[cairo] JIT for pixman

[keita abdoul-kaker]

Can't we use a static compiler to all those transformation and
optimisation at compile time ?

On Sat, Jan 10, 2009 at 11:18 AM, Soeren Sandmann <sandmann at daimi.au.dk> wrote:
> Bobby Salazar <bobby8934 at inbox.com> writes:
>
>> Could someone please explain the benefits of JIT for pixman? I seen
>> a lot of talk about the best ways to approach JIT for pixman, but I
>> so far haven't been able to figure out what the benefits are? Does
>> it yield faster code/better performance for pixman, or easier
>> maintainability?
>
> A JIT compiler can potentially yield both better performance and
> better maintainability.
>
> There are a lot of combinations of formats and operators. It is true
> that only relatively few of them show up in any given app/environment,
> and we do have reasonably optimized versions of many common ones.
>
> But it is still possible to do a lot better. At the moment anything
> involving transformations or filters hits the slow path. Anything
> involving formats other than a8, argb32 and rgb16 hits the slow
> path. Anything involving operators outside OVER, IN, and ADD are hits
> the slow path.
>
> It is not going to be possible to cover all those combinations with
> handwritten fast paths, especially considering that there are plans to
> add more operators and that correct color management will require more
> image formats.
>
> Also, there is a ton of SIMD instruction sets. Just for x86 the
> currently available ones are: MMX, 3DNow!, SSE, SSE2, SSE3, SSE4,
> SSE4.1, and SSE4.2. The announced ones are SSE5, AVX, and
> Larrabee. There is also Altivec for PowerPC, and I believe two
> different ones for ARM.
>
> Putting all of these instruction sets to use without a JIT compiler is
> essentially impossible.
>
>
> Soren
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