change is_subtype to relate_types

Author: ouz-a

src/base.rs

@@ -876,7 +876,7 @@ 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, ty),
+            PlaceElem::Subtype(ty) => cplace = cplace.place_transmute_type(fx, fx.monomorphize(ty)),
             PlaceElem::Field(field, _ty) => {
                 cplace = cplace.place_field(fx, field);
             }

src/value_and_place.rs

@@ -674,12 +674,14 @@ impl<'tcx> CPlace<'tcx> {
         }
     }
 
+    /// Used for `ProjectionElem::Subtype`, ty has to be monomorphized before
+    /// passed on.
     pub(crate) fn place_transmute_type(
         self,
         fx: &mut FunctionCx<'_, '_, 'tcx>,
         ty: Ty<'tcx>,
     ) -> CPlace<'tcx> {
-        CPlace { inner: self.inner, layout: fx.layout_of(fx.monomorphize(ty)) }
+        CPlace { inner: self.inner, layout: fx.layout_of(ty) }
     }
 
     pub(crate) fn place_field(