[Bug tree-optimization/91183] New: strlen of a strcpy result with a conditional source not folded

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91183

            Bug ID: 91183
           Summary: strlen of a strcpy result with a conditional source
                    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: ---

While testing a solutuion for pr91147 I noticed that in the following GCC folds
the strlen call in f() into a constant but it doesn't know how to do that for
the second strlen call.

$ cat a.c && gcc -O2 -S -Wall -Wextra -Wpedantic
-fdump-tree-optimized=/dev/stdout a.c
void f (int i)
{
  if (__builtin_strlen (i ? "123" : "456") != 3)   // folded to false
    __builtin_abort ();
}

void g (int i)
{
  char a[4];
  __builtin_strcpy (a, i ? "123" : "456");   // transformed to MEM_REF
  if (3 != __builtin_strlen (a))             // not folded but could be
    __builtin_abort ();
}

;; Function f (f, funcdef_no=0, decl_uid=1908, cgraph_uid=1, symbol_order=0)

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

}



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

Removing basic block 3
g (int i)
{
  char a[4];
  long unsigned int _1;
  unsigned int _4;

  <bb 2> [local count: 1073741824]:
  if (i_3(D) != 0)
    goto <bb 3>; [50.00%]
  else
    goto <bb 4>; [50.00%]

  <bb 3> [local count: 536870912]:

  <bb 4> [local count: 1073741824]:
  # _4 = PHI <3552564(2), 3355185(3)>
  MEM <unsigned int> [(char * {ref-all})&a] = _4;
  _1 = __builtin_strlen (&a);
  if (_1 != 3)
    goto <bb 5>; [0.00%]
  else
    goto <bb 6>; [100.00%]

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

  <bb 6> [local count: 1073741824]:
  a ={v} {CLOBBER};
  return;

}