Generator objects can suspend

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 564c3def865d6b3535209e5bcf8fb32f19605a3c..672d7cc9fd9c273039de2253e3c8ce609cd592fb 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -1907,6 +1907,46 @@ void FullCodeGenerator::VisitAssignment(Assignment* expr) {
 }
 
 
+void FullCodeGenerator::VisitYield(Yield* expr) {
+  Comment cmnt(masm_, "[ Yield");
+  // Evaluate yielded value first; the initial iterator definition depends on
+  // this.  It stays on the stack while we update the iterator.
+  VisitForStackValue(expr->expression());
+  VisitForStackValue(expr->generator_object());
+
+  if (expr->kind() == Yield::FINAL) {
+    // TODO(wingo): Mark the iterator as closed.
+  } else {
+    __ CallRuntime(Runtime::kSuspendJSGeneratorObject, 1);
+    __ movq(context_register(),
+            Operand(rbp, StandardFrameConstants::kContextOffset));
+  }
+
+  Label resume;
+  __ CompareRoot(result_register(), Heap::kTheHoleValueRootIndex);
+  __ j(not_equal, &resume);
+  switch (expr->kind()) {
+    case Yield::INITIAL:
+      __ pop(result_register());
+      break;
+    case Yield::SUSPEND:
+      // TODO(wingo): Box into { value: VALUE, done: false }.
+      __ pop(result_register());
+      break;
+    case Yield::FINAL:
+      // TODO(wingo): Box into { value: VALUE, done: true }.
+      __ pop(result_register());
+      break;
+    case Yield::DELEGATING:
+      UNIMPLEMENTED();
+  }
+  EmitReturnSequence();
+
+  __ bind(&resume);
+  context()->Plug(result_register());
+}
+
+
 void FullCodeGenerator::EmitNamedPropertyLoad(Property* prop) {
   SetSourcePosition(prop->position());
   Literal* key = prop->key()->AsLiteral();