Re: undefined behaviour findings in bitset

[Akim Demaille]

Hi Bruno,

> Le 19 mars 2019 à 07:07, Akim Demaille <address@hidden> a écrit :
> 
> Hi Bruno,
> 
>> Le 18 mars 2019 à 22:03, Bruno Haible <address@hidden> a écrit :
>> 
>> Hi Akim,
>> 
>>> Also, the relationship with noreturn.h is not completely clear for
>>> me either.
>> 
>> There are a couple of comment in noreturn.h lines 33..41. But I agree,
>> some text in the documentation would be better.
>> 
>>> Clang 7 pretends to be GCC 4.2 (__GNUC__ __GNUC_MINOR__).
>> 
>>> For instance I see it already has the above fix for
>>> GCC 4.7, but in a different way.
>>> 
>>> /* Use ISO C++11 syntax when the compiler supports it. */
>>> # if (__cplusplus >= 201103 && !(__GNUC__ == 4 && __GNUC_MINOR__ == 7)) \
>>> || (_MSC_VER >= 1900)
>>> # define _GL_NORETURN_FUNC [[noreturn]]
>> 
>> Right, this snippet gets clang++ and MSVC++ support right. How about this
>> patch?
> 
> Yes, I agree this is the best option so far, thanks!

Well, it does not work with G++ in C++98 mode: _Noreturn is not supported there.

This works with Bison's CI:

commit b2a7dec46c0b702b5f7618994641e7381c8ff86f
Author: Akim Demaille <address@hidden>
Date:   Fri Mar 22 08:25:53 2019 +0100

  _Noreturn: beware of C's _Noreturn in C++ pre C++11

  * lib/_Noreturn.h, m4/gnulib-common.m4: Using C's _Noreturn in
  C++98 appears to be supported by Clang, but not by GCC nor ICC.

diff --git a/ChangeLog b/ChangeLog
index 62c522e65..b694c3512 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2019-03-22  Akim Demaille  <address@hidden>
+
+       _Noreturn: beware of C's _Noreturn in C++ pre C++11.
+       * lib/_Noreturn.h, m4/gnulib-common.m4: Using C's _Noreturn in
+       C++98 appears to be supported by Clang, but not by GCC nor ICC.
+
2019-03-19  Akim Demaille  <address@hidden>

        bitset: fix memory leaks
diff --git a/lib/_Noreturn.h b/lib/_Noreturn.h
index 1629cef39..7594e4b0c 100644
--- a/lib/_Noreturn.h
+++ b/lib/_Noreturn.h
@@ -3,8 +3,9 @@
     && ((201103 <= __cplusplus && !(__GNUC__ == 4 && __GNUC_MINOR__ == 7)) \
         || (defined _MSC_VER && 1900 <= _MSC_VER)))
#  define _Noreturn [[noreturn]]
-# elif (201112 <= (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0) \
-        || 4 < __GNUC__ + (7 <= __GNUC_MINOR__))
+# elif ((!defined __cplusplus || defined __clang__)                     \
+        && (201112 <= (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0)  \
+            || 4 < __GNUC__ + (7 <= __GNUC_MINOR__)))
  /* _Noreturn works as-is.  */
# elif 2 < __GNUC__ + (8 <= __GNUC_MINOR__) || 0x5110 <= __SUNPRO_C
#  define _Noreturn __attribute__ ((__noreturn__))
diff --git a/m4/gnulib-common.m4 b/m4/gnulib-common.m4
index 8ad963e35..57b94ed53 100644
--- a/m4/gnulib-common.m4
+++ b/m4/gnulib-common.m4
@@ -21,8 +21,9 @@ AC_DEFUN([gl_COMMON_BODY], [
     && ((201103 <= __cplusplus && !(__GNUC__ == 4 && __GNUC_MINOR__ == 7)) \
         || (defined _MSC_VER && 1900 <= _MSC_VER)))
#  define _Noreturn [[noreturn]]
-# elif (201112 <= (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0) \
-        || 4 < __GNUC__ + (7 <= __GNUC_MINOR__))
+# elif ((!defined __cplusplus || defined __clang__) \
+        && (201112 <= (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0)  \
+            || 4 < __GNUC__ + (7 <= __GNUC_MINOR__)))
  /* _Noreturn works as-is.  */
# elif 2 < __GNUC__ + (8 <= __GNUC_MINOR__) || 0x5110 <= __SUNPRO_C
#  define _Noreturn __attribute__ ((__noreturn__))