Auto merge of #94597 - nnethercote:ConstAllocation, r=fee1-dead

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.

r? `@fee1-dead`

1 files changed, 4 insertions, 4 deletions

diff --git a/compiler/rustc_mir_transform/src/const_prop.rs b/compiler/rustc_mir_transform/src/const_prop.rs
index d849bc408fa..34c539f3191 100644
--- a/compiler/rustc_mir_transform/src/const_prop.rs
+++ b/compiler/rustc_mir_transform/src/const_prop.rs
@@ -31,8 +31,8 @@ use rustc_trait_selection::traits;
 use crate::MirPass;
 use rustc_const_eval::const_eval::ConstEvalErr;
 use rustc_const_eval::interpret::{
-    self, compile_time_machine, AllocId, Allocation, ConstValue, CtfeValidationMode, Frame, ImmTy,
-    Immediate, InterpCx, InterpResult, LocalState, LocalValue, MemPlace, MemoryKind, OpTy,
+    self, compile_time_machine, AllocId, ConstAllocation, ConstValue, CtfeValidationMode, Frame,
+    ImmTy, Immediate, InterpCx, InterpResult, LocalState, LocalValue, MemPlace, MemoryKind, OpTy,
     Operand as InterpOperand, PlaceTy, Scalar, ScalarMaybeUninit, StackPopCleanup, StackPopUnwind,
 };
 
@@ -274,7 +274,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine<'mir, 'tcx>
     fn before_access_global(
         _memory_extra: &(),
         _alloc_id: AllocId,
-        allocation: &Allocation<Self::PointerTag, Self::AllocExtra>,
+        alloc: ConstAllocation<'tcx, Self::PointerTag, Self::AllocExtra>,
         _static_def_id: Option<DefId>,
         is_write: bool,
     ) -> InterpResult<'tcx> {
@@ -283,7 +283,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine<'mir, 'tcx>
         }
         // If the static allocation is mutable, then we can't const prop it as its content
         // might be different at runtime.
-        if allocation.mutability == Mutability::Mut {
+        if alloc.inner().mutability == Mutability::Mut {
             throw_machine_stop_str!("can't access mutable globals in ConstProp");
         }