Eliminate type checks that can successfully be performed at compile time.

runtime/vm/code_generator_x64.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/code_generator.h"
 
 #include "lib/error.h"
@@ skipping 639 matching lines @@
     } else {
       __ LoadObject(RAX, literal);
     }
   } else {
     // Pop the previously evaluated result value into RAX.
     __ popq(RAX);
   }
 
   // Generate type check.
   if (FLAG_enable_type_checks) {
-    const bool returns_null = node->value()->IsLiteralNode() &&
-       node->value()->AsLiteralNode()->literal().IsNull();
     const RawFunction::Kind kind = parsed_function().function().kind();
     const bool is_implicit_getter =
         (kind == RawFunction::kImplicitGetter) ||
         (kind == RawFunction::kConstImplicitGetter);
     const bool is_static = parsed_function().function().is_static();
     // Implicit getters do not need a type check at return, unless they compute
     // the initial value of a static field.
-    if (!returns_null && (is_static || !is_implicit_getter)) {
+    if (is_static || !is_implicit_getter) {
       GenerateAssertAssignable(
           node->id(),
           node->value()->token_index(),
+          node->value(),
           AbstractType::ZoneHandle(parsed_function().function().result_type()),
           String::ZoneHandle(String::NewSymbol("function result")));
     }
   }
   GenerateReturnEpilog(node);
 }
 
 
 void CodeGenerator::VisitLiteralNode(LiteralNode* node) {
   if (!IsResultNeeded(node)) return;
   __ PushObject(node->literal());
 }
 
 
 void CodeGenerator::VisitTypeNode(TypeNode* node) {
   // Type nodes are handled specially by the code generator.
   UNREACHABLE();
 }
 
 
 void CodeGenerator::VisitAssignableNode(AssignableNode* node) {
   ASSERT(FLAG_enable_type_checks);
   node->expr()->Visit(this);
   __ popq(RAX);
   GenerateAssertAssignable(node->id(),
                            node->token_index(),
+                           node->expr(),
                            node->type(),
                            node->dst_name());
   if (IsResultNeeded(node)) {
     __ pushq(RAX);
   }
 }
 
 
 void CodeGenerator::VisitClosureNode(ClosureNode* node) {
   const Function& function = node->function();
@@ skipping 191 matching lines @@
   }
 }
 
 
 void CodeGenerator::VisitStoreLocalNode(StoreLocalNode* node) {
   node->value()->Visit(this);
   __ popq(RAX);
   if (FLAG_enable_type_checks) {
     GenerateAssertAssignable(node->id(),
                              node->value()->token_index(),
+                             node->value(),
                              node->local().type(),
                              node->local().name());
   }
   GenerateStoreVariable(node->local(), RAX, R10);
   if (IsResultNeeded(node)) {
     __ pushq(RAX);
   }
 }
 
 
 void CodeGenerator::VisitLoadInstanceFieldNode(LoadInstanceFieldNode* node) {
   node->instance()->Visit(this);
   MarkDeoptPoint(node->id(), node->token_index());
   __ popq(RAX);  // Instance.
   __ movq(RAX, FieldAddress(RAX, node->field().Offset()));
   if (IsResultNeeded(node)) {
     __ pushq(RAX);
   }
 }
 
 
 void CodeGenerator::VisitStoreInstanceFieldNode(StoreInstanceFieldNode* node) {
   node->instance()->Visit(this);
   node->value()->Visit(this);
   MarkDeoptPoint(node->id(), node->token_index());
   __ popq(RAX);  // Value.
   if (FLAG_enable_type_checks) {
     GenerateAssertAssignable(node->id(),
                              node->value()->token_index(),
+                             node->value(),
                              AbstractType::ZoneHandle(node->field().type()),
                              String::ZoneHandle(node->field().name()));
   }
   __ popq(R10);  // Instance.
   __ StoreIntoObject(R10, FieldAddress(R10, node->field().Offset()), RAX);
   ASSERT(!IsResultNeeded(node));
 }
 
 
 // Expects array and index on stack and returns result in RAX.
@@ skipping 83 matching lines @@
 }
 
 
 void CodeGenerator::VisitStoreStaticFieldNode(StoreStaticFieldNode* node) {
   node->value()->Visit(this);
   MarkDeoptPoint(node->id(), node->token_index());
   __ popq(RAX);  // Value.
   if (FLAG_enable_type_checks) {
     GenerateAssertAssignable(node->id(),
                              node->value()->token_index(),
+                             node->value(),
                              AbstractType::ZoneHandle(node->field().type()),
                              String::ZoneHandle(node->field().name()));
   }
   __ LoadObject(RDX, node->field());
   __ StoreIntoObject(RDX, FieldAddress(RDX, Field::value_offset()), RAX);
   if (IsResultNeeded(node)) {
     // The result is the input value.
     __ pushq(RAX);
   }
 }
@@ skipping 66 matching lines @@
   }
   const Immediate value = Immediate(reinterpret_cast<int64_t>(Smi::New(1)));
   const char* operator_name = (node->kind() == Token::kINCR) ? "+" : "-";
   __ pushq(RAX);
   __ pushq(value);
   GenerateBinaryOperatorCall(node->id(), node->token_index(), operator_name);
   // result is in RAX.
   if (FLAG_enable_type_checks) {
     GenerateAssertAssignable(node->id(),
                              node->token_index(),
+                             NULL,
                              node->local().type(),
                              node->local().name());
   }
   GenerateStoreVariable(node->local(), RAX, RDX);
   if (node->prefix() && IsResultNeeded(node)) {
     __ pushq(RAX);
   }
 }
 
