[Bug tree-optimization/99739] New: [11 Regression] missing optimization of a repeated conditional

[msebor at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99739

            Bug ID: 99739
           Summary: [11 Regression] missing optimization of a repeated
                    conditional
           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: ---

Prior to r11-5805 both ff() and gg() in the test case below resulted in optimal
code.  With the change, the second conditional in g() is no longer recognized
as equivalent to the first and so the function isn't optimized as expected.

Incidentally, the same regression was also introduced once before: in r235653.

$ cat x.c && gcc -O1 -S -Wall -fdump-tree-optimized=/dev/stdout x.c
static inline int f (int i, int j, int k)
{
  int x = 1;

  if (i && j && k)
    x = 2;

  if (i && j && k)
    return x;

  return -1;
}

void ff (int i, int j, int k)
{
  int x = f (i, j, k);
  if (x == 1)
    __builtin_abort ();
}


static inline int g (int i, int j, int k)
{
  int x = 1;

  if (i && j && k)
    x = 2;

  if (i && k && j)
    return x;

  return -1;
}

void gg (int i, int j, int k)
{
  int x = g (i, j, k);
  if (x == 1)
    __builtin_abort ();
}

;; Function ff (ff, funcdef_no=1, decl_uid=1951, cgraph_uid=2, symbol_order=1)

void ff (int i, int j, int k)
{
  <bb 2> [local count: 1073741824]:
  return;

}



;; Function gg (gg, funcdef_no=3, decl_uid=1963, cgraph_uid=4, symbol_order=3)

Removing basic block 6
Removing basic block 7
void gg (int i, int j, int k)
{
  _Bool _7;
  _Bool _8;
  _Bool _11;
  _Bool _14;
  _Bool _16;

  <bb 2> [local count: 1073741824]:
  _7 = i_2(D) != 0;
  _8 = j_3(D) != 0;
  _14 = k_4(D) != 0;
  _11 = _7 & _14;
  _16 = _8 & _11;
  if (_16 != 0)
    goto <bb 3>; [94.27%]
  else
    goto <bb 5>; [5.73%]

  <bb 3> [local count: 1012175616]:
  if (k_4(D) != 0)
    goto <bb 5>; [100.00%]
  else
    goto <bb 4>; [0.00%]

  <bb 4> [count: 0]:
  __builtin_abort ();

  <bb 5> [local count: 1073741824]:
  return;

}