Generators return boxed values

Generators now box their return values in object literals of the form

  { value: VAL, done: DONE }

where DONE is false for yield expressions, and true for return
statements.

BUG=v8:2355
TEST=mjsunit/harmony/generators-iteration
R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/13870007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14563 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/full-codegen-arm.cc

@@ -1939,11 +1939,12 @@ void FullCodeGenerator::VisitYield(Yield* expr) {
       Label resume;
       __ CompareRoot(result_register(), Heap::kTheHoleValueRootIndex);
       __ b(ne, &resume);
-      __ pop(result_register());
       if (expr->yield_kind() == Yield::SUSPEND) {
-        // TODO(wingo): Box into { value: VALUE, done: false }.
+        EmitReturnIteratorResult(false);
+      } else {
+        __ pop(result_register());
+        EmitReturnSequence();
       }
-      EmitReturnSequence();
 
       __ bind(&resume);
       context()->Plug(result_register());
@@ -1955,18 +1956,7 @@ void FullCodeGenerator::VisitYield(Yield* expr) {
       __ mov(r1, Operand(Smi::FromInt(JSGeneratorObject::kGeneratorClosed)));
       __ str(r1, FieldMemOperand(result_register(),
                                  JSGeneratorObject::kContinuationOffset));
-      __ pop(result_register());
-      // TODO(wingo): Box into { value: VALUE, done: true }.
-
-      // Exit all nested statements.
-      NestedStatement* current = nesting_stack_;
-      int stack_depth = 0;
-      int context_length = 0;
-      while (current != NULL) {
-        current = current->Exit(&stack_depth, &context_length);
-      }
-      __ Drop(stack_depth);
-      EmitReturnSequence();
+      EmitReturnIteratorResult(true);
       break;
     }
 
@@ -2074,6 +2064,55 @@ void FullCodeGenerator::EmitGeneratorResume(Expression *generator,
 }
 
 
+void FullCodeGenerator::EmitReturnIteratorResult(bool done) {
+  Label gc_required;
+  Label allocated;
+
+  Handle<Map> map(isolate()->native_context()->generator_result_map());
+
+  __ Allocate(map->instance_size(), r0, r2, r3, &gc_required, TAG_OBJECT);
+
+  __ bind(&allocated);
+  __ mov(r1, Operand(map));
+  __ pop(r2);
+  __ mov(r3, Operand(isolate()->factory()->ToBoolean(done)));
+  __ mov(r4, Operand(isolate()->factory()->empty_fixed_array()));
+  ASSERT_EQ(map->instance_size(), 5 * kPointerSize);
+  __ str(r1, FieldMemOperand(r0, HeapObject::kMapOffset));
+  __ str(r4, FieldMemOperand(r0, JSObject::kPropertiesOffset));
+  __ str(r4, FieldMemOperand(r0, JSObject::kElementsOffset));
+  __ str(r2,
+         FieldMemOperand(r0, JSGeneratorObject::kResultValuePropertyOffset));
+  __ str(r3,
+         FieldMemOperand(r0, JSGeneratorObject::kResultDonePropertyOffset));
+
+  // Only the value field needs a write barrier, as the other values are in the
+  // root set.
+  __ RecordWriteField(r0, JSGeneratorObject::kResultValuePropertyOffset,
+                      r2, r3, kLRHasBeenSaved, kDontSaveFPRegs);
+
+  if (done) {
+    // Exit all nested statements.
+    NestedStatement* current = nesting_stack_;
+    int stack_depth = 0;
+    int context_length = 0;
+    while (current != NULL) {
+      current = current->Exit(&stack_depth, &context_length);
+    }
+    __ Drop(stack_depth);
+  }
+
+  EmitReturnSequence();
+
+  __ bind(&gc_required);
+  __ Push(Smi::FromInt(map->instance_size()));
+  __ CallRuntime(Runtime::kAllocateInNewSpace, 1);
+  __ ldr(context_register(),
+         MemOperand(fp, StandardFrameConstants::kContextOffset));
+  __ jmp(&allocated);
+}
+
+
 void FullCodeGenerator::EmitNamedPropertyLoad(Property* prop) {
   SetSourcePosition(prop->position());
   Literal* key = prop->key()->AsLiteral();

