[Bug middle-end/97425] New: bogus array bounds in -Warray-bounds for a function array parameter

[Bug middle-end/97425] New: bogus array bounds in -Warray-bounds for a function array parameter

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97425

            Bug ID: 97425
           Summary: bogus array bounds in -Warray-bounds for a function
                    array parameter
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

The -Wartray-bounds warnings in the test case below are all expected but the
bounds of the array types referenced in the messages for f3 and and f4 don't
correspond to those in the array parameters.

In f3 the warning should mention ‘int[2][3][4]’ instead and in f4 it should
reference ‘int[1][2][3][4]’.

$ cat z.c && gcc -O2 -S -Wall z.c
void f1 (int a[4])
{
  int *p = &a[0];
  p[4] = 0;
}

void f2 (int a[3][4])
{ 
  int *p = &a[0][0];
  p[3 * 4] = 0;
}

void f3 (int a[2][3][4])
{
  int *p = &a[0][0][0];
  p[2 * 3 * 4] = 0;
}

void f4 (int a[1][2][3][4])
{
  int *p = &a[0][0][0][0];
  p[1 * 2 * 3 * 4] = 0;
}

z.c: In function ‘f1’:
z.c:4:4: warning: array subscript 4 is outside array bounds of ‘int[4]’
[-Warray-bounds]
    4 |   p[4] = 0;
      |   ~^~~
z.c:1:14: note: while referencing ‘a’
    1 | void f1 (int a[4])
      |          ~~~~^~~~
z.c: In function ‘f2’:
z.c:10:4: warning: array subscript 12 is outside array bounds of ‘int[3]’
[-Warray-bounds]
   10 |   p[3 * 4] = 0;
      |   ~^~~~~~~
z.c:7:14: note: while referencing ‘a’
    7 | void f2 (int a[3][4])
      |          ~~~~^~~~~~~
z.c: In function ‘f3’:
z.c:16:4: warning: array subscript 24 is outside array bounds of ‘int[2][4]’
[-Warray-bounds]
   16 |   p[2 * 3 * 4] = 0;
      |   ~^~~~~~~~~~~
z.c:13:14: note: while referencing ‘a’
   13 | void f3 (int a[2][3][4])
      |          ~~~~^~~~~~~~~~
z.c: In function ‘f4’:
z.c:16:16: warning: array subscript 24 is outside array bounds of
‘int[1][3][4]’ [-Warray-bounds]
   16 |   p[2 * 3 * 4] = 0;
      |   ~~~~~~~~~~~~~^~~
z.c:19:14: note: while referencing ‘a’
   19 | void f4 (int a[1][2][3][4])
      |          ~~~~^~~~~~~~~~~~~

[Bug middle-end/97425] bogus array bounds in -Warray-bounds for a function array parameter

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97425

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
In addition to the bounds in the array type the subscript in some of the
warnings issued for array parameters isn't right.

$ cat z.c && gcc -O2 -S -Wall -fdump-tree-vrp1=/dev/stdout z.c
void f (void)
{
  extern int a[2][3][4];
  a[2][0][0] = 0;            // correct subscript
}

void g (int a[2][3][4])
{ 
  a[2][0][0] = 0;            // wrong subscript
}

void h (int (*p)[2][3][4])
{
  (*p)[2][0][0] = 0;         // correct subscript
}


;; Function f (f, funcdef_no=0, decl_uid=1931, cgraph_uid=1, symbol_order=0)

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

Value ranges after VRP:



z.c: In function ‘f’:
z.c:4:4: warning: array subscript 2 is above array bounds of ‘int[2][3][4]’
[-Warray-bounds]
    4 |   a[2][0][0] = 0;            // correct subscript (2)
      |   ~^~~
z.c:3:14: note: while referencing ‘a’
    3 |   extern int a[2][3][4];
      |              ^
f ()
{
  <bb 2> [local count: 1073741824]:
  a[2][0][0] = 0;
  return;

}



;; Function g (g, funcdef_no=1, decl_uid=1936, cgraph_uid=2, symbol_order=1)

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

Value ranges after VRP:



z.c: In function ‘g’:
z.c:9:4: warning: array subscript 24 is outside array bounds of ‘int[2][4]’
[-Warray-bounds]
    9 |   a[2][0][0] = 0;            // wrong subscript (24)
      |   ~^~~
z.c:7:13: note: while referencing ‘a’
    7 | void g (int a[2][3][4])
      |         ~~~~^~~~~~~~~~
g (int[3][4] * a)
{
  <bb 2> [local count: 1073741824]:
  MEM[(int[3][4] *)a_1(D) + 96B][0][0] = 0;
  return;

}



;; Function h (h, funcdef_no=2, decl_uid=1939, cgraph_uid=3, symbol_order=2)

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

Value ranges after VRP:



z.c: In function ‘h’:
z.c:14:7: warning: array subscript 2 is above array bounds of ‘int[2][3][4]’
[-Warray-bounds]
   14 |   (*p)[2][0][0] = 0;         // correct subscript (2)
      |   ~~~~^~~
z.c:12:15: note: while referencing ‘p’
   12 | void h (int (*p)[2][3][4])
      |         ~~~~~~^~~~~~~~~~~
h (int[2][3][4] * p)
{
  <bb 2> [local count: 1073741824]:
  (*p_2(D))[2][0][0] = 0;
  return;

}

[Bug middle-end/97425] bogus array bounds in -Warray-bounds for a function array parameter

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97425

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-09-26
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.