Revert "Remove SminessPropagator and FlowGraphTypePropagator and all associated infrastructure and …

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
diff --git a/runtime/vm/intermediate_language.cc b/runtime/vm/intermediate_language.cc
index d3fb7d295292c81d52523656fe9535dc4d7ce6a7..7b8e997150c84ea4da8d6cf68d74312d98a54121 100644
--- a/runtime/vm/intermediate_language.cc
+++ b/runtime/vm/intermediate_language.cc
@@ -25,15 +25,15 @@ DEFINE_FLAG(bool, new_identity_spec, true,
 DEFINE_FLAG(bool, propagate_ic_data, true,
     "Propagate IC data from unoptimized to optimized IC calls.");
 DECLARE_FLAG(bool, enable_type_checks);
-DECLARE_FLAG(bool, eliminate_type_checks);
 DECLARE_FLAG(int, max_polymorphic_checks);
 DECLARE_FLAG(bool, trace_optimization);
 
 Definition::Definition()
     : range_(NULL),
-      type_(NULL),
       temp_index_(-1),
       ssa_temp_index_(-1),
+      propagated_type_(AbstractType::Handle()),
+      propagated_cid_(kIllegalCid),
       input_use_list_(NULL),
       env_use_list_(NULL),
       use_kind_(kValue),  // Phis and parameters rely on this default.
@@ -146,7 +146,10 @@ bool LoadFieldInstr::AttributesEqual(Instruction* other) const {
   LoadFieldInstr* other_load = other->AsLoadField();
   ASSERT(other_load != NULL);
   ASSERT((offset_in_bytes() != other_load->offset_in_bytes()) ||
-         ((immutable_ == other_load->immutable_)));
+         ((immutable_ == other_load->immutable_) &&
+          ((ResultCid() == other_load->ResultCid()) ||
+           (ResultCid() == kDynamicCid) ||
+           (other_load->ResultCid() == kDynamicCid))));
   return offset_in_bytes() == other_load->offset_in_bytes();
 }
 
@@ -404,17 +407,178 @@ void FlowGraphVisitor::VisitBlocks() {
 }
 
 
-bool Value::NeedsStoreBuffer() {
-  if (Type()->IsNull() ||
-      (Type()->ToNullableCid() == kSmiCid) ||
-      (Type()->ToNullableCid() == kBoolCid)) {
+// TODO(regis): Support a set of compile types for the given value.
+bool Value::CanComputeIsNull(bool* is_null) const {
+  ASSERT(is_null != NULL);
+  // For now, we can only return a meaningful result if the value is constant.
+  if (!BindsToConstant()) {
     return false;
   }
 
