Generators: Avoid calling into runtime if operand stack is empty

src/ia32/full-codegen-ia32.cc

Index: src/ia32/full-codegen-ia32.cc
diff --git a/src/ia32/full-codegen-ia32.cc b/src/ia32/full-codegen-ia32.cc
index 54e9eaf1d60969a65cd0ac17dd852e1a3bcf411e..21b2a3add69f2d28fdaeeb4f6fdf07f01a967194 100644
--- a/src/ia32/full-codegen-ia32.cc
+++ b/src/ia32/full-codegen-ia32.cc
@@ -1953,14 +1953,30 @@ 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()));
+      __ mov(FieldOperand(eax, JSGeneratorObject::kContinuationOffset),
+             Immediate(Smi::FromInt(continuation.pos())));

[Michael Starzinger, 2013/06/20 12:08:32]

It's too bad that we cannot reliably predict the binding offset of "resume"
here, otherwise the two jumps at the top would be obsolete. Damn! <sarcasm>Maybe
leave a comment in that regard to eternalize our disappointment. :)</sarcasm>

+      __ mov(FieldOperand(eax, JSGeneratorObject::kContextOffset), esi);
+      __ mov(ecx, esi);
+      __ RecordWriteField(eax, JSGeneratorObject::kContextOffset, ecx, edx,
+                          kDontSaveFPRegs);
+      __ lea(ebx, Operand(ebp, StandardFrameConstants::kExpressionsOffset));
+      __ cmp(esp, ebx);
+      __ j(equal, &post_runtime);
+      __ push(eax);  // generator object
       __ CallRuntime(Runtime::kSuspendJSGeneratorObject, 1);
       __ mov(context_register(),
              Operand(ebp, StandardFrameConstants::kContextOffset));
-
-      Label resume;
-      __ CompareRoot(result_register(), Heap::kTheHoleValueRootIndex);
-      __ j(not_equal, &resume);
+      __ bind(&post_runtime);
       __ pop(result_register());
       EmitReturnSequence();
 
@@ -1988,7 +2004,8 @@ 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.
       __ mov(eax, isolate()->factory()->undefined_value());
       __ jmp(&l_next);
@@ -2010,12 +2027,22 @@ void FullCodeGenerator::VisitYield(Yield* expr) {
       __ PushTryHandler(StackHandler::CATCH, expr->index());
       const int handler_size = StackHandlerConstants::kSize;
       __ push(eax);                                      // result
-      __ push(Operand(esp, (0 + 1) * kPointerSize + handler_size));  // g
+      __ jmp(&l_suspend);
+      __ bind(&l_continuation);
+      __ jmp(&l_resume);
+      __ bind(&l_suspend);
+      __ mov(eax, Operand(esp, (0 + 1) * kPointerSize + handler_size));  // g

[Michael Starzinger, 2013/06/20 12:08:32]

nit: The trailing '// g' comment is somewhat duplicated, let's drop it for the
'__mov' instruction.

+      __ push(eax);                                      // g
+      ASSERT(l_continuation.pos() > 0 && Smi::IsValid(l_continuation.pos()));
+      __ mov(FieldOperand(eax, JSGeneratorObject::kContinuationOffset),
+             Immediate(Smi::FromInt(l_continuation.pos())));
+      __ mov(FieldOperand(eax, JSGeneratorObject::kContextOffset), esi);
+      __ mov(ecx, esi);
+      __ RecordWriteField(eax, JSGeneratorObject::kContextOffset, ecx, edx,
+                          kDontSaveFPRegs);
       __ CallRuntime(Runtime::kSuspendJSGeneratorObject, 1);
       __ mov(context_register(),
              Operand(ebp, StandardFrameConstants::kContextOffset));
-      __ CompareRoot(eax, Heap::kTheHoleValueRootIndex);
-      __ j(not_equal, &l_resume);
       __ pop(eax);                                       // result
       EmitReturnSequence();
       __ bind(&l_resume);                                // received in eax