[Bug tree-optimization/86203] New: duplicate non-constant call to strlen() not folded

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86203

            Bug ID: 86203
           Summary: duplicate non-constant call to strlen() not folded
           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: ---

In the test case below, GCC emits two calls to strlen() even though only one is
necessary: the second call can be replaced by the assignment 'n1 = n0'  Cl

$ cat d.c && gcc -O2 -S -Wall -Wextra -fdump-tree-optimized=/dev/stdout d.c
unsigned n0, n1;

void f (const char *s)
{
  n0 = __builtin_strlen (s);
  n1 = __builtin_strlen (s);   // should substitute: n1 = n0;
}

;; Function f (f, funcdef_no=0, decl_uid=1958, cgraph_uid=0, symbol_order=2)

f (const char * s)
{
  long unsigned int _1;
  unsigned int _2;
  long unsigned int _3;
  unsigned int _4;

  <bb 2> [local count: 1073741825]:
  _1 = __builtin_strlen (s_6(D));
  _2 = (unsigned int) _1;
  n0 = _2;
  _3 = __builtin_strlen (s_6(D));   // unnecessary strlen() call
  _4 = (unsigned int) _3;
  n1 = _4;
  return;

}