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Re: [PATCH, alpha]: Add earlyclobber to sqrtt/sqrtf insns.
* Uros Bizjak:
> On Fri, Apr 14, 2017 at 2:38 PM, Florian Weimer <fw@deneb.enyo.de> wrote:
>> * Uros Bizjak:
>>
>>> Add earlyclobber to sqrtt/sqrtf insns.
>>>
>>> When using software completions, we have to prevent assembler to match
>>> input and output operands of sqrtt/sqrtf insn. Add earlyclobber to
>>> output operand to avoid unwanted operand matching.
>>
>> Is this so that the trap handler can recover the original input?
>>
>> In this case, please add this to the commit message for those of us
>> who are not familiar with the Alpha architecture.
>
> I don't know the low-level details, perhaps Richard can explain these
> requirements.
>
> The sqrtt simply returns zero for subnormal operand with software
> completions when input and output reg are matched.
Did you see that in an emulator, or on actual hardware?
The architecture manual suggests that we also need to take measures to
limit the trap shadow.