The draft was just updated two days ago.
Are you saying that the direct mapping requirements I quoted above have been abandoned?
Yes.
See these quotes:
Apple: "Having an isolated focus on SPIR-V is not a good perspective, we have MSL etc. to consider too"
...
Apple: "Extreme A is no interaction with SPIRV?, extreme B is very tightly coupled to SPIRV, we should find a middle point"
...
Google: "We take all targets into consideration. We can allow developers do runtime probing and maybe branch according to that. Optimization occurs in existence of uncertainty. Dealing with fuzziness is a fact of life and we should give the tools to developers to determine in runtime."
From https://docs.google.com/document/d/15Pi1fYzr5F-aP92mosOLtRL4...
See also:
https://github.com/gpuweb/gpuweb/pull/599
https://github.com/gpuweb/gpuweb/issues/582
https://github.com/gpuweb/gpuweb/issues/566
http://kvark.github.io/spirv/2021/05/01/spirv-horrors.html
https://github.com/gpuweb/gpuweb/issues/847#issuecomment-642...
https://news.ycombinator.com/item?id=24858172
The process has been very implementation driven, with Naga, the Rust tooling that does the whole conversion shenanigans, growing and changing its IR and semantics steadily. It's ironic that a group that is usually very adverse to having a single implementation of things is now pointing to Naga and arguing that we don't need an easy conversion step because we have all the compiler infrastructure build already.
The group has slowly redefined "bijective" to mean "easily compilable", which would be pretty hilarious, if it weren't so sad.
It's a textbook case of: Embrace, Extend, Extinguish
Google tried to save it, but that proposal was rejected: https://docs.google.com/presentation/d/1ybmnmmzsZZTA0Y9awTDU...
The Proposal to work with both WGSL, was also not accepted because it would "weaken the position of WGSL".
"But think of the children/open web!"
Apple knows how to push the right buttons on the Mozilla folks so that they tag along: Rust, wEB-StAnDARds, not invented here.
- SPIRV was done by an evil technological group, not an open and inclusive standard body. We would tie our standard to whatever the SPRIV says, that's not open web. The open web can only flourish if everything is text based! cough WASM cough Rust ist such a modern language! -
It's similar to what happened to WebSQL, except this time it's much worse as it also ruins any hope that WASM might be able to replace all the other technological cruft. Playing the old guessing game of how the transpiler will mangle your SPIRV is simply not something that people want to go back to.