d3dx9: Avoid expensive computations

[David Laight]

On Mon, Feb 25, 2013 at 11:08:02AM +0100, Henri Verbeet wrote:
> On 25 February 2013 10:24, Rico Sch?ller <kgbricola at web.de> wrote:
> > I did some small tests for speed with the following results. You may also
> > avoid such a lot of variable assignments like *pout = out and you may use 4
> > vecs instead. This should save ~48 assignments and it should also improve
> > the speed a bit more (~10%). Though, native is still 40% faster than that.
> >
> I'd somewhat expect native to use SSE versions of this kind of thing
> when the CPU supports those instructions. You also generally want to
> pay attention to the order in which you access memory, although
> perhaps it doesn't matter so much here because an entire matrix should
> be able to fit in a single cacheline, provided it's properly aligned.

Also make sure that are memory that is written to can't be aliased
by the memory that is read.
If aliasing is possible the compiler has sequence the code to
ensure the writes and reads happen in the correct order.

That function probably has too many live values for the normal
registers - so some values will get flushed to stack.
SSE might be better.

	David

-- 
David Laight: david at l8s.co.uk