X-Git-Url: http://nitlanguage.org

diff --git a/src/vm.nit b/src/vm.nit
index 754b8ec..b253533 100644
--- a/src/vm.nit
+++ b/src/vm.nit
@@ -17,18 +17,17 @@
 # Implementation of the Nit virtual machine
 module vm
 
-intrude import naive_interpreter
-import model_utils
+import interpreter::naive_interpreter
 import perfect_hashing
 
 redef class ModelBuilder
-	redef fun run_naive_interpreter(mainmodule: MModule, arguments: Array[String])
+	fun run_virtual_machine(mainmodule: MModule, arguments: Array[String])
 	do
 		var time0 = get_time
 		self.toolcontext.info("*** NITVM STARTING ***", 1)
 
 		var interpreter = new VirtualMachine(self, mainmodule, arguments)
-		init_naive_interpreter(interpreter, mainmodule)
+		interpreter.start(mainmodule)
 
 		var time1 = get_time
 		self.toolcontext.info("*** NITVM STOPPING : {time1-time0} ***", 2)
@@ -41,13 +40,34 @@ class VirtualMachine super NaiveInterpreter
 	# Perfect hashing and perfect numbering
 	var ph: Perfecthashing = new Perfecthashing
 
-	# Handles memory and garbage collection
+	# Handles memory allocated in C
 	var memory_manager: MemoryManager = new MemoryManager
 
-	# Subtyping test for the virtual machine
+	# The unique instance of the `MInit` value
+	var initialization_value: Instance is noinit
+
+	init
+	do
+		var init_type = new MInitType(mainmodule.model)
+		initialization_value = new MutableInstance(init_type)
+		super
+	end
+
+	# Runtime subtyping test
 	redef fun is_subtype(sub, sup: MType): Bool
 	do
+		if sub == sup then return true
+
 		var anchor = self.frame.arguments.first.mtype.as(MClassType)
+
+		# `sub` or `sup` are formal or virtual types, resolve them to concrete types
+		if sub isa MParameterType or sub isa MVirtualType then
+			sub = sub.resolve_for(anchor.mclass.mclass_type, anchor, mainmodule, false)
+		end
+		if sup isa MParameterType or sup isa MVirtualType then
+			sup = sup.resolve_for(anchor.mclass.mclass_type, anchor, mainmodule, false)
+		end
+
 		var sup_accept_null = false
 		if sup isa MNullableType then
 			sup_accept_null = true
@@ -67,11 +87,6 @@ class VirtualMachine super NaiveInterpreter
 		end
 		# Now the case of direct null and nullable is over
 
-		# An unfixed formal type can only accept itself
-		if sup isa MParameterType or sup isa MVirtualType then
-			return sub == sup
-		end
-		
 		if sub isa MParameterType or sub isa MVirtualType then
 			sub = sub.anchor_to(mainmodule, anchor)
 			# Manage the second layer of null/nullable
@@ -90,45 +105,57 @@ class VirtualMachine super NaiveInterpreter
 
 		assert sup isa MClassType
 
-		# Create the sup vtable if not create
+		# `sub` and `sup` can be discovered inside a Generic type during the subtyping test
 		if not sup.mclass.loaded then create_class(sup.mclass)
-
-		# Sub can be discovered inside a Generic type during the subtyping test
 		if not sub.mclass.loaded then create_class(sub.mclass)
 
-		if anchor == null then anchor = sub
-		if sup isa MGenericType then
-			var sub2 = sub.supertype_to(mainmodule, anchor, sup.mclass)
-			assert sub2.mclass == sup.mclass
-
-			for i in [0..sup.mclass.arity[ do
-				var sub_arg = sub2.arguments[i]
-				var sup_arg = sup.arguments[i]
-				var res = is_subtype(sub_arg, sup_arg)
-
-				if res == false then return false
-			end
-			return true
-		end
-
+		# For now, always use perfect hashing for subtyping test
 		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)
+		var res = inter_is_subtype_ph(super_id, mask, sub.mclass.vtable.internal_vtable)
+		if res == false then return false
+		# sub and sup can be generic types, each argument of generics has to be tested
+
+		if not sup isa MGenericType then return true
+		var sub2 = sub.supertype_to(mainmodule, anchor, sup.mclass)
+
+		# Test each argument of a generic by recursive calls
+		for i in [0..sup.mclass.arity[ do
+			var sub_arg = sub2.arguments[i]
+			var sup_arg = sup.arguments[i]
+			var res2 = is_subtype(sub_arg, sup_arg)
+			if res2 == false then return false
+		end
+		return true
 	end
 
