[patch] tuning gcc for Intel Core2

[H. J. Lu]

On Tue, Nov 14, 2006 at 10:07:54AM -0500, Vladimir Makarov wrote:
> H.J., I don't pretend that the code is final.  I will be glad if people 
> find a better tuning.   I did this tuning because it was needed for my 
> work.  That is strange situation we have no tuning for major processor 
> which is available public for a few months.  Ideally tunning should be 
> availiable before the processor became available to public (that is what 
> IBM is doing this for their power6 now).  Unfortunately only Intel can 
> make it because they do microacrhitecture documentation public too late. 
> For example, I started the work long before the documenation was made 
> public (a few days ago) using unjustified different information from 
> internet.

As you have discovered, -mtune=generic isn't too bad for Core 2.

> 
> And the patch is useful even if I get the same score because as I wrote 
> the code is smaller.
> 
> >x86_rep_movl_optimal
> >
> >for Core 2, which will avoid external calls to memset. There
> >are known serious performance problems with x86-64 memory functions,
> >especially on Core 2. We are working on improving x86-64 memory
> >functions. A better external memset can improve gcc in SPEC CPU 2K by
> >more than 20%.
> >
> >BTW, when Jan and I were working on -mtune=generic, we determined that
> >turning on x86_rep_movl_optimal wasn't a good idea. What do you get
> >if you turn off x86_rep_movl_optimal?
> > 
> >
> It is the same as generic (may be a bit better).

Can you turn on x86_rep_movl_optimal for -mtune=generic to see what
it does for SPEC CPU 2K on both 32bit and 64bit?

> 
> 
> Here, the results with -m32 as you asked on the mainline few days ago. 
> The code is smaller and Int score is a bit better (not because of gcc 
> which is actually 0.4% worse)
> 
> base: -O2 -m32 -mtune=generic
> peak: -O2 -m32 -mtune=core2
> 
> Est. SPECint_base2000                 1832
> Est. SPECint2000                                                    1843
> 
> Est. SPECfp_base2000                  1479
> Est. SPECfp2000                                                     1477
> 

Thanks.

H.J.