Generate deterministic ptx for OptiX cache hits

[chellmuth]

Description

In multithreaded environments, use of global counter ids inside function and variable identifiers in generated ptx code leads to cache misses during OptiX module compilation.

With this change we assume unique shadergroup names, and remove the non-deterministic ids. In my testing, everything is still OptiX-compatible even with duplicate shadergroup names, but I'm not sure I've considered all the valid cases.

Tests

Existing tests pass; I can add tests that run shaders twice and grep the logs for cache misses if desired.

Checklist:

• I have read the contribution guidelines.
• I have previously submitted a Contributor License Agreement.
• I have updated the documentation, if applicable.
• I have ensured that the change is tested somewhere in the testsuite (adding new test cases if necessary).
• My code follows the prevailing code style of this project.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: chellmuth / name: Chris Hellmuth (09b6e10, d4bc8e0, 05e85f7)

[lgritz]

LGTM, pending that one extremely minor change I suggested, and squaring away the CLA. (Is this really your first OSL patch?)

[lgritz]

@timgrant @ee33 You may find this interesting, especially the change in src/liboslexec/llvm_util.cpp

[tgrant-nv]

Thanks for the heads-up, Larry. Stripping the callseq comments from the PTX string is something Chris and I had discussed. It seems like the best solution short of patching LLVM, since as far as we can tell there is no way to manage these comments through the LLVM API.