Reland transformation of async functions.

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index ba8b6255848ac66218019d4fbcd804be02cde665..96da2e4aafae2a9d877a622e19762d1e3aca1c5c 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -1665,6 +1665,10 @@ class Function : public Object {
     return KindBits::decode(raw_ptr()->kind_tag_);
   }
 
+  RawFunction::AsyncModifier modifier() const {
+    return ModifierBits::decode(raw_ptr()->kind_tag_);
+  }
+
   static const char* KindToCString(RawFunction::Kind kind);
 
   bool is_static() const { return StaticBit::decode(raw_ptr()->kind_tag_); }
@@ -1811,6 +1815,11 @@ class Function : public Object {
   void SetIsOptimizable(bool value) const;
   void SetIsNativeAutoSetupScope(bool value) const;
 
+  bool is_async_closure() const {
+    return AsyncClosureBit::decode(raw_ptr()->kind_tag_);
+  }
+  void set_is_async_closure(bool value) const;
+
   bool is_native() const { return NativeBit::decode(raw_ptr()->kind_tag_); }
   void set_is_native(bool value) const;
 
@@ -1961,6 +1970,10 @@ class Function : public Object {
     return kind() == RawFunction::kSignatureFunction;
   }
 
+  bool IsAsyncFunction() const {
+    return modifier() == RawFunction::kAsync;
+  }
+
   static intptr_t InstanceSize() {
     return RoundedAllocationSize(sizeof(RawFunction));
   }
@@ -2015,6 +2028,8 @@ class Function : public Object {
   static const int kCtorPhaseBody = 1 << 1;
   static const int kCtorPhaseAll = (kCtorPhaseInit | kCtorPhaseBody);
 
+  void set_modifier(RawFunction::AsyncModifier value) const;
+
  private:
   void set_ic_data_array(const Array& value) const;
 
@@ -2033,6 +2048,8 @@ class Function : public Object {
     kRedirectingBit = 13,
     kExternalBit = 14,
     kAllowsHoistingCheckClassBit = 15,
+    kModifierPos = 16,
+    kAsyncClosureBit = 18,
   };
   class KindBits :
     public BitField<RawFunction::Kind, kKindTagPos, kKindTagSize> {};  // NOLINT
@@ -2049,6 +2066,9 @@ class Function : public Object {
   class RedirectingBit : public BitField<bool, kRedirectingBit, 1> {};
   class AllowsHoistingCheckClassBit :
       public BitField<bool, kAllowsHoistingCheckClassBit, 1> {};  // NOLINT
+  class ModifierBits :
+      public BitField<RawFunction::AsyncModifier, kModifierPos, 2> {};  // NOLINT

[Ivan Posva, 2014/07/29 23:56:14]

There is still a mismatch between the number of bits and the number of states
you need to encode here. Please fix. Iff we need to add more states then we can
add bits.

+  class AsyncClosureBit : public BitField<bool, kAsyncClosureBit, 1> {};
 
   void set_name(const String& value) const;
   void set_kind(RawFunction::Kind value) const;