[Bug ipa/109914] New: --suggest-attribute=pure misdiagnoses static functions

["bruno at clisp dot org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109914

            Bug ID: 109914
           Summary: --suggest-attribute=pure misdiagnoses static functions
           Product: gcc
           Version: 13.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ipa
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bruno at clisp dot org
                CC: marxin at gcc dot gnu.org
  Target Milestone: ---

Created attachment 55125
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55125&action=edit
test case

GCC's --suggest-attribute=pure diagnoses static functions, even though the
'pure' attribute is useless for static functions (after all, the compiler has
deduced the property on its own). This is leading to my having to litter code
with '__attribute__ (pure)' declarations merely to pacify GCC. GCC should treat
the 'pure' attribute like other attributes (e.g., malloc, const), and should
issue the diagnostic only for non-static functions where the attribute is in
fact useful.

How to reproduce:
$ gcc --version
gcc (GCC) 13.1.0
...
$ gcc -Wsuggest-attribute=pure -O2 -S file-has-acl.c
file-has-acl.c: In function ‘have_xattr’:
file-has-acl.c:3385:14: warning: function might be candidate for attribute
‘pure’ if it is known to return normally [-Wsuggest-attribute=pure]
 3385 | static _Bool have_xattr (char const *attr, char const *listbuf, ssize_t
listsize)
      |              ^~~~~~~~~~