Linter Demo

Errors: 0

Warnings: 47

File: /home/fstrocco/Dart/dart/benchmark/compiler/lib/src/cps_ir/type_propagation.dart

// Copyright (c) 2014, 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. part of dart2js.cps_ir.optimizers; abstract class TypeSystem<T> { T get dynamicType; T get typeType; T get functionType; T get boolType; T get intType; T get stringType; T get listType; T get mapType; T getReturnType(FunctionElement element); T getParameterType(ParameterElement element); bool areAssignable(T a, T b); T join(T a, T b); T typeOf(ConstantValue constant); } class UnitTypeSystem implements TypeSystem<String> { static const String UNIT = 'unit'; get boolType => UNIT; get dynamicType => UNIT; get functionType => UNIT; get intType => UNIT; get listType => UNIT; get mapType => UNIT; get stringType => UNIT; get typeType => UNIT; bool areAssignable(a, b) => true; getParameterType(_) => UNIT; getReturnType(_) => UNIT; join(a, b) => UNIT; typeOf(_) => UNIT; } class TypeMaskSystem implements TypeSystem<TypeMask> { final TypesTask inferrer; final ClassWorld classWorld; TypeMask get dynamicType => inferrer.dynamicType; TypeMask get typeType => inferrer.typeType; TypeMask get functionType => inferrer.functionType; TypeMask get boolType => inferrer.boolType; TypeMask get intType => inferrer.intType; TypeMask get stringType => inferrer.stringType; TypeMask get listType => inferrer.listType; TypeMask get mapType => inferrer.mapType; // TODO(karlklose): remove compiler here. TypeMaskSystem(dart2js.Compiler compiler) : inferrer = compiler.typesTask, classWorld = compiler.world; TypeMask getParameterType(ParameterElement parameter) { return inferrer.getGuaranteedTypeOfElement(parameter); } TypeMask getReturnType(FunctionElement function) { return inferrer.getGuaranteedReturnTypeOfElement(function); } @override // TODO(karlklose): Do not base this on containsMask. bool areAssignable(TypeMask a, TypeMask b) { return a.containsMask(b, classWorld) || b.containsMask(a, classWorld); } @override TypeMask join(TypeMask a, TypeMask b) { return a.union(b, classWorld); } @override TypeMask typeOf(ConstantValue constant) { return computeTypeMask(inferrer.compiler, constant); } } /** * Propagates types (including value types for constants) throughout the IR, and * replaces branches with fixed jumps as well as side-effect free expressions * with known constant results. * * Should be followed by the [ShrinkingReducer] pass. * * Implemented according to 'Constant Propagation with Conditional Branches' * by Wegman, Zadeck. */ class TypePropagator<T> extends Pass { String get passName => 'Sparse constant propagation'; final types.DartTypes _dartTypes; // The constant system is used for evaluation of expressions with constant // arguments. final dart2js.ConstantSystem _constantSystem; final TypeSystem _typeSystem; final dart2js.InternalErrorFunction _internalError; final Map<Node, _AbstractValue> _types; TypePropagator(this._dartTypes, this._constantSystem, this._typeSystem, this._internalError) : _types = <Node, _AbstractValue>{}; @override void rewrite(RootNode root) { if (root.isEmpty) return; // Set all parent pointers. new ParentVisitor().visit(root); // Analyze. In this phase, the entire term is analyzed for reachability // and the abstract value of each expression. _TypePropagationVisitor<T> analyzer = new _TypePropagationVisitor<T>( _constantSystem, _typeSystem, _types, _internalError, _dartTypes); analyzer.analyze(root); // Transform. Uses the data acquired in the previous analysis phase to // replace branches with fixed targets and side-effect-free expressions // with constant results. _TransformingVisitor transformer = new _TransformingVisitor( analyzer.reachableNodes, analyzer.values, _internalError); transformer.transform(root); } getType(Node node) => _types[node]; } /** * Uses the information from a preceding analysis pass in order to perform the * actual transformations on the CPS graph. */ class _TransformingVisitor extends RecursiveVisitor { final Set<Node> reachable; final Map<Node, _AbstractValue> values; final dart2js.InternalErrorFunction internalError; _TransformingVisitor(this.reachable, this.values, this.internalError); void transform(RootNode root) { visit(root); } /// Given an expression with a known constant result and a continuation, /// replaces the expression by a new LetPrim / InvokeContinuation construct. /// `unlink` is a closure responsible for unlinking all removed references. LetPrim constifyExpression(Expression node, Continuation continuation, void unlink()) { _AbstractValue value = values[node]; if (value == null || !value.isConstant) { return null; } assert(continuation.parameters.length == 1); // Set up the replacement structure. PrimitiveConstantValue primitiveConstant = value.constant; ConstantExpression constExp = new PrimitiveConstantExpression(primitiveConstant); Constant constant = new