Carry float flags through lowering and lifting

[jlogan03]

This will simplify the addition of float controls to rust-gpu, which would otherwise require a workaround to preserve the flags.

[eddyb]

I've been playing with a slightly different version of this, that can also support e.g. OpDecorateId, if we ever need that, etc.

(leaving this review so we don't accidentally land both)

[jlogan03]

@eddyb Want me to take a swing at generalizing this on my branch as well? I test-drove generalizing it locally and it actually made the change about 10 lines shorter, which feels like a good sign

[jlogan03]

I went ahead and pushed the generalization since it's an improvement over the original even without considering the added functionality.

[eddyb]

I test-drove generalizing it locally and it actually made the change about 10 lines shorter, which feels like a good sign

I was hoping to avoid anyone else spending any more effort on this, by pushing my version sooner, but it's up now, so you can check out the first 3 commits from:

• Minimal support for several SPIR-V features (either new, or rare edge cases, some Rust-GPU specific). #52

(notably, Attr::SpvAnnotation is extended, forcing all use sites of Attr::SpvAnnotation to consider whether they need to care about ID operands, and spv::Inst is still outside the OrdAssertEq<Vec<_>>)