Re: An unusual Performance approach using Synthetic registers

[dewar at gnat dot com (Robert Dewar)]

> What I think Diego is trying to say is, creating synthetic registers
> for the x86 isn't going to help much, possibly not at all, because the
> optimizer passes that could benefit already have unlimited registers
> to work with.

I would put it a different way. If "synthetic registers" help, it would
just indicate that the optimizer and code generator is operating very
poorly. I certainly don't have the impression that this is the case,
at least not at the level that this naive synthetic register approach
would help.

Wouldn't it be best to take some typical kernels, look at the code generated
by GCC, and then try by hand to see how much help SR's would be. I am pretty
sure this will quickly discourage the approach and save a lot of wasted
effort in modifying gcc.

An approach that might really be helpful is to have the register allocator
and scheduler understand the existence and behavior of renamed registers.
Quite often you see gcc generated code use two registers when it could
use one, under the illusion that this helps, when in fact it does not
since the hardware would in any case use two registers using register
renmaing.