Based on #123377 by @brecht, but Gitea doesn't like the rebase these
so here's a new PR.
The purpose here is to switch to fused OptiX programs for OSL execution
on CUDA. On the one hand, this makes the code easier since, but there's
also another advantage - how memory allocation is managed.
OSL shaders need memory to store intermediate values, but how much is
needed depends on the complexity of the shader. With the split program
approach, Cycles had to provide that memory, so we had to allocate a
certain amount (2 KiB, to be precise) statically and show an error if
the shader would need more. If the shader used less (which is the case
for the vast majority), the memory was just wasted.
By switching to fused kernels, OSL knows the required amount during JIT
codegen, so it can allocate only what's required, which avoids this
waste. One still needs to set a maximum, and in theory, OSL would also
support spilling over into a Cycles-provided alternative memory region.
However, we currently don't implement that - instead, we default to the
same 2048 limit as before and let advanced users override it via the
CYCLES_OSL_GROUPDATA_ALLOC environment variable if really needed.
Co-authored-by: Brecht Van Lommel <brecht@blender.org>
Pull Request: https://projects.blender.org/blender/blender/pulls/130149
0de1cea5c5