[Bug tree-optimization/83776] New: missing -Warray-bounds indexing past the end of a string literal

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83776

            Bug ID: 83776
           Summary: missing -Warray-bounds indexing past the end of a
                    string literal
           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: ---

MEM_REF gets in the way of diagnosing -Warray-bounds in other cases where it's
quite difficult to deal with but it should be straightforward to diagnose the
cases where the operand is a string literal like in the test case below.

$ cat d.c && gcc -O2 -S -Wall -fdump-tree-optimized=/dev/stdout d.c
#define S "0123456789"

int f (void)
{
  return S[16];   // -Warray-bounds (good)
}

int g (void)
{
  const char *p = S + 16;   // missing -Warray-bounds
  return *p;                // either here or above 
}

int h (void)
{
  const char *p = S;
  return p[16];   // missing -Warray-bounds
}

d.c: In function ‘f’:
d.c:5:11: warning: array subscript 16 is above array bounds of ‘char[11]’
[-Warray-bounds]
   return S[16];   // -Warray-bounds (good)
           ^

;; Function f (f, funcdef_no=0, decl_uid=1950, cgraph_uid=0, symbol_order=0)

f ()
{
  char _1;
  int _2;

  <bb 2> [local count: 1073741825]:
  _1 = "0123456789"[16];
  _2 = (int) _1;
  return _2;

}



;; Function g (g, funcdef_no=1, decl_uid=1953, cgraph_uid=1, symbol_order=1)

g ()
{
  char _1;
  int _3;

  <bb 2> [local count: 1073741825]:
  _1 = MEM[(const char *)"0123456789" + 16B];
  _3 = (int) _1;
  return _3;

}



;; Function h (h, funcdef_no=4, decl_uid=1957, cgraph_uid=2, symbol_order=2)

h ()
{
  char _3;
  int _4;

  <bb 2> [local count: 1073741825]:
  _3 = MEM[(const char *)"0123456789" + 16B];
  _4 = (int) _3;
  return _4;

}