 
@@ skipping 72 matching lines @@
 
 static const Class* CoreClass(const char* c_name) {
   const String& class_name = String::Handle(String::NewSymbol(c_name));
   const Class& cls = Class::ZoneHandle(Library::Handle(
       Library::CoreImplLibrary()).LookupClass(class_name));
   ASSERT(!cls.IsNull());
   return &cls;
 }
 
 
-// Optimize instanceof type test by adding inlined tests for:
+// If instanceof type test cannot be performed successfully at compile time and
+// therefore eliminated, optimize it by adding inlined tests for:
 // - NULL -> return false.
 // - Smi -> compile time subtype check (only if dst class is not parameterized).
 // - Class equality (only if class is not parameterized).
 // Inputs:
 // - RAX: object.
 // Destroys RCX.
 // Returns:
 // - true or false on stack.
 void CodeGenerator::GenerateInstanceOf(intptr_t node_id,
                                        intptr_t token_index,
+                                       AstNode* value,
                                        const AbstractType& type,
                                        bool negate_result) {
   ASSERT(type.IsFinalized() && !type.IsMalformed());
   const Bool& bool_true = Bool::ZoneHandle(Bool::True());
   const Bool& bool_false = Bool::ZoneHandle(Bool::False());
 
-  // All instances are of a subtype of the Object type.
+  // All objects are instances of type T if Object type is a subtype of type T.
   const Type& object_type =
       Type::Handle(Isolate::Current()->object_store()->object_type());
   Error& malformed_error = Error::Handle();
   if (type.IsInstantiated() &&
       object_type.IsSubtypeOf(type, &malformed_error)) {
     __ PushObject(negate_result ? bool_false : bool_true);
     return;
   }
 
+  // Eliminate the test if it can be performed successfully at compile time.
+  if ((value != NULL) && value->IsLiteralNode() && type.IsInstantiated()) {
+    const Instance& literal_value = value->AsLiteralNode()->literal();
+    const Class& cls = Class::Handle(literal_value.clazz());
+    if (cls.IsNullClass()) {
+      ASSERT(literal_value.IsNull() ||
+             (literal_value.raw() == Object::sentinel()) ||
+             (literal_value.raw() == Object::transition_sentinel()));
+      // A null object is only an instance of Object and Dynamic, which has
+      // already been checked above (if the type is instantiated). So we can
+      // return false here if the instance is null (and if the type is
+      // instantiated).
+      __ PushObject(negate_result ? bool_true : bool_false);
+    } else {
+      Error& malformed_error = Error::Handle();
+      if (literal_value.IsInstanceOf(type,
+                                     TypeArguments::Handle(),
+                                     &malformed_error)) {
+        __ PushObject(negate_result ? bool_false : bool_true);
+      } else {
+        ASSERT(malformed_error.IsNull());
+        __ PushObject(negate_result ? bool_true : bool_false);
+      }
+    }
+    return;
+  }
+
   const Immediate raw_null =
       Immediate(reinterpret_cast<intptr_t>(Object::null()));
   Label done;
   // If type is instantiated and non-parameterized, we can inline code
   // checking whether the tested instance is a Smi.
   if (type.IsInstantiated()) {
     // A null object is only an instance of Object and Dynamic, which has
     // already been checked above (if the type is instantiated). So we can
     // return false here if the instance is null (and if the type is
     // instantiated).
@@ skipping 38 matching lines @@
           __ movq(RCX, FieldAddress(RAX, Object::class_offset()));
           __ CompareObject(RCX, type_class);
           __ j(NOT_EQUAL, &runtime_call, Assembler::kNearJump);
           __ PushObject(negate_result ? bool_false : bool_true);
           __ jmp(&done);
         }
       }
       __ Bind(&runtime_call);
       // Fall through to runtime call.
     } else {
+      ASSERT(!requires_type_arguments);
+      // Test if object is Smi and for a couple known test-classes.
       Label compare_classes;
       __ testq(RAX, Immediate(kSmiTagMask));
       __ j(NOT_ZERO, &compare_classes, Assembler::kNearJump);
       // Object is Smi.
       const Class& smi_class = Class::Handle(Smi::Class());
       // TODO(regis): We should introduce a SmiType.
       Error& malformed_error = Error::Handle();
       if (smi_class.IsSubtypeOf(TypeArguments::Handle(),
                                 type_class,
                                 TypeArguments::Handle(),
@@ skipping 61 matching lines @@
 
