Introduce `ConstAllocation`.

Currently some `Allocation`s are interned, some are not, and it's very
hard to tell at a use point which is which.

This commit introduces `ConstAllocation` for the known-interned ones,
which makes the division much clearer. `ConstAllocation::inner()` is
used to get the underlying `Allocation`.

In some places it's natural to use an `Allocation`, in some it's natural
to use a `ConstAllocation`, and in some places there's no clear choice.
I've tried to make things look as nice as possible, while generally
favouring `ConstAllocation`, which is the type that embodies more
information. This does require quite a few calls to `inner()`.

The commit also tweaks how `PartialOrd` works for `Interned`. The
previous code was too clever by half, building on `T: Ord` to make the
code shorter. That caused problems with deriving `PartialOrd` and `Ord`
for `ConstAllocation`, so I changed it to build on `T: PartialOrd`,
which is slightly more verbose but much more standard and avoided the
problems.

1 files changed, 3 insertions, 3 deletions

diff --git a/compiler/rustc_codegen_ssa/src/traits/consts.rs b/compiler/rustc_codegen_ssa/src/traits/consts.rs
index 5260b7cc331..918f3684169 100644
--- a/compiler/rustc_codegen_ssa/src/traits/consts.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/consts.rs
@@ -1,6 +1,6 @@
 use super::BackendTypes;
 use crate::mir::place::PlaceRef;
-use rustc_middle::mir::interpret::{Allocation, Scalar};
+use rustc_middle::mir::interpret::{ConstAllocation, Scalar};
 use rustc_middle::ty::layout::TyAndLayout;
 use rustc_span::Symbol;
 use rustc_target::abi::{self, Size};
@@ -26,13 +26,13 @@ pub trait ConstMethods<'tcx>: BackendTypes {
     fn const_to_opt_uint(&self, v: Self::Value) -> Option<u64>;
     fn const_to_opt_u128(&self, v: Self::Value, sign_ext: bool) -> Option<u128>;
 
-    fn const_data_from_alloc(&self, alloc: &Allocation) -> Self::Value;
+    fn const_data_from_alloc(&self, alloc: ConstAllocation<'tcx>) -> Self::Value;
 
     fn scalar_to_backend(&self, cv: Scalar, layout: abi::Scalar, llty: Self::Type) -> Self::Value;
     fn from_const_alloc(
         &self,
         layout: TyAndLayout<'tcx>,
-        alloc: &Allocation,
+        alloc: ConstAllocation<'tcx>,
         offset: Size,
     ) -> PlaceRef<'tcx, Self::Value>;