[Bug tree-optimization/86042] New: [8 Regression] missing strlen optimization after second strcpy

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86042

            Bug ID: 86042
           Summary: [8 Regression] missing strlen optimization after
                    second strcpy
           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: ---

GCC 7 and prior eliminate both strlen() calls in the program below.  GCC 8 only
eliminates the first call, emitting worse code than prior versions.

$ cat c.c && gcc -O2 -S -Wall -Wextra -fdump-tree-optimized=/dev/stdout c.c
char a[3];

int main ()
{
  int n[2];

  __builtin_strcpy (a, "12");
  n[0] = __builtin_strlen (a);

  __builtin_strcpy (a, "12");
  n[1] = __builtin_strlen (a);

  __builtin_printf ("%i %i\n", n[0], n[1]);
}

;; Function main (main, funcdef_no=0, decl_uid=1956, cgraph_uid=0,
symbol_order=1) (executed once)

main ()
{
  long unsigned int _3;
  int _4;

  <bb 2> [local count: 1073741825]:
  MEM[(char * {ref-all})&a] = MEM[(char * {ref-all})"12"];
  _3 = __builtin_strlen (&a);
  _4 = (int) _3;
  __builtin_printf ("%i %i\n", 2, _4);
  return 0;
}