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

runtime/vm/isolate.h

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_ISOLATE_H_
 #define VM_ISOLATE_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/atomic.h"
@@ skipping 791 matching lines @@
     mutator_thread_ = thread;
   }
 #if defined(DEBUG)
   bool IsIsolateOf(Thread* thread);
 #endif  // DEBUG
 
   template<class T> T* AllocateReusableHandle();
 
   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_;
   char* name_;
   char* debugger_name_;
   int64_t start_time_;
   Dart_Port main_port_;
   Dart_Port origin_id_;  // Isolates created by spawnFunc have some origin id.
   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_;
   Dart_EnvironmentCallback environment_callback_;
   Dart_LibraryTagHandler library_tag_handler_;
   ApiState* api_state_;
   Debugger* debugger_;
   bool single_step_;
   bool resume_request_;
   int64_t last_resume_timestamp_;
@@ skipping 281 matching lines @@
   uint8_t* serialized_message_;
   intptr_t serialized_message_len_;
   Isolate::Flags isolate_flags_;
   bool paused_;
   bool errors_are_fatal_;
 };
 
 }  // namespace dart
 
 #endif  // VM_ISOLATE_H_