add mplace_to_mut_ref

Author: WaffleLapkin

compiler/rustc_const_eval/src/interpret/place.rs

@@ -418,7 +418,7 @@ 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 `mplace_to_ptr()`.
+    /// 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!
@@ -440,7 +440,7 @@ where
 
     /// 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`.
+    /// This is the inverse of `ptr_to_mplace`.
     pub fn mplace_to_ptr(
         &self,
         mplace: &MPlaceTy<'tcx, M::Provenance>,
@@ -450,6 +450,22 @@ where
         interp_ok(ImmTy::from_immediate(imm, layout))
     }
 
+    /// Turn a mplace into a (thin or wide) mutable reference, pointing to the same space.
+    /// `align` information is lost!
+    /// This is the inverse of `ref_to_mplace`.
+    pub fn mplace_to_mut_ref(
+        &self,
+        mplace: &MPlaceTy<'tcx, M::Provenance>,
+    ) -> InterpResult<'tcx, ImmTy<'tcx, M::Provenance>> {
+        let imm = mplace.mplace.to_ref(self);
+        let layout = self.layout_of(Ty::new_mut_ref(
+            self.tcx.tcx,
+            self.tcx.tcx.lifetimes.re_erased,
+            mplace.layout.ty,
+        ))?;
+        interp_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 = "trace")]