[Bug tree-optimization/84725] New: enable attribute nonstring for all narrow character types

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84725

            Bug ID: 84725
           Summary: enable attribute nonstring for all narrow character
                    types
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

Attribute nonstring newly added in GCC is only accepted on arrays or pointers
to plain char (see the test case below).  However, as discussed in the thread
Re: [PATCH] Support the nonstring variable attribute (gcc >= 8), Linux kernel
developers would find the new attribute nonstring useful with all narrow
character types, including signed char and unsigned char:
  https://www.spinics.net/lists/kernel/msg2737596.html

This bug tracks that change.

$ cat z.c && gcc -O2 -S -Wall z.c
struct S
{
  char __attribute__ ((nonstring)) a[4];
  signed char __attribute__ ((nonstring)) b[4];
  unsigned char __attribute__ ((nonstring)) c[4];

  char __attribute__ ((nonstring)) *p;
  signed char __attribute__ ((nonstring)) *q;
  unsigned char __attribute__ ((nonstring)) *r;
}; 
z.c:4:3: warning: ‘nonstring’ attribute ignored on objects of type ‘signed
char[4]’ [-Wattributes]
   signed char __attribute__ ((nonstring)) b[4];
   ^~~~~~
z.c:5:3: warning: ‘nonstring’ attribute ignored on objects of type ‘unsigned
char[4]’ [-Wattributes]
   unsigned char __attribute__ ((nonstring)) c[4];
   ^~~~~~~~
z.c:8:3: warning: ‘nonstring’ attribute ignored on objects of type ‘signed char
*’ [-Wattributes]
   signed char __attribute__ ((nonstring)) *q;
   ^~~~~~
z.c:9:3: warning: ‘nonstring’ attribute ignored on objects of type ‘unsigned
char *’ [-Wattributes]
   unsigned char __attribute__ ((nonstring)) *r;
   ^~~~~~~~