2020-08-17 Paul Eggert <eggert@cs.ucla.edu>
+ 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.
+
libc-config: avoid Clang’s __diagnose_if__
* lib/cdefs.h (__warndecl, __warnattr, __errordecl):
For now, do not use __diagnose_if__ here, as this fails
/* @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
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 Clang’s __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)