 	# Subtyping test with perfect hashing
-	private fun inter_is_subtype(id: Int, mask:Int, vtable: Pointer): Bool `{
+	# * `id` is the identifier of the target class
+	# * `mask` is the perfect hashing mask of the receiver class
+	# * `vtable` is the pointer to the virtual table of the receiver class
+	fun inter_is_subtype_ph(id: Int, mask:Int, vtable: Pointer): Bool `{
 		// hv is the position in hashtable
 		int hv = id & mask;
 
 		// Follow the pointer to somewhere in the vtable
 		long unsigned int *offset = (long unsigned int*)(((long int *)vtable)[-hv]);
-		
+
 		// If the pointed value is corresponding to the identifier, the test is true, otherwise false
 		return *offset == id;
 	`}
-	
+
+	# Subtyping test with Cohen test (direct access)
+	# * `id` is the identifier of the target class
+	# * `mask` is the absolute position of the target identifier in the virtual table
+	# * `vtable` is the pointer to the virtual table of the receiver class
+	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
@@ -136,83 +163,185 @@ class VirtualMachine super NaiveInterpreter
 
 		recv.vtable = recv.mtype.as(MClassType).mclass.vtable
 
-		assert(recv isa MutableInstance)
- 
-		recv.internal_attributes = init_internal_attributes(null_instance, recv.mtype.as(MClassType).mclass.cached_attributes.length)
+		assert recv isa MutableInstance
 
+		recv.internal_attributes = init_internal_attributes(initialization_value, recv.mtype.as(MClassType).mclass.mattributes.length)
 		super
 	end
-		
+
+	# Associate a `PrimitiveInstance` to its `VTable`
+	redef fun init_instance_primitive(recv: Instance)
+	do
+		if not recv.mtype.as(MClassType).mclass.loaded then create_class(recv.mtype.as(MClassType).mclass)
+
+		recv.vtable = recv.mtype.as(MClassType).mclass.vtable
+	end
+
+	# Create a virtual table for this `MClass` if not already done
+	redef fun get_primitive_class(name: String): MClass
+	do
+		var mclass = super
+
+		if not mclass.loaded then create_class(mclass)
+
+		return mclass
+	end
+
 	# Initialize the internal representation of an object (its attribute values)
-	private fun init_internal_attributes(null_instance: Instance, size: Int): Pointer
+	# `init_instance` is the initial value of attributes
+	private fun init_internal_attributes(init_instance: Instance, size: Int): Pointer
 		import Array[Instance].length, Array[Instance].[] `{
-		
+
 		Instance* attributes = malloc(sizeof(Instance) * size);
 
 		int i;
 		for(i=0; i<size; i++)
-			attributes[i] = null_instance;
+			attributes[i] = init_instance;
 
-		Instance_incr_ref(null_instance);
+		Instance_incr_ref(init_instance);
 		return attributes;
 	`}
 
