Allow cast of any pointer to cast to a trait pointer (rust-lang#98)

* Allow cast of any pointer to cast to a trait pointer

Also:
* Add predicates `use_*_pointer(mir_type)` to use mir pointer metadata
  to identify the correct type of pointer to a mir type.
* Use predicates `use_*_pointer(mir_type)` in fat pointer construction

Resolves model-checking/kani#83

Co-authored-by: Mark R. Tuttle <[email protected]>

Author: 2 people

compiler/rustc_codegen_llvm/src/gotoc/rvalue.rs

@@ -750,9 +750,9 @@ impl<'tcx> GotocCtx<'tcx> {
     fn codegen_vtable_size_and_align(&self, operand_type: Ty<'tcx>) -> (Expr, Expr) {
         debug!("vtable_size_and_align {:?}", operand_type.kind());
         let vtable_layout = match operand_type.kind() {
-            ty::Ref(_region, inner_type, _mutability) => self.layout_of(inner_type), //DSN was operand type
-            ty::Adt(..) => self.layout_of(operand_type),
-            _ => unreachable!("We got a vtable type that wasn't a ref or adt."),
+            ty::Ref(_, inner_type, ..) => self.layout_of(inner_type),
+            ty::RawPtr(ty::TypeAndMut { ty: inner_type, .. }) => self.layout_of(inner_type),
+            _ => self.layout_of(operand_type),
         };
         let vt_size = Expr::int_constant(vtable_layout.size.bytes(), Type::size_t());
         let vt_align = Expr::int_constant(vtable_layout.align.abi.bytes(), Type::size_t());
@@ -882,30 +882,29 @@ impl<'tcx> GotocCtx<'tcx> {
         let src_pointee_type = pointee_type(src_mir_type).unwrap();
         let dst_pointee_type = pointee_type(dst_mir_type).unwrap();
 
-        let dst_pointee_metadata_type = dst_pointee_type.ptr_metadata_ty(self.tcx);
-        let unit = self.tcx.types.unit;
-        let usize = self.tcx.types.usize;
-
-        if dst_pointee_metadata_type == unit {
+        if self.use_thin_pointer(dst_pointee_type) {
             assert_eq!(src_pointee_type, dst_pointee_type);
             None
-        } else if dst_pointee_metadata_type == usize {
+        } else if self.use_slice_fat_pointer(dst_pointee_type) {
             self.cast_sized_pointer_to_slice_fat_pointer(
                 src_goto_expr,
                 src_mir_type,
                 dst_mir_type,
                 src_pointee_type,
                 dst_pointee_type,
             )
-        } else {
-            // dst_pointee_metadata_type == std::ptr::DynMetadata<dyn trait> (a vtable is required)
+        } else if self.use_vtable_fat_pointer(dst_pointee_type) {
             self.cast_sized_pointer_to_trait_fat_pointer(
                 src_goto_expr,
                 src_mir_type,
                 dst_mir_type,
                 src_pointee_type,
                 dst_pointee_type,
             )
+        } else {
+            unreachable!(
+                "A pointer is either a thin pointer, slice fat pointer, or vtable fat pointer."
+            );
         }
     }
 
@@ -1027,7 +1026,7 @@ impl<'tcx> GotocCtx<'tcx> {
         dst_mir_type: Ty<'tcx>,
     ) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
         match (src_mir_type.kind(), dst_mir_type.kind()) {
-            (ty::Adt(..), ty::Dynamic(..)) => Some((src_mir_type.clone(), dst_mir_type.clone())),
+            (_, ty::Dynamic(..)) => Some((src_mir_type.clone(), dst_mir_type.clone())),
             (ty::Adt(..), ty::Adt(..)) => {
                 let src_fields = self.mir_struct_field_types(src_mir_type);
                 let dst_fields = self.mir_struct_field_types(dst_mir_type);

compiler/rustc_codegen_llvm/src/gotoc/typ.rs

@@ -1015,3 +1015,19 @@ pub fn pointee_type(pointer_type: Ty<'tcx>) -> Option<Ty<'tcx>> {
         _ => None,
     }
 }
+
+impl<'tcx> GotocCtx<'tcx> {
+    /// A pointer to the mir type should be a thin pointer.
+    pub fn use_thin_pointer(&self, mir_type: Ty<'tcx>) -> bool {
+        return mir_type.ptr_metadata_ty(self.tcx) == self.tcx.types.unit;
+    }
+    /// A pointer to the mir type should be a slice fat pointer.
+    pub fn use_slice_fat_pointer(&self, mir_type: Ty<'tcx>) -> bool {
+        return mir_type.ptr_metadata_ty(self.tcx) == self.tcx.types.usize;
+    }
+    /// A pointer to the mir type should be a vtable fat pointer.
+    pub fn use_vtable_fat_pointer(&self, mir_type: Ty<'tcx>) -> bool {
+        let metadata = mir_type.ptr_metadata_ty(self.tcx);
+        return metadata != self.tcx.types.unit && metadata != self.tcx.types.usize;
+    }
+}

rust-tests/cbmc-reg/Closure/main.rs

@@ -2,17 +2,11 @@
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 //! test that we implement closures correctly
 
-// Commenting out the test that induces the issue described in
-// https://github.com/model-checking/rmc/issues/83
-// until this issue is resolved.
-
-/*
 fn closure_with_empty_args() {
     let bytes = vec![0];
     let b = bytes.get(0).ok_or_else(|| ()).unwrap();
     assert!(*b == 0);
 }
-*/
 
 fn closure_with_1_arg() {
     let b = Some(3);
@@ -45,7 +39,7 @@ fn test_env() {
 }
 
 fn main() {
-    // closure_with_empty_args();
+    closure_with_empty_args();
     closure_with_1_arg();
     test_three_args();
     test_unit_args();