 // Jumps to label if RCX equals the given class.
 // Inputs:
 // - RCX: tested class.
 void CodeGenerator::TestClassAndJump(const Class& cls, Label* label) {
   __ CompareObject(RCX, cls);
   __ j(EQUAL, label);
 }
 
 
-// Optimize assignable type check by adding inlined tests for:
+// If type check cannot be performed successfully at compile time and therefore
+// eliminated, optimize it by adding inlined tests for:
 // - NULL -> return NULL.
 // - Smi -> compile time subtype check (only if dst class is not parameterized).
 // - Class equality (only if class is not parameterized).
 // Inputs:
 // - RAX: object.
 // Destroys RCX and RDX.
 // Returns:
 // - object in RAX for successful assignable check (or throws TypeError).
+// Performance notes: positive checks must be quick, negative checks can be slow
+// as they throw an exception.
 void CodeGenerator::GenerateAssertAssignable(intptr_t node_id,
                                              intptr_t token_index,
+                                             AstNode* value,
                                              const AbstractType& dst_type,
                                              const String& dst_name) {
   ASSERT(FLAG_enable_type_checks);
   ASSERT(token_index >= 0);
   ASSERT(!dst_type.IsNull());
   ASSERT(dst_type.IsFinalized());
 
   // Any expression is assignable to the Dynamic type and to the Object type.
   // Skip the test.
   if (!dst_type.IsMalformed() &&
       (dst_type.IsDynamicType() || dst_type.IsObjectType())) {
     return;
   }
 
   // It is a compile-time error to explicitly return a value (including null)
   // from a void function. However, functions that do not explicitly return a
   // value, implicitly return null. This includes void functions. Therefore, we
   // skip the type test here and trust the parser to only return null in void
   // function.
   if (dst_type.IsVoidType()) {
     return;
   }
 
+  // Eliminate the test if it can be performed successfully at compile time.
+  if ((value != NULL) && value->IsLiteralNode()) {
+    const Instance& literal_value = value->AsLiteralNode()->literal();
+    const Class& cls = Class::Handle(literal_value.clazz());
+    if (cls.IsNullClass()) {
+      ASSERT(literal_value.IsNull() ||
+             (literal_value.raw() == Object::sentinel()) ||
+             (literal_value.raw() == Object::transition_sentinel()));
+      return;
+    }
+    Error& malformed_error = Error::Handle();
+    if (!dst_type.IsMalformed() &&
+        dst_type.IsInstantiated() &&
+        literal_value.IsInstanceOf(dst_type,
+                                   TypeArguments::Handle(),
+                                   &malformed_error)) {
+      return;
+    }
+  }
+
   // A null object is always assignable and is returned as result.
   const Immediate raw_null =
       Immediate(reinterpret_cast<intptr_t>(Object::null()));
   Label done, runtime_call;
   __ cmpq(RAX, raw_null);
   __ j(EQUAL, &done);
 
   // Generate throw new TypeError() if the type is malformed.
   if (dst_type.IsMalformed()) {
     const Error& error = Error::Handle(dst_type.malformed_error());
@@ skipping 142 matching lines @@
   const Function& function = parsed_function_.function();
   LocalScope* scope = parsed_function_.node_sequence()->scope();
   const int num_fixed_params = function.num_fixed_parameters();
   const int num_opt_params = function.num_optional_parameters();
   ASSERT(num_fixed_params + num_opt_params <= scope->num_variables());
   for (int i = 0; i < num_fixed_params + num_opt_params; i++) {
     LocalVariable* parameter = scope->VariableAt(i);
     GenerateLoadVariable(RAX, *parameter);
     GenerateAssertAssignable(AstNode::kNoId,
                              parameter->token_index(),
+                             NULL,
                              parameter->type(),
                              parameter->name());
   }
 }
 
 
 void CodeGenerator::GenerateConditionTypeCheck(intptr_t node_id,
                                                intptr_t token_index) {
   if (!FLAG_enable_type_checks) {
     return;
@@ skipping 36 matching lines @@
   const Bool& bool_true = Bool::ZoneHandle(Bool::True());
   const Bool& bool_false = Bool::ZoneHandle(Bool::False());
   node->left()->Visit(this);
 
   // The instanceof operator needs special handling.
   if (Token::IsInstanceofOperator(node->kind())) {
     __ popq(RAX);  // Left operand.
     ASSERT(node->right()->IsTypeNode());
     GenerateInstanceOf(node->id(),
                        node->token_index(),
+                       node->left(),
                        node->right()->AsTypeNode()->type(),
                        (node->kind() == Token::kISNOT));
     if (!IsResultNeeded(node)) {
       __ popq(RAX);  // Pop the result of the instanceof operation.
     }
     return;
   }
 
   node->right()->Visit(this);
   // Both left and right values on stack.
@@ skipping 1015 matching lines @@
   const Error& error = Error::Handle(
       Parser::FormatError(script, token_index, "Error", format, args));
   va_end(args);
   Isolate::Current()->long_jump_base()->Jump(1, error);
   UNREACHABLE();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64