Cycles: Useful Metal backend debug & profiling functionality
This patch adds some useful debugging & profiling env vars to the Metal backend:
- `CYCLES_METAL_PROFILING`: output a per-kernel timing report at the end of the render
- `CYCLES_METAL_DEBUG`: enable per-dispatch tracing (very verbose)
- `CYCLES_DEBUG_METAL_CAPTURE_KERNEL`: enable programatic .gputrace capture for a specified kernel index
Here's an example of the timing report with `CYCLES_METAL_PROFILING` enabled:
```
---------------------------------------------------------------------------------------------------
Kernel name Total threads Dispatches Avg. T/D Time Time%
---------------------------------------------------------------------------------------------------
integrator_init_from_camera 657,407,232 161 4,083,274 0.24s 0.51%
integrator_intersect_closest 1,629,288,440 681 2,392,494 15.18s 32.12%
integrator_intersect_shadow 751,652,291 470 1,599,260 5.80s 12.28%
integrator_shade_background 304,612,074 263 1,158,220 1.16s 2.45%
integrator_shade_surface 1,159,764,041 676 1,715,627 20.57s 43.52%
integrator_shade_shadow 598,885,847 418 1,432,741 1.27s 2.69%
integrator_queued_paths_array 2,969,650,130 805 3,689,006 0.35s 0.74%
integrator_queued_shadow_paths_array 593,936,619 379 1,567,115 0.14s 0.29%
integrator_terminated_paths_array 22,205,417 155 143,260 0.05s 0.10%
integrator_sorted_paths_array 2,517,140,043 676 3,723,579 1.65s 3.50%
integrator_compact_paths_array 648,912,748 155 4,186,533 0.03s 0.07%
integrator_compact_states 20,872,687 155 134,662 0.14s 0.29%
integrator_terminated_shadow_paths_array 374,100,675 438 854,111 0.16s 0.33%
integrator_compact_shadow_paths_array 503,768,657 438 1,150,156 0.05s 0.10%
integrator_compact_shadow_states 37,664,941 202 186,460 0.23s 0.50%
integrator_reset 25,165,824 6 4,194,304 0.06s 0.12%
film_convert_combined_half_rgba 3,110,400 6 518,400 0.00s 0.01%
prefix_sum 676 676 1 0.19s 0.40%
---------------------------------------------------------------------------------------------------
6,760 47.27s 100.00%
---------------------------------------------------------------------------------------------------
```
Reviewed By: brecht
Differential Revision: https://developer.blender.org/D15044
4412e14708