[Bug tree-optimization/101139] Unable to remove double byteswap in fast path

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101139

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #1)
>   if (b_13 < h.0_15)
>     goto <bb 4>; [51.12%]
>   else
>     goto <bb 5>; [48.88%]
> 
>   <bb 4> [local count: 548896825]:
>   _16 = (short unsigned int) f$ab_14;
>   _17 = (int) _16;
>   _18 = __builtin_bswap16 (_17);
>   goto <bb 6>; [100.00%]
> 
>   <bb 5> [local count: 524845000]:
>   k_22 = i ();
>   c.1_23 = (short unsigned int) k_22;
>   _24 = (int) c.1_23;
>   _25 = __builtin_bswap16 (_24);
> 
>   <bb 6> [local count: 1073741824]:
>   # prephitmp_32 = PHI <_18(4), _25(5)>
> 
> Basically the same issue as PR 13563.

Once that issue is fixed we should get:
  if (b_13 < h.0_15)
    goto <bb 4>; [51.12%]
  else
    goto <bb 5>; [48.88%]

  <bb 4> [local count: 548896825]:
  _16 = (short unsigned int) f$ab_14;
  goto <bb 6>; [100.00%]

  <bb 5> [local count: 524845000]:
  k_22 = i ();
  c.1_23 = (short unsigned int) k_22;

  <bb 6> [local count: 1073741824]:
  # c.1_23 = PHI <_16(4), c.1_23(5)>

  _24 = (int) c.1_23;
  prephitmp_32 = __builtin_bswap16 (_32);
  _2 = (int) prephitmp_32;
  _3 = __builtin_bswap16 (_2);
  _4 = (int) _3;

Which then should just optimize later on to:  if (b_13 < h.0_15)
    goto <bb 4>; [51.12%]
  else
    goto <bb 5>; [48.88%]

  <bb 4> [local count: 548896825]:
  _16 = (short unsigned int) f$ab_14;
  goto <bb 6>; [100.00%]

  <bb 5> [local count: 524845000]:
  k_22 = i ();
  c.1_23 = (short unsigned int) k_22;

  <bb 6> [local count: 1073741824]:
  # c.1_23 = PHI <_16(4), c.1_23(5)>

  _24 = (int) c.1_23;
  _4 = _24;
(If I did this conversion right)