Re: [PATCH RFC] mips: add TARGET_ZERO_CALL_USED_REGS hook [PR104817, PR104820]

[Richard Sandiford <richard.sandiford@arm.com>]

Xi Ruoyao <xry111@mengyan1223.wang> writes:
>> 
>> If we have to go this way, I think it’s better to make the change you
>> suggested above, 
>> and then also update the documentation, both internal documentation on
>> how to define
>>  the hook and the user level documentation on what the user might
>> expect when using 
>> this option (i.e, it’s possible that the compiler might clear more
>> registers than the user 
>> requests on some targets due to the implementation limitation). 
>> 
>> I can make this change if we decide to do this.
>
> I'd vote for this.  Richard?

Fine by me too, although I don't think this should be mentioned
in the user documentation.  E.g. used-arg means that non-argument,
non-return registers can have any value on return from the function;
the compiler doesn't make any guarantees.  If the compiler happens to
use a temporary register in the implementation of the option, and if
that temporary register happens to still be zero on return, then
that's OK.  It's just an internal implementation detail.  The same
thing could happen for any part of the epilogue.

Thanks,
Richard