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

[Richard Henderson <rth@twiddle.net>]

On 08/17/2015 02:09 PM, Chen Gang wrote:
> On 8/18/15 01:31, Richard Henderson wrote:
>> On 08/15/2015 11:16 AM, Chen Gang wrote:
>>
>>> 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.
>>
>> Plausible.
>>
>>>
>>>   - 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.
>>
>> No, that's a bad idea.  No state external to the inputs to the insns.

...

>      float32 val32s[TILEGX_F_COUNT]; /* results roudup array for fsingle */
>      float64 val64s[TILEGX_F_COUNT]; /* results roudup array for fdouble */

I repeat: This is an extremely bad idea.
I will certainly not sign off on any patch that includes this.


r~