[Bug middle-end/46554] New: Less inlining leads to CSiBE regression

[Bug middle-end/46554] New: Less inlining leads to CSiBE regression

[hubicka at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46554

           Summary: Less inlining leads to CSiBE regression
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: hubicka@gcc.gnu.org


Created attachment 22451
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=22451
testcase flex-2.5.31/regex.c

The loss here is not inlining regmatch_len. The catch is that the test if (m ==
((void *)0) || m->rm_so < 0) is tested before all uses of regmatch_len and thus
optimized out.  So it simplifies into m->rm_so < 0 test and arithmetic that
ends up being cheaper than call.

int regmatch_len (regmatch_t * m)
{
 if (m == ((void *)0) || m->rm_so < 0) {
  return 0;
 }

 return m->rm_eo - m->rm_so;
}

It is used as:

 if (m == ((void *)0) || m->rm_so < 0)
  return 0;

 if (regmatch_len (m) < 20)
  s = regmatch_cpy (m, buf, src);
 else
  s = regmatch_dup (m, src);

Tricky.  Inliner sees it as:

Analyzing function body size: regmatch_len
  freq:  1000 size:  2 time:  2 if (m_2(D) == 0B)
  freq:   898 size:  1 time:  1 D.7268_3 = m_2(D)->rm_so;
    50% will be eliminated by inlining
  freq:   898 size:  2 time:  2 if (D.7268_3 < 0)
  freq:   726 size:  1 time:  1 D.7270_4 = m_2(D)->rm_eo;
    50% will be eliminated by inlining
  freq:   726 size:  1 time:  1 D.7268_5 = m_2(D)->rm_so;
    50% will be eliminated by inlining
  freq:   726 size:  1 time:  1 D.7269_6 = D.7270_4 - D.7268_5;
  freq:  1000 size:  1 time:  2 return D.7269_1;
    will eliminated by inlining
Overall function body time: 9-3 size: 11-5
With function call overhead time: 9-15 size: 11-8

I can imagine we can try to get summary based on value ranges, instead of known
constants, do early VRP and work out first test well.

Even optimizing the first conditoinal away won't make it inlined, it will be
still considered to have size 9, so code will be expected to grow by 1 byte.
Optimizing second conditoinal is even trickier.

The code can be optimized away by IP-value range propagation that would
be interesting optimization to have...

[Bug middle-end/46554] Less inlining leads to CSiBE regression

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46554

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2010.11.19 10:52:53
     Ever Confirmed|0                           |1

--- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2010-11-19 10:52:53 UTC ---
I thought partial inlining would maybe fix this?  Otherwise it's really a
case that needs IP analysis.

Re: [Bug middle-end/46554] Less inlining leads to CSiBE regression

[Jan Hubicka]

> I thought partial inlining would maybe fix this?  Otherwise it's really a
> case that needs IP analysis.

Not with -Os, we really know that it will optimize away.

Honza

[Bug middle-end/46554] Less inlining leads to CSiBE regression

[hubicka at ucw dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46554

--- Comment #2 from Jan Hubicka <hubicka at ucw dot cz> 2010-11-19 10:57:57 UTC ---
> I thought partial inlining would maybe fix this?  Otherwise it's really a
> case that needs IP analysis.

Not with -Os, we really know that it will optimize away.

Honza

[Bug ipa/46554] Less inlining leads to CSiBE regression

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=46554

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|middle-end                  |ipa
           Keywords|                            |missed-optimization
                 CC|                            |marxin at gcc dot gnu.org

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Many things has changed since GCC 4.6 with respect to the inliner, has this
been fixed?