Generators: Avoid calling into runtime if operand stack is empty

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 e5d190ade934156e0e62fbde8150e853ed5956e4..f2d98eb052893a09b2e9eaea4f25af6c5a01bb1d 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -1976,14 +1976,31 @@ void FullCodeGenerator::VisitYield(Yield* expr) {
       __ 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();
 
@@ -2011,7 +2028,8 @@ void FullCodeGenerator::VisitYield(Yield* expr) {
       // [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);
@@ -2033,12 +2051,23 @@ void FullCodeGenerator::VisitYield(Yield* expr) {
       __ 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