Link function contexts directly to the previous context.

src/x64/macro-assembler-x64.cc

 // Copyright 2011 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 3599 matching lines @@
     j(not_equal, &short_loop);
 
     bind(&done);
   }
 }
 
 
 void MacroAssembler::LoadContext(Register dst, int context_chain_length) {
   if (context_chain_length > 0) {
     // Move up the chain of contexts to the context containing the slot.
-    movq(dst, Operand(rsi, Context::SlotOffset(Context::CLOSURE_INDEX)));
-    // Load the function context (which is the incoming, outer context).
-    movq(dst, FieldOperand(dst, JSFunction::kContextOffset));
+    movq(dst, Operand(rsi, Context::SlotOffset(Context::PREVIOUS_INDEX)));
     for (int i = 1; i < context_chain_length; i++) {
-      movq(dst, Operand(dst, Context::SlotOffset(Context::CLOSURE_INDEX)));
-      movq(dst, FieldOperand(dst, JSFunction::kContextOffset));
+      movq(dst, Operand(dst, Context::SlotOffset(Context::PREVIOUS_INDEX)));
     }
-    // The context may be an intermediate context, not a function context.
-    movq(dst, Operand(dst, Context::SlotOffset(Context::FCONTEXT_INDEX)));
   } else {
     // Slot is in the current function context.  Move it into the
     // destination register in case we store into it (the write barrier
     // cannot be allowed to destroy the context in rsi).
     movq(dst, rsi);
   }
 
   // We should not have found a 'with' context by walking the context chain
   // (i.e., the static scope chain and runtime context chain do not agree).
   // A variable occurring in such a scope should have slot type LOOKUP and
@@ skipping 109 matching lines @@
   CPU::FlushICache(address_, size_);
 
   // Check that the code was patched as expected.
   ASSERT(masm_.pc_ == address_ + size_);
   ASSERT(masm_.reloc_info_writer.pos() == address_ + size_ + Assembler::kGap);
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64