Use movw/movt on ARM to load constant roots

src/heap.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1433 matching lines @@
     kStrongRootListLength = kSymbolTableRootIndex,
     kRootListLength
   };
 
   STATIC_CHECK(kUndefinedValueRootIndex == Internals::kUndefinedValueRootIndex);
   STATIC_CHECK(kNullValueRootIndex == Internals::kNullValueRootIndex);
   STATIC_CHECK(kTrueValueRootIndex == Internals::kTrueValueRootIndex);
   STATIC_CHECK(kFalseValueRootIndex == Internals::kFalseValueRootIndex);
   STATIC_CHECK(kempty_symbolRootIndex == Internals::kEmptySymbolRootIndex);
 
+  // Generated code can embed direct references to non-writable roots if
+  // they are in new space.

[danno, 2012/11/07 21:51:36]

I don't think this comment is correct. The comment about being in new space
isn't accurate, and this patch doesn't check for it. I'll adjust before landing.

+  static bool RootCanBeWrittenAfterInitialization(RootListIndex root_index);
+
   MUST_USE_RESULT MaybeObject* NumberToString(
       Object* number, bool check_number_string_cache = true);
   MUST_USE_RESULT MaybeObject* Uint32ToString(
       uint32_t value, bool check_number_string_cache = true);
 
   Map* MapForExternalArrayType(ExternalArrayType array_type);
   RootListIndex RootIndexForExternalArrayType(
       ExternalArrayType array_type);
 
   void RecordStats(HeapStats* stats, bool take_snapshot = false);
@@ skipping 1354 matching lines @@
   AssertNoAllocation no_alloc;  // i.e. no gc allowed.
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG || LIVE_OBJECT_LIST
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_H_