Re: [Qemu-devel] [PATCH] translate: optimize gen_intermediate_code_internal

[li guang]

在 2013-04-09二的 17:20 +0800，陳韋任 (Wei-Ren Chen)写道：
> Hi liguang,
> 
> On Tue, Apr 09, 2013 at 04:21:10PM +0800, li guang wrote:
> > 在 2013-04-09二的 10:11 +0200，Paolo Bonzini写道：
> > > Il 09/04/2013 10:05, 陳韋任 (Wei-Ren Chen) ha scritto:
> > > > Hi liguang,
> > > > 
> > > >   Just to be curious, how much performance improvement this patch can 
> > > > get?
> > > 
> > > I think zero.  It is indeed making the code a tiny bit more readable in
> > > the 2nd/3rd/5th/6th hunks.
> > 
> > I think maybe a little greater than 0,
> > for it optimizes a variable 'lj' increment.
> 
>   As Peter said, only profiling can show if there is a performance
> improvement.
> 
> > > But the 1st and 4th hunks, which do
> > > 
> > > -    num_insns = 0;
> > > 
> > > are wrong.  I'm surprised the compiler doesn't report usage of an
> > > uninitialized variable.  liguang, how did you test them?
> > 
> > I do normal compile and run guest OS for TCG,
> > I think 'max_insns = tb->cflags & CF_COUNT_MASK;' is enough
> > to feed compiler.
> 
>   num_insns and max_insns are two different variables, right? So this
> assignment does not do anything with num_insns.

Yes, you're right.
Thanks!

> 
> Regards,
> chenwj
>