rust/compiler/rustc_traits
bors 0978a9eb99 Auto merge of #83207 - oli-obk:valtree2, r=lcnr
normalize mir::Constant differently from ty::Const in preparation for valtrees

Valtrees are unable to represent many kind of constant values (this is on purpose). For constants that are used at runtime, we do not need a valtree representation and can thus use a different form of evaluation. In order to make this explicit and less fragile, I added a `fold_constant` method to `TypeFolder` and implemented it for normalization. Normalization can now, when it wants to eagerly evaluate a constant, normalize `mir::Constant` directly into a `mir::ConstantKind::Val` instead of relying on the `ty::Const` evaluation.

In the future we can get rid of the `ty::Const` in there entirely and add our own `Unevaluated` variant to `mir::ConstantKind`. This would allow us to remove the `promoted` field from `ty::ConstKind::Unevaluated`, as promoteds can never occur in the type system.

cc `@rust-lang/wg-const-eval`

r? `@lcnr`
2021-04-02 10:28:12 +00:00
..
src Auto merge of #83207 - oli-obk:valtree2, r=lcnr 2021-04-02 10:28:12 +00:00
Cargo.toml bumped smallvec deps 2021-02-14 18:03:11 +03:00