Move try_to_bits from Const to Valtree

[FedericoBruzzone]

This PR is a follow-up to #135158

What's in this PR?

• Move try_to_bits: Transitioned from Const to Valtree.
• Rename validate_const_with_value: Renamed to extract_valtree_and_ty for better clarity.

Benefits

• Extracting bits directly from Valtree avoids the need to re-evaluate a Const, improving efficiency where this re-evaluation was previously performed. For instance, in:
  • compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs (a FIXME was left behind), and
  • compiler/rustc_ty_utils/src/layout.rs (introduced in Add TooGeneric variant to LayoutError and emit Unknown #135158).

---

r? @lukas-code @oli-obk

[rustbot]

Some changes occurred in compiler/rustc_sanitizers

cc @rust-lang/project-exploit-mitigations, @rcvalle

[lukas-code]

IMO we should eventually add a proper type for type-level const values rather that use a tuple of (Ty, ValTree) everywhere, but this PR is already an improvement :)

[FedericoBruzzone]

IMO we should eventually add a proper type for type-level const values rather that use a tuple of (Ty, ValTree) everywhere, but this PR is already an improvement :)

Currently, I introduced the proper type (ValTreeAndTy) locally to compiler/rustc_ty_utils/src/layout.rs. Let me know if a better solution could be move it externally.

[oli-obk]

cc @BoxyUwU this is a practical type we could use in more places, and implement methods like try_to_bits directly on, to avoid having to pass the type separately

[BoxyUwU]

Ah yeah sorry this was intended to be follow up work from the original PR that removed Ty from ty::Const but it just didn't wind up happening 👍

[lukas-code]

I have a branch that implements this PR's approach more globally (master...lukas-code:rust:typed-valtree), will send PR soon.

[FedericoBruzzone]

I will look at that PR as soon as possible.