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Re: [RFC] Support register groups in inline asm


2016-11-16 8:02 GMT+03:00 Andrew Pinski <pinskia@gmail.com>:
> On Tue, Nov 15, 2016 at 9:36 AM, Andrew Senkevich
> <andrew.n.senkevich@gmail.com> wrote:
>> Hi,
>>
>> new Intel instructions AVX512_4FMAPS and AVX512_4VNNIW introduce use
>> of register groups.
>>
>> To support register groups feature in inline asm needed some extension
>> with new constraints.
>>
>> Current proposal is the following syntax:
>>
>> __asm__ (“SMTH %[group], %[single]" :
>>                                                             [single] "+x"(v0) :
>>                                                             [group]
>> "Yg4"(v1),  “1+1"(v2), “1+2"(v3), “1+3"(v4));
>>
>> where "YgN" constraint specifies group of N consecutive registers
>> (which is started from register having number as "0 mod
>> 2^ceil(log2(N))"),
>> and "1+K" specifies the next registers in the group.
>>
>> Is this syntax ok? How to implement it?
>
>
> Have you looked into how AARCH64 back-end handles this via OI, etc.
> Like:
> /* Oct Int: 256-bit integer mode needed for 32-byte vector arguments.  */
> INT_MODE (OI, 32);
>
> /* Opaque integer modes for 3 or 4 Neon q-registers / 6 or 8 Neon d-registers
>    (2 d-regs = 1 q-reg = TImode).  */
> INT_MODE (CI, 48);
> INT_MODE (XI, 64);
>
>
> And then it implements TARGET_ARRAY_MODE_SUPPORTED_P. target hook?
> And the x2 types are defined as a struct of an array like:
> typedef struct int8x8x2_t
> {
>   int8x8_t val[2];
> } int8x8x2_t;

Thanks!

We have to update proposal with changing "+" symbol to "#" specifying
offset in a group (to avoid overloading the other meaning of “+”
specifying that operand is both input and output).

So current proposal of syntax is:

__asm__ (“INSTR %[group], %[single]" :
                                                            [single] "+x"(v0) :
                                                            [group]
"Yg4"(v1),  “1#1"(v2), “1#2"(v3), “1#3"(v4));

where "YgN" constraint specifies group of N consecutive registers
(which is started from register having number as "0 mod 2^ceil(log2(N))"),
and "1#K" specifies the next registers in the group.

Some other questions or comments?

What about consensus on this syntax?


--
WBR,
Andrew


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