 	# Creates the runtime structures for this class
 	fun create_class(mclass: MClass) do	mclass.make_vt(self)
 
-	# Return the value of the attribute `mproperty for the object `recv
+	# Execute `mproperty` for a `args` (where `args[0]` is the receiver).
+	redef fun send(mproperty: MMethod, args: Array[Instance]): nullable Instance
+	do
+		var recv = args.first
+		var mtype = recv.mtype
+		var ret = send_commons(mproperty, args, mtype)
+		if ret != null then return ret
+
+		var propdef = method_dispatch(mproperty, recv.vtable.as(not null), recv)
+
+		return self.call(propdef, args)
+	end
+
+	# Method dispatch, for a given global method `mproperty`
+	# returns the most specific local method in the class corresponding to `vtable`
+	private fun method_dispatch(mproperty: MMethod, vtable: VTable, recv: Instance): MMethodDef
+	do
+		if mproperty.intro_mclassdef.mclass.positions_methods[recv.mtype.as(MClassType).mclass] != -1 then
+			return method_dispatch_sst(vtable.internal_vtable, mproperty.absolute_offset)
+		else
+			return method_dispatch_ph(vtable.internal_vtable, vtable.mask,
+				mproperty.intro_mclassdef.mclass.vtable.id, mproperty.offset)
+		end
+	end
+
+	# Execute a method dispatch with perfect hashing and return the appropriate `MMethodDef`
+	# * `vtable` Pointer to the internal virtual table of the class
+	# * `mask` Perfect hashing mask of the receiver class
+	# * `id` Identifier of the class which introduce the method
+	# * `offset` Relative offset of the method from the beginning of the block
+	fun method_dispatch_ph(vtable: Pointer, mask: Int, id: Int, offset: Int): MMethodDef `{
+		// Perfect hashing position
+		int hv = mask & id;
+		long unsigned int *pointer = (long unsigned int*)(((long int *)vtable)[-hv]);
+
+		// pointer+2 is the position where methods are
+		// Add the offset of property and get the method implementation
+		MMethodDef propdef = (MMethodDef)*(pointer + 2 + offset);
+
+		return propdef;
+	`}
+
+	# Execute a method dispatch with direct access and return the appropriate `MMethodDef`
+	# * `vtable` Pointer to the internal virtual table of the class
+	# * `absolute_offset` Absolute offset from the beginning of the virtual table
+	fun method_dispatch_sst(vtable: Pointer, absolute_offset: Int): MMethodDef `{
+		// pointer+2 is the position where methods are
+		// Add the offset of property and get the method implementation
+		MMethodDef propdef = (MMethodDef)((long int *)vtable)[absolute_offset];
+
+		return propdef;
+	`}
+
+	# Return the value of the attribute `mproperty` for the object `recv`
 	redef fun read_attribute(mproperty: MAttribute, recv: Instance): Instance
 	do
 		assert recv isa MutableInstance
 
-		# Read the attribute value with perfect hashing
-		var id = mproperty.intro_mclassdef.mclass.vtable.id
-		
-		var i = read_attribute_ph(recv.internal_attributes, recv.vtable.internal_vtable,
+		var i: Instance
+
+		if mproperty.intro_mclassdef.mclass.positions_attributes[recv.mtype.as(MClassType).mclass] != -1 then
+			# if this attribute class has an unique position for this receiver, then use direct access
+			i = read_attribute_sst(recv.internal_attributes, mproperty.absolute_offset)
+		else
+			# Otherwise, read the attribute value with perfect hashing
+			var id = mproperty.intro_mclassdef.mclass.vtable.id
+
+			i = read_attribute_ph(recv.internal_attributes, recv.vtable.internal_vtable,
 					recv.vtable.mask, id, mproperty.offset)
-		
+		end
+
+		# If we get a `MInit` value, throw an error
+		if i == initialization_value then
+			fatal("Uninitialized attribute {mproperty.name}")
+			abort
+		end
+
 		return i
 	end
 
-	# Return the attribute value in `instance with a sequence of perfect_hashing
-	#     `instance is the attributes array of the receiver
-	#     `vtable is the pointer to the virtual table of the class (of the receiver)
-	#     `mask is the perfect hashing mask of the class
-	#     `id is the identifier of the class
-	#     `offset is the relative offset of this attribute
-	private fun read_attribute_ph(instance: Pointer, vtable: Pointer, mask: Int, id: Int, offset: Int): Instance `{
+	# Return the attribute value in `instance` with a sequence of perfect_hashing
+	# * `instance` is the attributes array of the receiver
+	# * `vtable` is the pointer to the virtual table of the class (of the receiver)
+	# * `mask` is the perfect hashing mask of the class
+	# * `id` is the identifier of the class
+	# * `offset` is the relative offset of this attribute
+	fun read_attribute_ph(instance: Pointer, vtable: Pointer, mask: Int, id: Int, offset: Int): Instance `{
 		// Perfect hashing position
 		int hv = mask & id;
 		long unsigned int *pointer = (long unsigned int*)(((long int *)vtable)[-hv]);
-		
+
 		// pointer+1 is the position where the delta of the class is
 		int absolute_offset = *(pointer + 1);
 
 		Instance res = ((Instance *)instance)[absolute_offset + offset];
-		
+
+		return res;
+	`}
+
+	# Return the attribute value in `instance` with a direct access (SST)
+	# * `instance` is the attributes array of the receiver
+	# * `offset` is the absolute offset of this attribute
+	fun read_attribute_sst(instance: Pointer, offset: Int): Instance `{
+		/* We can make a direct access to the attribute value
+		   because this attribute is always at the same position
+		   for the class of this receiver */
+		Instance res = ((Instance *)instance)[offset];
+
 		return res;
 	`}
 
-	# Replace in `recv the value of the attribute `mproperty by `value
+	# Replace in `recv` the value of the attribute `mproperty` by `value`
 	redef fun write_attribute(mproperty: MAttribute, recv: Instance, value: Instance)
 	do
 		assert recv isa MutableInstance
 
-		var id = mproperty.intro_mclassdef.mclass.vtable.id
-		
 		# Replace the old value of mproperty in recv
-		write_attribute_ph(recv.internal_attributes, recv.vtable.internal_vtable,
+		if mproperty.intro_mclassdef.mclass.positions_attributes[recv.mtype.as(MClassType).mclass] != -1 then
+			# if this attribute class has an unique position for this receiver, then use direct access
+			write_attribute_sst(recv.internal_attributes, mproperty.absolute_offset, value)
+		else
+			# Otherwise, use perfect hashing to replace the old value
+			var id = mproperty.intro_mclassdef.mclass.vtable.id
+
+			write_attribute_ph(recv.internal_attributes, recv.vtable.internal_vtable,
 					recv.vtable.mask, id, mproperty.offset, value)
+		end
 	end
 
 	# Replace the value of an attribute in an instance
-	#     `instance is the attributes array of the receiver
-	#     `vtable is the pointer to the virtual table of the class (of the receiver)
-	#     `mask is the perfect hashing mask of the class
-	#     `id is the identifier of the class
-	#     `offset is the relative offset of this attribute
-	# 	  `value is the new value for this attribute
-	private fun write_attribute_ph(instance: Pointer, vtable: Pointer, mask: Int, id: Int, offset: Int, value: Instance) `{
+	# * `instance` is the attributes array of the receiver
+	# * `vtable` is the pointer to the virtual table of the class (of the receiver)
+	# * `mask` is the perfect hashing mask of the class
+	# * `id` is the identifier of the class
+	# * `offset` is the relative offset of this attribute
+	# * `value` is the new value for this attribute
+	fun write_attribute_ph(instance: Pointer, vtable: Pointer, mask: Int, id: Int, offset: Int, value: Instance) `{
 		// Perfect hashing position
 		int hv = mask & id;
 		long unsigned int *pointer = (long unsigned int*)(((long int *)vtable)[-hv]);
@@ -223,6 +352,31 @@ class VirtualMachine super NaiveInterpreter
 		((Instance *)instance)[absolute_offset + offset] = value;
 		Instance_incr_ref(value);
 	`}
+
+	# Replace the value of an attribute in an instance with direct access
+	# * `instance` is the attributes array of the receiver
+	# * `offset` is the absolute offset of this attribute
+	# * `value` is the new value for this attribute
+	fun write_attribute_sst(instance: Pointer, offset: Int, value: Instance) `{
+		// Direct access to the position with the absolute offset
+		((Instance *)instance)[offset] = value;
+		Instance_incr_ref(value);
+	`}
+
+	# Is the attribute `mproperty` initialized in the instance `recv`?
+	redef fun isset_attribute(mproperty: MAttribute, recv: Instance): Bool
+	do
+		assert recv isa MutableInstance
+
+		# Read the attribute value with internal perfect hashing read
+		# because we do not want to throw an error if the value is `initialization_value`
+		var id = mproperty.intro_mclassdef.mclass.vtable.id
+
+		var i = read_attribute_ph(recv.internal_attributes, recv.vtable.internal_vtable,
+					recv.vtable.mask, id, mproperty.offset)
+
+		return i != initialization_value
+	end
 end
 
 redef class MClass
@@ -232,55 +386,108 @@ redef class MClass
 	# True when the class is effectively loaded by the vm, false otherwise
 	var loaded: Bool = false
 
-	# Cached attributes for faster instanciations of this class
-	var cached_attributes: Array[MAttribute] = new Array[MAttribute]
+	# 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]
+
+	# For each loaded subclass, keep the position of the group of methods
+	# introduced by self class in the vtable
+	var positions_methods: HashMap[MClass, Int] = new HashMap[MClass, Int]
+
+	# The `MAttribute` this class introduced
+	var intro_mattributes = new Array[MAttribute]
+
+	# The `MMethod` this class introduced
+	var intro_mmethods = new Array[MMethod]
+
+	# All `MAttribute` this class contains
+	var mattributes = new Array[MAttribute]
+
+	# All `MMethod` this class contains
+	var mmethods = new Array[MMethod]
 
 	# Allocates a VTable for this class and gives it an id
 	private fun make_vt(v: VirtualMachine)
 	do
 		if loaded then return
 
-		# Superclasses contains all superclasses except self
-		var superclasses = new Array[MClass]
-		superclasses.add_all(ancestors)
+		# `superclasses` contains the order of superclasses for virtual tables
+		var superclasses = superclasses_ordering(v)
 		superclasses.remove(self)
-		v.mainmodule.linearize_mclasses(superclasses)
 
 		# Make_vt for super-classes
 		var ids = new Array[Int]
 		var nb_methods = new Array[Int]
 		var nb_attributes = new Array[Int]
 
+		# Absolute offset of attribute from the beginning of the attributes table
+		var offset_attributes = 0
+
+		# Absolute offset of method from the beginning of the methods table,
+		# is initialize to 3 because the first position is empty in the virtual table
+		# and the second and third are respectively class id and delta
+		var offset_methods = 3
+
+		# The previous element in `superclasses`
+		var previous_parent: nullable MClass = null
+		if superclasses.length > 0 then	previous_parent = superclasses[0]
 		for parent in superclasses do
-			if parent.vtable == null then parent.make_vt(v)
-			
+			if not parent.loaded then parent.make_vt(v)
+
 			# Get the number of introduced methods and attributes for this class
-			var methods = 0
-			var attributes = 0
+			var methods = parent.intro_mmethods.length
+			var attributes = parent.intro_mattributes.length
+
+			# Updates `mmethods` and `mattributes`
+			mmethods.add_all(parent.intro_mmethods)
+			mattributes.add_all(parent.intro_mattributes)
 
-			for p in parent.intro_mproperties(none_visibility) do
-				if p isa MMethod then methods += 1
-				if p isa MAttribute then
-					attributes += 1
-				end
-			end
-			
 			ids.push(parent.vtable.id)
 			nb_methods.push(methods)
 			nb_attributes.push(attributes)
+
+			# Update `positions_attributes` and `positions_methods` in `parent`.
+			# If the position is invariant for this parent, store this position
+			# else store a special value (-1)
+			var pos_attr = -1
+			var pos_meth = -1
+
+			if previous_parent.as(not null).positions_attributes[parent] == offset_attributes then pos_attr = offset_attributes
+			if previous_parent.as(not null).positions_methods[parent] == offset_methods then pos_meth = offset_methods
+
+			parent.update_positions(pos_attr, pos_meth, self)
+
+			offset_attributes += attributes
+			offset_methods += methods
+			offset_methods += 2 # Because each block starts with an id and the delta
 		end
-		
+
 		# When all super-classes have their identifiers and vtables, allocate current one
-		allocate_vtable(v, ids, nb_methods, nb_attributes)
+		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
+			fill_vtable(v, vtable.as(not null), cl)
+		end
 	end
 
 	# Allocate a single vtable
-	# 	ids : Array of superclasses identifiers
-	# 	nb_methods : Array which contain the number of introducted methods for each class in ids
-	# 	nb_attributes : Array which contain the number of introducted attributes for each class in ids
-	private fun allocate_vtable(v: VirtualMachine, ids: Array[Int], nb_methods: Array[Int], nb_attributes: Array[Int])
+	# * `ids : Array of superclasses identifiers
+	# * `nb_methods : Array which contain the number of introduced methods for each class in ids
+	# * `nb_attributes : Array which contain the number of introduced attributes for each class in ids
+	# * `offset_attributes : Offset from the beginning of the table of the group of attributes
+	# * `offset_methods : Offset from the beginning of the table of the group of methods
+	private fun allocate_vtable(v: VirtualMachine, ids: Array[Int], nb_methods: Array[Int], nb_attributes: Array[Int],
+			offset_attributes: Int, offset_methods: Int)
 	do
 		vtable = new VTable
 		var idc = new Array[Int]
@@ -298,35 +505,75 @@ redef class MClass
 		var nb_attributes_total = new Array[Int]
 
 		var self_methods = 0
-		var self_attributes = 0
-		
-		# For self attributes, fixing offsets
-		var relative_offset = 0
-		for p in intro_mproperties(none_visibility) do
-			if p isa MMethod then self_methods += 1
-			if p isa MAttribute then 
-				self_attributes += 1
-				p.offset = relative_offset
-				relative_offset += 1
-				cached_attributes.push(p)
+		var nb_introduced_attributes = 0
+
+		# Fixing offsets for self attributes and methods
+		var relative_offset_attr = 0
+		var relative_offset_meth = 0
+
+		# Update `intro_mmethods` and `intro_mattributes`
+		# For each MClassdef this MClass has
+		for classdef in mclassdefs do
+			# For each property this MClassdef introduce
+			for p in classdef.intro_mproperties do
+				# Collect properties and fixing offsets
+				if p isa MMethod then
+					self_methods += 1
+					p.offset = relative_offset_meth
+					p.absolute_offset = offset_methods + relative_offset_meth
+					relative_offset_meth += 1
+
+					intro_mmethods.add(p)
+				end
+				if p isa MAttribute then
+					nb_introduced_attributes += 1
+					p.offset = relative_offset_attr
+					p.absolute_offset = offset_attributes + relative_offset_attr
+					relative_offset_attr += 1
+
+					intro_mattributes.add(p)
+				end
 			end
 		end
 
+		# Updates caches with introduced attributes of `self` class
+		mattributes.add_all(intro_mattributes)
+		mmethods.add_all(intro_mmethods)
+
 		nb_methods_total.add_all(nb_methods)
 		nb_methods_total.push(self_methods)
 
 		nb_attributes_total.add_all(nb_attributes)
-		nb_attributes_total.push(self_attributes)
+		nb_attributes_total.push(nb_introduced_attributes)
 
-		# Since we have the number of attributes for each class, calculate the delta 
-		var d = calculate_delta(nb_attributes_total)
-		vtable.internal_vtable = v.memory_manager.init_vtable(ids_total, nb_methods_total, d, vtable.mask)
+		# Save the offsets of self class
+		update_positions(offset_attributes, offset_methods, self)
+
+		# Since we have the number of attributes for each class, calculate the delta
+		var deltas = calculate_delta(nb_attributes_total)
+		vtable.internal_vtable = v.memory_manager.init_vtable(ids_total, nb_methods_total, deltas, vtable.mask)
+	end
+
+	# Fill the vtable with methods of `self` class
+	# * `v` : Current instance of the VirtualMachine
+	# * `table` : the table of self class, will be filled with its methods
+	private fun fill_vtable(v:VirtualMachine, table: VTable, cl: MClass)
+	do
+		var methods = new Array[MMethodDef]
+		for m in cl.intro_mmethods do
+			# `propdef` is the most specific implementation for this MMethod
+			var propdef = m.lookup_first_definition(v.mainmodule, self.intro.bound_mtype)
+			methods.push(propdef)
+		end
+
+		# Call a method in C to put propdefs of self methods in the vtables
+		v.memory_manager.put_methods(vtable.internal_vtable, vtable.mask, cl.vtable.id, methods)
 	end
 
 	# Computes delta for each class
 	# A delta represents the offset for this group of attributes in the object
-	#    nb_attributes : number of attributes for each class (classes are linearized from Object to current)
-	#    return deltas for each class
+	# *`nb_attributes` : number of attributes for each class (classes are linearized from Object to current)
+	# * return deltas for each class
 	private fun calculate_delta(nb_attributes: Array[Int]): Array[Int]
 	do
 		var deltas = new Array[Int]
@@ -339,20 +586,145 @@ redef class MClass
 
