[turbofan] Load immortal heap objects from the heap roots.

src/compiler/code-generator.h

Index: src/compiler/code-generator.h
diff --git a/src/compiler/code-generator.h b/src/compiler/code-generator.h
index 641bbed1a1d6498af477f9eddb5a8c1bd1b25b37..9b3c51f97cb89b4d8ac7d48dfc65f1e9450456b2 100644
--- a/src/compiler/code-generator.h
+++ b/src/compiler/code-generator.h
@@ -58,6 +58,15 @@ class CodeGenerator FINAL : public GapResolver::Assembler {
   void RecordSafepoint(ReferenceMap* references, Safepoint::Kind kind,
                        int arguments, Safepoint::DeoptMode deopt_mode);
 
+  // Check if a heap object can be materialized by loading from the frame, which
+  // is usually way cheaper than materializing the actual heap object constant.
+  bool IsMaterializableFromFrame(Handle<HeapObject> object, int* offset_return);
+  // Check if a heap object can be materialized by loading from a heap root,
+  // which is cheaper on some platforms than materializing the actual heap
+  // object constant.
+  bool IsMaterializableFromRoot(Handle<HeapObject> object,
+                                Heap::RootListIndex* index_return);
+
   // Assemble code for the specified instruction.
   void AssembleInstruction(Instruction* instr);
   void AssembleSourcePosition(Instruction* instr);