miri cast: avoid unnecessary to_scalar_ptr

Author: RalfJung

src/librustc_mir/interpret/cast.rs

@@ -260,7 +260,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
         match (&src_pointee_ty.kind, &dest_pointee_ty.kind) {
             (&ty::Array(_, length), &ty::Slice(_)) => {
-                let ptr = self.read_immediate(src)?.to_scalar_ptr()?;
+                let ptr = self.read_immediate(src)?.to_scalar()?;
                 // u64 cast is from usize to u64, which is always good
                 let val = Immediate::new_slice(
                     ptr,
@@ -279,7 +279,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             (_, &ty::Dynamic(ref data, _)) => {
                 // Initial cast from sized to dyn trait
                 let vtable = self.get_vtable(src_pointee_ty, data.principal())?;
-                let ptr = self.read_immediate(src)?.to_scalar_ptr()?;
+                let ptr = self.read_immediate(src)?.to_scalar()?;
                 let val = Immediate::new_dyn_trait(ptr, vtable);
                 self.write_immediate(val, dest)
             }

src/librustc_mir/interpret/place.rs

@@ -287,7 +287,9 @@ where
         &self,
         val: ImmTy<'tcx, M::PointerTag>,
     ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
-        let pointee_type = val.layout.ty.builtin_deref(true).unwrap().ty;
+        let pointee_type = val.layout.ty.builtin_deref(true)
+            .expect("`ref_to_mplace` called on non-ptr type")
+            .ty;
         let layout = self.layout_of(pointee_type)?;
 
         let mplace = MemPlace {