Re: 'const' function attribute

[Bruno Haible]

Hi Paul,

I did this:
>       (gl_tree_iterator_free): Mark as 'const'.

and now GCC gives me this warning:

  In file included from gl_avltree_oset.c:46:
  gl_anytree_oset.h:442:1: warning: 'const' attribute on function returning 
'void' [-Wattributes]

for

  static void _GL_ATTRIBUTE_CONST
  gl_tree_iterator_free (gl_oset_iterator_t *iterator 
_GL_ATTRIBUTE_MAYBE_UNUSED)
  {
  }

The description you added in attribute.h:

  /* It is OK for a compiler to omit duplicate calls with the same arguments.
     This attribute is safe for a function that neither depends on
     nor affects observable state, and always returns exactly once -
     e.g., does not loop forever, and does not call longjmp.
     (This attribute is stricter than ATTRIBUTE_PURE.)  */
  /* Applies to: functions.  */
  #define ATTRIBUTE_CONST _GL_ATTRIBUTE_CONST

makes perfect sense for a function that returns void. However, in view of the
GCC documentation [1] the GCC warning basically means "the 'const' attribute
here does not help me in doing common-subexpression elimination, since the
return type is 'void'".

To me, this is a pointless warning. Would you agree that a bug report to
the GCC people makes sense?

Bruno

[1] 
https://gcc.gnu.org/onlinedocs/gcc-10.2.0/gcc/Common-Function-Attributes.html