Resolve some disagreements between SIMARM and XARM on offsets used in compiled code.

runtime/vm/heap.h

 // Copyright (c) 2012, 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_HEAP_H_
 #define VM_HEAP_H_
 
 #include "platform/assert.h"
 #include "vm/allocation.h"
 #include "vm/flags.h"
@@ skipping 292 matching lines @@
 
   // Updates gc_in_progress.
   void BeginGC();
   void EndGC();
 
   // If this heap is non-empty, updates start and end to the smallest range that
   // contains both the original [start, end) and the [lowest, highest) addresses
   // of this heap.
   void GetMergedAddressRange(uword* start, uword* end) const;
 
-  Isolate* isolate_;
-
   // The different spaces used for allocation.
   Scavenger new_space_;
   PageSpace old_space_;
 
+  Isolate* isolate_;

[Florian Schneider, 2015/09/30 09:38:13]

This seems still fragile, since there are members of Scavenger that may be
packed differently. I think we would need to add ALIGNx to all those as well to
be sure that isolate_ is at the same offset.

Maybe add a COMPILE_ASSERT for 32 and 64 bit to be sure it does not break.

[rmacnak, 2015/10/01 22:00:49]

This is to get Heap::Top/EndOffset(kNew) consistent. We shouldn't be using
isolate_ or anything below.

+
   WeakTable* new_weak_tables_[kNumWeakSelectors];
   WeakTable* old_weak_tables_[kNumWeakSelectors];
 
   // GC stats collection.
   GCStats stats_;
 
   // This heap is in read-only mode: No allocation is allowed.
   bool read_only_;
 
   // GC on the heap is in progress.
@@ skipping 25 matching lines @@
   NoHeapGrowthControlScope();
   ~NoHeapGrowthControlScope();
  private:
   bool current_growth_controller_state_;
   DISALLOW_COPY_AND_ASSIGN(NoHeapGrowthControlScope);
 };
 
 }  // namespace dart
 
 #endif  // VM_HEAP_H_