Generators: Avoid calling into runtime if operand stack is empty

src/x64/full-codegen-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 1958 matching lines @@
   // this.  It stays on the stack while we update the iterator.
   VisitForStackValue(expr->expression());
 
   switch (expr->yield_kind()) {
     case Yield::SUSPEND:
       // Pop value from top-of-stack slot; box result into result register.
       EmitCreateIteratorResult(false);
       __ push(result_register());
       // Fall through.
     case Yield::INITIAL: {
-      VisitForStackValue(expr->generator_object());
+      Label suspend, continuation, post_runtime, resume;
+
+      __ jmp(&suspend);
+
+      __ bind(&continuation);
+      __ jmp(&resume);
+
+      __ bind(&suspend);
+      VisitForAccumulatorValue(expr->generator_object());
+      ASSERT(continuation.pos() > 0 && Smi::IsValid(continuation.pos()));
+      __ Move(FieldOperand(rax, JSGeneratorObject::kContinuationOffset),
+              Smi::FromInt(continuation.pos()));
+      __ movq(FieldOperand(rax, JSGeneratorObject::kContextOffset), rsi);
+      __ movq(rcx, rsi);
+      __ RecordWriteField(rax, JSGeneratorObject::kContextOffset, rcx, rdx,
+                          kDontSaveFPRegs);
+      __ lea(rbx, Operand(rbp, StandardFrameConstants::kExpressionsOffset));
+      __ cmpq(rsp, rbx);
+      __ j(equal, &post_runtime);
+      __ push(rax);  // generator object
       __ CallRuntime(Runtime::kSuspendJSGeneratorObject, 1);
       __ movq(context_register(),
               Operand(rbp, StandardFrameConstants::kContextOffset));
+      __ bind(&post_runtime);
 
-      Label resume;
-      __ CompareRoot(result_register(), Heap::kTheHoleValueRootIndex);
-      __ j(not_equal, &resume);
       __ pop(result_register());
       EmitReturnSequence();
 
       __ bind(&resume);
       context()->Plug(result_register());
       break;
     }
 
     case Yield::FINAL: {
       VisitForAccumulatorValue(expr->generator_object());
       __ Move(FieldOperand(result_register(),
                            JSGeneratorObject::kContinuationOffset),
               Smi::FromInt(JSGeneratorObject::kGeneratorClosed));
       // Pop value from top-of-stack slot, box result into result register.
       EmitCreateIteratorResult(true);
       EmitUnwindBeforeReturn();
       EmitReturnSequence();
       break;
     }
 
     case Yield::DELEGATING: {
       VisitForStackValue(expr->generator_object());
 
       // Initial stack layout is as follows:
       // [sp + 1 * kPointerSize] iter
       // [sp + 0 * kPointerSize] g
 
-      Label l_catch, l_try, l_resume, l_next, l_call, l_loop;
+      Label l_catch, l_try, l_suspend, l_continuation, l_resume;
+      Label l_next, l_call, l_loop;
       // Initial send value is undefined.
       __ LoadRoot(rax, Heap::kUndefinedValueRootIndex);
       __ jmp(&l_next);
 
       // catch (e) { receiver = iter; f = 'throw'; arg = e; goto l_call; }
       __ bind(&l_catch);
       handler_table()->set(expr->index(), Smi::FromInt(l_catch.pos()));
       __ LoadRoot(rcx, Heap::kthrow_stringRootIndex);    // "throw"
       __ push(rcx);
       __ push(Operand(rsp, 2 * kPointerSize));           // iter
       __ push(rax);                                      // exception
       __ jmp(&l_call);
 
       // try { received = %yield result }
       // Shuffle the received result above a try handler and yield it without
       // re-boxing.
       __ bind(&l_try);
       __ pop(rax);                                       // result
       __ PushTryHandler(StackHandler::CATCH, expr->index());
       const int handler_size = StackHandlerConstants::kSize;
       __ push(rax);                                      // result
-      __ push(Operand(rsp, (0 + 1) * kPointerSize + handler_size));  // g
+      __ jmp(&l_suspend);
+      __ bind(&l_continuation);
+      __ jmp(&l_resume);
+      __ bind(&l_suspend);
+      const int generator_object_depth = kPointerSize + handler_size;
+      __ movq(rax, Operand(rsp, generator_object_depth));
+      __ push(rax);                                      // g
+      ASSERT(l_continuation.pos() > 0 && Smi::IsValid(l_continuation.pos()));
+      __ Move(FieldOperand(rax, JSGeneratorObject::kContinuationOffset),
+              Smi::FromInt(l_continuation.pos()));
+      __ movq(FieldOperand(rax, JSGeneratorObject::kContextOffset), rsi);
+      __ movq(rcx, rsi);
+      __ RecordWriteField(rax, JSGeneratorObject::kContextOffset, rcx, rdx,
+                          kDontSaveFPRegs);
       __ CallRuntime(Runtime::kSuspendJSGeneratorObject, 1);
       __ movq(context_register(),
               Operand(rbp, StandardFrameConstants::kContextOffset));
-      __ CompareRoot(rax, Heap::kTheHoleValueRootIndex);
-      __ j(not_equal, &l_resume);
       __ pop(rax);                                       // result
       EmitReturnSequence();
       __ bind(&l_resume);                                // received in rax
       __ PopTryHandler();
 
       // receiver = iter; f = 'next'; arg = received;
       __ bind(&l_next);
       __ LoadRoot(rcx, Heap::knext_stringRootIndex);     // "next"
       __ push(rcx);
       __ push(Operand(rsp, 2 * kPointerSize));           // iter
@@ skipping 2828 matching lines @@
   *context_length = 0;
   return previous_;
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64