Move pointer Isolate::heap_ above bool Isolate::errors_fatal_ so Ubuntu's gcc 4.8.4 and Linaro's gc…

runtime/vm/isolate.h

Index: runtime/vm/isolate.h
diff --git a/runtime/vm/isolate.h b/runtime/vm/isolate.h
index cc6b54da6aca38d244df7b2c176b68973431b8b6..9d5358bc34e10a420039d8b0da88008fd6386716 100644
--- a/runtime/vm/isolate.h
+++ b/runtime/vm/isolate.h
@@ -809,6 +809,7 @@ class Isolate : public BaseIsolate {
 
   uword vm_tag_;
   StoreBuffer* store_buffer_;
+  Heap* heap_;

[Ivan Posva, 2015/09/15 22:25:40]

Please ensure the following ordering:
64-bit fields
pointer/word sized
32-bit fields
16-bit fields
8-bit fields
bool fields

Thanks!

There is still the remaining question about embedded structs.

[koda, 2015/09/15 22:34:45]

For the fields that are frequently accessed (e.g., from generated code),
shouldn't we try to fit them within the same cache line(s)?

Also, on ARM, the range of offsets that can be encoded in a single load
instruction is somewhat limited, although I'm not sure we have *that* many
fields yet.

[rmacnak, 2015/09/16 00:36:13]

Yes, we should sort those first. Currently 32-bit sizeof(Isolate) is 13952 (!)
which exceeds ARM's 4096 single instruction range.

   ThreadRegistry* thread_registry_;
   ClassTable class_table_;
   Dart_MessageNotifyCallback message_notify_callback_;
@@ -820,7 +821,6 @@ class Isolate : public BaseIsolate {
   uint64_t pause_capability_;
   uint64_t terminate_capability_;
   bool errors_fatal_;
-  Heap* heap_;
   ObjectStore* object_store_;
   uword top_exit_frame_info_;
   void* init_callback_data_;