Re: [Lightning] More on work on lightning

[Paolo Bonzini]

On 09/27/2010 10:53 PM, Paulo César Pereira de Andrade wrote:
> I was thinking about it more on the sense of a function that
> receives less arguments than those passed in registers, and in its
> body, the register used for arguments are not used. But if an
> argument is known to not be required anymore, the register could also
> be used for other purposes.

I had thought of making JIT_R_NUM return a variable number depending on
the number of arguments in the current function, but actually it would
depend also on the maximum number of arguments of _called_ functions and
that is not available at jit_prolog time.

> I just timed it on 3 different computers, and there is no difference;
> timing of some loops running 10 million times oscillate 1-5 percent
> to less or more, so, effectively it is the same, just that the new
> approach should make prettier assembly dump.

I'd rather avoid that.  For prettier dumps, on x86-64 you can move to a
temporary register and push that.  For 32-bit the limited number of
registers makes everything a challenge. :/

> current code using lightning is still more the 2 times slower

Did you profile to see where lightning code is spending time?

>   Ok. If I could keep some states in xmm registers, it would help a lot,
> but AFAIK there is no callee save xmm registers in the SytemV ABI.

You can just throw away the stack registers and require SSE2 for 32-bit 
x86.  Anyway both the stack registers and the XMM registers are caller-save.

Paolo