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

[Wei-Ren Chen]

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.

Regards,
chenwj

-- 
Wei-Ren Chen (陳韋任)
Computer Systems Lab, Institute of Information Science,
Academia Sinica, Taiwan (R.O.C.)
Tel:886-2-2788-3799 #1667
Homepage: http://people.cs.nctu.edu.tw/~chenwj