+  // Return true if the constant value is Object::null.
+  if (BindsToConstantNull()) {
+    *is_null = true;
+    return true;
+  }
+
+  // Consider the compile type of the value to check for sentinels, which are
+  // also treated as null.
+  const AbstractType& compile_type = AbstractType::Handle(CompileType());
+  ASSERT(!compile_type.IsMalformed());
+  ASSERT(!compile_type.IsVoidType());
+
+  // There are only three instances that can be of type Null:
+  // Object::null(), Object::sentinel(), and Object::transition_sentinel().
+  // The inline code and run time code performing the type check will only
+  // encounter the 2 sentinel values if type check elimination was disabled.
+  // Otherwise, the type check of a sentinel value will be eliminated here,
+  // because these sentinel values can only be encountered as constants, never
+  // as actual value of a heap object being type checked.
+  if (compile_type.IsNullType()) {
+    *is_null = true;
+    return true;
+  }
+
+  return false;
+}
+
+
+// TODO(regis): Support a set of compile types for the given value.
+bool Value::CanComputeIsInstanceOf(const AbstractType& type,
+                                   bool* is_instance) const {
+  ASSERT(is_instance != NULL);
+  // We cannot give an answer if the given type is malformed.
+  if (type.IsMalformed()) {
+    return false;
+  }
+
+  // We should never test for an instance of null.
+  ASSERT(!type.IsNullType());
+
+  // Consider the compile type of the value.
+  const AbstractType& compile_type = AbstractType::Handle(CompileType());
+  if (compile_type.IsMalformed()) {
+    return false;
+  }
+
+  // If the compile type of the value is void, we are type checking the result
+  // of a void function, which was checked to be null at the return statement
+  // inside the function.
+  if (compile_type.IsVoidType()) {
+    ASSERT(FLAG_enable_type_checks);
+    *is_instance = true;
+    return true;
+  }
+
+  // The Null type is only a subtype of Object and of dynamic.
+  // Functions that do not explicitly return a value, implicitly return null,
+  // except generative constructors, which return the object being constructed.
+  // It is therefore acceptable for void functions to return null.
+  if (compile_type.IsNullType()) {
+    *is_instance =
+        type.IsObjectType() || type.IsDynamicType() || type.IsVoidType();
+    return true;
+  }
+
+  // Until we support a set of compile types, we can only give answers for
+  // constant values. Indeed, a variable of the proper compile time type may
+  // still hold null at run time and therefore fail the test.
+  if (!BindsToConstant()) {
+    return false;
+  }
+
+  // A non-null constant is not an instance of void.
+  if (type.IsVoidType()) {
+    *is_instance = false;
+    return true;
+  }
+
+  // Since the value is a constant, its type is instantiated.
+  ASSERT(compile_type.IsInstantiated());
+
+  // The run time type of the value is guaranteed to be a subtype of the
+  // compile time type of the value. However, establishing here that the
+  // compile time type is a subtype of the given type does not guarantee that
+  // the run time type will also be a subtype of the given type, because the
+  // subtype relation is not transitive when an uninstantiated type is
+  // involved.
+  Error& malformed_error = Error::Handle();
+  if (type.IsInstantiated()) {
+    // Perform the test on the compile-time type and provide the answer, unless
+    // the type test produced a malformed error (e.g. an upper bound error).
+    *is_instance = compile_type.IsSubtypeOf(type, &malformed_error);
+  } else {
+    // However, the 'more specific than' relation is transitive and used here.
+    // In other words, if the compile type of the value is more specific than
+    // the given type, the run time type of the value, which is guaranteed to be
+    // a subtype of the compile type, is also guaranteed to be a subtype of the
+    // given type.
+    *is_instance = compile_type.IsMoreSpecificThan(type, &malformed_error);
+  }
+  return malformed_error.IsNull();
+}
+
+
+bool Value::NeedsStoreBuffer() const {
+  const intptr_t cid = ResultCid();
+  if ((cid == kSmiCid) || (cid == kBoolCid) || (cid == kNullCid)) {
+    return false;
+  }
   return !BindsToConstant();
 }
 
 
+RawAbstractType* PhiInstr::CompileType() const {
+  ASSERT(!HasPropagatedType());
+  // Since type propagation has not yet occured, we are reaching this phi via a
+  // back edge phi input. Return null as compile type so that this input is
+  // ignored in the first iteration of type propagation.
+  return AbstractType::null();
+}
+
+
+RawAbstractType* PhiInstr::LeastSpecificInputType() const {
+  AbstractType& least_specific_type = AbstractType::Handle();
+  AbstractType& input_type = AbstractType::Handle();
+  for (intptr_t i = 0; i < InputCount(); i++) {
+    input_type = InputAt(i)->CompileType();
+    if (input_type.IsNull()) {
+      // This input is on a back edge and we are in the first iteration of type
+      // propagation. Ignore it.
+      continue;
+    }
+    ASSERT(!input_type.IsNull());
+    if (least_specific_type.IsNull() ||
+        least_specific_type.IsMoreSpecificThan(input_type, NULL)) {
+      // Type input_type is less specific than the current least_specific_type.
+      least_specific_type = input_type.raw();
+    } else if (input_type.IsMoreSpecificThan(least_specific_type, NULL)) {
+      // Type least_specific_type is less specific than input_type. No change.
+    } else {
+      // The types are unrelated. No need to continue.
+      least_specific_type = Type::ObjectType();
+      break;
+    }
+  }
+  return least_specific_type.raw();
+}
+
+
+RawAbstractType* ParameterInstr::CompileType() const {
+  ASSERT(!HasPropagatedType());
+  // Note that returning the declared type of the formal parameter would be
+  // incorrect, because ParameterInstr is used as input to the type check
+  // verifying the run time type of the passed-in parameter and this check would
+  // always be wrongly eliminated.
+  return Type::DynamicType();
+}
+
+
+RawAbstractType* PushArgumentInstr::CompileType() const {
+  return AbstractType::null();
+}
+
+
 void JoinEntryInstr::AddPredecessor(BlockEntryInstr* predecessor) {
   // Require the predecessors to be sorted by block_id to make managing
   // their corresponding phi inputs simpler.
@@ -563,6 +727,45 @@ void Definition::ReplaceWith(Definition* other,
 }
 
