[Bug tree-optimization/79547] New: duplicate strlen calls with same argument not folded

["msebor at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79547

            Bug ID: 79547
           Summary: duplicate strlen calls with same argument not folded
           Product: gcc
           Version: 7.0
            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: ---

As mentioned in bug 71315 comment 3, GCC folds the first of a series of calls
to strlen with the same argument but not the subsequent ones:

$ cat t.c && gcc -O2 -S -Wall -Wextra -fdump-tree-optimized=/dev/stdout t.c
void f (unsigned);

void f1 (void)
{
    char s[] = "1234";

    f (__builtin_strlen (s));
}

void f2 (void)
{
    char s[] = "1234";

    f (__builtin_strlen (s));
    f (__builtin_strlen (s));
}


void f3 (void)
{
    char s[] = "1234";

    f (__builtin_strlen (s));
    f (__builtin_strlen (s));
    f (__builtin_strlen (s));
}


;; Function f1 (f1, funcdef_no=0, decl_uid=1797, cgraph_uid=0, symbol_order=0)

f1 ()
{
  char s[5];

  <bb 2> [100.00%]:
  s = "1234";
  f (4);
  s ={v} {CLOBBER};
  return;

}



;; Function f2 (f2, funcdef_no=1, decl_uid=1801, cgraph_uid=1, symbol_order=1)

f2 ()
{
  char s[5];
  long unsigned int _3;
  unsigned int _4;

  <bb 2> [100.00%]:
  s = "1234";
  f (4);
  _3 = __builtin_strlen (&s);
  _4 = (unsigned int) _3;
  f (_4);
  s ={v} {CLOBBER};
  return;

}



;; Function f3 (f3, funcdef_no=2, decl_uid=1805, cgraph_uid=2, symbol_order=2)

f3 ()
{
  char s[5];
  long unsigned int _3;
  unsigned int _4;
  long unsigned int _5;
  unsigned int _6;

  <bb 2> [100.00%]:
  s = "1234";
  f (4);
  _3 = __builtin_strlen (&s);
  _4 = (unsigned int) _3;
  f (_4);
  _5 = __builtin_strlen (&s);
  _6 = (unsigned int) _5;
  f (_6);
  s ={v} {CLOBBER};
  return;

}