[Bug c++/89149] Out of bounds array access not detected as ill-formed in a constant expression context in some cases

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89149

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2019-02-07
                 CC|                            |msebor at gcc dot gnu.org
             Blocks|                            |56456, 55004
     Ever confirmed|0                           |1

--- Comment #5 from Martin Sebor <msebor at gcc dot gnu.org> ---
Confirmed.  The missing diagnostic isn't specific to C++ but also affects C. 
The problem is worse in C++ because it requires an error in the constexpr
context.

$ cat pr89149.c && gcc -O2 -S -Wall -Warray-bounds=2
-fdump-tree-optimized=/dev/stdout pr89149.c
int f (void)
{
  char a = (&(&(&"abc"[3])[-1])[-2])[5];
  return a;
}

int g (void)
{
  char a = (&(&(&"abc"[2])[-1])[-3])[4];
  return a;
}
pr89149.c: In function ‘f’:
pr89149.c:3:37: warning: array subscript 5 is outside array bounds of ‘char[4]’
[-Warray-bounds]
    3 |   char a = (&(&(&"abc"[3])[-1])[-2])[5];
      |            ~~~~~~~~~~~~~~~~~~~~~~~~~^~~

;; Function f (f, funcdef_no=0, decl_uid=1906, cgraph_uid=1, symbol_order=0)

f ()
{
  char a;
  int _3;

  <bb 2> [local count: 1073741824]:
  a_2 = MEM[(char *)"abc" + 5B];
  _3 = (int) a_2;
  return _3;

}



;; Function g (g, funcdef_no=1, decl_uid=1910, cgraph_uid=2, symbol_order=1)

g ()
{
  <bb 2> [local count: 1073741824]:
  return 99;

}


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55004
[Bug 55004] [meta-bug] constexpr issues
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56456
[Bug 56456] [meta-bug] bogus/missing -Warray-bounds