WIP [esnext] implement async iteration proposal

src/builtins/x64/builtins-x64.cc

Index: src/builtins/x64/builtins-x64.cc
diff --git a/src/builtins/x64/builtins-x64.cc b/src/builtins/x64/builtins-x64.cc
index 87dfc7d3a6b6305a4d7ec63c05c36e47b5418a7c..16e9d00cf56e96ca24953e9f5558c5f67f5844a8 100644
--- a/src/builtins/x64/builtins-x64.cc
+++ b/src/builtins/x64/builtins-x64.cc
@@ -559,6 +559,132 @@ void Builtins::Generate_ResumeGeneratorTrampoline(MacroAssembler* masm) {
   __ jmp(&stepping_prepared);
 }
 
+// static
+void Builtins::Generate_ResumeAwaitedGeneratorTrampoline(MacroAssembler* masm) {
+  // ----------- S t a t e -------------
+  //  -- rax    : the value to pass to the generator
+  //  -- rbx    : the JSGeneratorObject to resume
+  //  -- rdx    : the resume mode (tagged)
+  //  -- rsp[0] : return address
+  // -----------------------------------
+  __ AssertGeneratorObject(rbx);
+
+  // Restore saved input
+  __ movp(rcx, FieldOperand(rbx, JSGeneratorObject::kAwaitInputOffset));
+  __ movp(FieldOperand(rbx, JSGeneratorObject::kInputOrDebugPosOffset), rcx);
+  __ RecordWriteField(rbx, JSGeneratorObject::kInputOrDebugPosOffset, rcx, rsi,
+                      kDontSaveFPRegs);
+
+  // Store input value into generator object.
+  __ movp(FieldOperand(rbx, JSGeneratorObject::kAwaitInputOffset), rax);
+  __ RecordWriteField(rbx, JSGeneratorObject::kAwaitInputOffset, rax, rcx,
+                      kDontSaveFPRegs);
+
+  // Store resume mode into generator object.
+  __ movp(FieldOperand(rbx, JSGeneratorObject::kResumeModeOffset), rdx);
+
+  // Load suspended function and context.
+  __ movp(rsi, FieldOperand(rbx, JSGeneratorObject::kContextOffset));
+  __ movp(rdi, FieldOperand(rbx, JSGeneratorObject::kFunctionOffset));
+
+  // Flood function if we are stepping.
+  Label prepare_step_in_if_stepping, prepare_step_in_suspended_generator;
+  Label stepping_prepared;
+  ExternalReference last_step_action =
+      ExternalReference::debug_last_step_action_address(masm->isolate());
+  Operand last_step_action_operand = masm->ExternalOperand(last_step_action);
+  STATIC_ASSERT(StepFrame > StepIn);
+  __ cmpb(last_step_action_operand, Immediate(StepIn));
+  __ j(greater_equal, &prepare_step_in_if_stepping);
+
+  // Flood function if we need to continue stepping in the suspended generator.
+  ExternalReference debug_suspended_generator =
+      ExternalReference::debug_suspended_generator_address(masm->isolate());
+  Operand debug_suspended_generator_operand =
+      masm->ExternalOperand(debug_suspended_generator);
+  __ cmpp(rbx, debug_suspended_generator_operand);
+  __ j(equal, &prepare_step_in_suspended_generator);
+  __ bind(&stepping_prepared);
+
+  // Pop return address.
+  __ PopReturnAddressTo(rax);
+
+  // Push receiver.
+  __ Push(FieldOperand(rbx, JSGeneratorObject::kReceiverOffset));
+
+  // ----------- S t a t e -------------
+  //  -- rax    : return address
+  //  -- rbx    : the JSGeneratorObject to resume
+  //  -- rdx    : the resume mode (tagged)
+  //  -- rdi    : generator function
+  //  -- rsi    : generator context
+  //  -- rsp[0] : generator receiver
+  // -----------------------------------
+
+  // Push holes for arguments to generator function. Since the parser forced
+  // context allocation for any variables in generators, the actual argument
+  // values have already been copied into the context and these dummy values
+  // will never be used.
+  __ movp(rcx, FieldOperand(rdi, JSFunction::kSharedFunctionInfoOffset));
+  __ LoadSharedFunctionInfoSpecialField(
+      rcx, rcx, SharedFunctionInfo::kFormalParameterCountOffset);
+  {
+    Label done_loop, loop;
+    __ bind(&loop);
+    __ subl(rcx, Immediate(1));
+    __ j(carry, &done_loop, Label::kNear);
+    __ PushRoot(Heap::kTheHoleValueRootIndex);
+    __ jmp(&loop);
+    __ bind(&done_loop);
+  }
+
+  // Underlying function needs to have bytecode available.
+  if (FLAG_debug_code) {
+    __ movp(rcx, FieldOperand(rdi, JSFunction::kSharedFunctionInfoOffset));
+    __ movp(rcx, FieldOperand(rcx, SharedFunctionInfo::kFunctionDataOffset));
+    __ CmpObjectType(rcx, BYTECODE_ARRAY_TYPE, rcx);
+    __ Assert(equal, kMissingBytecodeArray);
+  }
+
+  // Resume (Ignition/TurboFan) generator object.
+  {
+    __ PushReturnAddressFrom(rax);
+    __ movp(rax, FieldOperand(rdi, JSFunction::kSharedFunctionInfoOffset));
+    __ LoadSharedFunctionInfoSpecialField(
+        rax, rax, SharedFunctionInfo::kFormalParameterCountOffset);
+    // We abuse new.target both to indicate that this is a resume call and to
+    // pass in the generator object.  In ordinary calls, new.target is always
+    // undefined because generator functions are non-constructable.
+    __ movp(rdx, rbx);
+    __ jmp(FieldOperand(rdi, JSFunction::kCodeEntryOffset));
+  }
+
+  __ bind(&prepare_step_in_if_stepping);
+  {
+    FrameScope scope(masm, StackFrame::INTERNAL);
+    __ Push(rbx);
+    __ Push(rdx);
+    __ Push(rdi);
+    __ CallRuntime(Runtime::kDebugPrepareStepInIfStepping);
+    __ Pop(rdx);
+    __ Pop(rbx);
+    __ movp(rdi, FieldOperand(rbx, JSGeneratorObject::kFunctionOffset));
+  }
+  __ jmp(&stepping_prepared);
+
+  __ bind(&prepare_step_in_suspended_generator);
+  {
+    FrameScope scope(masm, StackFrame::INTERNAL);
+    __ Push(rbx);
+    __ Push(rdx);
+    __ CallRuntime(Runtime::kDebugPrepareStepInSuspendedGenerator);
+    __ Pop(rdx);
+    __ Pop(rbx);
+    __ movp(rdi, FieldOperand(rbx, JSGeneratorObject::kFunctionOffset));
+  }
+  __ jmp(&stepping_prepared);
+}
+
 static void LeaveInterpreterFrame(MacroAssembler* masm, Register scratch1,
                                   Register scratch2) {
   Register args_count = scratch1;