src/bootstrapper.cc

@@ -1387,6 +1387,40 @@ void Genesis::InitializeExperimentalGlobal() {
         *generator_object_prototype);
     native_context()->set_generator_object_prototype_map(
         *generator_object_prototype_map);
+
+    // Create a map for generator result objects.
+    ASSERT(object_map->inobject_properties() == 0);
+    STATIC_ASSERT(JSGeneratorObject::kResultPropertyCount == 2);
+    Handle<Map> generator_result_map = factory()->CopyMap(object_map,
+        JSGeneratorObject::kResultPropertyCount);
+    ASSERT(generator_result_map->inobject_properties() ==
+        JSGeneratorObject::kResultPropertyCount);
+
+    Handle<DescriptorArray> descriptors = factory()->NewDescriptorArray(0,
+        JSGeneratorObject::kResultPropertyCount);
+    DescriptorArray::WhitenessWitness witness(*descriptors);
+    generator_result_map->set_instance_descriptors(*descriptors);
+
+    Handle<String> value_string = factory()->InternalizeOneByteString(
+        STATIC_ASCII_VECTOR("value"));
+    FieldDescriptor value_descr(*value_string,
+                                JSGeneratorObject::kResultValuePropertyIndex,
+                                NONE,
+                                Representation::Tagged());
+    generator_result_map->AppendDescriptor(&value_descr, witness);
+
+    Handle<String> done_string = factory()->InternalizeOneByteString(
+        STATIC_ASCII_VECTOR("done"));
+    FieldDescriptor done_descr(*done_string,
+                               JSGeneratorObject::kResultDonePropertyIndex,
+                               NONE,
+                               Representation::Tagged());
+    generator_result_map->AppendDescriptor(&done_descr, witness);
+
+    generator_result_map->set_unused_property_fields(0);
+    ASSERT_EQ(JSGeneratorObject::kResultSize,
+              generator_result_map->instance_size());
+    native_context()->set_generator_result_map(*generator_result_map);
   }
 }
 

src/contexts.h

@@ -180,6 +180,7 @@ enum BindingFlags {
     strict_mode_generator_function_map) \
   V(GENERATOR_OBJECT_PROTOTYPE_MAP_INDEX, Map, \
     generator_object_prototype_map) \
+  V(GENERATOR_RESULT_MAP_INDEX, Map, generator_result_map) \
   V(RANDOM_SEED_INDEX, ByteArray, random_seed)
 
 // JSFunctions are pairs (context, function code), sometimes also called
@@ -323,6 +324,7 @@ class Context: public FixedArray {
     GENERATOR_FUNCTION_MAP_INDEX,
     STRICT_MODE_GENERATOR_FUNCTION_MAP_INDEX,
     GENERATOR_OBJECT_PROTOTYPE_MAP_INDEX,
+    GENERATOR_RESULT_MAP_INDEX,
     RANDOM_SEED_INDEX,
 
     // Properties from here are treated as weak references by the full GC.

src/full-codegen.h

@@ -410,6 +410,11 @@ class FullCodeGenerator: public AstVisitor {
   // this has to be a separate pass _before_ populating or executing any module.
   void AllocateModules(ZoneList<Declaration*>* declarations);
 
+  // Generator code to return a fresh iterator result object.  The "value"
+  // property is set to a value popped from the stack, and "done" is set
+  // according to the argument.
+  void EmitReturnIteratorResult(bool done);
+
   // Try to perform a comparison as a fast inlined literal compare if
   // the operands allow it.  Returns true if the compare operations
   // has been matched and all code generated; false otherwise.

src/ia32/full-codegen-ia32.cc

@@ -1900,11 +1900,12 @@ void FullCodeGenerator::VisitYield(Yield* expr) {
       Label resume;
       __ CompareRoot(result_register(), Heap::kTheHoleValueRootIndex);
       __ j(not_equal, &resume);
-      __ pop(result_register());
       if (expr->yield_kind() == Yield::SUSPEND) {
-        // TODO(wingo): Box into { value: VALUE, done: false }.
+        EmitReturnIteratorResult(false);
+      } else {
+        __ pop(result_register());
+        EmitReturnSequence();
       }
-      EmitReturnSequence();
 
       __ bind(&resume);
       context()->Plug(result_register());
@@ -1916,18 +1917,7 @@ void FullCodeGenerator::VisitYield(Yield* expr) {
       __ mov(FieldOperand(result_register(),
                           JSGeneratorObject::kContinuationOffset),
              Immediate(Smi::FromInt(JSGeneratorObject::kGeneratorClosed)));
-      __ pop(result_register());
-      // TODO(wingo): Box into { value: VALUE, done: true }.
-
-      // Exit all nested statements.
-      NestedStatement* current = nesting_stack_;
-      int stack_depth = 0;
-      int context_length = 0;
-      while (current != NULL) {
-        current = current->Exit(&stack_depth, &context_length);
-      }
-      __ Drop(stack_depth);
-      EmitReturnSequence();
+      EmitReturnIteratorResult(true);
       break;
     }
 
