Time to revert bad commits?

[Fabian Bieler]

On Monday 02 June 2008 12:04:54 Stefan Dösinger wrote:
> Am Montag, 2. Juni 2008 11:57:21 schrieb Ivan Gyurdiev:
> > The patch being reverted seems interesting - it basically undoes a prior
> > effort to get local constants into the same namespace as global ones due
> > to relative addressing. I assume this is done for performance reasons,
> > is this correct ?  I see your patch is special-case disabled in the case
> > of relative addressing. Do we really want to support multiple constant
> > loading code paths for performance savings ?
>
> Yes, it is for performance reasons, and yes, we want the multiple paths. It
> may be a small, non-algorithmic improvement, but those small improvements
> are where you get the performance from in 3D rendering.
>
> The reason for this is not only avoiding reloading the local constants each
> shader change or constant change, but by moving the local constants away
> from the global constant space we don't have to reload unchanged global
> constants due to a local constant change.
>
> On MacOS I achived a 5-15% performance gain with those constant loading
> optimizations, depending on the app, this is quite a lot. On the Linux
> Nvidia driver it was smaller, around 2-3% because the constant loading
> seems to be more efficient there.
The shader compiler can also do better optimization with hard-coded constants 
(particularly if the constants are 0 or 1). I've seen the nvidia-compiler 
remove entire code paths because of this in a hl2-shader.