 
+bool Definition::SetPropagatedCid(intptr_t cid) {
+  if (cid == kIllegalCid) {
+    return false;
+  }
+  if (propagated_cid_ == kIllegalCid) {
+    // First setting, nothing has changed.
+    propagated_cid_ = cid;
+    return false;
+  }
+  bool has_changed = (propagated_cid_ != cid);
+  propagated_cid_ = cid;
+  return has_changed;
+}
+
+
+intptr_t Definition::GetPropagatedCid() {
+  if (has_propagated_cid()) return propagated_cid();
+  intptr_t cid = ResultCid();
+  ASSERT(cid != kIllegalCid);
+  SetPropagatedCid(cid);
+  return cid;
+}
+
+
+intptr_t PhiInstr::GetPropagatedCid() {
+  return propagated_cid();
+}
+
+
+intptr_t ParameterInstr::GetPropagatedCid() {
+  return propagated_cid();
+}
+
+
+intptr_t AssertAssignableInstr::GetPropagatedCid() {
+  return propagated_cid();
+}
+
+
 // ==== Postorder graph traversal.
 static bool IsMarked(BlockEntryInstr* block,
                      GrowableArray<BlockEntryInstr*>* preorder) {
@@ -824,6 +1027,154 @@ void Instruction::Goto(JoinEntryInstr* entry) {
 }
 
