[Migrated] We should ensure entry interface types have reliable layout.

Issue automatically imported from old repo: https://github.com/EmbarkStudios/rust-gpu/issues/575
Old labels: t: enhancement,c: rustc_codegen_spirv
Originally creatd by eddyb on 2021-04-05T07:04:27Z 👍: 3

Sadly, it's hard/impossible to account for #[cfg]s in e.g. glam, and vector types in general tend to have weirder alignment rules than scalars (and aggregates thereof).

But we should at the very least require #[repr(C)], and maybe even disallow any interior padding or wildly varying alignments (as that would imply potentially different alignments on the host).

I almost wish Rust had explicit field offsets with a per-field attribute - we could require that to guarantee that the host would see the same layout and it would let us have the weirder layouts mentioned in #11.

Inizia esaminando l’area rustc_codegen_spirv e i vincoli descritti per #[repr(C)], il padding interno e gli allineamenti variabili. Leggi la discussione correlata nell’issue #11; questa issue sarà completa solo quando sarà specificata e implementata una policy di layout decisa e affidabile per i tipi di interfaccia di ingresso.