Re: ST(i) and MMj

[Eli Zaretskii <eliz at gnu dot org>]

> >   1) Define REGISTER_RAW_SIZE to be 8 for MMX registers, and define
> >      REGISTER_BYTE so that for MMX registers it goes to the data of
> >      the according ST(i) register using the current TOS.
> > 
> >   2) target_fetch_registers then will actually bring the value of the
> >      appropriate ST(i) register when passed a regno of an MMX
> >      register.
> 
> I thought we had posited that the MMX registers, when stored in
> memory, have zero length --- i.e., REGISTER_RAW_SIZE (MM0_REGNO) == 0
> --- to avoid overlap problems in loops.

The above still avoids overlap, by keeping only a single copy of each
FPU register in the register file.  However, the zero-size definition
isn't useful when you want to read the value of an MMX register from
the register file.  So I changed my mind ;-).

> What concerns me is that it be reasonable enough that people who are
> not familiar with the x86 won't write code that breaks it.

Hiding the complexity behind REGISTER_BYTE should prevent this.