MIPS: Generators: Avoid calling into runtime if operand stack is empty

src/mips/full-codegen-mips.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 1983 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()));
+      __ li(a1, Operand(Smi::FromInt(continuation.pos())));
+      __ sw(a1, FieldMemOperand(v0, JSGeneratorObject::kContinuationOffset));
+      __ sw(cp, FieldMemOperand(v0, JSGeneratorObject::kContextOffset));
+      __ mov(a1, cp);
+      __ RecordWriteField(v0, JSGeneratorObject::kContextOffset, a1, a2,
+                          kRAHasBeenSaved, kDontSaveFPRegs);
+      __ Addu(a1, fp, Operand(StandardFrameConstants::kExpressionsOffset));
+      __ Branch(&post_runtime, eq, sp, Operand(a1));
+      __ push(v0);  // generator object
       __ CallRuntime(Runtime::kSuspendJSGeneratorObject, 1);
-      __ lw(context_register(),
-            MemOperand(fp, StandardFrameConstants::kContextOffset));
-
-      Label resume;
-      __ LoadRoot(at, Heap::kTheHoleValueRootIndex);
-      __ Branch(&resume, ne, result_register(), Operand(at));
+      __ lw(cp, MemOperand(fp, StandardFrameConstants::kContextOffset));
+      __ bind(&post_runtime);
       __ pop(result_register());
       EmitReturnSequence();
 
       __ bind(&resume);
       context()->Plug(result_register());
       break;
     }
 
     case Yield::FINAL: {
       VisitForAccumulatorValue(expr->generator_object());
       __ li(a1, Operand(Smi::FromInt(JSGeneratorObject::kGeneratorClosed)));
       __ sw(a1, FieldMemOperand(result_register(),
                                 JSGeneratorObject::kContinuationOffset));
       // 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(a0, Heap::kUndefinedValueRootIndex);
       __ Branch(&l_next);
 
       // catch (e) { receiver = iter; f = 'throw'; arg = e; goto l_call; }
       __ bind(&l_catch);
       __ mov(a0, v0);
       handler_table()->set(expr->index(), Smi::FromInt(l_catch.pos()));
       __ LoadRoot(a2, Heap::kthrow_stringRootIndex);     // "throw"
       __ lw(a3, MemOperand(sp, 1 * kPointerSize));       // iter
       __ push(a3);                                       // iter
       __ push(a0);                                       // 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(a0);                                        // result
       __ PushTryHandler(StackHandler::CATCH, expr->index());
       const int handler_size = StackHandlerConstants::kSize;
       __ push(a0);                                       // result
-      __ lw(a3, MemOperand(sp, (0 + 1) * kPointerSize + handler_size));  // g
-      __ push(a3);                                       // g
+      __ jmp(&l_suspend);
+      __ bind(&l_continuation);
+      __ mov(a0, v0);
+      __ jmp(&l_resume);
+      __ bind(&l_suspend);
+      const int generator_object_depth = kPointerSize + handler_size;
+      __ lw(a0, MemOperand(sp, generator_object_depth));
+      __ push(a0);                                       // g
+      ASSERT(l_continuation.pos() > 0 && Smi::IsValid(l_continuation.pos()));
+      __ li(a1, Operand(Smi::FromInt(l_continuation.pos())));
+      __ sw(a1, FieldMemOperand(a0, JSGeneratorObject::kContinuationOffset));
+      __ sw(cp, FieldMemOperand(a0, JSGeneratorObject::kContextOffset));
+      __ mov(a1, cp);
+      __ RecordWriteField(a0, JSGeneratorObject::kContextOffset, a1, a2,
+                          kRAHasBeenSaved, kDontSaveFPRegs);
       __ CallRuntime(Runtime::kSuspendJSGeneratorObject, 1);
-      __ mov(a0, v0);
-      __ lw(context_register(),
-            MemOperand(fp, StandardFrameConstants::kContextOffset));
-      __ LoadRoot(at, Heap::kTheHoleValueRootIndex);
-      __ Branch(&l_resume, ne, a0, Operand(at));
+      __ lw(cp, MemOperand(fp, StandardFrameConstants::kContextOffset));
       __ pop(v0);                                        // result
       EmitReturnSequence();
       __ mov(a0, v0);
       __ bind(&l_resume);                                // received in a0
       __ PopTryHandler();
 
       // receiver = iter; f = 'next'; arg = received;
       __ bind(&l_next);
       __ LoadRoot(a2, Heap::knext_stringRootIndex);      // "next"
       __ lw(a3, MemOperand(sp, 1 * kPointerSize));       // iter
@@ skipping 2847 matching lines @@
   *context_length = 0;
   return previous_;
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_MIPS