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

[Chen Gang]

On 8/9/15 09:10, Chen Gang wrote:
> 
> On 8/9/15 01:23, Chen Gang wrote:
>> Hello all:
>>
>> Below is my current idea for all floating point insns. For me, it is not
>> the precise implementation, even not completely implement -- assume pack
>> insns can only for packing (u)int32_t when they are used individually:
>>
>>   fsingle_add1        ; return calc flags, save calc result to env.
>>
>>   fsingle_sub1        ; return calc flags, save calc result to env.
>>
>>   fsingle_addsub2     ; set "has result" flag.
>>
>>   fsingle_mul1        ; skip return value, save calc result to env.
>>                         set "has result" flag.
>>
>>   fsingle_mul2        ; skipped.
>>
>>
>>   fsingle_pack1       ; skipped.
>>
>>   fsingle_pack1       ; if "has result"
>>                             reset "has result" flag.
>>                             return calc result from env.
>>                         else
>>                             pack srca 
>>                             reference from tilegx.md: float(uns)sisf2.
>>                             get (u)int32_t a, then (u)int32_to_float32.
> 
> For "pack srca and srcb", the related demo like below (srca and srcb
> are uint64_t):
> 

Oh, sorry, for "pack srca" (not for "pack srca and srcb")

>     switch (srca & 0x3ff) {
> 
>     /* treat it as uint32_t */
>     case 0x9e:
>         return uint32_to_float32(srca >> 32, &FP_STATUS);
> 
>     /* treat it as int32_t, must be negative number */
>     case 0x29e:
>         return int32_to_float32(srca >> 32 | 0x80000000, &FP_STATUS);
> 
>     default:
>         unimplemented (gen_exception).
>     }
> 
>>
>>   fdouble_unpack_max: ; skipped.
>>
>>   fdouble_unpack_min: ; skipped.
>>
>>   fdouble_add_flags:  ; return calc flags, save calc result to env.
>>
>>   fdouble_sub_flags:  ; return calc flags, save calc result to env.
>>
>>   fdouble_addsub:     ; set "has result" flag.
>>
>>   fdouble_mul_flags:  ; skip return flags, save calc result to env.
>>                         set "has result" flag.
>>
>>   fdouble_pack1:      ; if "has result" 
>>                             reset "has result" flag.
>>                             return calc result from env.
>>                         else
>>                             pack srca and srcb.
>>                             reference from tilegx.md: float(uns)sidf2.
>>                             get (u)int32_t a, then (u)int32_to_float64.
>>
>  
> For "pack srca and srcb", the related demo like below (srca and srcb
> are uint64_t):
> 
>     switch (srcb & 0xffff) {
> 

Oh, sorry, should use 0xfffff instead of 0xffff.

>     /* treat it as uint32_t */
>     case 0x21b00:
>         return uint32_to_float64(srca >> 4, &FP_STATUS);
> 
>     /* treat it as int32_t, must be negative number */
>     case 0xa1b00:
>         return int32_to_float64(srca >> 4 | 0x80000000, &FP_STATUS);
> 
>     default:
>         unimplemented (gen_exception).
>     }
> 
>>   fdouble_pack2:      ; skipped.
>>
>>
>>   (fsingle_add1/sub1, fdouble_add/sub_flags can be used individually,
>>    e.g gcc testsuit for complex number).
>>
>>
>> Next, I shall implement the floating point insns, welcome any related
>> ideas, suggestions, and completions.
>>
>> Thanks.
>>
>>
>> On 8/5/15 22:16, Chen Gang wrote:
>>> On 8/4/15 23:04, Richard Henderson wrote:
>>>> On 08/04/2015 06:56 AM, Chen Gang wrote:
>>>>>
>>>>> On 8/4/15 04:47, Chen Gang wrote:
>>>>>> On 8/4/15 00:40, Richard Henderson wrote:
>>>>>>> On 08/01/2015 02:47 AM, Chen Gang wrote:
>>>>>>>> I am just adding floating point instructions (e.g. fsingle_add1),
>>>>>>>> but for me, I can not find any details about them (the ISA
>>>>>>>> documents only give a summary description, but not details), e.g.
>>>>>>>
>>>>>>> The tilegx splits the four/six cycle arithmetic into multiple
>>>>>>> black-box instructions.  You need only really implement one of the
>>>>>>> four, with the rest of them being implemented as nops or moves.
>>>>>>>
>>>>>>> Looking at what gcc produces gives the hints:
>>>>>>>
>>>>>>> fdouble_unpack_min      min, srca, srcb fdouble_unpack_max      max, 
>>>>>>> srca,
>>>>>>> srcb fdouble_add_flags  flg, srca, srcb fdouble_addsub          max, 
>>>>>>> min, flg 
>>>>>>> fdouble_pack1           dst, max, flg fdouble_pack2             dst, 
>>>>>>> max, zero
>>>>>>>
>>>>>>> The unpack, addsub, and pack2 insns can be ignored, the add_flags
>>>>>>> insn can perform the whole operation, the pack1 insn performs a move
>>>>>>> from "flg" to "dst".
>>>>>>>
>>>>>>> Similarly for the single-precision:
>>>>>>>
>>>>>>> fsingle_add1            tmp, srca, srcb fsingle_addsub2         tmp, 
>>>>>>> srca, srcb 
>>>>>>> fsingle_pack1           flg, tmp fsingle_pack2          dst, tmp, flg
>>>>>>>
>>>>>>> The add1 insn performs the whole operation, the addsub2 and pack1
>>>>>>> insns are ignored, and the pack2 insn is a move from tmp to dst.
>>>>>>>
>>>>>
>>>>> After check the tilegx.md completely, for me, we still need implement
>>>>> each of them precisely, or we can not emulate all cases (e.g. muldf3).
>>>>
>>>> No, you can still implement all of muldf3 in fdouble_mul_flags.
>>>> Again, the fdouble_pack1 copies from the flag input to the output.
>>>>
>>>> Yes, there is a 64-bit multiply in there, but the tcg optimizer
>>>> should be able to delete all of that as unused.  Especially if you have the
>>>> fdouble_unpack* insns store zero into their destinations.
>>>>
>>>
>>> For me, I am not quite sure. But I guess, what you said should be OK (at
>>> least, what you said is very useful for the implementation).
>>>
>>>
>>>> Don't get me wrong -- more accurate implementation of the actual
>>>> insns would be nice, especially for debugging.  But if the insns
>>>> aren't accurately documented I don't see what choice we have.
>>>>
>>>
>>> For me, I guess, we can still try to implement the details.
>>>
>>>  - The document has all floating point instructions' summary, so we can
>>>    think of, or guess its implementation entirely.
>>>
>>>  - gcc uses them all and completely, so it is our good sample and good
>>>    reference (but we should not assume gcc must be correct, since we
>>>    just use qemu for gcc testsuite).
>>>
>>>  - Tilegx floating point format should be standard (at least, reference
>>>    to the standard format), so we can reference the related information
>>>    from google/baidu.
>>>
>>>
>>>> On the good side, implementing the entire operation as part of the "flags" 
>>>> step
>>>> probably results in faster emulation.
>>>>
>>>
>>> I guess so, too.
>>>
>>>
>>> I shall try to finish the simple implementation, firstly. Then try to
>>> implement the floating point instructions in details in the future (it
>>> should be lower priority).
>>>
>>>
>>> Thanks.
>>>
>>
> 

-- 
Chen Gang

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