[Bug tree-optimization/83693] New: missing strlen optimization for array of arrays

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83693

            Bug ID: 83693
           Summary: missing strlen optimization for array of arrays
           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 strlen optimization is ineffective for constant arrays of arrays like in
the case of b and c below.  It looks like the string_constant() function in
expr.c that strlen relies on isn't equipped handle multi-dimensional arrays.

$ cat z.c && gcc -O2 -S -Wall -fdump-tree-optimized=/dev/stdout z.c
const char a[4] = "012";
const char b[][4] = { "012", "234" };
const char c[][2][4] = { { "012", "234" }, { "345", "456" } };

void f0 (void)
{
  if (__builtin_strlen (a) != 3)   // folded
    __builtin_abort ();
}

void f1 (void)
{
  if (__builtin_strlen (b[1]) != 3)   // not folded
    __builtin_abort ();
}

void f2 (void)
{
  if (__builtin_strlen (c[1][1]) != 3)   // not folded
    __builtin_abort ();
}


;; Function f0 (f0, funcdef_no=0, decl_uid=1955, cgraph_uid=0, symbol_order=3)

f0 ()
{
  <bb 2> [local count: 1073741825]:
  return;

}



;; Function f1 (f1, funcdef_no=1, decl_uid=1958, cgraph_uid=1, symbol_order=4)

f1 ()
{
  long unsigned int _1;

  <bb 2> [local count: 1073741825]:
  _1 = __builtin_strlen (&b[1]);
  if (_1 != 3)
    goto <bb 3>; [0.00%]
  else
    goto <bb 4>; [99.96%]

  <bb 3> [count: 0]:
  __builtin_abort ();

  <bb 4> [local count: 1073312327]:
  return;

}



;; Function f2 (f2, funcdef_no=2, decl_uid=1961, cgraph_uid=2, symbol_order=5)

f2 ()
{
  long unsigned int _1;

  <bb 2> [local count: 1073741825]:
  _1 = __builtin_strlen (&c[1][1]);
  if (_1 != 3)
    goto <bb 3>; [0.00%]
  else
    goto <bb 4>; [99.96%]

  <bb 3> [count: 0]:
  __builtin_abort ();

  <bb 4> [local count: 1073312327]:
  return;

}