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Re: subreg against register allocation?
Bernd Schmidt <bernds@codesourcery.com> writes:
> On 06/14/2010 07:58 PM, Ian Lance Taylor wrote:
>> "Amker.Cheng" <amker.cheng@gmail.com> writes:
>>
>>> Wondering whether possible to handle multi-word mode with more accuracy,
>>> in either subreg or IRA pass?
>>
>> Yes, it is possible. What you need to do is to write a split which
>> turns the mult:DI insn into an insn which sets two separate subregs.
>
> Is it valid to have an insn set two different subregs of the same pseudo
> in parallel? I have the same problem on ARM, but I couldn't convince
> myself that writing such a split was safe so I'm currently trying to
> solve the problem in the register allocator.
Well, as you know, subregs have two meanings which look similar but
are in fact entirely different. It's valid to set subregs of the same
pseudo in parallel if the subregs represent different hard registers.
It's not valid if the subregs represent different pieces of the same
hard register.
Ian