Re: Fw: RFC: Representing vector lane load/store operations

[Ira Rosen <ira.rosen@linaro.org>]

>> ...Ira would know best, but I don't think it would be used for this
>> kind of loop.  It would be more something like:
>>
>>   for (i=0; i<N; ++i)
>>     X[i] = Y[i].red + Y[i].blue + Y[i].green;
>>
>> (not a realistic example).  You'd then have:
>>
>>    compoundY = __builtin_load_lanes (Y);
>>    red = ARRAY_REF <compoundY, 0>
>>    green = ARRAY_REF <compoundY, 1>
>>    blue = ARRAY_REF <compoundY, 2>
>>    D1 = red + green
>>    D2 = D1 + blue
>>    MEM_REF <X> = D2;
>>
>> My understanding is that'd we never do any operations besides ARRAY_REFs
>> on the compound value, and that the individual vectors would be treated
>> pretty much like any other.
>
> Ok, I thought it might be used to have a larger vectorization factor for
> loads and stores, basically make further unrolling cheaper because you
> don't have to duplicate the loads and stores.

Right, we can do that using vld1/vst1 instructions (full load/store
with N=1) and operate on up to 4 doubleword vectors in parallel. But
at the moment we are concentrating on efficient support of strided
memory accesses.

Ira