On 13 March 2007 19:56, Ian Lance Taylor wrote:
> "Dave Korn" <[EMAIL PROTECTED]> writes:
>
>> The intermediate cause is that lreg considers all the special-purpose reg
>> classes when allocating, and for some reason decides that several of the
>> special-purpose classes have equal cost (zero) to GENERAL_REGS. The bit I
>> find strange about this is that it then decides to take the
>> highest-numbered class as the preferred register class, despite the fact
>> that it has a lot less members in it than GENERAL_REGS. (There is no
>> overlap between the classes, so I haven't put them in the "wrong order",
>> as one is not a subset of the other).
>
> Did you set REGISTER_MOVE_COST for your new registers?
Ah, no I didn't. Having said that, do I really want to? At the moment I
have no definition of it at all, so everything has the default cost 2. Isn't
this right? I want to use reloads to get the input operands from gprs into
the memory-mapped registers, and I have defined movsi3 patterns to exchange
between any of the specialised registers and the gprs, and I'm not sure in
what way you're suggesting I should uuse REGISTER_MOVE_COST.
>> Q. Is it possible to do what I really want: to make the compiler aware of
>> some registers, but limit their usage to a single insn; to allow reload to
>> use these registers when directed to by a constraint letter, but for the
>> rest of the compiler to basically pretend they don't even exist.
>
> This is more or less what the MIPS backend does with the HI and LO
> registers. You might want to look at that.
Thanks Ian, that sounds very much like what I'm looking for, I'll take a dig
through it.
cheers,
DaveK
--
Can't think of a witty .sigline today....
