Link function contexts directly to the previous context.

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index 0fc75028b304bd965d9b937e2b70155d61134a5c..1d375e15f8a3e295ca346104838dd9f0873ba2da 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -3617,15 +3617,10 @@ void MacroAssembler::CopyBytes(Register destination,
 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