[Bug tree-optimization/96621] New: fold strlen relational expressions after nul stores

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96621

            Bug ID: 96621
           Summary: fold strlen relational expressions after nul stores
           Product: gcc
           Version: 11.0
            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: ---

strlen(s) <= N can be folded to true after nul has been stored into s[N].

$ cat t.c && gcc -O2 -S -Wall -fdump-tree-optimized=/dev/stdout t.c
void f0 (char *s)
{
  s[0] = 0;
  if (__builtin_strlen (s) > 0)   // folded to false
    __builtin_abort ();
}

void f1 (char *s)
{ 
  s[1] = 0;
  if (__builtin_strlen (s) > 1)   // not folded but can be
    __builtin_abort ();
}


;; Function f0 (f0, funcdef_no=0, decl_uid=1931, cgraph_uid=1, symbol_order=0)

f0 (char * s)
{
  <bb 2> [local count: 1073741824]:
  *s_2(D) = 0;
  return;

}



;; Function f1 (f1, funcdef_no=1, decl_uid=1934, cgraph_uid=2, symbol_order=1)

f1 (char * s)
{
  long unsigned int _1;

  <bb 2> [local count: 1073741824]:
  MEM[(char *)s_2(D) + 1B] = 0;
  _1 = __builtin_strlen (s_2(D));
  if (_1 > 1)
    goto <bb 3>; [0.00%]
  else
    goto <bb 4>; [100.00%]

  <bb 3> [count: 0]:
  __builtin_abort ();

  <bb 4> [local count: 1073741824]:
  return;

}