C Compiler to SPIR-V

Have a look at QBE as it may provide basic optimizations and some significant performant boost: cproc + QBE and I get 70% of gcc 13.2 -O2 speed in my benchmarks, tinycc is 2 times slower than gcc 13.2 -O2 in the same benchmarks (my benchmarks are very basic, but it shows...).

We are talking gcc complexity is grotesque/absurd for those 30%, not to mention this is now brain damaged c++ (one of the biggest mistakes in open source software ever).

I know QBE is for CPUs, but maybe there is something there for GPUs.

QBE has no support for SIMD last I looked into it, so I don't think it would be appropriate for an SPMD language. https://todo.sr.ht/~mpu/qbe/5

It's common for shader compilers to invent their own IR, like Shadey and Slang IR.

That link just says that the maintainer of the fork mpu for hare has no will nor abilities to add full SIMD support. But qbe is still written and maintained by Brian Callahan here: https://c9x.me/compile/