[Bug tree-optimization/90766] New: strlen(a + i) missing range for arrays of unknown bound with strings of known length and variable i

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90766

            Bug ID: 90766
           Summary: strlen(a + i) missing range for arrays of unknown
                    bound with strings of known length and variable i
           Product: gcc
           Version: 9.0
            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: ---

GCC manages to fold the first two conditionals involving strlen but not the
third, even though it has all the information to do that.  The
maybe_set_strlen_range() function in tree-ssa-strlen.c doesn't take the known
length of the string stored in b into consideration.

$ cat a.c && gcc -O2 -S -Wall -Wextra -Wpedantic
-fdump-tree-optimized=/dev/stdout a.c
const char s[] = "123";

void f (int i)
{
  if (__builtin_strlen (&s[i]) > 3)   // folded to false, good
    __builtin_abort ();
}

extern char a[8];

void g (int i)
{
  __builtin_strcpy (a, "123");
  if (__builtin_strlen (&s[i]) > 3)   // folded to false, good
    __builtin_abort ();
}

extern char b[];

void h (int i)
{
  __builtin_strcpy (b, "123");
  if (__builtin_strlen (&b[i]) > 3)   // not folded but could be
    __builtin_abort ();
}

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

f (int i)
{
  <bb 2> [local count: 1073741824]:
  return;

}



;; Function g (g, funcdef_no=1, decl_uid=1911, cgraph_uid=2, symbol_order=2)

g (int i)
{
  <bb 2> [local count: 1073741824]:
  __builtin_memcpy (&a, "123", 4); [tail call]
  return;

}



;; Function h (h, funcdef_no=2, decl_uid=1915, cgraph_uid=3, symbol_order=3)

h (int i)
{
  char * _1;
  long unsigned int _2;
  sizetype _7;

  <bb 2> [local count: 1073741824]:
  __builtin_memcpy (&b, "123", 4);
  _7 = (sizetype) i_5(D);
  _1 = &b + _7;
  _2 = __builtin_strlen (_1);
  if (_2 > 3)
    goto <bb 3>; [0.00%]
  else
    goto <bb 4>; [100.00%]

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

  <bb 4> [local count: 1073741824]:
  return;

}