[Bug tree-optimization/91147] New: strlen of conditional plus index in known range not folded

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91147

            Bug ID: 91147
           Summary: strlen of conditional plus index in known range not
                    folded
           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: ---

The strlen optimization in get_range_strlen in gimple-fold.c successfully
handles the case in f() below but misses the equivalent one in g().

$ cat b.c && gcc -O2 -S -Wall -Wextra -Wpedantic
-fdump-tree-optimized=/dev/stdout b.c
const char a3[] = "123";
const char a5[] = "12345";

void f (int i, int j)
{
  if (j < 1)
    j = 1;

  unsigned n;
  if (i)
    n = __builtin_strlen (a3 + j);
  else
    n = __builtin_strlen (a5 + j);

  if (n > 4)                          // folded to false
    __builtin_abort ();
}

void g (int i, int j)
{
  if (j < 1)
    j = 1;

  const char *p = i ? a3 : a5;

  if (__builtin_strlen (p + j) > 4)   // not folded but could be
    __builtin_abort ();
}


;; Function f (f, funcdef_no=0, decl_uid=1911, cgraph_uid=1, symbol_order=2)

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

}



;; Function g (g, funcdef_no=1, decl_uid=1916, cgraph_uid=2, symbol_order=3)

Removing basic block 3
g (int i, int j)
{
  sizetype _1;
  const char * _2;
  long unsigned int _3;
  const char * iftmp.4_4;

  <bb 2> [local count: 1073741824]:
  j_6 = MAX_EXPR <j_5(D), 1>;
  if (i_7(D) != 0)
    goto <bb 4>; [50.00%]
  else
    goto <bb 3>; [50.00%]

  <bb 3> [local count: 536870912]:

  <bb 4> [local count: 1073741824]:
  # iftmp.4_4 = PHI <&a3(2), &a5(3)>
  _1 = (sizetype) j_6;
  _2 = iftmp.4_4 + _1;
  _3 = __builtin_strlen (_2);
  if (_3 > 4)
    goto <bb 5>; [0.00%]
  else
    goto <bb 6>; [100.00%]

  <bb 5> [count: 0]:
  __builtin_abort ();

  <bb 6> [local count: 1073741824]:
  return;

}