radeonsi: zero init variable by default
This MR tries to resolve rendering bugs caused by uninitialized variables in a way the doesn't penalize correct applications.
It solves the problem for at least the following apps/shadertoy:
- https://www.shadertoy.com/view/XlGcRD
- https://www.shadertoy.com/view/ldKyzR
- https://www.shadertoy.com/view/Xt3cWS
- #2689 (closed)
- #2598 (closed)
shader-db results summary is (updated for v2):
| PERCENTAGE DELTAS | Shaders | SGPRs | VGPRs | SpillSGPR | SpillVGPR | PrivVGPR | Scratch | CodeSize | MaxWaves | Waits |
|---|---|---|---|---|---|---|---|---|---|---|
| All affected | 6.5% | -0.10% | 1.78 % | 4.20 % | . | . | . | 0.70 % | -0.04 % | . |
All affected shaders I've looked at have use-uninitialized-variable kind of bugs.