 
+RawAbstractType* Value::CompileType() const {
+  if (definition()->HasPropagatedType()) {
+    return definition()->PropagatedType();
+  }
+  // The compile type may be requested when building the flow graph, i.e. before
+  // type propagation has occurred. To avoid repeatedly computing the compile
+  // type of the definition, we store it as initial propagated type.
+  AbstractType& type = AbstractType::Handle(definition()->CompileType());
+  definition()->SetPropagatedType(type);
+  return type.raw();
+}
+
+
+intptr_t Value::ResultCid() const {
+  if (reaching_cid() == kIllegalCid) {
+    return definition()->GetPropagatedCid();
+  }
+  return reaching_cid();
+}
+
+
+
+RawAbstractType* ConstantInstr::CompileType() const {
+  if (value().IsNull()) {
+    return Type::NullType();
+  }
+  if (value().IsInstance()) {
+    return Instance::Cast(value()).GetType();
+  } else {
+    ASSERT(value().IsAbstractTypeArguments());
+    return AbstractType::null();
+  }
+}
+
+
+intptr_t ConstantInstr::ResultCid() const {
+  if (value().IsNull()) {
+    return kNullCid;
+  }
+  if (value().IsInstance()) {
+    return Class::Handle(value().clazz()).id();
+  } else {
+    ASSERT(value().IsAbstractTypeArguments());
+    return kDynamicCid;
+  }
+}
+
+
+RawAbstractType* AssertAssignableInstr::CompileType() const {
+  const AbstractType& value_compile_type =
+      AbstractType::Handle(value()->CompileType());
+  if (!value_compile_type.IsNull() &&
+      value_compile_type.IsMoreSpecificThan(dst_type(), NULL)) {
+    return value_compile_type.raw();
+  }
+  return dst_type().raw();
+}
+
+
+RawAbstractType* AssertBooleanInstr::CompileType() const {
+  return Type::BoolType();
+}
+
+
+RawAbstractType* ArgumentDefinitionTestInstr::CompileType() const {
+  return Type::BoolType();
+}
+
+
+RawAbstractType* CurrentContextInstr::CompileType() const {
+  return AbstractType::null();
+}
+
+
+RawAbstractType* StoreContextInstr::CompileType() const {
+  return AbstractType::null();
+}
+
+
+RawAbstractType* ClosureCallInstr::CompileType() const {
+  // Because of function subtyping rules, the declared return type of a closure
+  // call cannot be relied upon for compile type analysis. For example, a
+  // function returning dynamic can be assigned to a closure variable declared
+  // to return int and may actually return a double at run-time.
+  return Type::DynamicType();
+}
+
+
+RawAbstractType* InstanceCallInstr::CompileType() const {
+  // TODO(regis): Return a more specific type than dynamic for recognized
+  // combinations of receiver type and method name.
+  return Type::DynamicType();
+}
+
+
+RawAbstractType* PolymorphicInstanceCallInstr::CompileType() const {
+  return Type::DynamicType();
+}
+
+
+RawAbstractType* StaticCallInstr::CompileType() const {
+  if (FLAG_enable_type_checks) {
+    return function().result_type();
+  }
+  return Type::DynamicType();
+}
+
+
+RawAbstractType* LoadLocalInstr::CompileType() const {
+  if (FLAG_enable_type_checks) {
+    return local().type().raw();
+  }
+  return Type::DynamicType();
+}
+
+
+RawAbstractType* StoreLocalInstr::CompileType() const {
+  return value()->CompileType();
+}
+
+
+RawAbstractType* StrictCompareInstr::CompileType() const {
+  return Type::BoolType();
+}
+
+
+// Only known == targets return a Boolean.
+RawAbstractType* EqualityCompareInstr::CompileType() const {
+  if ((receiver_class_id() == kSmiCid) ||
+      (receiver_class_id() == kDoubleCid) ||
+      (receiver_class_id() == kNumberCid)) {
+    return Type::BoolType();
+  }
+  return Type::DynamicType();
+}
+
+
+intptr_t EqualityCompareInstr::ResultCid() const {
+  if ((receiver_class_id() == kSmiCid) ||
+      (receiver_class_id() == kDoubleCid) ||
+      (receiver_class_id() == kNumberCid)) {
+    // Known/library equalities that are guaranteed to return Boolean.
+    return kBoolCid;
+  }
+  return kDynamicCid;
+}
+
+
 bool EqualityCompareInstr::IsPolymorphic() const {
   return HasICData() &&
       (ic_data()->NumberOfChecks() > 0) &&
@@ -831,6 +1182,194 @@ bool EqualityCompareInstr::IsPolymorphic() const {
 }
 
