[Bug tree-optimization/84624] New: bogus -Wstringop-truncation in a catch statement and nul assignment outside it

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84624

            Bug ID: 84624
           Summary: bogus -Wstringop-truncation in a catch statement and
                    nul assignment outside it
           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: ---

The -Wstringop-truncation warning for the strncpy call below should have been
suppressed by the subsequent assignment to d but the suppression logic is
thwarted by the __cxa_end_catch () call.

$ cat b.C && gcc -O2 -S -Wall -Wextra -fdump-tree-optimized=/dev/stdout b.C
char d[3];

void f ();

void g (const char *s)
{
  try
    {
      f ();
    }
  catch (...)
    {
      __builtin_strncpy (d, s, sizeof d);   // bogus warning
    }

  d[sizeof d - 1] = 0;   // because of this
}

b.C: In function ‘void g(const char*)’:
b.C:13:25: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned
int)’ specified bound 3 equals destination size [-Wstringop-truncation]
       __builtin_strncpy (d, s, sizeof d);   // bogus warning
       ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~

;; Function g (_Z1gPKc, funcdef_no=0, decl_uid=2362, cgraph_uid=0,
symbol_order=1)

g (const char * s)
{
  void * _1;

  <bb 2> [local count: 1073741825]:
  f ();

  <bb 3> [local count: 1073741825]:
  d[2] = 0;
  return;

  <bb 4> [count: 0]:
<L1>:
  _1 = __builtin_eh_pointer (1);
  __cxa_begin_catch (_1);
  __builtin_strncpy (&d, s_7(D), 3);
  __cxa_end_catch ();
  goto <bb 3>; [100.00%]

}