[PING^2][PATCH] -fuse-caller-save - Implement TARGET_FN_OTHER_HARD_REG_USAGE hook for MIPS

[Tom de Vries]

On 10-01-14 09:47, Richard Sandiford wrote:
> Tom de Vries <Tom_deVries@mentor.com> writes:
>>>   Why not just collect the usage information at
>>> the end of final rather than at the beginning, so that all splits during
>>> final have been done?
>>
>> If we have a call to a leaf function, the final rtl representation does not
>> contain calls. The problem does not lie in the final pass where the callee is
>> analyzed, but in the caller, where information is used, and where the unsplit
>> call is missing the clobber of r6.
>
> Ah, so when you're using this hook in final, you're actually adding in
> the set of registers that will be clobbered by a future caller's CALL_INSN,
> as well as the registers that are clobbered by the callee itself?

Right. The first part is not the intended usage of the hook, but it was the 
simplest fix.

> That seems a bit error-prone, since we don't know at this stage what
> the future caller will look like.  (Things like the target attribute
> make this harder to predict.)
>
> I think it would be cleaner to just calculate the callee-clobbered
> registers during final and leave the caller to say what it clobbers.
>

Agree. I've rewritten the patch as such.

> FWIW, I still think it'd be better to collect the set at the end of final
> (after any final splits) rather than at the beginning.
>

Hmm. I was not aware that splits can happen during final. I'll try to update 
that patch as well.

>>> For other cases (where the usage isn't explicit
>>> at the rtl level), why not record the usage in CALL_INSN_FUNCTION_USAGE
>>> instead?
>>>
>>
>> Right, we could add the r6 clobber that way. But to keep things simple, I've
>> used the hook instead.
>
> Why's it simpler though?  That's the kind of thing CALL_INSN_FUNCTION_USAGE
> is there for.
>

It was simpler to implement. But you're right, using CALL_INSN_FUNCTION_USAGE 
was simple as well.

build and reg-tested on MIPS. OK for stage1? (You've alread OK-ed the test-case 
part).

Thanks,
- Tom

> Thanks,
> Richard
>

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