[Bug c/53896] New: nonreturning function suggested as 'pure' candidate

[Bug c/53896] New: nonreturning function suggested as 'pure' candidate

[eggert at gnu dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53896

             Bug #: 53896
           Summary: nonreturning function suggested as 'pure' candidate
    Classification: Unclassified
           Product: gcc
           Version: 4.7.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: eggert@gnu.org


I ran into this problem when building a test version of Emacs
with GCC 4.7.1 (x86-64).  I simplified it to a small test case.

Take this program:

   void lose (const char *msg) __attribute__((__noreturn__));

   const char *
   get_prefix (int running_suid)
   {
     if (!running_suid)
       lose ("Not using a shared game directory, and no prefix given.");
     return "foo";
   }

Compile it with:

   gcc -c -O2 -Wsuggest-attribute=pure t.c

The output will be:

   t.c:4:1: warning: function might be candidate for attribute 'pure' if it is
known to return normally [-Wsuggest-attribute=pure]

But the get_prefix function is obviously not a candidate for attribute
'pure', since it might not return.

This bug may be related to Bug#50021 (currently apparently fixed in
GCC 4.7.0) and to Bug#51971 (documentation unclear for 'pure').