Constant(constExp); LetPrim letPrim = new LetPrim(constant); InvokeContinuation invoke = new InvokeContinuation(continuation, <Primitive>[constant]); invoke.parent = constant.parent = letPrim; letPrim.body = invoke; // Replace the method invocation. InteriorNode parent = node.parent; letPrim.parent = parent; parent.body = letPrim; unlink(); return letPrim; } // A branch can be eliminated and replaced by an invocation if only one of // the possible continuations is reachable. Removal often leads to both dead // primitives (the condition variable) and dead continuations (the unreachable // branch), which are both removed by the shrinking reductions pass. // // (Branch (IsTrue true) k0 k1) -> (InvokeContinuation k0) void visitBranch(Branch node) { bool trueReachable = reachable.contains(node.trueContinuation.definition); bool falseReachable = reachable.contains(node.falseContinuation.definition); bool bothReachable = (trueReachable && falseReachable); bool noneReachable = !(trueReachable || falseReachable); if (bothReachable || noneReachable) { // Nothing to do, shrinking reductions take care of the unreachable case. super.visitBranch(node); return; } Continuation successor = (trueReachable) ? node.trueContinuation.definition : node.falseContinuation.definition; // Replace the branch by a continuation invocation. assert(successor.parameters.isEmpty); InvokeContinuation invoke = new InvokeContinuation(successor, <Primitive>[]); InteriorNode parent = node.parent; invoke.parent = parent; parent.body = invoke; // Unlink all removed references. node.trueContinuation.unlink(); node.falseContinuation.unlink(); IsTrue isTrue = node.condition; isTrue.value.unlink(); visitInvokeContinuation(invoke); } // Side-effect free method calls with constant results can be replaced by // a LetPrim / InvokeContinuation pair. May lead to dead primitives which // are removed by the shrinking reductions pass. // // (InvokeMethod v0 == v1 k0) // -> (assuming the result is a constant `true`) // (LetPrim v2 (Constant true)) // (InvokeContinuation k0 v2) void visitInvokeMethod(InvokeMethod node) { Continuation cont = node.continuation.definition; LetPrim letPrim = constifyExpression(node, cont, () { node.receiver.unlink(); node.continuation.unlink(); node.arguments.forEach((Reference ref) => ref.unlink()); }); if (letPrim == null) { super.visitInvokeMethod(node); } else { visitLetPrim(letPrim); } } // See [visitInvokeMethod]. void visitConcatenateStrings(ConcatenateStrings node) { Continuation cont = node.continuation.definition; LetPrim letPrim = constifyExpression(node, cont, () { node.continuation.unlink(); node.arguments.forEach((Reference ref) => ref.unlink()); }); if (letPrim == null) { super.visitConcatenateStrings(node); } else { visitLetPrim(letPrim); } } // See [visitInvokeMethod]. void visitTypeOperator(TypeOperator node) { Continuation cont = node.continuation.definition; LetPrim letPrim = constifyExpression(node, cont, () { node.receiver.unlink(); node.continuation.unlink(); }); if (letPrim == null) { super.visitTypeOperator(node); } else { visitLetPrim(letPrim); } } } /** * Runs an analysis pass on the given function definition in order to detect * const-ness as well as reachability, both of which are used in the subsequent * transformation pass. */ class _TypePropagationVisitor<T> implements Visitor { // The node worklist stores nodes that are both reachable and need to be // processed, but have not been processed yet. Using a worklist avoids deep // recursion. // The node worklist and the reachable set operate in concert: nodes are // only ever added to the worklist when they have not yet been marked as // reachable, and adding a node to the worklist is always followed by marking // it reachable. // TODO(jgruber): Storing reachability per-edge instead of per-node would // allow for further optimizations. final List<Node> nodeWorklist = <Node>[]; final Set<Node> reachableNodes = new Set<Node>(); // The definition workset stores all definitions which need to be reprocessed // since their lattice value has changed. final Set<Definition> defWorkset = new Set<Definition>(); final dart2js.ConstantSystem constantSystem; final TypeSystem<T> typeSystem; final dart2js.InternalErrorFunction internalError; final types.DartTypes _dartTypes; _AbstractValue<T> unknownDynamic; _AbstractValue<T> unknown([T t]) { if (t == null) { return unknownDynamic; } else { return new _AbstractValue<T>.unknown(t); } } _AbstractValue<T> nonConst([T type]) { if (type == null) { type = typeSystem.dynamicType; } return new _AbstractValue<T>.nonConst(type); } _AbstractValue<T> constantValue(ConstantValue constant, T type) { return new _AbstractValue<T>(constant, type); } // Stores the current lattice value for nodes. Note that it contains not only // definitions as keys, but also expressions such as method invokes. // Access through [getValue] and [setValue]. final