add context save for GenerateFastApiCall

src/x64/macro-assembler-x64.cc

 // 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 676 matching lines @@
 
 void MacroAssembler::PrepareCallApiFunction(int arg_stack_space) {
   EnterApiExitFrame(arg_stack_space);
 }
 
 
 void MacroAssembler::CallApiFunctionAndReturn(Address function_address,
                                               Address thunk_address,
                                               Register thunk_last_arg,
                                               int stack_space,
-                                              int return_value_offset) {
+                                              int return_value_offset,
+                                              int restore_context_offset) {
   Label prologue;
   Label promote_scheduled_exception;
+  Label exception_handled;
   Label delete_allocated_handles;
   Label leave_exit_frame;
   Label write_back;
 
   Factory* factory = isolate()->factory();
   ExternalReference next_address =
       ExternalReference::handle_scope_next_address(isolate());
   const int kNextOffset = 0;
   const int kLimitOffset = Offset(
       ExternalReference::handle_scope_limit_address(isolate()),
@@ skipping 65 matching lines @@
   subl(Operand(base_reg, kLevelOffset), Immediate(1));
   movq(Operand(base_reg, kNextOffset), prev_next_address_reg);
   cmpq(prev_limit_reg, Operand(base_reg, kLimitOffset));
   j(not_equal, &delete_allocated_handles);
   bind(&leave_exit_frame);
 
   // Check if the function scheduled an exception.
   movq(rsi, scheduled_exception_address);
   Cmp(Operand(rsi, 0), factory->the_hole_value());
   j(not_equal, &promote_scheduled_exception);
+  bind(&exception_handled);
 
 #if ENABLE_EXTRA_CHECKS
   // Check if the function returned a valid JavaScript value.
   Label ok;
   Register return_value = rax;
   Register map = rcx;
 
   JumpIfSmi(return_value, &ok, Label::kNear);
   movq(map, FieldOperand(return_value, HeapObject::kMapOffset));
 
@@ skipping 16 matching lines @@
   j(equal, &ok, Label::kNear);
 
   CompareRoot(return_value, Heap::kNullValueRootIndex);
   j(equal, &ok, Label::kNear);
 
   Abort(kAPICallReturnedInvalidObject);
 
   bind(&ok);
 #endif
 
-  LeaveApiExitFrame();
+  bool restore_context = restore_context_offset != 0;

[Michael Starzinger, 2013/09/12 18:38:51]

Hmpf! The context is not restored when the offset is 0? That is not exactly
intuitive. Also I don't really understand why the CallIC for an API function
needs to restore the context of the callee at all. The context should be
restored by the caller IIUC.

So can't we just not restore Isolate::Context at all for API functions and just
always restore what's in the saved context slot?

+  if (restore_context) {
+    movq(rsi, Operand(rbp, restore_context_offset * kPointerSize));
+  }
+  LeaveApiExitFrame(!restore_context);
   ret(stack_space * kPointerSize);
 
   bind(&promote_scheduled_exception);
-  TailCallRuntime(Runtime::kPromoteScheduledException, 0, 1);
+  CallRuntime(Runtime::kPromoteScheduledException, 0);
+  jmp(&exception_handled);
 
   // HandleScope limit has changed. Delete allocated extensions.
   bind(&delete_allocated_handles);
   movq(Operand(base_reg, kLimitOffset), prev_limit_reg);
   movq(prev_limit_reg, rax);
   LoadAddress(arg_reg_1, ExternalReference::isolate_address(isolate()));
   LoadAddress(rax,
               ExternalReference::delete_handle_scope_extensions(isolate()));
   call(rax);
   movq(rax, prev_limit_reg);
@@ skipping 2728 matching lines @@
   // Get the return address from the stack and restore the frame pointer.
   movq(rcx, Operand(rbp, 1 * kPointerSize));
   movq(rbp, Operand(rbp, 0 * kPointerSize));
 
   // Drop everything up to and including the arguments and the receiver
   // from the caller stack.
   lea(rsp, Operand(r15, 1 * kPointerSize));
 
   PushReturnAddressFrom(rcx);
 
-  LeaveExitFrameEpilogue();
+  LeaveExitFrameEpilogue(true);
 }
 
 
-void MacroAssembler::LeaveApiExitFrame() {
+void MacroAssembler::LeaveApiExitFrame(bool restore_context) {
   movq(rsp, rbp);
   pop(rbp);
 
-  LeaveExitFrameEpilogue();
+  LeaveExitFrameEpilogue(restore_context);
 }
 
 
-void MacroAssembler::LeaveExitFrameEpilogue() {
+void MacroAssembler::LeaveExitFrameEpilogue(bool restore_context) {
   // Restore current context from top and clear it in debug mode.
   ExternalReference context_address(Isolate::kContextAddress, isolate());
   Operand context_operand = ExternalOperand(context_address);
-  movq(rsi, context_operand);
+  if (restore_context) {
+    movq(rsi, context_operand);
+  }
 #ifdef DEBUG
   movq(context_operand, Immediate(0));
 #endif
 
   // Clear the top frame.
   ExternalReference c_entry_fp_address(Isolate::kCEntryFPAddress,
                                        isolate());
   Operand c_entry_fp_operand = ExternalOperand(c_entry_fp_address);
   movq(c_entry_fp_operand, Immediate(0));
 }
@@ skipping 1094 matching lines @@
   j(greater, &no_memento_available);
   CompareRoot(MemOperand(scratch_reg, -AllocationMemento::kSize),
               Heap::kAllocationMementoMapRootIndex);
   bind(&no_memento_available);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64