Merge pull request #502 from savi-lang/perf/trait-bitmap-reach

Compiler performance improvement: optimize trait bitmapping reachable subtype checks

Author: jemc

src/savi/compiler/code_gen/ponyrt.cr

@@ -444,9 +444,7 @@ class Savi::Compiler::CodeGen::PonyRT
     is_asio_event_actor = false
     traits_bitmap = g.trait_bitmap_size.times.map { 0 }.to_a
     g.ctx.reach.each_type_def.each { |other_def|
-      g.ctx.reach.each_reached_subtype_of(g.ctx, other_def) { |sub_def|
-        next unless sub_def == gtype.type_def
-
+      if gtype.type_def.is_subtype_of?(g.ctx, other_def)
         index = other_def.desc_id >> Math.log2(g.bitwidth).to_i
         raise "bad index or trait_bitmap_size" unless index < g.trait_bitmap_size
 
@@ -455,7 +453,7 @@ class Savi::Compiler::CodeGen::PonyRT
 
         # Take special note if this type is a subtype of AsioEvent.Actor.
         is_asio_event_actor = true if other_def.llvm_name == "AsioEvent.Actor"
-      }
+      end
     }
     traits_bitmap_global = g.gen_global_for_const \
       @isize.const_array(traits_bitmap.map { |bits| @isize.const_int(bits) }),

src/savi/compiler/reach.cr

@@ -542,6 +542,20 @@ class Savi::Compiler::Reach < Savi::AST::Visitor
       Ref.new(Infer::MetaType.new(@reified))
     end
 
+    def is_subtype_of?(ctx, super_def : Def)
+      super_link = super_def.link
+
+      # Nothing can be a subtype of a non-abstract type.
+      return false unless super_link.is_abstract?
+
+      # The possible subtype list is a cheap first check with no false negatives.
+      possible_subtype_links = ctx.pre_subtyping[super_link].possible_subtypes
+      return false unless possible_subtype_links.includes?(self.link)
+
+      # Check the actual subtyping rules
+      return ctx.subtyping.is_subtype_of?(ctx, self.reified, super_def.reified)
+    end
+
     def ordered_fields(ctx, target_info : Target)
       t = @reified.link.resolve(ctx)
       metadata = t.metadata