[Openmcl-devel] Speed, compilers and multi-core processors

[Glen Foy]

On May 18, 2009, at 10:45 AM, Brian Mastenbrook wrote:

> On Mon, 2009-05-18 at 10:13 -0400, Glen Foy wrote:
>
>> My ignorance of compiler design is breathtaking, but could multi-core
>> compiler techniques be used to compensate for Intel's register- 
>> starved
>> architecture?
>
> In a word, no.
>
> The problem with Intel's register-starved architecture is that as a
> compiler author it's difficult to work with a very small set of
> registers without overflowing to locations on the stack. Dealing with
> temporaries on the stack, while usually quite performant due to  
> register
> renaming at the hardware level, gets quite difficult to juggle
> especially if your compiler was originally developed on an  
> architecture
> where there are enough registers to always leave a few open for
> temporaries.
>
> Talking about "multi-core compiler techniques" is a bit like "alchemy"
> right now. Nobody's really quite sure what works, especially when it
> comes to languages that mere mortals can write. There's also quite a  
> bit
> of tension between the desire for functional programming as a means to
> save ourselves from mutable shared state and the intrinsic  
> dependency of
> garbage collection on same.
>
> The relationship between multi-core and the register-poor x86
> architecture isn't great, except that it probably increases the number
> of things you've got to keep in a register and thus exacerbates the
> issue.
>
> For what it's worth, x86-64 isn't all that register-starved, which is
> why some programs show a great improvement when compiled for 64-bit  
> even
> when you'd expect only a performance loss due to the increase in  
> pointer
> width. It's not quite like working on PowerPC or SPARC, but it isn't
> half bad. As a practical matter, it's probably safe to assume that any
> system with more than two cores (real or virtual hyper-threaded) is
> 64-bit; all of Intel's existing CPUs certainly hold to this pattern.

Thanks for the info.

The quality of the responses on this list is really quite remarkable.