[Bug ipa/88702] New: [6/7/8 regression] We do terrible job optimizing IsHTMLWhitespace from Firefox

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88702

            Bug ID: 88702
           Summary: [6/7/8 regression] We do terrible job optimizing
                    IsHTMLWhitespace from Firefox
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ipa
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hubicka at gcc dot gnu.org
                CC: marxin at gcc dot gnu.org
  Target Milestone: ---

compiling:

int IsHTMLWhitespace(int aChar) {                         
  return aChar == 0x0009 || aChar == 0x000A ||              
         aChar == 0x000C || aChar == 0x000D ||              
         aChar == 0x0020;                                             
}
q(int a,int b, int c)
{
  return IsHTMLWhitespace (a) && IsHTMLWhitespace (b) && IsHTMLWhitespace (c);
}

we do quite funny things by ipa-splitting IsHTMLWhitespace:

IsHTMLWhitespace (int aChar)
{
  unsigned int aChar.1_1;
  unsigned int _2;
  _Bool _3;
  _Bool _4;
  _Bool _5;
  int iftmp.0_6;
  int iftmp.0_8;

  <bb 2> [100.00%]:
  aChar.1_1 = (unsigned int) aChar_7(D);
  _2 = aChar.1_1 + 4294967287;
  _3 = _2 <= 1;
  _4 = aChar_7(D) == 12;
  _5 = _3 | _4;
  if (_5 != 0)
    goto <bb 4>; [46.00%]
  else
    goto <bb 3>; [54.00%]

  <bb 3> [54.00%]:
  iftmp.0_8 = IsHTMLWhitespace.part.0 (aChar_7(D));

  <bb 4> [100.00%]:
  # iftmp.0_6 = PHI <1(2), iftmp.0_8(3)>
  return iftmp.0_6;

}

this is partly caused by the fact that we are not able to optimize early the
sequence of compares to shift. In Firefox later we fail to inline the functions
and produce some terrible code which slows down rerf-reftest/dep-check-1.html
Firefox benchmark