 
+RawAbstractType* RelationalOpInstr::CompileType() const {
+  if ((operands_class_id() == kSmiCid) ||
+      (operands_class_id() == kDoubleCid) ||
+      (operands_class_id() == kNumberCid)) {
+    // Known/library relational ops that are guaranteed to return Boolean.
+    return Type::BoolType();
+  }
+  return Type::DynamicType();
+}
+
+
+intptr_t RelationalOpInstr::ResultCid() const {
+  if ((operands_class_id() == kSmiCid) ||
+      (operands_class_id() == kDoubleCid) ||
+      (operands_class_id() == kNumberCid)) {
+    // Known/library relational ops that are guaranteed to return Boolean.
+    return kBoolCid;
+  }
+  return kDynamicCid;
+}
+
+
+RawAbstractType* NativeCallInstr::CompileType() const {
+  // The result type of the native function is identical to the result type of
+  // the enclosing native Dart function. However, we prefer to check the type
+  // of the value returned from the native call.
+  return Type::DynamicType();
+}
+
+
+RawAbstractType* StringFromCharCodeInstr::CompileType() const {
+  return Type::StringType();
+}
+
+
+RawAbstractType* LoadIndexedInstr::CompileType() const {
+  switch (class_id_) {
+    case kArrayCid:
+    case kImmutableArrayCid:
+      return Type::DynamicType();
+    case kFloat32ArrayCid :
+    case kFloat64ArrayCid :
+      return Type::Double();
+    case kInt8ArrayCid:
+    case kUint8ArrayCid:
+    case kUint8ClampedArrayCid:
+    case kExternalUint8ArrayCid:
+    case kExternalUint8ClampedArrayCid:
+    case kInt16ArrayCid:
+    case kUint16ArrayCid:
+    case kInt32ArrayCid:
+    case kUint32ArrayCid:
+    case kOneByteStringCid:
+    case kTwoByteStringCid:
+      return Type::IntType();
+    default:
+      UNIMPLEMENTED();
+      return Type::IntType();
+  }
+}
+
+
+RawAbstractType* StoreIndexedInstr::CompileType() const {
+  return AbstractType::null();
+}
+
+
+RawAbstractType* StoreInstanceFieldInstr::CompileType() const {
+  return value()->CompileType();
+}
+
+
+RawAbstractType* LoadStaticFieldInstr::CompileType() const {
+  if (FLAG_enable_type_checks) {
+    return field().type();
+  }
+  return Type::DynamicType();
+}
+
+
+RawAbstractType* StoreStaticFieldInstr::CompileType() const {
+  return value()->CompileType();
+}
+
+
+RawAbstractType* BooleanNegateInstr::CompileType() const {
+  return Type::BoolType();
+}
+
+
+RawAbstractType* InstanceOfInstr::CompileType() const {
+  return Type::BoolType();
+}
+
+
+RawAbstractType* CreateArrayInstr::CompileType() const {
+  return type().raw();
+}
+
+
+RawAbstractType* CreateClosureInstr::CompileType() const {
+  const Function& fun = function();
+  const Class& signature_class = Class::Handle(fun.signature_class());
+  return signature_class.SignatureType();
+}
+
+
+RawAbstractType* AllocateObjectInstr::CompileType() const {
+  // TODO(regis): Be more specific.
+  return Type::DynamicType();
+}
+
+
+RawAbstractType* AllocateObjectWithBoundsCheckInstr::CompileType() const {
+  // TODO(regis): Be more specific.
+  return Type::DynamicType();
+}
+
+
+RawAbstractType* LoadFieldInstr::CompileType() const {
+  // Type may be null if the field is a VM field, e.g. context parent.
+  // Keep it as null for debug purposes and do not return dynamic in production
+  // mode, since misuse of the type would remain undetected.
+  if (type().IsNull()) {
+    return AbstractType::null();
+  }
+  if (FLAG_enable_type_checks) {
+    return type().raw();
+  }
+  return Type::DynamicType();
+}
+
+
+RawAbstractType* StoreVMFieldInstr::CompileType() const {
+  return value()->CompileType();
+}
+
+
+RawAbstractType* InstantiateTypeArgumentsInstr::CompileType() const {
+  return AbstractType::null();
+}
+
+
+RawAbstractType* ExtractConstructorTypeArgumentsInstr::CompileType() const {
+  return AbstractType::null();
+}
+
+
+RawAbstractType* ExtractConstructorInstantiatorInstr::CompileType() const {
+  return AbstractType::null();
+}
+
+
+RawAbstractType* AllocateContextInstr::CompileType() const {
+  return AbstractType::null();
+}
+
+
+RawAbstractType* ChainContextInstr::CompileType() const {
+  return AbstractType::null();
+}
+
+
+RawAbstractType* CloneContextInstr::CompileType() const {
+  return AbstractType::null();
+}
+
+
+RawAbstractType* CatchEntryInstr::CompileType() const {
+  return AbstractType::null();
+}
+
+
+RawAbstractType* CheckStackOverflowInstr::CompileType() const {
+  return AbstractType::null();
+}
+
+
+RawAbstractType* BinarySmiOpInstr::CompileType() const {
+  return Type::SmiType();
+}
+
+
+intptr_t BinarySmiOpInstr::ResultCid() const {
+  return kSmiCid;
+}
+
+
 bool BinarySmiOpInstr::CanDeoptimize() const {
   switch (op_kind()) {
     case Token::kBIT_AND:
@@ -859,6 +1398,47 @@ bool BinarySmiOpInstr::RightIsPowerOfTwoConstant() const {
 }
 
