Re: [Qemu-devel] [Consult] tilegx: About floating point instructions

[Chen Gang]

On 8/15/15 23:47, Richard Henderson wrote:
> On Aug 15, 2015 2:56 AM, Chen Gang <address@hidden>
>> Oh, we are unlucky, after continue gcc testsuite, add/sub floating point 
>> insns also can be mixed together! The related C code, -save-temps, and 
>> objdump files are in attachments (is it gcc's issue? I guess not). 
>>
>> So, I guess, we have to 'crack' all floating point insns, precisely, or 
>> we can not pass gcc testsuite. 
>>
> 
> If you go back to my first message to you on the subject, you'll find that my 
> suggestion was to not split the operation at all, using move for pack1.  
> Which would nicely handle any such interleaving.
> 

OK, thanks, but for float(uns)sisf2 and float(uns)sidf2, we can not only
simply move.  :-(

But what you said is really quite valuable to me!! we can treat the flag
as a caller saved context, then can let the caller can use callee freely
(in fact, I guess, the real hardware treats it as caller context, too).

 - we have to define the flag format based on the existing format in the
   related docs and tilegx.md (reserve 0-20 and 25-31 bits).

 - We can only use 21-24 for mark addsub, mul, or typecast result. If
   21-24 bits are all zero, it means typecast result. For fsingle: 32-63
   bits is the input integer; for fdouble: srca is the input integer.

 - For addsub and mul result, we use 32-63 bits for an index of resource
   handler (like 'fd' returned by open). fsingle_addsub2, fsingle_mul1,
   fdouble_mul_flags, fdouble_addsub allocate resource, and pack1 free.

But if caller "make mistakes", our implementation can not avoid related
resource leak (but the real hardware can, it also lets caller save all
related resources; when it needs them, it can let caller pass them to).


Thanks.
-- 
Chen Gang

Open, share, and attitude like air, water, and life which God blessed