1 files changed, 25 insertions, 16 deletions

diff --git a/lib/verify.h b/lib/verify.h
index 58172f3cb7f..d485a0283a9 100644
--- a/lib/verify.h
+++ b/lib/verify.h
@@ -23,11 +23,15 @@
 
 /* Define _GL_HAVE__STATIC_ASSERT to 1 if _Static_assert (R, DIAGNOSTIC)
    works as per C11.  This is supported by GCC 4.6.0 and later, in C
-   mode.
+   mode, and by clang (also in C++ mode).
 
    Define _GL_HAVE__STATIC_ASSERT1 to 1 if _Static_assert (R) works as
-   per C2X, and define _GL_HAVE_STATIC_ASSERT1 if static_assert (R)
-   works as per C++17.  This is supported by GCC 9.1 and later.
+   per C2X.  This is supported by GCC 9.1 and later, and by clang in
+   C++1z mode.
+
+   Define _GL_HAVE_STATIC_ASSERT1 if static_assert (R) works as per
+   C++17.  This is supported by GCC 9.1 and later, and by clang in
+   C++1z mode.
 
    Support compilers claiming conformance to the relevant standard,
    and also support GCC when not pedantic.  If we were willing to slow
@@ -35,7 +39,8 @@
    since this affects only the quality of diagnostics, why bother?  */
 #ifndef __cplusplus
 # if (201112L <= __STDC_VERSION__ \
-      || (!defined __STRICT_ANSI__ && 4 < __GNUC__ + (6 <= __GNUC_MINOR__)))
+      || (!defined __STRICT_ANSI__ \
+          && (4 < __GNUC__ + (6 <= __GNUC_MINOR__) || 4 <= __clang_major__)))
 #  define _GL_HAVE__STATIC_ASSERT 1
 # endif
 # if (202000L <= __STDC_VERSION__ \
@@ -43,7 +48,15 @@
 #  define _GL_HAVE__STATIC_ASSERT1 1
 # endif
 #else
-# if 201703L <= __cplusplus || 9 <= __GNUC__
+# if 4 <= __clang_major__
+#  define _GL_HAVE__STATIC_ASSERT 1
+# endif
+# if 4 <= __clang_major__ && 201411 <= __cpp_static_assert
+#  define _GL_HAVE__STATIC_ASSERT1 1
+# endif
+# if 201703L <= __cplusplus \
+     || 9 <= __GNUC__ \
+     || (4 <= __clang_major__ && 201411 <= __cpp_static_assert)
 #  define _GL_HAVE_STATIC_ASSERT1 1
 # endif
 #endif
@@ -233,13 +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
@@ -299,11 +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 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)