On Fri, Jan 6, 2012 at 2:43 AM, Walter Bright
<
newshound2@digitalmars.com> wrote:
> On 1/5/2012 5:42 PM, Manu wrote:
>>
>> So I've been hassling about this for a while now, and Walter asked me to
>> pitch
>> an email detailing a minimal implementation with some initial thoughts.
>
>
> Takeaways:
>
> 1. SIMD behavior is going to be very machine specific.
>
> 2. Even trying to do something with + is fraught with peril, as integer adds
> with SIMD can be saturated or unsaturated.
>
> 3. Trying to build all the details about how each of the various adds and
> other ops work into the compiler/optimizer is a large undertaking. D would
> have to support internally maybe a 100 or more new operators.
>
> So some simplification is in order, perhaps a low level layer that is fairly
> extensible for new instructions, and for which a library can be layered over
> for a more presentable interface. A half-formed idea of mine is, taking a
> cue from yours:
>
> Declare one new basic type:
>
> __v128
>
> which represents the 16 byte aligned 128 bit vector type. The only
> operations defined to work on it would be construction and assignment. The
> __ prefix signals that it is non-portable.
>
> Then, have:
>
> import core.simd;
>
> which provides two functions:
>
> __v128 simdop(operator, __v128 op1);
> __v128 simdop(operator, __v128 op1, __v128 op2);
>
> This will be a function built in to the compiler, at least for the x86.
> (Other architectures can provide an implementation of it that simulates its
> operation, but I doubt that it would be worth anyone's while to use that.)
>
> The operators would be an enum listing of the SIMD opcodes,
>
> PFACC, PFADD, PFCMPEQ, etc.
>
> For:
>
> z = simdop(PFADD, x, y);
>
> the compiler would generate:
>
> MOV z,x
> PFADD z,y
>