Please see the SPIR-T repository for more information, but to quote the top of its README:

SPIR-🇹

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SPIR-🇹 is a research project aimed at exploring shader-oriented IR designs derived from SPIR-V, and producing a framework around such an IR to facilitate advanced compilation pipelines, beyond what existing SPIR-V tooling allows for.

This PR integrates it into Rust-GPU in a very limited capacity, in the middle of a sequence of passes operating on SPIR-V, as a ... -> SPIR-V -> SPIR-T -> SPIR-V -> ... conversion, with the only SPIR-T -> SPIR-T pass being the CFG structurizer (substituting our own structurizer, which we may want to delete?).

That alone is enough to show some compile-time speedups of over 30% in some workloads, while adding only marginal overhead (~0.1%), and it's still being limited by our existing passes (see EmbarkStudios/spirt#6).

To enable, you can use RUSTGPU_CODEGEN_ARGS=--spirt - to quote the (more detailed) codegen-args.md docs:

--spirt

Enables using the experimental SPIR-🇹 shader IR framework in the linker - more specifically, this:

• adds a SPIR-V -> SPIR-🇹 -> SPIR-V roundtrip
  (future SPIR-🇹 passes would go in the middle of this, and eventually codegen might not produce SPIR-V at all)
• replaces the existing structurizer with SPIR-🇹 structurization (which is more robust and can e.g. handle OpPhis)
• runs some existing SPIR-V legalization/optimization passes (mem2reg) before inlining, instead of only after (as the OpPhis they would produce are no longer an issue for structurization)

For more information, also see the SPIR-🇹 repository.

--dump-spirt-passes FILE

Dump the SPIR-🇹 module across passes (i.e. all of the versions before/after each pass), as a combined report, to FILE and FILE.html.
_{(the .html version of the report is the recommended form for viewing, as it uses tabling for versions, syntax-highlighting-like styling, and use->def linking)}

Opening this PR as a draft because there are some discussions that need to be had, i.e.: