sepcomp: use the new `POSetGroupColorer` to color properties
[nit.git] / src / compiler / separate_compiler.nit
index 33e8d8a..e611f3d 100644 (file)
@@ -29,12 +29,28 @@ redef class ToolContext
        var opt_no_union_attribute = new OptionBool("Put primitive attibutes in a box instead of an union", "--no-union-attribute")
        # --no-shortcut-equate
        var opt_no_shortcut_equate = new OptionBool("Always call == in a polymorphic way", "--no-shortcut-equal")
+       # --no-tag-primitives
+       var opt_no_tag_primitives = new OptionBool("Use only boxes for primitive types", "--no-tag-primitives")
+
+       # --colors-are-symbols
+       var opt_colors_are_symbols = new OptionBool("Store colors as symbols (link-boost)", "--colors-are-symbols")
+       # --trampoline-call
+       var opt_trampoline_call = new OptionBool("Use an indirection when calling", "--trampoline-call")
+       # --guard-call
+       var opt_guard_call = new OptionBool("Guard VFT calls with a direct call", "--guard-call")
+       # --substitute-monomorph
+       var opt_substitute_monomorph = new OptionBool("Replace monomorph trampoline with direct call (link-boost)", "--substitute-monomorph")
+       # --link-boost
+       var opt_link_boost = new OptionBool("Enable all link-boost optimizations", "--link-boost")
+
        # --inline-coloring-numbers
        var opt_inline_coloring_numbers = new OptionBool("Inline colors and ids (semi-global)", "--inline-coloring-numbers")
        # --inline-some-methods
        var opt_inline_some_methods = new OptionBool("Allow the separate compiler to inline some methods (semi-global)", "--inline-some-methods")
        # --direct-call-monomorph
        var opt_direct_call_monomorph = new OptionBool("Allow the separate compiler to direct call monomorph sites (semi-global)", "--direct-call-monomorph")
+       # --direct-call-monomorph0
+       var opt_direct_call_monomorph0 = new OptionBool("Allow the separate compiler to direct call monomorph sites (semi-global)", "--direct-call-monomorph0")
        # --skip-dead-methods
        var opt_skip_dead_methods = new OptionBool("Do not compile dead methods (semi-global)", "--skip-dead-methods")
        # --semi-global
@@ -51,6 +67,8 @@ redef class ToolContext
                self.option_context.add_option(self.opt_no_inline_intern)
                self.option_context.add_option(self.opt_no_union_attribute)
                self.option_context.add_option(self.opt_no_shortcut_equate)
+               self.option_context.add_option(self.opt_no_tag_primitives)
+               self.option_context.add_option(opt_colors_are_symbols, opt_trampoline_call, opt_guard_call, opt_direct_call_monomorph0, opt_substitute_monomorph, opt_link_boost)
                self.option_context.add_option(self.opt_inline_coloring_numbers, opt_inline_some_methods, opt_direct_call_monomorph, opt_skip_dead_methods, opt_semi_global)
                self.option_context.add_option(self.opt_colo_dead_methods)
                self.option_context.add_option(self.opt_tables_metrics)
@@ -67,6 +85,13 @@ redef class ToolContext
                        tc.opt_direct_call_monomorph.value = true
                        tc.opt_skip_dead_methods.value = true
                end
+               if tc.opt_link_boost.value then
+                       tc.opt_colors_are_symbols.value = true
+                       tc.opt_substitute_monomorph.value = true
+               end
+               if tc.opt_substitute_monomorph.value then
+                       tc.opt_trampoline_call.value = true
+               end
        end
 
        var separate_compiler_phase = new SeparateCompilerPhase(self, null)
@@ -90,14 +115,56 @@ redef class ModelBuilder
                self.toolcontext.info("*** GENERATING C ***", 1)
 
                var compiler = new SeparateCompiler(mainmodule, self, runtime_type_analysis)
+               compiler.do_compilation
+               compiler.display_stats
+
+               var time1 = get_time
+               self.toolcontext.info("*** END GENERATING C: {time1-time0} ***", 2)
+               write_and_make(compiler)
+       end
+
+       # Count number of invocations by VFT
+       private var nb_invok_by_tables = 0
+       # Count number of invocations by direct call
+       private var nb_invok_by_direct = 0
+       # Count number of invocations by inlining
+       private var nb_invok_by_inline = 0
+end
+
+# Singleton that store the knowledge about the separate compilation process
+class SeparateCompiler
+       super AbstractCompiler
+
+       redef type VISITOR: SeparateCompilerVisitor
+
+       # The result of the RTA (used to know live types and methods)
+       var runtime_type_analysis: nullable RapidTypeAnalysis
+
+       private var undead_types: Set[MType] = new HashSet[MType]
+       private var live_unresolved_types: Map[MClassDef, Set[MType]] = new HashMap[MClassDef, HashSet[MType]]
+
+       private var type_ids: Map[MType, Int] is noinit
+       private var type_colors: Map[MType, Int] is noinit
+       private var opentype_colors: Map[MType, Int] is noinit
+
+       init do
+               var file = new_file("nit.common")
+               self.header = new CodeWriter(file)
+               self.compile_box_kinds
+       end
+
+       redef fun do_compilation
+       do
+               var compiler = self
                compiler.compile_header
 
                var c_name = mainmodule.c_name
 
                # compile class structures
-               self.toolcontext.info("Property coloring", 2)
+               modelbuilder.toolcontext.info("Property coloring", 2)
                compiler.new_file("{c_name}.classes")
                compiler.do_property_coloring
+               compiler.compile_class_infos
                for m in mainmodule.in_importation.greaters do
                        for mclass in m.intro_mclasses do
                                #if mclass.kind == abstract_kind or mclass.kind == interface_kind then continue
@@ -110,17 +177,26 @@ redef class ModelBuilder
                compiler.compile_nitni_global_ref_functions
                compiler.compile_main_function
                compiler.compile_finalizer_function
+               compiler.link_mmethods
 
                # compile methods
                for m in mainmodule.in_importation.greaters do
-                       self.toolcontext.info("Generate C for module {m.full_name}", 2)
+                       modelbuilder.toolcontext.info("Generate C for module {m.full_name}", 2)
                        compiler.new_file("{m.c_name}.sep")
                        compiler.compile_module_to_c(m)
                end
 
                # compile live & cast type structures
-               self.toolcontext.info("Type coloring", 2)
+               modelbuilder.toolcontext.info("Type coloring", 2)
                compiler.new_file("{c_name}.types")
+               compiler.compile_types
+       end
+
+       # Color and compile type structures and cast information
+       fun compile_types
+       do
+               var compiler = self
+
                var mtypes = compiler.do_type_coloring
                for t in mtypes do
                        compiler.compile_type_to_c(t)
@@ -131,43 +207,6 @@ redef class ModelBuilder
                        compiler.compile_type_to_c(t)
                end
 
-               compiler.display_stats
-
-               var time1 = get_time
-               self.toolcontext.info("*** END GENERATING C: {time1-time0} ***", 2)
-               write_and_make(compiler)
-       end
-
-       # Count number of invocations by VFT
-       private var nb_invok_by_tables = 0
-       # Count number of invocations by direct call
-       private var nb_invok_by_direct = 0
-       # Count number of invocations by inlining
-       private var nb_invok_by_inline = 0
-end
-
-# Singleton that store the knowledge about the separate compilation process
-class SeparateCompiler
-       super AbstractCompiler
-
-       redef type VISITOR: SeparateCompilerVisitor
-
-       # The result of the RTA (used to know live types and methods)
-       var runtime_type_analysis: nullable RapidTypeAnalysis
-
-       private var undead_types: Set[MType] = new HashSet[MType]
-       private var live_unresolved_types: Map[MClassDef, Set[MType]] = new HashMap[MClassDef, HashSet[MType]]
-
-       private var type_ids: Map[MType, Int] is noinit
-       private var type_colors: Map[MType, Int] is noinit
-       private var opentype_colors: Map[MType, Int] is noinit
-       protected var method_colors: Map[PropertyLayoutElement, Int] is noinit
-       protected var attr_colors: Map[MAttribute, Int] is noinit
-
-       init do
-               var file = new_file("nit.common")
-               self.header = new CodeWriter(file)
-               self.compile_box_kinds
        end
 
        redef fun compile_header_structs do
@@ -180,6 +219,11 @@ class SeparateCompiler
                self.header.add_decl("struct instance \{ const struct type *type; const struct class *class; nitattribute_t attrs[]; \}; /* general C type representing a Nit instance. */")
                self.header.add_decl("struct types \{ int dummy; const struct type *types[]; \}; /* a list types (used for vts, fts and unresolved lists). */")
                self.header.add_decl("typedef struct instance val; /* general C type representing a Nit instance. */")
+
+               if not modelbuilder.toolcontext.opt_no_tag_primitives.value then
+                       self.header.add_decl("extern const struct class *class_info[];")
+                       self.header.add_decl("extern const struct type *type_info[];")
+               end
        end
 
        fun compile_header_attribute_structs
@@ -238,177 +282,135 @@ class SeparateCompiler
 
        fun compile_color_const(v: SeparateCompilerVisitor, m: Object, color: Int) do
                if color_consts_done.has(m) then return
-               if m isa MProperty then
+               if m isa MEntity then
                        if modelbuilder.toolcontext.opt_inline_coloring_numbers.value then
                                self.provide_declaration(m.const_color, "#define {m.const_color} {color}")
-                       else
+                       else if not modelbuilder.toolcontext.opt_colors_are_symbols.value or not v.compiler.target_platform.supports_linker_script then
                                self.provide_declaration(m.const_color, "extern const int {m.const_color};")
                                v.add("const int {m.const_color} = {color};")
-                       end
-               else if m isa MPropDef then
-                       if modelbuilder.toolcontext.opt_inline_coloring_numbers.value then
-                               self.provide_declaration(m.const_color, "#define {m.const_color} {color}")
                        else
-                               self.provide_declaration(m.const_color, "extern const int {m.const_color};")
-                               v.add("const int {m.const_color} = {color};")
-                       end
-               else if m isa MType then
-                       if modelbuilder.toolcontext.opt_inline_coloring_numbers.value then
-                               self.provide_declaration(m.const_color, "#define {m.const_color} {color}")
-                       else
-                               self.provide_declaration(m.const_color, "extern const int {m.const_color};")
-                               v.add("const int {m.const_color} = {color};")
+                               # The color 'C' is the ``address'' of a false static variable 'XC'
+                               self.provide_declaration(m.const_color, "#define {m.const_color} ((long)&X{m.const_color})\nextern const void X{m.const_color};")
+                               if color == -1 then color = 0 # Symbols cannot be negative, so just use 0 for dead things
+                               # Teach the linker that the address of 'XC' is `color`.
+                               linker_script.add("X{m.const_color} = {color};")
                        end
+               else
+                       abort
                end
                color_consts_done.add(m)
        end
 
        private var color_consts_done = new HashSet[Object]
 
+       # The conflict graph of classes used for coloration
+       var class_conflict_graph: POSetConflictGraph[MClass] is noinit
+
        # colorize classe properties
        fun do_property_coloring do
 
                var rta = runtime_type_analysis
 
-               # Layouts
-               var poset = mainmodule.flatten_mclass_hierarchy
-               var mclasses = new HashSet[MClass].from(poset)
-               var colorer = new POSetColorer[MClass]
-               colorer.colorize(poset)
-
-               # The dead methods, still need to provide a dead color symbol
-               var dead_methods = new Array[MMethod]
+               # Class graph
+               var mclasses = mainmodule.flatten_mclass_hierarchy
+               class_conflict_graph = mclasses.to_conflict_graph
 
-               # lookup properties to build layout with
+               # Prepare to collect elements to color and build layout with
                var mmethods = new HashMap[MClass, Set[PropertyLayoutElement]]
                var mattributes = new HashMap[MClass, Set[MAttribute]]
+
+               # The dead methods and super-call, still need to provide a dead color symbol
+               var dead_methods = new Array[PropertyLayoutElement]
+
                for mclass in mclasses do
                        mmethods[mclass] = new HashSet[PropertyLayoutElement]
                        mattributes[mclass] = new HashSet[MAttribute]
-                       for mprop in self.mainmodule.properties(mclass) do
-                               if mprop isa MMethod then
-                                       if not modelbuilder.toolcontext.opt_colo_dead_methods.value and rta != null and not rta.live_methods.has(mprop) then
-                                               dead_methods.add(mprop)
-                                               continue
-                                       end
-                                       mmethods[mclass].add(mprop)
-                               else if mprop isa MAttribute then
-                                       mattributes[mclass].add(mprop)
-                               end
+               end
+
+               # Pre-collect known live things
+               if rta != null then
+                       for m in rta.live_methods do
+                               mmethods[m.intro_mclassdef.mclass].add m
+                       end
+                       for m in rta.live_super_sends do
+                               var mclass = m.mclassdef.mclass
+                               mmethods[mclass].add m
                        end
                end
 
-               # Collect all super calls (dead or not)
-               var all_super_calls = new HashSet[MMethodDef]
-               for mmodule in self.mainmodule.in_importation.greaters do
-                       for mclassdef in mmodule.mclassdefs do
-                               for mpropdef in mclassdef.mpropdefs do
-                                       if not mpropdef isa MMethodDef then continue
-                                       if mpropdef.has_supercall then
-                                               all_super_calls.add(mpropdef)
+               for m in mainmodule.in_importation.greaters do for cd in m.mclassdefs do
+                       var mclass = cd.mclass
+                       # Collect methods ad attributes
+                       for p in cd.intro_mproperties do
+                               if p isa MMethod then
+                                       if rta == null then
+                                               mmethods[mclass].add p
+                                       else if not rta.live_methods.has(p) then
+                                               dead_methods.add p
                                        end
+                               else if p isa MAttribute then
+                                       mattributes[mclass].add p
                                end
                        end
-               end
 
-               # lookup super calls and add it to the list of mmethods to build layout with
-               var super_calls
-               if rta != null then
-                       super_calls = rta.live_super_sends
-               else
-                       super_calls = all_super_calls
-               end
-
-               for mmethoddef in super_calls do
-                       var mclass = mmethoddef.mclassdef.mclass
-                       mmethods[mclass].add(mmethoddef)
-                       for descendant in mclass.in_hierarchy(self.mainmodule).smallers do
-                               mmethods[descendant].add(mmethoddef)
+                       # Collect all super calls (dead or not)
+                       for mpropdef in cd.mpropdefs do
+                               if not mpropdef isa MMethodDef then continue
+                               if mpropdef.has_supercall then
+                                       if rta == null then
+                                               mmethods[mclass].add mpropdef
+                                       else if not rta.live_super_sends.has(mpropdef) then
+                                               dead_methods.add mpropdef
+                                       end
+                               end
                        end
                end
 
                # methods coloration
-               var meth_colorer = new POSetBucketsColorer[MClass, PropertyLayoutElement](poset, colorer.conflicts)
-               method_colors = meth_colorer.colorize(mmethods)
-               method_tables = build_method_tables(mclasses, super_calls)
+               var meth_colorer = new POSetGroupColorer[MClass, PropertyLayoutElement](class_conflict_graph, mmethods)
+               var method_colors = meth_colorer.colors
                compile_color_consts(method_colors)
 
-               # attribute null color to dead methods and supercalls
-               for mproperty in dead_methods do
-                       compile_color_const(new_visitor, mproperty, -1)
-               end
-               for mpropdef in all_super_calls do
-                       if super_calls.has(mpropdef) then continue
-                       compile_color_const(new_visitor, mpropdef, -1)
-               end
+               # give null color to dead methods and supercalls
+               for mproperty in dead_methods do compile_color_const(new_visitor, mproperty, -1)
 
-               # attributes coloration
-               var attr_colorer = new POSetBucketsColorer[MClass, MAttribute](poset, colorer.conflicts)
-               attr_colors = attr_colorer.colorize(mattributes)
-               attr_tables = build_attr_tables(mclasses)
+               # attribute coloration
+               var attr_colorer = new POSetGroupColorer[MClass, MAttribute](class_conflict_graph, mattributes)
+               var attr_colors = attr_colorer.colors#ize(poset, mattributes)
                compile_color_consts(attr_colors)
-       end
 
-       fun build_method_tables(mclasses: Set[MClass], super_calls: Set[MMethodDef]): Map[MClass, Array[nullable MPropDef]] do
-               var tables = new HashMap[MClass, Array[nullable MPropDef]]
+               # Build method and attribute tables
+               method_tables = new HashMap[MClass, Array[nullable MPropDef]]
+               attr_tables = new HashMap[MClass, Array[nullable MProperty]]
                for mclass in mclasses do
-                       var table = new Array[nullable MPropDef]
-                       tables[mclass] = table
+                       #if mclass.kind == abstract_kind or mclass.kind == interface_kind then continue
+                       if rta != null and not rta.live_classes.has(mclass) then continue
 
-                       var mproperties = self.mainmodule.properties(mclass)
                        var mtype = mclass.intro.bound_mtype
 
-                       for mproperty in mproperties do
-                               if not mproperty isa MMethod then continue
-                               if not method_colors.has_key(mproperty) then continue
-                               var color = method_colors[mproperty]
-                               if table.length <= color then
-                                       for i in [table.length .. color[ do
-                                               table[i] = null
-                                       end
-                               end
-                               table[color] = mproperty.lookup_first_definition(mainmodule, mtype)
-                       end
-
-                       for supercall in super_calls do
-                               if not mtype.collect_mclassdefs(mainmodule).has(supercall.mclassdef) then continue
-
-                               var color = method_colors[supercall]
-                               if table.length <= color then
-                                       for i in [table.length .. color[ do
-                                               table[i] = null
-                                       end
+                       # Resolve elements in the layout to get the final table
+                       var meth_layout = meth_colorer.build_layout(mclass)
+                       var meth_table = new Array[nullable MPropDef].with_capacity(meth_layout.length)
+                       method_tables[mclass] = meth_table
+                       for e in meth_layout do
+                               if e == null then
+                                       meth_table.add null
+                               else if e isa MMethod then
+                                       # Standard method call of `e`
+                                       meth_table.add e.lookup_first_definition(mainmodule, mtype)
+                               else if e isa MMethodDef then
+                                       # Super-call in the methoddef `e`
+                                       meth_table.add e.lookup_next_definition(mainmodule, mtype)
+                               else
+                                       abort
                                end
-                               var mmethoddef = supercall.lookup_next_definition(mainmodule, mtype)
-                               table[color] = mmethoddef
                        end
 
+                       # Do not need to resolve attributes as only the position is used
+                       attr_tables[mclass] = attr_colorer.build_layout(mclass)
                end
-               return tables
-       end
 
-       fun build_attr_tables(mclasses: Set[MClass]): Map[MClass, Array[nullable MPropDef]] do
-               var tables = new HashMap[MClass, Array[nullable MPropDef]]
-               for mclass in mclasses do
-                       var table = new Array[nullable MPropDef]
-                       tables[mclass] = table
-
-                       var mproperties = self.mainmodule.properties(mclass)
-                       var mtype = mclass.intro.bound_mtype
 
-                       for mproperty in mproperties do
-                               if not mproperty isa MAttribute then continue
-                               if not attr_colors.has_key(mproperty) then continue
-                               var color = attr_colors[mproperty]
-                               if table.length <= color then
-                                       for i in [table.length .. color[ do
-                                               table[i] = null
-                                       end
-                               end
-                               table[color] = mproperty.lookup_first_definition(mainmodule, mtype)
-                       end
-               end
-               return tables
        end
 
        # colorize live types of the program
@@ -416,14 +418,9 @@ class SeparateCompiler
                # Collect types to colorize
                var live_types = runtime_type_analysis.live_types
                var live_cast_types = runtime_type_analysis.live_cast_types
-               var mtypes = new HashSet[MType]
-               mtypes.add_all(live_types)
-               for c in self.box_kinds.keys do
-                       mtypes.add(c.mclass_type)
-               end
 
                # Compute colors
-               var poset = poset_from_mtypes(mtypes, live_cast_types)
+               var poset = poset_from_mtypes(live_types, live_cast_types)
                var colorer = new POSetColorer[MType]
                colorer.colorize(poset)
                type_ids = colorer.ids
@@ -431,20 +428,42 @@ class SeparateCompiler
                type_tables = build_type_tables(poset)
 
                # VT and FT are stored with other unresolved types in the big resolution_tables
-               self.compile_resolution_tables(mtypes)
+               self.compute_resolution_tables(live_types)
 
                return poset
        end
 
        private fun poset_from_mtypes(mtypes, cast_types: Set[MType]): POSet[MType] do
                var poset = new POSet[MType]
+
+               # Instead of doing the full matrix mtypes X cast_types,
+               # a grouping is done by the base classes of the type so
+               # that we compare only types whose base classes are in inheritance.
+
+               var mtypes_by_class = new MultiHashMap[MClass, MType]
                for e in mtypes do
+                       var c = e.as_notnullable.as(MClassType).mclass
+                       mtypes_by_class[c].add(e)
                        poset.add_node(e)
-                       for o in cast_types do
-                               if e == o then continue
-                               poset.add_node(o)
-                               if e.is_subtype(mainmodule, null, o) then
-                                       poset.add_edge(e, o)
+               end
+
+               var casttypes_by_class = new MultiHashMap[MClass, MType]
+               for e in cast_types do
+                       var c = e.as_notnullable.as(MClassType).mclass
+                       casttypes_by_class[c].add(e)
+                       poset.add_node(e)
+               end
+
+               for c1, ts1 in mtypes_by_class do
+                       for c2 in c1.in_hierarchy(mainmodule).greaters do
+                               var ts2 = casttypes_by_class[c2]
+                               for e in ts1 do
+                                       for o in ts2 do
+                                               if e == o then continue
+                                               if e.is_subtype(mainmodule, null, o) then
+                                                       poset.add_edge(e, o)
+                                               end
+                                       end
                                end
                        end
                end
@@ -470,29 +489,33 @@ class SeparateCompiler
                return tables
        end
 
-       protected fun compile_resolution_tables(mtypes: Set[MType]) do
-               # resolution_tables is used to perform a type resolution at runtime in O(1)
-
+       # resolution_tables is used to perform a type resolution at runtime in O(1)
+       private fun compute_resolution_tables(mtypes: Set[MType]) do
                # During the visit of the body of classes, live_unresolved_types are collected
                # and associated to
                # Collect all live_unresolved_types (visited in the body of classes)
 
                # Determinate fo each livetype what are its possible requested anchored types
-               var mtype2unresolved = new HashMap[MClassType, Set[MType]]
+               var mtype2unresolved = new HashMap[MClass, Set[MType]]
                for mtype in self.runtime_type_analysis.live_types do
-                       var set = new HashSet[MType]
+                       var mclass = mtype.mclass
+                       var set = mtype2unresolved.get_or_null(mclass)
+                       if set == null then
+                               set = new HashSet[MType]
+                               mtype2unresolved[mclass] = set
+                       end
                        for cd in mtype.collect_mclassdefs(self.mainmodule) do
                                if self.live_unresolved_types.has_key(cd) then
                                        set.add_all(self.live_unresolved_types[cd])
                                end
                        end
-                       mtype2unresolved[mtype] = set
                end
 
                # Compute the table layout with the prefered method
-               var colorer = new BucketsColorer[MType, MType]
+               var colorer = new BucketsColorer[MClass, MType]
+
                opentype_colors = colorer.colorize(mtype2unresolved)
-               resolution_tables = self.build_resolution_tables(mtype2unresolved)
+               resolution_tables = self.build_resolution_tables(self.runtime_type_analysis.live_types, mtype2unresolved)
 
                # Compile a C constant for each collected unresolved type.
                # Either to a color, or to -1 if the unresolved type is dead (no live receiver can require it)
@@ -517,9 +540,10 @@ class SeparateCompiler
                #print ""
        end
 
-       fun build_resolution_tables(elements: Map[MClassType, Set[MType]]): Map[MClassType, Array[nullable MType]] do
+       fun build_resolution_tables(elements: Set[MClassType], map: Map[MClass, Set[MType]]): Map[MClassType, Array[nullable MType]] do
                var tables = new HashMap[MClassType, Array[nullable MType]]
-               for mclasstype, mtypes in elements do
+               for mclasstype in elements do
+                       var mtypes = map[mclasstype.mclass]
                        var table = new Array[nullable MType]
                        for mtype in mtypes do
                                var color = opentype_colors[mtype]
@@ -549,12 +573,75 @@ class SeparateCompiler
                                var r = pd.separate_runtime_function
                                r.compile_to_c(self)
                                var r2 = pd.virtual_runtime_function
-                               r2.compile_to_c(self)
+                               if r2 != r then r2.compile_to_c(self)
+
+                               # Generate trampolines
+                               if modelbuilder.toolcontext.opt_trampoline_call.value then
+                                       r2.compile_trampolines(self)
+                               end
                        end
                end
                self.mainmodule = old_module
        end
 
+       # Process all introduced methods and compile some linking information (if needed)
+       fun link_mmethods
+       do
+               if not modelbuilder.toolcontext.opt_substitute_monomorph.value and not modelbuilder.toolcontext.opt_guard_call.value then return
+
+               for mmodule in mainmodule.in_importation.greaters do
+                       for cd in mmodule.mclassdefs do
+                               for m in cd.intro_mproperties do
+                                       if not m isa MMethod then continue
+                                       link_mmethod(m)
+                               end
+                       end
+               end
+       end
+
+       # Compile some linking information (if needed)
+       fun link_mmethod(m: MMethod)
+       do
+               var n2 = "CALL_" + m.const_color
+
+               # Replace monomorphic call by a direct call to the virtual implementation
+               var md = is_monomorphic(m)
+               if md != null then
+                       linker_script.add("{n2} = {md.virtual_runtime_function.c_name};")
+               end
+
+               # If opt_substitute_monomorph then a trampoline is used, else a weak symbol is used
+               if modelbuilder.toolcontext.opt_guard_call.value then
+                       var r = m.intro.virtual_runtime_function
+                       provide_declaration(n2, "{r.c_ret} {n2}{r.c_sig} __attribute__((weak));")
+               end
+       end
+
+       # The single mmethodef called in case of monomorphism.
+       # Returns nul if dead or polymorphic.
+       fun is_monomorphic(m: MMethod): nullable MMethodDef
+       do
+               var rta = runtime_type_analysis
+               if rta == null then
+                       # Without RTA, monomorphic means alone (uniq name)
+                       if m.mpropdefs.length == 1 then
+                               return m.mpropdefs.first
+                       else
+                               return null
+                       end
+               else
+                       # With RTA, monomorphic means only live methoddef
+                       var res: nullable MMethodDef = null
+                       for md in m.mpropdefs do
+                               if rta.live_methoddefs.has(md) then
+                                       if res != null then return null
+                                       res = md
+                               end
+                       end
+                       return res
+               end
+       end
+
        # Globaly compile the type structure of a live type
        fun compile_type_to_c(mtype: MType)
        do
@@ -669,8 +756,6 @@ class SeparateCompiler
                var mtype = mclass.intro.bound_mtype
                var c_name = mclass.c_name
 
-               var vft = self.method_tables[mclass]
-               var attrs = self.attr_tables[mclass]
                var v = new_visitor
 
                var rta = runtime_type_analysis
@@ -684,7 +769,8 @@ class SeparateCompiler
                        v.add_decl("const struct class class_{c_name} = \{")
                        v.add_decl("{self.box_kind_of(mclass)}, /* box_kind */")
                        v.add_decl("\{")
-                       for i in [0 .. vft.length[ do
+                       var vft = self.method_tables.get_or_null(mclass)
+                       if vft != null then for i in [0 .. vft.length[ do
                                var mpropdef = vft[i]
                                if mpropdef == null then
                                        v.add_decl("NULL, /* empty */")
@@ -706,6 +792,8 @@ class SeparateCompiler
                if mtype.ctype != "val*" or mtype.mclass.name == "Pointer" then
                        # Is a primitive type or the Pointer class, not any other extern class
 
+                       if mtype.is_tagged then return
+
                        #Build instance struct
                        self.header.add_decl("struct instance_{c_name} \{")
                        self.header.add_decl("const struct type *type;")
@@ -811,18 +899,78 @@ class SeparateCompiler
                else
                        var res = v.new_named_var(mtype, "self")
                        res.is_exact = true
-                       v.add("{res} = nit_alloc(sizeof(struct instance) + {attrs.length}*sizeof(nitattribute_t));")
+                       var attrs = self.attr_tables.get_or_null(mclass)
+                       if attrs == null then
+                               v.add("{res} = nit_alloc(sizeof(struct instance));")
+                       else
+                               v.add("{res} = nit_alloc(sizeof(struct instance) + {attrs.length}*sizeof(nitattribute_t));")
+                       end
                        v.add("{res}->type = type;")
                        hardening_live_type(v, "type")
                        v.require_declaration("class_{c_name}")
                        v.add("{res}->class = &class_{c_name};")
-                       self.generate_init_attr(v, res, mtype)
-                       v.set_finalizer res
+                       if attrs != null then
+                               self.generate_init_attr(v, res, mtype)
+                               v.set_finalizer res
+                       end
                        v.add("return {res};")
                end
                v.add("\}")
        end
 
+       # Compile structures used to map tagged primitive values to their classes and types.
+       # This method also determines which class will be tagged.
+       fun compile_class_infos
+       do
+               if modelbuilder.toolcontext.opt_no_tag_primitives.value then return
+
+               # Note: if you change the tagging scheme, do not forget to update
+               # `autobox` and `extract_tag`
+               var class_info = new Array[nullable MClass].filled_with(null, 4)
+               for t in box_kinds.keys do
+                       # Note: a same class can be associated to multiple slots if one want to
+                       # use some Huffman coding.
+                       if t.name == "Int" then
+                               class_info[1] = t
+                       else if t.name == "Char" then
+                               class_info[2] = t
+                       else if t.name == "Bool" then
+                               class_info[3] = t
+                       else
+                               continue
+                       end
+                       t.mclass_type.is_tagged = true
+               end
+
+               # Compile the table for classes. The tag is used as an index
+               var v = self.new_visitor
+               v.add_decl "const struct class *class_info[4] = \{"
+               for t in class_info do
+                       if t == null then
+                               v.add_decl("NULL,")
+                       else
+                               var s = "class_{t.c_name}"
+                               v.require_declaration(s)
+                               v.add_decl("&{s},")
+                       end
+               end
+               v.add_decl("\};")
+
+               # Compile the table for types. The tag is used as an index
+               v.add_decl "const struct type *type_info[4] = \{"
+               for t in class_info do
+                       if t == null then
+                               v.add_decl("NULL,")
+                       else
+                               var s = "type_{t.c_name}"
+                               undead_types.add(t.mclass_type)
+                               v.require_declaration(s)
+                               v.add_decl("&{s},")
+                       end
+               end
+               v.add_decl("\};")
+       end
+
        # Add a dynamic test to ensure that the type referenced by `t` is a live type
        fun hardening_live_type(v: VISITOR, t: String)
        do
@@ -843,7 +991,7 @@ class SeparateCompiler
        private var type_tables: Map[MType, Array[nullable MType]] = new HashMap[MType, Array[nullable MType]]
        private var resolution_tables: Map[MClassType, Array[nullable MType]] = new HashMap[MClassType, Array[nullable MType]]
        protected var method_tables: Map[MClass, Array[nullable MPropDef]] = new HashMap[MClass, Array[nullable MPropDef]]
-       protected var attr_tables: Map[MClass, Array[nullable MPropDef]] = new HashMap[MClass, Array[nullable MPropDef]]
+       protected var attr_tables: Map[MClass, Array[nullable MProperty]] = new HashMap[MClass, Array[nullable MProperty]]
 
        redef fun display_stats
        do
@@ -982,8 +1130,30 @@ class SeparateCompilerVisitor
                else if value.mtype.ctype == "val*" and mtype.ctype == "val*" then
                        return value
                else if value.mtype.ctype == "val*" then
+                       if mtype.is_tagged then
+                               if mtype.name == "Int" then
+                                       return self.new_expr("(long)({value})>>2", mtype)
+                               else if mtype.name == "Char" then
+                                       return self.new_expr("(char)((long)({value})>>2)", mtype)
+                               else if mtype.name == "Bool" then
+                                       return self.new_expr("(short int)((long)({value})>>2)", mtype)
+                               else
+                                       abort
+                               end
+                       end
                        return self.new_expr("((struct instance_{mtype.c_name}*){value})->value; /* autounbox from {value.mtype} to {mtype} */", mtype)
                else if mtype.ctype == "val*" then
+                       if value.mtype.is_tagged then
+                               if value.mtype.name == "Int" then
+                                       return self.new_expr("(val*)({value}<<2|1)", mtype)
+                               else if value.mtype.name == "Char" then
+                                       return self.new_expr("(val*)((long)({value})<<2|2)", mtype)
+                               else if value.mtype.name == "Bool" then
+                                       return self.new_expr("(val*)((long)({value})<<2|3)", mtype)
+                               else
+                                       abort
+                               end
+                       end
                        var valtype = value.mtype.as(MClassType)
                        if mtype isa MClassType and mtype.mclass.kind == extern_kind and mtype.mclass.name != "NativeString" then
                                valtype = compiler.mainmodule.pointer_type
@@ -991,7 +1161,7 @@ class SeparateCompilerVisitor
                        var res = self.new_var(mtype)
                        if compiler.runtime_type_analysis != null and not compiler.runtime_type_analysis.live_types.has(valtype) then
                                self.add("/*no autobox from {value.mtype} to {mtype}: {value.mtype} is not live! */")
-                               self.add("PRINT_ERROR(\"Dead code executed!\\n\"); show_backtrace(1);")
+                               self.add("PRINT_ERROR(\"Dead code executed!\\n\"); fatal_exit(1);")
                                return res
                        end
                        self.require_declaration("BOX_{valtype.c_name}")
@@ -1005,7 +1175,7 @@ class SeparateCompilerVisitor
                        # Bad things will appen!
                        var res = self.new_var(mtype)
                        self.add("/* {res} left unintialized (cannot convert {value.mtype} to {mtype}) */")
-                       self.add("PRINT_ERROR(\"Cast error: Cannot cast %s to %s.\\n\", \"{value.mtype}\", \"{mtype}\"); show_backtrace(1);")
+                       self.add("PRINT_ERROR(\"Cast error: Cannot cast %s to %s.\\n\", \"{value.mtype}\", \"{mtype}\"); fatal_exit(1);")
                        return res
                end
        end
@@ -1031,7 +1201,7 @@ class SeparateCompilerVisitor
                        var res = self.new_var(mtype)
                        if compiler.runtime_type_analysis != null and not compiler.runtime_type_analysis.live_types.has(value.mtype.as(MClassType)) then
                                self.add("/*no boxing of {value.mtype}: {value.mtype} is not live! */")
-                               self.add("PRINT_ERROR(\"Dead code executed!\\n\"); show_backtrace(1);")
+                               self.add("PRINT_ERROR(\"Dead code executed!\\n\"); fatal_exit(1);")
                                return res
                        end
                        self.require_declaration("BOX_{valtype.c_name}")
@@ -1046,11 +1216,42 @@ class SeparateCompilerVisitor
                end
        end
 
-       # Return a C expression returning the runtime type structure of the value
-       # The point of the method is to works also with primitives types.
+       # Returns a C expression containing the tag of the value as a long.
+       #
+       # If the C expression is evaluated to 0, it means there is no tag.
+       # Thus the expression can be used as a condition.
+       fun extract_tag(value: RuntimeVariable): String
+       do
+               assert value.mtype.ctype == "val*"
+               return "((long){value}&3)" # Get the two low bits
+       end
+
+       # Returns a C expression of the runtime class structure of the value.
+       # The point of the method is to work also with primitive types.
+       fun class_info(value: RuntimeVariable): String
+       do
+               if value.mtype.ctype == "val*" then
+                       if can_be_primitive(value) and not compiler.modelbuilder.toolcontext.opt_no_tag_primitives.value then
+                               var tag = extract_tag(value)
+                               return "({tag}?class_info[{tag}]:{value}->class)"
+                       end
+                       return "{value}->class"
+               else
+                       compiler.undead_types.add(value.mtype)
+                       self.require_declaration("class_{value.mtype.c_name}")
+                       return "(&class_{value.mtype.c_name})"
+               end
+       end
+
+       # Returns a C expression of the runtime type structure of the value.
+       # The point of the method is to work also with primitive types.
        fun type_info(value: RuntimeVariable): String
        do
                if value.mtype.ctype == "val*" then
+                       if can_be_primitive(value) and not compiler.modelbuilder.toolcontext.opt_no_tag_primitives.value then
+                               var tag = extract_tag(value)
+                               return "({tag}?type_info[{tag}]:{value}->type)"
+                       end
                        return "{value}->type"
                else
                        compiler.undead_types.add(value.mtype)
@@ -1062,25 +1263,37 @@ class SeparateCompilerVisitor
        redef fun compile_callsite(callsite, args)
        do
                var rta = compiler.runtime_type_analysis
-               var mmethod = callsite.mproperty
-               # TODO: Inlining of new-style constructors
-               if compiler.modelbuilder.toolcontext.opt_direct_call_monomorph.value and rta != null and not mmethod.is_root_init then
+               # TODO: Inlining of new-style constructors with initializers
+               if compiler.modelbuilder.toolcontext.opt_direct_call_monomorph.value and rta != null and callsite.mpropdef.initializers.is_empty then
                        var tgs = rta.live_targets(callsite)
                        if tgs.length == 1 then
-                               # DIRECT CALL
-                               var res0 = before_send(mmethod, args)
-                               var res = call(tgs.first, tgs.first.mclassdef.bound_mtype, args)
-                               if res0 != null then
-                                       assert res != null
-                                       self.assign(res0, res)
-                                       res = res0
-                               end
-                               add("\}") # close the before_send
-                               return res
+                               return direct_call(tgs.first, args)
                        end
                end
+               # Shortcut intern methods as they are not usually redefinable
+               if callsite.mpropdef.is_intern and callsite.mproperty.name != "object_id" then
+                       # `object_id` is the only redefined intern method, so it can not be directly called.
+                       # TODO find a less ugly approach?
+                       return direct_call(callsite.mpropdef, args)
+               end
                return super
        end
+
+       # Fully and directly call a mpropdef
+       #
+       # This method is used by `compile_callsite`
+       private fun direct_call(mpropdef: MMethodDef, args: Array[RuntimeVariable]): nullable RuntimeVariable
+       do
+               var res0 = before_send(mpropdef.mproperty, args)
+               var res = call(mpropdef, mpropdef.mclassdef.bound_mtype, args)
+               if res0 != null then
+                       assert res != null
+                       self.assign(res0, res)
+                       res = res0
+               end
+               add("\}") # close the before_send
+               return res
+       end
        redef fun send(mmethod, arguments)
        do
                if arguments.first.mcasttype.ctype != "val*" then
@@ -1093,7 +1306,7 @@ class SeparateCompilerVisitor
                        return res
                end
 
-               return table_send(mmethod, arguments, mmethod.const_color)
+               return table_send(mmethod, arguments, mmethod)
        end
 
        # Handle common special cases before doing the effective method invocation
@@ -1159,7 +1372,7 @@ class SeparateCompilerVisitor
                return res
        end
 
-       private fun table_send(mmethod: MMethod, arguments: Array[RuntimeVariable], const_color: String): nullable RuntimeVariable
+       private fun table_send(mmethod: MMethod, arguments: Array[RuntimeVariable], mentity: MEntity): nullable RuntimeVariable
        do
                compiler.modelbuilder.nb_invok_by_tables += 1
                if compiler.modelbuilder.toolcontext.opt_invocation_metrics.value then add("count_invoke_by_tables++;")
@@ -1169,8 +1382,10 @@ class SeparateCompilerVisitor
 
                var res0 = before_send(mmethod, arguments)
 
+               var runtime_function = mmethod.intro.virtual_runtime_function
+               var msignature = runtime_function.called_signature
+
                var res: nullable RuntimeVariable
-               var msignature = mmethod.intro.msignature.resolve_for(mmethod.intro.mclassdef.bound_mtype, mmethod.intro.mclassdef.bound_mtype, mmethod.intro.mclassdef.mmodule, true)
                var ret = msignature.return_mtype
                if ret == null then
                        res = null
@@ -1178,10 +1393,8 @@ class SeparateCompilerVisitor
                        res = self.new_var(ret)
                end
 
-               var s = new FlatBuffer
                var ss = new FlatBuffer
 
-               s.append("val*")
                ss.append("{recv}")
                for i in [0..msignature.arity[ do
                        var a = arguments[i+1]
@@ -1189,21 +1402,46 @@ class SeparateCompilerVisitor
                        if i == msignature.vararg_rank then
                                t = arguments[i+1].mcasttype
                        end
-                       s.append(", {t.ctype}")
                        a = self.autobox(a, t)
                        ss.append(", {a}")
                end
 
-
-               var r
-               if ret == null then r = "void" else r = ret.ctype
-               self.require_declaration(const_color)
-               var call = "(({r} (*)({s}))({arguments.first}->class->vft[{const_color}]))({ss}) /* {mmethod} on {arguments.first.inspect}*/"
-
+               var const_color = mentity.const_color
+               var ress
                if res != null then
-                       self.add("{res} = {call};")
+                       ress = "{res} = "
+               else
+                       ress = ""
+               end
+               if mentity isa MMethod and compiler.modelbuilder.toolcontext.opt_direct_call_monomorph0.value then
+                       # opt_direct_call_monomorph0 is used to compare the efficiency of the alternative lookup implementation, ceteris paribus.
+                       # The difference with the non-zero option is that the monomorphism is looked-at on the mmethod level and not at the callsite level.
+                       # TODO: remove this mess and use per callsite service to detect monomorphism in a single place.
+                       var md = compiler.is_monomorphic(mentity)
+                       if md != null then
+                               var callsym = md.virtual_runtime_function.c_name
+                               self.require_declaration(callsym)
+                               self.add "{ress}{callsym}({ss}); /* {mmethod} on {arguments.first.inspect}*/"
+                       else
+                               self.require_declaration(const_color)
+                               self.add "{ress}(({runtime_function.c_funptrtype})({class_info(arguments.first)}->vft[{const_color}]))({ss}); /* {mmethod} on {arguments.first.inspect}*/"
+                       end
+               else if mentity isa MMethod and compiler.modelbuilder.toolcontext.opt_guard_call.value then
+                       var callsym = "CALL_" + const_color
+                       self.require_declaration(callsym)
+                       self.add "if (!{callsym}) \{"
+                       self.require_declaration(const_color)
+                       self.add "{ress}(({runtime_function.c_funptrtype})({class_info(arguments.first)}->vft[{const_color}]))({ss}); /* {mmethod} on {arguments.first.inspect}*/"
+                       self.add "\} else \{"
+                       self.add "{ress}{callsym}({ss}); /* {mmethod} on {arguments.first.inspect}*/"
+                       self.add "\}"
+               else if mentity isa MMethod and compiler.modelbuilder.toolcontext.opt_trampoline_call.value then
+                       var callsym = "CALL_" + const_color
+                       self.require_declaration(callsym)
+                       self.add "{ress}{callsym}({ss}); /* {mmethod} on {arguments.first.inspect}*/"
                else
-                       self.add("{call};")
+                       self.require_declaration(const_color)
+                       self.add "{ress}(({runtime_function.c_funptrtype})({class_info(arguments.first)}->vft[{const_color}]))({ss}); /* {mmethod} on {arguments.first.inspect}*/"
                end
 
                if res0 != null then
@@ -1234,7 +1472,7 @@ class SeparateCompilerVisitor
                        (compiler.modelbuilder.toolcontext.opt_inline_some_methods.value and mmethoddef.can_inline(self)) then
                        compiler.modelbuilder.nb_invok_by_inline += 1
                        if compiler.modelbuilder.toolcontext.opt_invocation_metrics.value then add("count_invoke_by_inline++;")
-                       var frame = new Frame(self, mmethoddef, recvtype, arguments)
+                       var frame = new StaticFrame(self, mmethoddef, recvtype, arguments)
                        frame.returnlabel = self.get_name("RET_LABEL")
                        frame.returnvar = res
                        var old_frame = self.frame
@@ -1274,7 +1512,7 @@ class SeparateCompilerVisitor
                        self.compiler.mainmodule = main
                        return res
                end
-               return table_send(m.mproperty, arguments, m.const_color)
+               return table_send(m.mproperty, arguments, m)
        end
 
        redef fun vararg_instance(mpropdef, recv, varargs, elttype)
@@ -1284,11 +1522,11 @@ class SeparateCompilerVisitor
                # of the method (ie recv) if the static type is unresolved
                # This is more complex than usual because the unresolved type must not be resolved
                # with the current receiver (ie self).
-               # Therefore to isolate the resolution from self, a local Frame is created.
+               # Therefore to isolate the resolution from self, a local StaticFrame is created.
                # One can see this implementation as an inlined method of the receiver whose only
                # job is to allocate the array
                var old_frame = self.frame
-               var frame = new Frame(self, mpropdef, mpropdef.mclassdef.bound_mtype, [recv])
+               var frame = new StaticFrame(self, mpropdef, mpropdef.mclassdef.bound_mtype, [recv])
                self.frame = frame
                #print "required Array[{elttype}] for recv {recv.inspect}. bound=Array[{self.resolve_for(elttype, recv)}]. selfvar={frame.arguments.first.inspect}"
                var res = self.array_instance(varargs, elttype)
@@ -1523,7 +1761,7 @@ class SeparateCompilerVisitor
                                self.add("count_type_test_resolved_{tag}++;")
                        end
                else
-                       self.add("PRINT_ERROR(\"NOT YET IMPLEMENTED: type_test(%s, {mtype}).\\n\", \"{value.inspect}\"); show_backtrace(1);")
+                       self.add("PRINT_ERROR(\"NOT YET IMPLEMENTED: type_test(%s, {mtype}).\\n\", \"{value.inspect}\"); fatal_exit(1);")
                end
 
                # check color is in table
@@ -1565,7 +1803,7 @@ class SeparateCompilerVisitor
                                self.add("{res} = ({value2} != NULL) && ({value2}->class == &class_{mtype1.c_name}); /* is_same_type_test */")
                        end
                else
-                       self.add("{res} = ({value1} == {value2}) || ({value1} != NULL && {value2} != NULL && {value1}->class == {value2}->class); /* is_same_type_test */")
+                       self.add("{res} = ({value1} == {value2}) || ({value1} != NULL && {value2} != NULL && {class_info(value1)} == {class_info(value2)}); /* is_same_type_test */")
                end
                return res
        end
@@ -1575,7 +1813,7 @@ class SeparateCompilerVisitor
                var res = self.get_name("var_class_name")
                self.add_decl("const char* {res};")
                if value.mtype.ctype == "val*" then
-                       self.add "{res} = {value} == NULL ? \"null\" : {value}->type->name;"
+                       self.add "{res} = {value} == NULL ? \"null\" : {type_info(value)}->name;"
                else if value.mtype isa MClassType and value.mtype.as(MClassType).mclass.kind == extern_kind and
                        value.mtype.as(MClassType).name != "NativeString" then
                        self.add "{res} = \"{value.mtype.as(MClassType).mclass}\";"
@@ -1599,6 +1837,8 @@ class SeparateCompilerVisitor
                                self.add("{res} = {value1} == {value2};")
                        else if value2.mtype.ctype != "val*" then
                                self.add("{res} = 0; /* incompatible types {value1.mtype} vs. {value2.mtype}*/")
+                       else if value1.mtype.is_tagged then
+                               self.add("{res} = ({value2} != NULL) && ({self.autobox(value2, value1.mtype)} == {value1});")
                        else
                                var mtype1 = value1.mtype.as(MClassType)
                                self.require_declaration("class_{mtype1.c_name}")
@@ -1635,6 +1875,13 @@ class SeparateCompilerVisitor
                        else if t2.ctype != "val*" then
                                incompatible = true
                        else if can_be_primitive(value2) then
+                               if t1.is_tagged then
+                                       self.add("{res} = {value1} == {value2};")
+                                       return res
+                               end
+                               if not compiler.modelbuilder.toolcontext.opt_no_tag_primitives.value then
+                                       test.add("(!{extract_tag(value2)})")
+                               end
                                test.add("{value1}->class == {value2}->class")
                        else
                                incompatible = true
@@ -1642,6 +1889,13 @@ class SeparateCompilerVisitor
                else if t2.ctype != "val*" then
                        primitive = t2
                        if can_be_primitive(value1) then
+                               if t2.is_tagged then
+                                       self.add("{res} = {value1} == {value2};")
+                                       return res
+                               end
+                               if not compiler.modelbuilder.toolcontext.opt_no_tag_primitives.value then
+                                       test.add("(!{extract_tag(value1)})")
+                               end
                                test.add("{value1}->class == {value2}->class")
                        else
                                incompatible = true
@@ -1660,13 +1914,25 @@ class SeparateCompilerVisitor
                        end
                end
                if primitive != null then
+                       if primitive.is_tagged then
+                               self.add("{res} = {value1} == {value2};")
+                               return res
+                       end
                        test.add("((struct instance_{primitive.c_name}*){value1})->value == ((struct instance_{primitive.c_name}*){value2})->value")
                else if can_be_primitive(value1) and can_be_primitive(value2) then
+                       if not compiler.modelbuilder.toolcontext.opt_no_tag_primitives.value then
+                               test.add("(!{extract_tag(value1)}) && (!{extract_tag(value2)})")
+                       end
                        test.add("{value1}->class == {value2}->class")
                        var s = new Array[String]
                        for t, v in self.compiler.box_kinds do
+                               if t.mclass_type.is_tagged then continue
                                s.add "({value1}->class->box_kind == {v} && ((struct instance_{t.c_name}*){value1})->value == ((struct instance_{t.c_name}*){value2})->value)"
                        end
+                       if s.is_empty then
+                               self.add("{res} = {value1} == {value2};")
+                               return res
+                       end
                        test.add("({s.join(" || ")})")
                else
                        self.add("{res} = {value1} == {value2};")
@@ -1733,7 +1999,10 @@ class SeparateCompilerVisitor
                var nclass = self.get_class("NativeArray")
                var recv = "((struct instance_{nclass.c_name}*){arguments[0]})->values"
                if pname == "[]" then
-                       self.ret(self.new_expr("{recv}[{arguments[1]}]", ret_type.as(not null)))
+                       # Because the objects are boxed, return the box to avoid unnecessary (or broken) unboxing/reboxing
+                       var res = self.new_expr("{recv}[{arguments[1]}]", compiler.mainmodule.object_type)
+                       res.mcasttype = ret_type.as(not null)
+                       self.ret(res)
                        return
                else if pname == "[]=" then
                        self.add("{recv}[{arguments[1]}]={arguments[2]};")
@@ -1767,108 +2036,118 @@ class SeparateCompilerVisitor
 end
 
 redef class MMethodDef
-       fun separate_runtime_function: AbstractRuntimeFunction
+       # The C function associated to a mmethoddef
+       fun separate_runtime_function: SeparateRuntimeFunction
        do
                var res = self.separate_runtime_function_cache
                if res == null then
-                       res = new SeparateRuntimeFunction(self)
+                       var recv = mclassdef.bound_mtype
+                       var msignature = msignature.resolve_for(recv, recv, mclassdef.mmodule, true)
+                       res = new SeparateRuntimeFunction(self, recv, msignature, c_name)
                        self.separate_runtime_function_cache = res
                end
                return res
        end
        private var separate_runtime_function_cache: nullable SeparateRuntimeFunction
 
-       fun virtual_runtime_function: AbstractRuntimeFunction
+       # The C function associated to a mmethoddef, that can be stored into a VFT of a class
+       # The first parameter (the reciever) is always typed by val* in order to accept an object value
+       # The C-signature is always compatible with the intro
+       fun virtual_runtime_function: SeparateRuntimeFunction
        do
                var res = self.virtual_runtime_function_cache
                if res == null then
-                       res = new VirtualRuntimeFunction(self)
+                       # Because the function is virtual, the signature must match the one of the original class
+                       var intromclassdef = mproperty.intro.mclassdef
+                       var recv = intromclassdef.bound_mtype
+
+                       res = separate_runtime_function
+                       if res.called_recv == recv then
+                               self.virtual_runtime_function_cache = res
+                               return res
+                       end
+
+                       var msignature = mproperty.intro.msignature.resolve_for(recv, recv, intromclassdef.mmodule, true)
+
+                       if recv.ctype == res.called_recv.ctype and msignature.c_equiv(res.called_signature) then
+                               self.virtual_runtime_function_cache = res
+                               return res
+                       end
+
+                       res = new SeparateRuntimeFunction(self, recv, msignature, "VIRTUAL_{c_name}")
                        self.virtual_runtime_function_cache = res
+                       res.is_thunk = true
                end
                return res
        end
-       private var virtual_runtime_function_cache: nullable VirtualRuntimeFunction
+       private var virtual_runtime_function_cache: nullable SeparateRuntimeFunction
+end
+
+redef class MSignature
+       # Does the C-version of `self` the same than the C-version of `other`?
+       fun c_equiv(other: MSignature): Bool
+       do
+               if self == other then return true
+               if arity != other.arity then return false
+               for i in [0..arity[ do
+                       if mparameters[i].mtype.ctype != other.mparameters[i].mtype.ctype then return false
+               end
+               if return_mtype != other.return_mtype then
+                       if return_mtype == null or other.return_mtype == null then return false
+                       if return_mtype.ctype != other.return_mtype.ctype then return false
+               end
+               return true
+       end
 end
 
 # The C function associated to a methoddef separately compiled
 class SeparateRuntimeFunction
        super AbstractRuntimeFunction
 
-       redef fun build_c_name: String do return "{mmethoddef.c_name}"
+       # The call-side static receiver
+       var called_recv: MType
 
-       redef fun to_s do return self.mmethoddef.to_s
+       # The call-side static signature
+       var called_signature: MSignature
 
-       redef fun compile_to_c(compiler)
-       do
-               var mmethoddef = self.mmethoddef
+       # The name on the compiled method
+       redef var build_c_name: String
 
-               var recv = self.mmethoddef.mclassdef.bound_mtype
-               var v = compiler.new_visitor
-               var selfvar = new RuntimeVariable("self", recv, recv)
-               var arguments = new Array[RuntimeVariable]
-               var frame = new Frame(v, mmethoddef, recv, arguments)
-               v.frame = frame
+       # Statically call the original body instead
+       var is_thunk = false
 
-               var msignature = mmethoddef.msignature.resolve_for(mmethoddef.mclassdef.bound_mtype, mmethoddef.mclassdef.bound_mtype, mmethoddef.mclassdef.mmodule, true)
+       redef fun to_s do return self.mmethoddef.to_s
 
