Remove the fcontext field from all contexts.

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index 77c687045c908fd819c0a6a7e3968e16aa1623bb..21ab4cb10e341ea97874a464f4192d45f7b02256 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -680,13 +680,16 @@ void FullCodeGenerator::EmitDeclaration(Variable* variable,
         // We bypass the general EmitSlotSearch because we know more about
         // this specific context.
 
-        // The variable in the decl always resides in the current context.
+        // The variable in the decl always resides in the current function
+        // context.
         ASSERT_EQ(0, scope()->ContextChainLength(variable->scope()));
         if (FLAG_debug_code) {
-          // Check if we have the correct context pointer.
-          __ movq(rbx, ContextOperand(rsi, Context::FCONTEXT_INDEX));
-          __ cmpq(rbx, rsi);
-          __ Check(equal, "Unexpected declaration in current context.");
+          // Check that we're not inside a with or catch context.
+          __ movq(rbx, FieldOperand(rsi, HeapObject::kMapOffset));
+          __ CompareRoot(rbx, Heap::kWithContextMapRootIndex);
+          __ Check(not_equal, "Declaration in with context.");
+          __ CompareRoot(rbx, Heap::kCatchContextMapRootIndex);
+          __ Check(not_equal, "Declaration in catch context.");
         }
         if (mode == Variable::CONST) {
           __ LoadRoot(kScratchRegister, Heap::kTheHoleValueRootIndex);
@@ -1778,17 +1781,7 @@ void FullCodeGenerator::EmitVariableAssignment(Variable* var,
         __ j(not_equal, &skip);
         __ movq(Operand(rbp, SlotOffset(slot)), rax);
         break;
-      case Slot::CONTEXT: {
-        __ movq(rcx, ContextOperand(rsi, Context::FCONTEXT_INDEX));
-        __ movq(rdx, ContextOperand(rcx, slot->index()));
-        __ CompareRoot(rdx, Heap::kTheHoleValueRootIndex);
-        __ j(not_equal, &skip);
-        __ movq(ContextOperand(rcx, slot->index()), rax);
-        int offset = Context::SlotOffset(slot->index());
-        __ movq(rdx, rax);  // Preserve the stored value in eax.
-        __ RecordWrite(rcx, offset, rdx, rbx);
-        break;
-      }
+      case Slot::CONTEXT:
       case Slot::LOOKUP:
         __ push(rax);
         __ push(rsi);