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

[Chen Gang]

Oh, it seems a little complex, for a testsuite case, it lets double add
and double mul together! We need save more information for the correct
calculation in pack1.

It is 20020314-1.exe, the related code (I guess it is correct):

        ...

        fdouble_unpack_max      r10, r3, zero
.LVL2:
        fdouble_unpack_max      r15, r2, zero
        fdouble_add_flags       r12, r0, r1
        mul_hu_lu       r13, r15, r10
        mul_lu_lu       r16, r15, r10
        mula_hu_lu      r13, r10, r15
        fdouble_unpack_min      r11, r0, r1
        {
        shli    r14, r13, 32
        fdouble_unpack_max      r17, r0, r1
        }
        {
        mul_hu_hu       r15, r15, r10
        add     r16, r16, r14
        }
        {
        shrui   r13, r13, 32
        fdouble_addsub  r17, r11, r12
        }
        {
        cmpltu  r14, r16, r14
        fdouble_mul_flags       r3, r2, r3
        }
.LVL3:
        {
        add     r13, r15, r13
        fdouble_pack1   r12, r17, r12
        }
        {
        add     r13, r13, r14
        fdouble_unpack_max      r10, r0, zero
        }
        fdouble_pack1   r3, r13, r3
        fdouble_pack2   r12, r17, zero
        fdouble_pack2   r3, r13, r16

        ... 

Welcome any additional ideas, suggestions and completions.

Thanks.

On 8/9/15 09:14, Chen Gang wrote:
> 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