>From: [email protected] [mailto:[email protected]] On Behalf Of
>Richard Henderson
>On 10/17/2011 03:50 AM, Paulo J. Matos wrote:
>>...
>> (for example, it would be ok to output negqi2, xorqi3 and
>> addc_internal since xorqi3 only sets N and Z, not the Carry bit)
>
>For that you'd have to model all of the flags bits independently.
>I don't believe any target has found that level of complexity to be worth the
>trouble.
Something like that shows up in the pdp11, where "mov" does not touch C. And C
matters for multi-word arithmetic, and also for unsigned compares. So I think
a CCmode implementation there would model C separately from the other three
flag bits. So not 4 separate elements but two. Right now it's a cc0 target
but I figure on changing that at some point. The reasons Paulo mentioned are
one of the main reasons for that.
paul
