[Bug c/85562] New: -Wsuggest-attribute=malloc misleads about "returning normally"

["eggert at cs dot ucla.edu" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85562

            Bug ID: 85562
           Summary: -Wsuggest-attribute=malloc misleads about "returning
                    normally"
           Product: gcc
           Version: 8.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: eggert at cs dot ucla.edu
  Target Milestone: ---

I ran into this problem when compiling Emacs with gcc (GCC) 8.0.1 20180324 (Red
Hat 8.0.1-0.20) x86-64.  When I use this command:

gcc -S -O2 -Wsuggest-attribute=malloc sample.c

to compile the following program:

#include <stdlib.h>

void *
xmalloc (size_t n)
{
  if (n == 0)
    abort ();
  return malloc (n);
}

the output is:

sample.c: In function ‘xmalloc’:
sample.c:4:1: warning: function might be candidate for attribute ‘malloc’ if it
is known to return normally [-Wsuggest-attribute=malloc]
 xmalloc (size_t n)
 ^~~~~~~

The phrase "if it is known to return normally" is misleading and should be
removed from the diagnostic.  Although the phrase is borrowed from similar
diagnostics for pure functions where the phrase is relevant (see GCC bug
51971), whether a function is known to return normally is irrelevant to how the
compiler should optimize the malloc attribute.  The GCC manual does not state
that the malloc attribute should be applied only to functions that return
normally, and GCC's diagnostics should not imply otherwise.