interpret: add mplace_to_ref helper method

compiler/rustc_const_eval/src/interpret/place.rs

@@ -157,7 +157,6 @@ impl<Prov: Provenance> MemPlace<Prov> {
     }
 
     /// Turn a mplace into a (thin or wide) pointer, as a reference, pointing to the same space.
-    /// This is the inverse of `ref_to_mplace`.
     #[inline(always)]
     pub fn to_ref(self, cx: &impl HasDataLayout) -> Immediate<Prov> {
         match self.meta {
@@ -415,7 +414,7 @@ where
     }
 
     /// Take a value, which represents a (thin or wide) reference, and make it a place.
-    /// Alignment is just based on the type. This is the inverse of `MemPlace::to_ref()`.
+    /// Alignment is just based on the type. This is the inverse of `mplace_to_ref()`.
     ///
     /// Only call this if you are sure the place is "valid" (aligned and inbounds), or do not
     /// want to ever use the place for memory access!
@@ -438,6 +437,18 @@ where
         Ok(MPlaceTy::from_aligned_ptr_with_meta(ptr.to_pointer(self)?, layout, meta))
     }
 
+    /// Turn a mplace into a (thin or wide) mutable raw pointer, pointing to the same space.
+    /// `align` information is lost!
+    /// This is the inverse of `ref_to_mplace`.
+    pub fn mplace_to_ref(
+        &self,
+        mplace: &MPlaceTy<'tcx, M::Provenance>,
+    ) -> InterpResult<'tcx, ImmTy<'tcx, M::Provenance>> {
+        let imm = mplace.to_ref(self);
+        let layout = self.layout_of(Ty::new_mut_ptr(self.tcx.tcx, mplace.layout.ty))?;
+        Ok(ImmTy::from_immediate(imm, layout))
+    }
+
     /// Take an operand, representing a pointer, and dereference it to a place.
     /// Corresponds to the `*` operator in Rust.
     #[instrument(skip(self), level = "debug")]

compiler/rustc_const_eval/src/interpret/terminator.rs

@@ -852,10 +852,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         let instance = ty::Instance::resolve_drop_in_place(*self.tcx, place.layout.ty);
         let fn_abi = self.fn_abi_of_instance(instance, ty::List::empty())?;
 
-        let arg = ImmTy::from_immediate(
-            place.to_ref(self),
-            self.layout_of(Ty::new_mut_ptr(self.tcx.tcx, place.layout.ty))?,
-        );
+        let arg = self.mplace_to_ref(&place)?;
         let ret = MPlaceTy::fake_alloc_zst(self.layout_of(self.tcx.types.unit)?);
 
         self.eval_fn_call(

src/tools/miri/src/borrow_tracker/stacked_borrows/mod.rs

@@ -15,7 +15,7 @@ use rustc_data_structures::fx::FxHashSet;
 use rustc_middle::mir::{Mutability, RetagKind};
 use rustc_middle::ty::{
     self,
-    layout::{HasParamEnv, LayoutOf},
+    layout::HasParamEnv,
     Ty,
 };
 use rustc_target::abi::{Abi, Align, Size};
@@ -993,8 +993,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
 
         // We have to turn the place into a pointer to use the usual retagging logic.
         // (The pointer type does not matter, so we use a raw pointer.)
-        let ptr_layout = this.layout_of(Ty::new_mut_ptr(this.tcx.tcx, place.layout.ty))?;
-        let ptr = ImmTy::from_immediate(place.to_ref(this), ptr_layout);
+        let ptr = this.mplace_to_ref(place)?;
         // Reborrow it. With protection! That is the entire point.
         let new_perm = NewPermission::Uniform {
             perm: Permission::Unique,

src/tools/miri/src/borrow_tracker/tree_borrows/mod.rs

@@ -7,7 +7,7 @@ use rustc_middle::{
     mir::{Mutability, RetagKind},
     ty::{
         self,
-        layout::{HasParamEnv, LayoutOf},
+        layout::HasParamEnv,
         Ty,
     },
 };
@@ -488,8 +488,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
 
         // We have to turn the place into a pointer to use the usual retagging logic.
         // (The pointer type does not matter, so we use a raw pointer.)
-        let ptr_layout = this.layout_of(Ty::new_mut_ptr(this.tcx.tcx, place.layout.ty))?;
-        let ptr = ImmTy::from_immediate(place.to_ref(this), ptr_layout);
+        let ptr = this.mplace_to_ref(place)?;
         // Reborrow it. With protection! That is the entire point.
         let new_perm = NewPermission {
             initial_state: Permission::new_active(),