[Mono-dev] Mono generates inefficient vectorized code

[Jerry Maine - KF5ADY]

And what needs to be done to get the global allocator to work?

Rodrigo Kumpera wrote:
> Hi Sergei,
>
> On Thu, Mar 11, 2010 at 8:30 PM, Sergei Dyshel 
> <qyron.private at gmail.com <mailto:qyron.private at gmail.com>> wrote:
>
>     Hello,
>     I'm doing some research on vectorization using Mono. I've noticed that
>     code generated by Mono's JIT contains many unnecessary memory loads
>     and stores. Here is simple example, the full code is attached:
>
>     public static unsafe int sum(int* a, int size) {
>      Vector4i temp = new Vector4i();
>      Vector4i* p = (Vector4i*) a;
>      for (int i = 0; i < size/4; i++) {
>        temp += *p;
>        p += 1;
>      }
>      return temp.X + temp.Y + temp.Z + temp.W;
>     }
>
>
>  
> The problem you're seen of going to memory when not needed is due to 
> the fact that
> mono lacks a working global register allocator. If you use a value in 
> a single basic block,
> you'll notice that it's kept in memory the whole time.
>
> We don't eliminate a lot of redundancies, even under SSA, because our 
> JIT doesn't know how
> to handle SIMD ops under that form. It's an open problem requiring 
> some work. The same
> applies to our global register allocator.
> ------------------------------------------------------------------------
>
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