[Bug tree-optimization/86889] s390x gcc build fails when configured with --disable-checking

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86889

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2018-08-09
     Ever confirmed|0                           |1

--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
Thank you.  With the small test case I can confirm the warning even on
x86_64-linux.  I've reduced it a tiny bit more.  Here's the smaller test case
and the VRP output:

$ cat f.c && gcc -S -O2 -Wall -fdump-tree-vrp=/dev/stdout f.c
struct a { long b[2]; };

int d (struct a *p)
{
  int g = 1;

  for (; g >= 0; g--)
    if (p->b[g])
      return g;

  __builtin_unreachable ();
}

;; Function d (d, funcdef_no=0, decl_uid=1907, cgraph_uid=1, symbol_order=0)

;; 2 loops found
;;
;; Loop 0
;;  header 0, latch 1
;;  depth 0, outer -1
;;  nodes: 0 1 2 3 4 5
;; 2 succs { 5 3 }
;; 3 succs { 5 4 }
;; 4 succs { 5 }
;; 5 succs { 1 }

SSA replacement table
N_i -> { O_1 ... O_j } means that N_i replaces O_1, ..., O_j

p_9 -> { p_4(D) }
Incremental SSA update started at block: 2
Number of blocks in CFG: 6
Number of blocks to update: 3 ( 50%)



Value ranges after VRP:

_1: VARYING
p_4(D): VARYING
g_5: [0, 1]
_8: VARYING
p_9: ~[0B, 0B]  EQUIVALENCES: { p_4(D) } (1 elements)
_11: VARYING


f.c: In function ‘d’:
f.c:8:13: warning: array subscript -1 is below array bounds of ‘long int[2]’
[-Warray-bounds]
8 |     if (p->b[g])
  |         ~~~~^~~
d (struct a * p)
{
  int g;
  long int _1;
  long int _8;
  long int _11;

  <bb 2> [local count: 357878152]:
  _8 = p_4(D)->b[1];
  if (_8 != 0)
    goto <bb 5>; [33.33%]
  else
    goto <bb 3>; [66.67%]

  <bb 3> [local count: 238597364]:
  _11 = p_4(D)->b[0];
  if (_11 != 0)
    goto <bb 5>; [33.33%]
  else
    goto <bb 4>; [66.67%]

  <bb 4> [local count: 159072864]:
  _1 = p_4(D)->b[-1];

  <bb 5> [local count: 357878150]:
  # g_5 = PHI <-1(4), 1(2), 0(3)>
  return g_5;

}



;; Function d (d, funcdef_no=0, decl_uid=1907, cgraph_uid=1, symbol_order=0)

;; 2 loops found
;;
;; Loop 0
;;  header 0, latch 1
;;  depth 0, outer -1
;;  nodes: 0 1 2 3 4
;; 2 succs { 4 3 }
;; 3 succs { 4 }
;; 4 succs { 1 }

SSA replacement table
N_i -> { O_1 ... O_j } means that N_i replaces O_1, ..., O_j

p_2 -> { p_4(D) }
Incremental SSA update started at block: 2
Number of blocks in CFG: 5
Number of blocks to update: 2 ( 40%)



Value ranges after VRP:

_1: [0, +INF]
p_2: ~[0B, 0B]  EQUIVALENCES: { p_4(D) } (1 elements)
p_4(D): VARYING
g_5: [0, 1]
_8: VARYING
_9: [0, 1]
_11: VARYING
_12: [-1, 0]


d (struct a * p)
{
  int g;
  _Bool _1;
  long int _8;
  int _9;
  long int _11;
  int _12;

  <bb 2> [local count: 357878152]:
  _8 = p_4(D)->b[1];
  if (_8 != 0)
    goto <bb 4>; [33.33%]
  else
    goto <bb 3>; [66.67%]

  <bb 3> [local count: 238597364]:
  _11 = p_4(D)->b[0];
  _1 = _11 == 0;
  _9 = (int) _1;
  _12 = -_9;

  <bb 4> [local count: 357878150]:
  # g_5 = PHI <_12(3), 1(2)>
  return g_5;

}