@@ -2033,6 +2023,54 @@ void FullCodeGenerator::EmitGeneratorResume(Expression *generator,
 }
 
 
+void FullCodeGenerator::EmitReturnIteratorResult(bool done) {
+  Label gc_required;
+  Label allocated;
+
+  Handle<Map> map(isolate()->native_context()->generator_result_map());
+
+  __ Allocate(map->instance_size(), eax, ecx, edx, &gc_required, TAG_OBJECT);
+
+  __ bind(&allocated);
+  __ mov(ebx, map);
+  __ pop(ecx);
+  __ mov(edx, isolate()->factory()->ToBoolean(done));
+  ASSERT_EQ(map->instance_size(), 5 * kPointerSize);
+  __ mov(FieldOperand(eax, HeapObject::kMapOffset), ebx);
+  __ mov(FieldOperand(eax, JSObject::kPropertiesOffset),
+         isolate()->factory()->empty_fixed_array());
+  __ mov(FieldOperand(eax, JSObject::kElementsOffset),
+         isolate()->factory()->empty_fixed_array());
+  __ mov(FieldOperand(eax, JSGeneratorObject::kResultValuePropertyOffset), ecx);
+  __ mov(FieldOperand(eax, JSGeneratorObject::kResultDonePropertyOffset), edx);
+
+  // Only the value field needs a write barrier, as the other values are in the
+  // root set.
+  __ RecordWriteField(eax, JSGeneratorObject::kResultValuePropertyOffset,
+                      ecx, edx, kDontSaveFPRegs);
+
+  if (done) {
+    // Exit all nested statements.
+    NestedStatement* current = nesting_stack_;
+    int stack_depth = 0;
+    int context_length = 0;
+    while (current != NULL) {
+      current = current->Exit(&stack_depth, &context_length);
+    }
+    __ Drop(stack_depth);
+  }
+
+  EmitReturnSequence();
+
+  __ bind(&gc_required);
+  __ Push(Smi::FromInt(map->instance_size()));
+  __ CallRuntime(Runtime::kAllocateInNewSpace, 1);
+  __ mov(context_register(),
+         Operand(ebp, StandardFrameConstants::kContextOffset));
+  __ jmp(&allocated);
+}
+
+
 void FullCodeGenerator::EmitNamedPropertyLoad(Property* prop) {
   SetSourcePosition(prop->position());
   Literal* key = prop->key()->AsLiteral();

src/objects.h

@@ -6435,6 +6435,17 @@ class JSGeneratorObject: public JSObject {
   // Resume mode, for use by runtime functions.
   enum ResumeMode { SEND, THROW };
 
+  // Yielding from a generator returns an object with the following inobject
+  // properties.  See Context::generator_result_map() for the map.
+  static const int kResultValuePropertyIndex = 0;
+  static const int kResultDonePropertyIndex = 1;
+  static const int kResultPropertyCount = 2;
+
+  static const int kResultValuePropertyOffset = JSObject::kHeaderSize;
+  static const int kResultDonePropertyOffset =
+      kResultValuePropertyOffset + kPointerSize;
+  static const int kResultSize = kResultDonePropertyOffset + kPointerSize;
+
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(JSGeneratorObject);
 };

src/x64/full-codegen-x64.cc

@@ -1924,11 +1924,12 @@ void FullCodeGenerator::VisitYield(Yield* expr) {
       Label resume;
       __ CompareRoot(result_register(), Heap::kTheHoleValueRootIndex);
       __ j(not_equal, &resume);
-      __ pop(result_register());
       if (expr->yield_kind() == Yield::SUSPEND) {
-        // TODO(wingo): Box into { value: VALUE, done: false }.
+        EmitReturnIteratorResult(false);
+      } else {
+        __ pop(result_register());
+        EmitReturnSequence();
       }
-      EmitReturnSequence();
 
       __ bind(&resume);
       context()->Plug(result_register());
@@ -1940,18 +1941,7 @@ void FullCodeGenerator::VisitYield(Yield* expr) {
       __ Move(FieldOperand(result_register(),
                            JSGeneratorObject::kContinuationOffset),
               Smi::FromInt(JSGeneratorObject::kGeneratorClosed));
-      __ pop(result_register());
-      // TODO(wingo): Box into { value: VALUE, done: true }.
-
-      // Exit all nested statements.
-      NestedStatement* current = nesting_stack_;
-      int stack_depth = 0;
-      int context_length = 0;
-      while (current != NULL) {
-        current = current->Exit(&stack_depth, &context_length);
-      }
-      __ Drop(stack_depth);
-      EmitReturnSequence();
+      EmitReturnIteratorResult(true);
       break;
     }
 