 
+RawAbstractType* BinaryMintOpInstr::CompileType() const {
+  return Type::IntType();
+}
+
+
+intptr_t BinaryMintOpInstr::ResultCid() const {
+  return kDynamicCid;
+}
+
+
+RawAbstractType* ShiftMintOpInstr::CompileType() const {
+  return Type::IntType();
+}
+
+
+intptr_t ShiftMintOpInstr::ResultCid() const {
+  return kDynamicCid;
+}
+
+
+RawAbstractType* UnaryMintOpInstr::CompileType() const {
+  return Type::IntType();
+}
+
+
+intptr_t UnaryMintOpInstr::ResultCid() const {
+  return kDynamicCid;
+}
+
+
+RawAbstractType* BinaryDoubleOpInstr::CompileType() const {
+  return Type::Double();
+}
+
+
+intptr_t BinaryDoubleOpInstr::ResultCid() const {
+  // The output is not an instance but when it is boxed it becomes double.
+  return kDoubleCid;
+}
+
+
 static bool ToIntegerConstant(Value* value, intptr_t* result) {
   if (!value->BindsToConstant()) {
     if (value->definition()->IsUnboxDouble()) {
@@ -1019,6 +1599,96 @@ Definition* BinaryMintOpInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
 }
 
 
+RawAbstractType* MathSqrtInstr::CompileType() const {
+  return Type::Double();
+}
+
+
+RawAbstractType* UnboxDoubleInstr::CompileType() const {
+  return Type::null();
+}
+
+
+intptr_t BoxDoubleInstr::ResultCid() const {
+  return kDoubleCid;
+}
+
+
+RawAbstractType* BoxDoubleInstr::CompileType() const {
+  return Type::Double();
+}
+
+
+intptr_t BoxIntegerInstr::ResultCid() const {
+  return kDynamicCid;
+}
+
+
+RawAbstractType* BoxIntegerInstr::CompileType() const {
+  return Type::IntType();
+}
+
+
+intptr_t UnboxIntegerInstr::ResultCid() const {
+  return kDynamicCid;
+}
+
+
+RawAbstractType* UnboxIntegerInstr::CompileType() const {
+  return Type::null();
+}
+
+
+RawAbstractType* UnarySmiOpInstr::CompileType() const {
+  return Type::SmiType();
+}
+
+
+RawAbstractType* SmiToDoubleInstr::CompileType() const {
+  return Type::Double();
+}
+
+
+RawAbstractType* DoubleToIntegerInstr::CompileType() const {
+  return Type::IntType();
+}
+
+
+RawAbstractType* DoubleToSmiInstr::CompileType() const {
+  return Type::SmiType();
+}
+
+
+RawAbstractType* DoubleToDoubleInstr::CompileType() const {
+  return Type::Double();
+}
+
+
+RawAbstractType* InvokeMathCFunctionInstr::CompileType() const {
+  return Type::Double();
+}
+
+
+RawAbstractType* CheckClassInstr::CompileType() const {
+  return AbstractType::null();
+}
+
+
+RawAbstractType* CheckSmiInstr::CompileType() const {
+  return AbstractType::null();
+}
+
+
+RawAbstractType* CheckArrayBoundInstr::CompileType() const {
+  return AbstractType::null();
+}
+
+
+RawAbstractType* CheckEitherNonSmiInstr::CompileType() const {
+  return AbstractType::null();
+}
+
+
 // Optimizations that eliminate or simplify individual instructions.
 Instruction* Instruction::Canonicalize(FlowGraphOptimizer* optimizer) {
   return this;
@@ -1082,7 +1752,7 @@ Definition* LoadFieldInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
   StaticCallInstr* call = value()->definition()->AsStaticCall();
   if (call != NULL &&
       call->is_known_constructor() &&
-      (call->Type()->ToCid() == kArrayCid)) {
+      call->ResultCid() == kArrayCid) {
     return call->ArgumentAt(1)->value()->definition();
   }
   return this;
@@ -1090,18 +1760,33 @@ Definition* LoadFieldInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
 
 
 Definition* AssertBooleanInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
-  if (FLAG_eliminate_type_checks && (value()->Type()->ToCid() == kBoolCid)) {
-    return value()->definition();
-  }
-
-  return this;
+  const intptr_t value_cid = value()->ResultCid();
+  return (value_cid == kBoolCid) ? value()->definition() : this;
 }
 
