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From: "msebor at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/99739] New: [11 Regression] missing
 optimization of a repeated conditional
Date: Tue, 23 Mar 2021 20:56:47 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99739

            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 opt=
imal
code.  With the change, the second conditional in g() is no longer recogniz=
ed
as equivalent to the first and so the function isn't optimized as expected.

Incidentally, the same regression was also introduced once before: in r2356=
53.

$ cat x.c && gcc -O1 -S -Wall -fdump-tree-optimized=3D/dev/stdout x.c
static inline int f (int i, int j, int k)
{
  int x =3D 1;

  if (i && j && k)
    x =3D 2;

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

  return -1;
}

void ff (int i, int j, int k)
{
  int x =3D f (i, j, k);
  if (x =3D=3D 1)
    __builtin_abort ();
}


static inline int g (int i, int j, int k)
{
  int x =3D 1;

  if (i && j && k)
    x =3D 2;

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

  return -1;
}

void gg (int i, int j, int k)
{
  int x =3D g (i, j, k);
  if (x =3D=3D 1)
    __builtin_abort ();
}

;; Function ff (ff, funcdef_no=3D1, decl_uid=3D1951, cgraph_uid=3D2, symbol=
_order=3D1)

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

}



;; Function gg (gg, funcdef_no=3D3, decl_uid=3D1963, cgraph_uid=3D4, symbol=
_order=3D3)

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

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

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

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

}=