[PATCH] intprops: say why not Clang __builtin_add_overflow

[PATCH] intprops: say why not Clang __builtin_add_overflow

[Paul Eggert]

* lib/intprops.h (_GL_HAS_BUILTIN_OVERFLOW):
Mention Clang in comment, responding to a query from
Mattias Engdegård.
---
 ChangeLog      | 7 +++++++
 lib/intprops.h | 4 +++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index 2a458f077..f7fbcf413 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2019-08-24  Paul Eggert  <eggert@cs.ucla.edu>
+
+	intprops: say why not Clang __builtin_add_overflow
+	* lib/intprops.h (_GL_HAS_BUILTIN_OVERFLOW):
+	Mention Clang in comment, responding to a query from
+	Mattias Engdegård.
+
 2019-08-24  Bruno Haible  <bruno@clisp.org>
 
 	doc: Document most of the files outside of modules.
diff --git a/lib/intprops.h b/lib/intprops.h
index 2c0256883..fbbc3cffe 100644
--- a/lib/intprops.h
+++ b/lib/intprops.h
@@ -220,7 +220,9 @@
    ? (a) < (min) >> (b)                                 \
    : (max) >> (b) < (a))
 
-/* True if __builtin_add_overflow (A, B, P) works when P is non-null.  */
+/* True if __builtin_add_overflow (A, B, P) works when P is non-null.
+   See <https://bugs.llvm.org/show_bug.cgi?id=16404> for why this is
+   false for Clang.  */
 #if 5 <= __GNUC__ && !defined __ICC
 # define _GL_HAS_BUILTIN_OVERFLOW 1
 #else
-- 
2.21.0