Re: An unusual Performance approach using Synthetic registers

[Daniel Egger <degger at fhm dot edu>]

Am Son, 2002-12-29 um 05.31 schrieb Andy Walker:

> Color-graphing works better, the more registers there are available for use.  
> Six registers is sub-optimal.  Sixteen registers is a good start.  Thirty-two 
> plus five gives thirty-seven, enough for the algorithm to excel.

However if you have a look at register rich architectures like PPC
you'll see that the generated code rarely exceeds a number of 16 used
registers, most of them being used for parameters and return values.
I believe this is because the compiler is quite good about figuring
out register/time dependencies and reusing the available registers as
soon as the content is dead. Further much code doesn't keep stuff in 
variables but writes it to allocated storage preventing any sensible
use of registers. 

There's really only very few specialized enough code that profits from
many registers which you're opting to simulate. 16 virtual registers are
probably more than enough and also fit nicely in modern processors'
cachelines (16 x 32bit = 64 byte).

-- 
Servus,
       Daniel

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