 
 Definition* AssertAssignableInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
-  if (FLAG_eliminate_type_checks &&
-      value()->Type()->IsAssignableTo(dst_type())) {
-    return value()->definition();
+  // (1) Replace the assert with its input if the input has a known compatible
+  // class-id. The class-ids handled here are those that are known to be
+  // results of IL instructions.
+  intptr_t cid = value()->ResultCid();
+  bool is_redundant = false;
+  if (dst_type().IsIntType()) {
+    is_redundant = (cid == kSmiCid) || (cid == kMintCid);
+  } else if (dst_type().IsDoubleType()) {
+    is_redundant = (cid == kDoubleCid);
+  } else if (dst_type().IsBoolType()) {
+    is_redundant = (cid == kBoolCid);
+  }
+  if (is_redundant) return value()->definition();
+
+  // (2) Replace the assert with its input if the input is the result of a
+  // compatible assert itself.
+  AssertAssignableInstr* check = value()->definition()->AsAssertAssignable();
+  if ((check != NULL) && check->dst_type().Equals(dst_type())) {
+    // TODO(fschneider): Propagate type-assertions across phi-nodes.
+    // TODO(fschneider): Eliminate more asserts with subtype relation.
+    return check;
   }
 
   // (3) For uninstantiated target types: If the instantiator type arguments
@@ -1174,7 +1859,7 @@ Definition* StrictCompareInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
   // Handles e === true.
   if ((kind() == Token::kEQ_STRICT) &&
       (right_constant.raw() == Bool::True().raw()) &&
-      (left()->Type()->ToCid() == kBoolCid)) {
+      (left()->ResultCid() == kBoolCid)) {
     // Return left subexpression as the replacement for this instruction.
     return left_defn;
   }
@@ -1183,10 +1868,7 @@ Definition* StrictCompareInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
 
 
 Instruction* CheckClassInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
-  // TODO(vegorov): Replace class checks with null checks when ToNullableCid
-  // matches.
-
-  const intptr_t value_cid = value()->Type()->ToCid();
+  const intptr_t value_cid = value()->ResultCid();
   if (value_cid == kDynamicCid) {
     return this;
   }
@@ -1205,14 +1887,14 @@ Instruction* CheckClassInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
 
 
 Instruction* CheckSmiInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
-  return (value()->Type()->ToCid() == kSmiCid) ?  NULL : this;
+  return (value()->ResultCid() == kSmiCid) ?  NULL : this;
 }
 
 
 Instruction* CheckEitherNonSmiInstr::Canonicalize(
     FlowGraphOptimizer* optimizer) {
-  if ((left()->Type()->ToCid() == kDoubleCid) ||
-      (right()->Type()->ToCid() == kDoubleCid)) {
+  if ((left()->ResultCid() == kDoubleCid) ||
+      (right()->ResultCid() == kDoubleCid)) {
     return NULL;  // Remove from the graph.
   }
   return this;
@@ -1431,11 +2113,13 @@ void StaticCallInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
 
 
 void AssertAssignableInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
-  compiler->GenerateAssertAssignable(token_pos(),
-                                     deopt_id(),
-                                     dst_type(),
-                                     dst_name(),
-                                     locs());
+  if (!is_eliminated()) {
+    compiler->GenerateAssertAssignable(token_pos(),
+                                       deopt_id(),
+                                       dst_type(),
+                                       dst_name(),
+                                       locs());
+  }
   ASSERT(locs()->in(0).reg() == locs()->out().reg());
 }
 
@@ -1707,7 +2391,7 @@ RangeBoundary RangeBoundary::Max(RangeBoundary a, RangeBoundary b) {
 
 
 void Definition::InferRange() {
-  ASSERT(Type()->ToCid() == kSmiCid);  // Has meaning only for smis.
+  ASSERT(GetPropagatedCid() == kSmiCid);  // Has meaning only for smis.
   if (range_ == NULL) {
     range_ = Range::Unknown();
   }