cg_llvm: Reduce the visibility of types, modules and using declarations in rustc_codegen_llvm.

[dpaoliello]

Final part of #135502

Reduces the visibility of types, modules and using declarations in the rustc_codegen_llvm to private or pub(crate) where possible, and marks unused fields and enum entries with #[expect(dead_code)].

r? @Zalathar

[Zalathar]

I've been thinking about how to deal with the enums that have more than 1-2 unused variants, especially the ones where almost all variants are unused.

Putting #[expect(dead_code)] on each individual variant is the most precise approach, but it has the massive practical downside of making the enums a nightmare to read/audit, which kind of defeats the point of wanting to keep them around while reducing visibility.

So for those enums, I think it's going to be better to just put #[expect(dead_code)] on the enum itself (instead of individual variants), and live with the fact that this makes it harder to see whether the enum is unused (or which variants are unused).

That's a bit of a shame, but it's still an improvement over the status quo of everything being pub.

[Zalathar]

Specifically, I'm proposing that these enums should have #[expect(dead_code)] on the enum itself, and not on its variants:

• AttributeKind
• TypeKind
• MetadataType
• Opcode

[dpaoliello]

Specifically, I'm proposing that these enums should have #[expect(dead_code)] on the enum itself, and not on its variants:

• AttributeKind
• TypeKind
• MetadataType
• Opcode

Done

[Zalathar]

Adding reasons for the expect attributes was a great idea, but some of them were slightly inaccurate, so I pushed a fix for that (diff).

[Zalathar]

@bors r+

[bors]

📌 Commit a5d4c5c has been approved by Zalathar

It is now in the queue for this repository.

[matthiaskrgr]

@bors r-
#137431 (comment)

[Zalathar]

Ah, this collided with some more pub items introduced by #136428.

[dpaoliello]

Ah, this collided with some more pub items introduced by #136428.

Updated.