provide a way to replace the tag in a Scalar/MemPlace

src/librustc/mir/interpret/value.rs

@@ -138,6 +138,14 @@ impl<'tcx, Tag> Scalar<Tag> {
         }
     }
 
+    #[inline]
+    pub fn with_tag(self, new_tag: Tag) -> Self {
+        match self {
+            Scalar::Ptr(ptr) => Scalar::Ptr(Pointer { tag: new_tag, ..ptr }),
+            Scalar::Bits { bits, size } => Scalar::Bits { bits, size },
+        }
+    }
+
     #[inline]
     pub fn ptr_null(cx: &impl HasDataLayout) -> Self {
         Scalar::Bits {

src/librustc_mir/interpret/place.rs

@@ -115,6 +115,16 @@ impl<Tag> MemPlace<Tag> {
         }
     }
 
+    #[inline]
+    pub fn with_tag(self, new_tag: Tag) -> Self
+    {
+        MemPlace {
+            ptr: self.ptr.with_tag(new_tag),
+            align: self.align,
+            meta: self.meta,
+        }
+    }
+
     #[inline(always)]
     pub fn from_scalar_ptr(ptr: Scalar<Tag>, align: Align) -> Self {
         MemPlace {
@@ -187,6 +197,16 @@ impl<'tcx, Tag> MPlaceTy<'tcx, Tag> {
         }
     }
 
+    #[inline]
+    pub fn with_tag(self, new_tag: Tag) -> Self
+    {
+        MPlaceTy {
+            mplace: self.mplace.with_tag(new_tag),
+            layout: self.layout,
+        }
+    }
+
+    #[inline]
     pub fn offset(
         self,
         offset: Size,