@@ -2058,6 +2048,56 @@ void FullCodeGenerator::EmitGeneratorResume(Expression *generator,
 }
 
 
+void FullCodeGenerator::EmitReturnIteratorResult(bool done) {
+  Label gc_required;
+  Label allocated;
+
+  Handle<Map> map(isolate()->native_context()->generator_result_map());
+
+  __ Allocate(map->instance_size(), rax, rcx, rdx, &gc_required, TAG_OBJECT);
+
+  __ bind(&allocated);
+  __ Move(rbx, map);
+  __ pop(rcx);
+  __ Move(rdx, isolate()->factory()->ToBoolean(done));
+  ASSERT_EQ(map->instance_size(), 5 * kPointerSize);
+  __ movq(FieldOperand(rax, HeapObject::kMapOffset), rbx);
+  __ Move(FieldOperand(rax, JSObject::kPropertiesOffset),
+          isolate()->factory()->empty_fixed_array());
+  __ Move(FieldOperand(rax, JSObject::kElementsOffset),
+          isolate()->factory()->empty_fixed_array());
+  __ movq(FieldOperand(rax, JSGeneratorObject::kResultValuePropertyOffset),
+          rcx);
+  __ movq(FieldOperand(rax, JSGeneratorObject::kResultDonePropertyOffset),
+          rdx);
+
+  // Only the value field needs a write barrier, as the other values are in the
+  // root set.
+  __ RecordWriteField(rax, JSGeneratorObject::kResultValuePropertyOffset,
+                      rcx, rdx, kDontSaveFPRegs);
+
+  if (done) {
+    // Exit all nested statements.
+    NestedStatement* current = nesting_stack_;
+    int stack_depth = 0;
+    int context_length = 0;
+    while (current != NULL) {
+      current = current->Exit(&stack_depth, &context_length);
+    }
+    __ Drop(stack_depth);
+  }
+
+  EmitReturnSequence();
+
+  __ bind(&gc_required);
+  __ Push(Smi::FromInt(map->instance_size()));
+  __ CallRuntime(Runtime::kAllocateInNewSpace, 1);
+  __ movq(context_register(),
+          Operand(rbp, StandardFrameConstants::kContextOffset));
+  __ jmp(&allocated);
+}
+
+
 void FullCodeGenerator::EmitNamedPropertyLoad(Property* prop) {
   SetSourcePosition(prop->position());
   Literal* key = prop->key()->AsLiteral();

test/mjsunit/harmony/generators-iteration.js

@@ -31,19 +31,36 @@
 
 var GeneratorFunction = (function*(){yield 1;}).__proto__.constructor;
 
+function TestGeneratorResultPrototype() {
+  function* g() { yield 1; }
+  var iter = g();
+  var result = iter.next();
+
+  assertSame(Object.prototype, Object.getPrototypeOf(result));
+  property_names = Object.getOwnPropertyNames(result);
+  property_names.sort();
+  assertEquals(["done", "value"], property_names);
+  assertEquals({ value: 1, done: false }, result);
+}
+TestGeneratorResultPrototype()
+
 function TestGenerator(g, expected_values_for_next,
                        send_val, expected_values_for_send) {
   function testNext(thunk) {
     var iter = thunk();
     for (var i = 0; i < expected_values_for_next.length; i++) {
-      assertEquals(expected_values_for_next[i], iter.next());
+      assertEquals({ value: expected_values_for_next[i],
+                     done: i == expected_values_for_next.length - 1 },
+                   iter.next());
     }
     assertThrows(function() { iter.next(); }, Error);
   }
   function testSend(thunk) {
     var iter = thunk();
     for (var i = 0; i < expected_values_for_send.length; i++) {
-      assertEquals(expected_values_for_send[i], iter.send(send_val));
+      assertEquals({ value: expected_values_for_send[i],
+                     done: i == expected_values_for_send.length - 1 },
+                   iter.send(send_val));
     }
     assertThrows(function() { iter.send(send_val); }, Error);
   }
@@ -51,7 +68,9 @@ function TestGenerator(g, expected_values_for_next,
     for (var i = 0; i < expected_values_for_next.length; i++) {
       var iter = thunk();
       for (var j = 0; j < i; j++) {
-        assertEquals(expected_values_for_next[j], iter.next());
+        assertEquals({ value: expected_values_for_next[j],
+                       done: j == expected_values_for_next.length - 1 },
+                     iter.next());
       }
       function Sentinel() {}
       assertThrows(function () { iter.throw(new Sentinel); }, Sentinel);