Re: Performance degradation on g++ 4.6

[Oleg Smolsky <oleg dot smolsky at riverbed dot com>]

On 2011/8/24 13:02, Xinliang David Li wrote:
> > On 2011/8/23 11:38, Xinliang David Li wrote:
> > > Partial register stall happens when there is a 32bit register read
> > > followed by a partial register write. In your case, the stall probably
> > > happens in the next iteration when 'add eax, 0Ah' executes, so your
> > > manual patch does not work.  Try change
> > >
> > > add al, [dx] into two instructions (assuming esi is available here)
> > >
> > > movzx esi, ds:data8[dx]
> > > add  eax, esi
> > I patched the code to use  "movzx edi" but the result is a little clumsy as
> > the loop is based on the virtual address rather than index.
> my bad -- I did copy&  paste without making it precise.
No worries. The fragment did fit into the padding :)

> > So, this is one test out of the suite. Many of them degraded... Are you guys
> > interested in looking at other ones? Or is there something to be fixed in
> > the register allocation logic?
> File bugs --- the isolated examples like this one would be very 
> helpful in the bug report. 
Done:
    http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50182

Regards,
Oleg.