47:45 +0000 (-0700) Subject: verify: avoid __built_assume on Clang X-Git-Tag: v1.0~3708 X-Git-Url: https://gitweb.git.savannah.gnu.org/gitweb/?a=commitdiff_plain;h=90599fb7db22298ec062a75f10e1a3b4c5578c55;p=gnulib.git verify: avoid __built_assume on Clang * lib/verify.h (assume): Do not use Clang’s __builtin_assume, as Clang 9 incorrectly diagnoses arguments as having side effects even when they do not. I guess Clang 9 considers any function call as if it had a side effect here. --- diff --git a/ChangeLog b/ChangeLog index ba521c265d..9ba0cda927 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,5 +1,11 @@ 2020-08-17 Paul Eggert <eggert@cs.ucla.edu> + verify: avoid __built_assume on Clang + * lib/verify.h (assume): Do not use Clangâs __builtin_assume, as + Clang 9 incorrectly diagnoses arguments as having side effects + even when they do not. I guess Clang 9 considers any function + call as if it had a side effect here. + libc-config: avoid Clangâs __diagnose_if__ * lib/cdefs.h (__warndecl, __warnattr, __errordecl): For now, do not use __diagnose_if__ here, as this fails diff --git a/lib/verify.h b/lib/verify.h index 0ba8d57907..d485a0283a 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 @@ -312,11 +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. */ + features such as function calls not inlined by the compiler. + + Avoid Clangâs __builtin_assume, as clang 9.0.1 -Wassume can + generate a bogus diagnostic "the argument to '__builtin_assume' has + side effects that will be discarded" even when the argument has no + side effects. */ -#if _GL_HAS_BUILTIN_ASSUME -# define assume(R) __builtin_assume (R) -#elif _GL_HAS_BUILTIN_UNREACHABLE +#if _GL_HAS_BUILTIN_UNREACHABLE # define assume(R) ((R) ? (void) 0 : __builtin_unreachable ()) #elif 1200 <= _MSC_VER # define assume(R) __assume (R)