1 files changed, 59 insertions, 0 deletions
diff --git a/compiler/rustc_const_eval/src/interpret/traits.rs b/compiler/rustc_const_eval/src/interpret/traits.rs
new file mode 100644
index 000000000..b3a511d5a
--- /dev/null
+++ b/compiler/rustc_const_eval/src/interpret/traits.rs
@@ -0,0 +1,59 @@
+use rustc_middle::mir::interpret::{InterpResult, Pointer};
+use rustc_middle::ty::layout::LayoutOf;
+use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_target::abi::{Align, Size};
+
+use super::util::ensure_monomorphic_enough;
+use super::{InterpCx, Machine};
+
+impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
+    /// Creates a dynamic vtable for the given type and vtable origin. This is used only for
+    /// objects.
+    ///
+    /// The `trait_ref` encodes the erased self type. Hence, if we are making an object `Foo<Trait>`
+    /// from a value of type `Foo<T>`, then `trait_ref` would map `T: Trait`. `None` here means that
+    /// this is an auto trait without any methods, so we only need the basic vtable (drop, size,
+    /// align).
+    pub fn get_vtable_ptr(
+        &self,
+        ty: Ty<'tcx>,
+        poly_trait_ref: Option<ty::PolyExistentialTraitRef<'tcx>>,
+    ) -> InterpResult<'tcx, Pointer<Option<M::Provenance>>> {
+        trace!("get_vtable(trait_ref={:?})", poly_trait_ref);
+
+        let (ty, poly_trait_ref) = self.tcx.erase_regions((ty, poly_trait_ref));
+
+        // All vtables must be monomorphic, bail out otherwise.
+        ensure_monomorphic_enough(*self.tcx, ty)?;
+        ensure_monomorphic_enough(*self.tcx, poly_trait_ref)?;
+
+        let vtable_symbolic_allocation = self.tcx.create_vtable_alloc(ty, poly_trait_ref);
+        let vtable_ptr = self.global_base_pointer(Pointer::from(vtable_symbolic_allocation))?;
+        Ok(vtable_ptr.into())
+    }
+
+    /// Returns a high-level representation of the entires of the given vtable.
+    pub fn get_vtable_entries(
+        &self,
+        vtable: Pointer<Option<M::Provenance>>,
+    ) -> InterpResult<'tcx, &'tcx [ty::VtblEntry<'tcx>]> {
+        let (ty, poly_trait_ref) = self.get_ptr_vtable(vtable)?;
+        Ok(if let Some(poly_trait_ref) = poly_trait_ref {
+            let trait_ref = poly_trait_ref.with_self_ty(*self.tcx, ty);
+            let trait_ref = self.tcx.erase_regions(trait_ref);
+            self.tcx.vtable_entries(trait_ref)
+        } else {
+            TyCtxt::COMMON_VTABLE_ENTRIES
+        })
+    }
+
+    pub fn get_vtable_size_and_align(
+        &self,
+        vtable: Pointer<Option<M::Provenance>>,
+    ) -> InterpResult<'tcx, (Size, Align)> {
+        let (ty, _trait_ref) = self.get_ptr_vtable(vtable)?;
+        let layout = self.layout_of(ty)?;
+        assert!(!layout.is_unsized(), "there are no vtables for unsized types");
+        Ok((layout.size, layout.align.abi))
+    }
+}