nitvm: Subtyping test is now implemented with direct access

Signed-off-by: Julien Pagès <julien.projet@gmail.com>

diff --git a/src/vm.nit b/src/vm.nit
index 1f6d574..b9a37c4 100644 (file)
--- a/src/vm.nit
+++ b/src/vm.nit
@@ -123,11 +123,12 @@ class VirtualMachine super NaiveInterpreter
                var super_id = sup.mclass.vtable.id
                var mask = sub.mclass.vtable.mask
 
-               return inter_is_subtype(super_id, mask, sub.mclass.vtable.internal_vtable)
+               # For now, we always use perfect hashing for subtyping test
+               return inter_is_subtype_ph(super_id, mask, sub.mclass.vtable.internal_vtable)
        end
 
        # Subtyping test with perfect hashing
-       private fun inter_is_subtype(id: Int, mask:Int, vtable: Pointer): Bool `{
+       private fun inter_is_subtype_ph(id: Int, mask:Int, vtable: Pointer): Bool `{
                // hv is the position in hashtable
                int hv = id & mask;
 
@@ -138,6 +139,14 @@ class VirtualMachine super NaiveInterpreter
                return *offset == id;
        `}
 
+       # Subtyping test with Cohen test (direct access)
+       private fun inter_is_subtype_sst(id: Int, position: Int, vtable: Pointer): Bool `{
+               // Direct access to the position given in parameter
+               int tableid = (long unsigned int)((long int *)vtable)[position];
+
+               return id == tableid;
+       `}
+
        # Redef init_instance to simulate the loading of a class
        redef fun init_instance(recv: Instance)
        do
@@ -364,6 +373,10 @@ redef class MClass
        # True when the class is effectively loaded by the vm, false otherwise
        var loaded: Bool = false
 
+       # Color for Cohen subtyping test : the absolute position of the id
+       # of this class in virtual tables
+       var color: Int
+
        # For each loaded subclass, keep the position of the group of attributes
        # introduced by self class in the object
        var positions_attributes: HashMap[MClass, Int] = new HashMap[MClass, Int]
@@ -433,6 +446,9 @@ redef class MClass
                allocate_vtable(v, ids, nb_methods, nb_attributes, offset_attributes, offset_methods)
                loaded = true
 
+               # Set the absolute position of the identifier of this class in the virtual table
+               color = offset_methods - 2
+
                # The virtual table now needs to be filled with pointer to methods
                superclasses.add(self)
                for cl in superclasses do