 		return deltas
 	end
+
+	# Order superclasses of self
+	# Return the order of superclasses in runtime structures of this class
+	private fun superclasses_ordering(v: VirtualMachine): Array[MClass]
+	do
+		var superclasses = new Array[MClass]
+
+		# Add all superclasses of `self`
+		superclasses.add_all(self.in_hierarchy(v.mainmodule).greaters)
+
+		var res = new Array[MClass]
+		if superclasses.length > 1 then
+			# Starting at self
+			var ordering = self.dfs(v, res)
+
+			return ordering
+		else
+			# There is no super-class, self is Object
+			return superclasses
+		end
+	end
+
+	# A kind of Depth-First-Search for superclasses ordering
+	# *`v` : the current executed instance of VirtualMachine
+	# * `res` : Result Array, ie current superclasses ordering
+	private fun dfs(v: VirtualMachine, res: Array[MClass]): Array[MClass]
+	do
+		# Add this class at the beginning
+		res.insert(self, 0)
+
+		var direct_parents = self.in_hierarchy(v.mainmodule).direct_greaters.to_a
+
+		if direct_parents.length > 1 then
+			# Prefix represents the class which has the most properties
+			# we try to choose it in first to reduce the number of potential recompilations
+			var prefix = null
+			var max = -1
+			for cl in direct_parents do
+				# If we never have visited this class
+				if not res.has(cl) then
+					var properties_length = cl.mmethods.length + cl.mattributes.length
+					if properties_length > max then
+						max = properties_length
+						prefix = cl
+					end
+				end
+			end
+
+			if prefix != null then
+				# Add the prefix class ordering at the beginning of our sequence
+				var prefix_res = new Array[MClass]
+				prefix_res = prefix.dfs(v, prefix_res)
+
+				# Then we recurse on other classes
+				for cl in direct_parents do
+					if cl != prefix then
+						res = new Array[MClass]
+						res = cl.dfs(v, res)
+
+						for cl_res in res do
+							if not prefix_res.has(cl_res) then prefix_res.push(cl_res)
+						end
+					end
+				end
+				res = prefix_res
+			end
+
+			res.push(self)
+		else
+			if direct_parents.length > 0 then
+				res = direct_parents.first.dfs(v, res)
+			end
+		end
+
+		if not res.has(self) then res.push(self)
+
+		return res
+	end
+
+	# Update positions of the class `cl`
+	# * `attributes_offset`: absolute offset of introduced attributes
+	# * `methods_offset`: absolute offset of introduced methods
+	private fun update_positions(attributes_offsets: Int, methods_offset:Int, cl: MClass)
+	do
+		positions_attributes[cl] = attributes_offsets
+		positions_methods[cl] = methods_offset
+	end
 end
 
 redef class MAttribute
-	# Represents the relative offset of this attribute in the runtime instance
+	# Relative offset of this attribute in the runtime instance
+	# (beginning of the block of its introducing class)
 	var offset: Int
+
+	# Absolute offset of this attribute in the runtime instance (beginning of the attribute table)
+	var absolute_offset: Int
+end
+
+redef class MMethod
+	# Relative offset of this method in the virtual table (from the beginning of the block)
+	var offset: Int
+
+	# Absolute offset of this method in the virtual table (from the beginning of the vtable)
+	var absolute_offset: Int
 end
 
 # Redef MutableInstance to improve implementation of attributes in objects
 redef class MutableInstance
-	
+
 	# C-array to store pointers to attributes of this Object
 	var internal_attributes: Pointer
 end
 
+# Redef to associate an `Instance` to its `VTable`
+redef class Instance
+
+	# Associate a runtime instance to its virtual table which contains methods, types etc.
+	var vtable: nullable VTable
+end
+
+# Is the type of the initial value inside attributes
+class MInitType
+	super MType
+
+	redef var model: Model
+
+	redef fun to_s do return "InitType"
+	redef fun as_nullable do return self
+	redef fun need_anchor do return false
+	redef fun resolve_for(mtype, anchor, mmodule, cleanup_virtual) do return self
+	redef fun can_resolve_for(mtype, anchor, mmodule) do return true
+
+	redef fun collect_mclassdefs(mmodule) do return new HashSet[MClassDef]
+
+	redef fun collect_mclasses(mmodule) do return new HashSet[MClass]
+
+	redef fun collect_mtypes(mmodule) do return new HashSet[MClassType]
+end
+
 # A VTable contains the virtual method table for the dispatch
 # and informations to perform subtyping tests
 class VTable
@@ -369,15 +741,11 @@ class VTable
 	var classname: String is noinit
 end
 
