Rollup merge of #130514 - compiler-errors:unsafe-binders, r=oli-obk

Implement MIR lowering for unsafe binders

This is the final bit of the unsafe binders puzzle. It implements MIR, CTFE, and codegen for unsafe binders, and enforces that (for now) they are `Copy`. Later on, I'll introduce a new trait that relaxes this requirement to being "is `Copy` or `ManuallyDrop<T>`" which more closely models how we treat union fields.

Namely, wrapping unsafe binders is now `Rvalue::WrapUnsafeBinder`, which acts much like an `Rvalue::Aggregate`. Unwrapping unsafe binders are implemented as a MIR projection `ProjectionElem::UnwrapUnsafeBinder`, which acts much like `ProjectionElem::Field`.

Tracking:
- https://github.com/rust-lang/rust/issues/130516

1 files changed, 7 insertions, 1 deletions

diff --git a/compiler/rustc_codegen_cranelift/src/base.rs b/compiler/rustc_codegen_cranelift/src/base.rs
index c7c9c6236d1..7a40d236b92 100644
--- a/compiler/rustc_codegen_cranelift/src/base.rs
+++ b/compiler/rustc_codegen_cranelift/src/base.rs
@@ -925,6 +925,10 @@ fn codegen_stmt<'tcx>(
                     }
                     crate::discriminant::codegen_set_discriminant(fx, lval, variant_index);
                 }
+                Rvalue::WrapUnsafeBinder(ref operand, _to_ty) => {
+                    let operand = codegen_operand(fx, operand);
+                    lval.write_cvalue_transmute(fx, operand);
+                }
             }
         }
         StatementKind::StorageLive(_)
@@ -993,7 +997,9 @@ pub(crate) fn codegen_place<'tcx>(
                 cplace = cplace.place_deref(fx);
             }
             PlaceElem::OpaqueCast(ty) => bug!("encountered OpaqueCast({ty}) in codegen"),
-            PlaceElem::Subtype(ty) => cplace = cplace.place_transmute_type(fx, fx.monomorphize(ty)),
+            PlaceElem::Subtype(ty) | PlaceElem::UnwrapUnsafeBinder(ty) => {
+                cplace = cplace.place_transmute_type(fx, fx.monomorphize(ty));
+            }
             PlaceElem::Field(field, _ty) => {
                 cplace = cplace.place_field(fx, field);
             }