[Bug middle-end/101679] New: duplicate warning offset outside bounds of constant string

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101679

            Bug ID: 101679
           Summary: duplicate warning offset outside bounds of constant
                    string
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

Only one instance of -Warray-bounds should be reported the access below but GCC
issues two.  The warning is issued from c_strlen() with the first instance
during lowering and the second during (or just before) expansion.  The first
instance calls suppress_warning(arg, OPT_Warray_bounds) which is checked again
before issuing the second instance by calling warning_suppressed_p (arg,
OPT_Warray_bounds).  The problem is that the first time arg is an ADDR_EXPR but
VAR_DECL the second.  Stripping the ADDR_EXPR and disabling the warning for its
operand is not a solution because it would disable warnings for invalid uses of
the same operand in other statements, both in the same function or (for global
variables) in others.

$ cat a.c && gcc -S -Wall a.c 
const char s0[0] = { };

char* f (char *d)
{
  return __builtin_strcpy (d, s0);
}

a.c: In function ‘f’:
a.c:5:31: warning: offset ‘0’ outside bounds of constant string
[-Warray-bounds]
    5 |   return __builtin_strcpy (d, s0);
      |                               ^~
a.c:1:12: note: ‘s0’ declared here
    1 | const char s0[0] = { };
      |            ^~
a.c:5:10: warning: offset ‘0’ outside bounds of constant string
[-Warray-bounds]
    5 |   return __builtin_strcpy (d, s0);
      |          ^~~~~~~~~~~~~~~~~~~~~~~~
a.c:1:12: note: ‘s0’ declared here
    1 | const char s0[0] = { };
      |            ^~