-redef class Instance
-	var vtable: nullable VTable
-end
-
 # Handle memory, used for allocate virtual table and associated structures
 class MemoryManager
 
 	# Allocate and fill a virtual table
-	fun init_vtable(ids: Array[Int], nb_methods: Array[Int], nb_attributes: Array[Int], mask: Int): Pointer 
+	fun init_vtable(ids: Array[Int], nb_methods: Array[Int], nb_attributes: Array[Int], mask: Int): Pointer
 	do
 		# Allocate in C current virtual table
 		var res = intern_init_vtable(ids, nb_methods, nb_attributes, mask)
@@ -386,7 +754,7 @@ class MemoryManager
 	end
 
 	# Construct virtual tables with a bi-dimensional layout
-	private fun intern_init_vtable(ids: Array[Int], nb_methods: Array[Int], deltas: Array[Int], mask: Int): Pointer 
+	private fun intern_init_vtable(ids: Array[Int], nb_methods: Array[Int], deltas: Array[Int], mask: Int): Pointer
 		import Array[Int].length, Array[Int].[] `{
 
 		// Allocate and fill current virtual table
@@ -396,7 +764,7 @@ class MemoryManager
 		for(i = 0; i<nb_classes; i++) {
 			/* - One for each method of this class
 			*  - One for the delta (offset of this group of attributes in objects)
-			*  - One for the id 
+			*  - One for the id
 			*/
 			total_size += Array_of_Int__index(nb_methods, i);
 			total_size += 2;
@@ -406,20 +774,20 @@ class MemoryManager
 		// Add one because we start to fill the vtable at position 1 (0 is the init position)
 		total_size += mask+2;
 		long unsigned int* vtable = malloc(sizeof(long unsigned int)*total_size);
-		
+
 		// Initialisation to the first position of the virtual table (ie : Object)
 		long unsigned int *init = vtable + mask + 2;
 		for(i=0; i<total_size; i++)
 			vtable[i] = (long unsigned int)init;
 
-		// Set the virtual table to its position 0 
+		// Set the virtual table to its position 0
 		// ie: after the hashtable
 		vtable = vtable + mask + 1;
-		
+
 		int current_size = 1;
 		for(i = 0; i < nb_classes; i++) {
 			/*
-				vtable[hv] contains a pointer to the group of introducted methods
+				vtable[hv] contains a pointer to the group of introduced methods
 				For each superclasse we have in virtual table :
 					(id | delta | introduced methods)
 			*/
@@ -428,11 +796,36 @@ class MemoryManager
 			vtable[current_size] = Array_of_Int__index(ids, i);
 			vtable[current_size + 1] = Array_of_Int__index(deltas, i);
 			vtable[-hv] = (long unsigned int)&(vtable[current_size]);
-			
+
 			current_size += 2;
 			current_size += Array_of_Int__index(nb_methods, i);
 		}
 
 		return vtable;
 	`}
+
+	# Put implementation of methods of a class in `vtable`
+	# * `vtable` : Pointer to the C-virtual table
+	# * `mask` : perfect-hashing mask of the class corresponding to the vtable
+	# * `id` : id of the target class
+	# * `methods` : array of MMethodDef of the target class
+	fun put_methods(vtable: Pointer, mask: Int, id: Int, methods: Array[MMethodDef])
+		import Array[MMethodDef].length, Array[MMethodDef].[] `{
+
+		// Get the area to fill with methods by a sequence of perfect hashing
+		int hv = mask & id;
+		long unsigned int *pointer = (long unsigned int*)(((long unsigned int *)vtable)[-hv]);
+
+		// pointer+2 is the beginning of the area for methods implementation
+		int length = Array_of_MMethodDef_length(methods);
+		long unsigned int *area = (pointer + 2);
+		int i;
+
+		for(i=0; i<length; i++)
+		{
+			MMethodDef method = Array_of_MMethodDef__index(methods, i);
+			area[i] = (long unsigned int)method;
+			MMethodDef_incr_ref(method);
+		}
+	`}
 end