-               var sig = new FlatBuffer
-               var comment = new FlatBuffer
-               var ret = msignature.return_mtype
+       # The C return type (something or `void`)
+       var c_ret: String is lazy do
+               var ret = called_signature.return_mtype
                if ret != null then
-                       sig.append("{ret.ctype} ")
+                       return ret.ctype
                else
-                       sig.append("void ")
+                       return "void"
                end
-               sig.append(self.c_name)
-               sig.append("({selfvar.mtype.ctype} {selfvar}")
-               comment.append("({selfvar}: {selfvar.mtype}")
-               arguments.add(selfvar)
-               for i in [0..msignature.arity[ do
-                       var mtype = msignature.mparameters[i].mtype
-                       if i == msignature.vararg_rank then
-                               mtype = v.get_class("Array").get_mtype([mtype])
+       end
+
+       # The C signature (only the parmeter part)
+       var c_sig: String is lazy do
+               var sig = new FlatBuffer
+               sig.append("({called_recv.ctype} self")
+               for i in [0..called_signature.arity[ do
+                       var mtype = called_signature.mparameters[i].mtype
+                       if i == called_signature.vararg_rank then
+                               mtype = mmethoddef.mclassdef.mmodule.get_primitive_class("Array").get_mtype([mtype])
                        end
-                       comment.append(", {mtype}")
                        sig.append(", {mtype.ctype} p{i}")
-                       var argvar = new RuntimeVariable("p{i}", mtype, mtype)
-                       arguments.add(argvar)
                end
                sig.append(")")
-               comment.append(")")
-               if ret != null then
-                       comment.append(": {ret}")
-               end
-               compiler.provide_declaration(self.c_name, "{sig};")
-
-               v.add_decl("/* method {self} for {comment} */")
-               v.add_decl("{sig} \{")
-               if ret != null then
-                       frame.returnvar = v.new_var(ret)
-               end
-               frame.returnlabel = v.get_name("RET_LABEL")
-
-               if recv != arguments.first.mtype then
-                       #print "{self} {recv} {arguments.first}"
-               end
-               mmethoddef.compile_inside_to_c(v, arguments)
-
-               v.add("{frame.returnlabel.as(not null)}:;")
-               if ret != null then
-                       v.add("return {frame.returnvar.as(not null)};")
-               end
-               v.add("\}")
-               if not self.c_name.has_substring("VIRTUAL", 0) then compiler.names[self.c_name] = "{mmethoddef.mclassdef.mmodule.name}::{mmethoddef.mclassdef.mclass.name}::{mmethoddef.mproperty.name} ({mmethoddef.location.file.filename}:{mmethoddef.location.line_start})"
+               return sig.to_s
        end
-end
 
-# The C function associated to a methoddef on a primitive type, stored into a VFT of a class
-# The first parameter (the reciever) is always typed by val* in order to accept an object value
-class VirtualRuntimeFunction
-       super AbstractRuntimeFunction
+       # The C type for the function pointer.
+       var c_funptrtype: String is lazy do return "{c_ret}(*){c_sig}"
 
-       redef fun build_c_name: String do return "VIRTUAL_{mmethoddef.c_name}"
-
-       redef fun to_s do return self.mmethoddef.to_s
+       # The arguments, as generated by `compile_to_c`
+       private var arguments: Array[RuntimeVariable] is noinit
 
        redef fun compile_to_c(compiler)
        do
@@ -1876,25 +2155,20 @@ class VirtualRuntimeFunction
 
                var recv = self.mmethoddef.mclassdef.bound_mtype
                var v = compiler.new_visitor
-               var selfvar = new RuntimeVariable("self", v.object_type, recv)
+               var selfvar = new RuntimeVariable("self", called_recv, recv)
                var arguments = new Array[RuntimeVariable]
-               var frame = new Frame(v, mmethoddef, recv, arguments)
+               var frame = new StaticFrame(v, mmethoddef, recv, arguments)
                v.frame = frame
 
+               var msignature = called_signature
+               var ret = called_signature.return_mtype
+
                var sig = new FlatBuffer
                var comment = new FlatBuffer
-
-               # Because the function is virtual, the signature must match the one of the original class
-               var intromclassdef = self.mmethoddef.mproperty.intro.mclassdef
-               var msignature = mmethoddef.mproperty.intro.msignature.resolve_for(intromclassdef.bound_mtype, intromclassdef.bound_mtype, intromclassdef.mmodule, true)
-               var ret = msignature.return_mtype
-               if ret != null then
-                       sig.append("{ret.ctype} ")
-               else
-                       sig.append("void ")
-               end
+               sig.append(c_ret)
+               sig.append(" ")
                sig.append(self.c_name)
-               sig.append("({selfvar.mtype.ctype} {selfvar}")
+               sig.append(c_sig)
                comment.append("({selfvar}: {selfvar.mtype}")
                arguments.add(selfvar)
                for i in [0..msignature.arity[ do
@@ -1903,16 +2177,15 @@ class VirtualRuntimeFunction
                                mtype = v.get_class("Array").get_mtype([mtype])
                        end
                        comment.append(", {mtype}")
-                       sig.append(", {mtype.ctype} p{i}")
                        var argvar = new RuntimeVariable("p{i}", mtype, mtype)
                        arguments.add(argvar)
                end
-               sig.append(")")
                comment.append(")")
                if ret != null then
                        comment.append(": {ret}")
                end
                compiler.provide_declaration(self.c_name, "{sig};")
+               self.arguments = arguments.to_a
 
                v.add_decl("/* method {self} for {comment} */")
                v.add_decl("{sig} \{")
@@ -1921,10 +2194,14 @@ class VirtualRuntimeFunction
                end
                frame.returnlabel = v.get_name("RET_LABEL")
 
-               var subret = v.call(mmethoddef, recv, arguments)
-               if ret != null then
-                       assert subret != null
-                       v.assign(frame.returnvar.as(not null), subret)
+               if is_thunk then
+                       var subret = v.call(mmethoddef, recv, arguments)
+                       if ret != null then
+                               assert subret != null
+                               v.assign(frame.returnvar.as(not null), subret)
+                       end
+               else
+                       mmethoddef.compile_inside_to_c(v, arguments)
                end
 
                v.add("{frame.returnlabel.as(not null)}:;")
@@ -1932,27 +2209,72 @@ class VirtualRuntimeFunction
                        v.add("return {frame.returnvar.as(not null)};")
                end
                v.add("\}")
-               if not self.c_name.has_substring("VIRTUAL", 0) then compiler.names[self.c_name] = "{mmethoddef.mclassdef.mmodule.name}::{mmethoddef.mclassdef.mclass.name}::{mmethoddef.mproperty.name} ({mmethoddef.location.file.filename}--{mmethoddef.location.line_start})"
+               compiler.names[self.c_name] = "{mmethoddef.full_name} ({mmethoddef.location.file.filename}:{mmethoddef.location.line_start})"
        end
 
-       # TODO ?
-       redef fun call(v, arguments) do abort
+       # Compile the trampolines used to implement late-binding.
+       #
+       # See `opt_trampoline_call`.
+       fun compile_trampolines(compiler: SeparateCompiler)
+       do
+               var recv = self.mmethoddef.mclassdef.bound_mtype
+               var selfvar = arguments.first
+               var ret = called_signature.return_mtype
+
+               if mmethoddef.is_intro and recv.ctype == "val*" then
+                       var m = mmethoddef.mproperty
+                       var n2 = "CALL_" + m.const_color
+                       compiler.provide_declaration(n2, "{c_ret} {n2}{c_sig};")
+                       var v2 = compiler.new_visitor
+                       v2.add "{c_ret} {n2}{c_sig} \{"
+                       v2.require_declaration(m.const_color)
+                       var call = "(({c_funptrtype})({selfvar}->class->vft[{m.const_color}]))({arguments.join(", ")});"
+                       if ret != null then
+                               v2.add "return {call}"
+                       else
+                               v2.add call
+                       end
+
+                       v2.add "\}"
+
+               end
+               if mmethoddef.has_supercall and recv.ctype == "val*" then
+                       var m = mmethoddef
+                       var n2 = "CALL_" + m.const_color
+                       compiler.provide_declaration(n2, "{c_ret} {n2}{c_sig};")
+                       var v2 = compiler.new_visitor
+                       v2.add "{c_ret} {n2}{c_sig} \{"
+                       v2.require_declaration(m.const_color)
+                       var call = "(({c_funptrtype})({selfvar}->class->vft[{m.const_color}]))({arguments.join(", ")});"
+                       if ret != null then
+                               v2.add "return {call}"
+                       else
+                               v2.add call
+                       end
+
+                       v2.add "\}"
+               end
+       end
 end
 
 redef class MType
-       fun const_color: String do return "COLOR_{c_name}"
+       # Are values of `self` tagged?
+       # If false, it means that the type is not primitive, or is boxed.
+       var is_tagged = false
+end
+
+redef class MEntity
+       var const_color: String is lazy do return "COLOR_{c_name}"
 end
 
 interface PropertyLayoutElement end
 
 redef class MProperty
        super PropertyLayoutElement
-       fun const_color: String do return "COLOR_{c_name}"
 end
 
 redef class MPropDef
        super PropertyLayoutElement
-       fun const_color: String do return "COLOR_{c_name}"
 end
 
 redef class AMethPropdef