[LLVMdev] x86 cogen quality

Alkis Evlogimenos
Wed, 21 Apr 2004 10:28:03 -0000

On Wed, Apr 21, 2004 at 11:01:48AM +0200, Finn S Andersen
wrote:
> For some of the benchmarks the linear scan regalloc
> works. When it does, results are in the x1.0 - 1.5
> range. Unfortunately, the linear scan allocator breaks
> on most of my code.

Is there a chance you can try cvs? I would be interested to
get a simplified test case where the allocator breaks. A lot of
improvements went into the x86 backend since 1.2 and we currently have
no test cases where the allocator breaks today.

> Currently, I am just playing with LLVM, but the longterm
> plan is to build a new backend for a new machine. It won't
> be register starved as the x86 is.

It would be very interesting to see the performance difference between
linear scan and local allocators on a machine that is less spill
happy than the x86. In that case I expect to see much bigger difference
between the two.

> 3) What is the expected timeframe for the new regalloc to
>    become stable ? .. or perhaps I should make a more general
>    question: what is the perceived status in terms of performance
>    for the two compiler backends and for the compiler backend
>    part of the infrastructure ?

As Chris said, I have been held back from other projects. I hope that
right after finals I will have some time to fix the regression of the
linear scan register allocator. There are some improvements I have in
mind as well, so expect the linear scan register allocator to be much
better in 1.3.


--

Alkis