Re: Pentium 4 GCC Optimizations

[Jan Hubicka <jh at suse dot cz>]

> 1. Does GCC have any Pentium 4 specific optimizations?
Kind of.
As a part of porting project to AMD x86-64 CPUs, I've implemented the SSE2
FP support, that is able to make P4 FP match about 5-20% faster in common
case.

For a fun, I've also implemented the -march=pentium4 flag, that alters costs
in code generation, disables code alignment and adds branch prediction hints.

All is in the 3.1 mainline and untuned, as I don't currently have time to play
with it.
The results of SSE code generation are promising, I didn't benchmarked yet
the rest.
> 
> 2. If so, what do they include?
See above.
> 
> 3. If so, in what version were they integrated?
too
> 
> 4. If not, are there plans for optimizations?  When will they be included?
> 
> 5. Have you had a chance to look at the Intel compiler?  If so, what are
> your thoughts and will we be seeing such optimizations in future gcc
> versions
Many optimizations of Intel compiler are missing, but number of them will
need major reorganization of gcc to be implemented well, so I can't tell much
at this point, if for instance, we will support autovectorization or memory
hiearchy optimizations soon.

3.1 also includes some work on profile driven optimization and I do have
primitive patch for data prefetching, that will need major reorganization before
it can be integrated to gcc, as it has aged somewhat.

Hope this helps,
Honza