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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/107767] [13 Regression] switch to table
 conversion happening even though using btq is better
Date: Fri, 02 Dec 2022 15:17:17 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107767

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Indeed, comparing that to
int firewall3(const uint8_t *restrict data) {
    const uint16_t dst_port =3D *((const uint16_t *)data + 32);

    switch (dst_port) {
    case 15: return 1;
    case 23: return 1;
    case 47: return 1;
    case 45: return 1;
    case 42: return 1;
    case 1: return 1;
    case 2: return 1;
    case 3: return 1;
    default: return 0;
    }
}
this one is optimized correctly.
In iftoswitch dump this one is much simpler though:
  dst_port_6 =3D MEM[(const uint16_t *)data_4(D) + 64B];
  switch (dst_port_6) <default: <L8> [INV], case 1 ... 3: <L10> [INV], case=
 15:
<L10> [INV], case 23: <L10> [INV], case 42: <L10> [INV], case 45: <L10> [IN=
V],
case 47: <L10> [INV]>

  <bb 3> :
<L8>:

  <bb 4> :
  # _3 =3D PHI <1(2), 0(3)>
<L10>:
  return _3;
vs.
  dst_port_5 =3D MEM[(const uint16_t *)data_3(D) + 64B];
  switch (dst_port_5) <default: <L25> [INV], case 1: <L22> [INV], case 2: <=
L23>
[INV], case 3: <L24> [INV], case 15: <L17> [INV], case 23: <L18> [INV], case
42: <L21> [INV], case 45:
 <L20> [INV], case 47: <L19> [INV]>

  <bb 3> :
<L17>:
  // predicted unlikely by early return (on trees) predictor.
  goto <bb 11>; [INV]

  <bb 4> :
<L18>:
  // predicted unlikely by early return (on trees) predictor.
  goto <bb 11>; [INV]

  <bb 5> :
<L19>:
  // predicted unlikely by early return (on trees) predictor.
  goto <bb 11>; [INV]

  <bb 6> :
<L20>:
  // predicted unlikely by early return (on trees) predictor.
  goto <bb 11>; [INV]

  <bb 7> :
<L21>:
  // predicted unlikely by early return (on trees) predictor.
  goto <bb 11>; [INV]

  <bb 8> :
<L22>:
  // predicted unlikely by early return (on trees) predictor.
  goto <bb 11>; [INV]

  <bb 9> :
<L23>:
  // predicted unlikely by early return (on trees) predictor.
  goto <bb 11>; [INV]

  <bb 10> :
<L24>:
  // predicted unlikely by early return (on trees) predictor.

  <bb 11> :
  # _2 =3D PHI <1(4), 1(5), 1(3), 1(10), 1(9), 1(8), 1(7), 1(6), 0(2)>
<L25>:
  return _2;

but I guess switchconv should be able to handle both the same.=