Map<Node, _AbstractValue<T>> values; _TypePropagationVisitor(this.constantSystem, TypeSystem typeSystem, this.values, this.internalError, this._dartTypes) : this.unknownDynamic = new _AbstractValue<T>.unknown(typeSystem.dynamicType), this.typeSystem = typeSystem; void analyze(RootNode root) { reachableNodes.clear(); defWorkset.clear(); nodeWorklist.clear(); // Initially, only the root node is reachable. setReachable(root); while (true) { if (nodeWorklist.isNotEmpty) { // Process a new reachable expression. Node node = nodeWorklist.removeLast(); visit(node); } else if (defWorkset.isNotEmpty) { // Process all usages of a changed definition. Definition def = defWorkset.first; defWorkset.remove(def); // Visit all uses of this definition. This might add new entries to // [nodeWorklist], for example by visiting a newly-constant usage within // a branch node. for (Reference ref = def.firstRef; ref != null; ref = ref.next) { visit(ref.parent); } } else { break; // Both worklists empty. } } } /// If the passed node is not yet reachable, mark it reachable and add it /// to the work list. void setReachable(Node node) { if (!reachableNodes.contains(node)) { reachableNodes.add(node); nodeWorklist.add(node); } } /// Returns the lattice value corresponding to [node], defaulting to unknown. /// /// Never returns null. _AbstractValue<T> getValue(Node node) { _AbstractValue<T> value = values[node]; return (value == null) ? unknown() : value; } /// Joins the passed lattice [updateValue] to the current value of [node], /// and adds it to the definition work set if it has changed and [node] is /// a definition. void setValue(Node node, _AbstractValue<T> updateValue) { _AbstractValue<T> oldValue = getValue(node); _AbstractValue<T> newValue = updateValue.join(oldValue, typeSystem); if (oldValue == newValue) { return; } // Values may only move in the direction UNKNOWN -> CONSTANT -> NONCONST. assert(newValue.kind >= oldValue.kind); values[node] = newValue; if (node is Definition) { defWorkset.add(node); } } // -------------------------- Visitor overrides ------------------------------ void visit(Node node) { node.accept(this); } void visitFieldDefinition(FieldDefinition node) { setReachable(node.body); } void visitFunctionDefinition(FunctionDefinition node) { if (node.thisParameter != null) { setValue(node.thisParameter, nonConst()); } node.parameters.forEach(visit); setReachable(node.body); } void visitConstructorDefinition(ConstructorDefinition node) { node.parameters.forEach(visit); node.initializers.forEach(visit); setReachable(node.body); } void visitBody(Body node) { setReachable(node.body); } void visitFieldInitializer(FieldInitializer node) { setReachable(node.body); } void visitSuperInitializer(SuperInitializer node) { node.arguments.forEach(setReachable); } // Expressions. void visitLetPrim(LetPrim node) { visit(node.primitive); // No reason to delay visits to primitives. setReachable(node.body); } void visitLetCont(LetCont node) { // The continuation is only marked as reachable on use. setReachable(node.body); } void visitLetHandler(LetHandler node) { setReachable(node.body); // The handler is assumed to be reachable (we could instead treat it as // unreachable unless we find something reachable that might throw in the // body --- it's not clear if we want to do that here or in some other // pass). The handler parameters are assumed to be unknown. // // TODO(kmillikin): we should set the type of the exception and stack // trace here. The way we do that depends on how we handle 'on T' catch // clauses. setReachable(node.handler); node.handler.parameters.forEach((Parameter p) => setValue(p, nonConst())); } void visitLetMutable(LetMutable node) { setValue(node.variable, getValue(node.value.definition)); setReachable(node.body); } void visitInvokeStatic(InvokeStatic node) { Continuation cont = node.continuation.definition; setReachable(cont); assert(cont.parameters.length == 1); Parameter returnValue = cont.parameters[0]; Entity target = node.target; T returnType = target is FieldElement ? typeSystem.dynamicType : typeSystem.getReturnType(node.target); setValue(returnValue, nonConst(returnType)); } void visitInvokeContinuation(InvokeContinuation node) { Continuation cont = node.continuation.definition; setReachable(cont); // Forward the constant status of all continuation invokes to the // continuation. Note that this is effectively a phi node in SSA terms. for (int i = 0; i < node.arguments.length; i++) { Definition def = node.arguments[i].definition; _AbstractValue<T> cell = getValue(def); setValue(cont.parameters[i], cell); } } void visitInvokeMethod(InvokeMethod node) { Continuation cont = node.continuation.definition; setReachable(cont); /// Sets the value of both the current node and the target continuation /// parameter. void setValues(_AbstractValue<T> updateValue) { setValue(node, updateValue); Parameter returnValue = cont.parameters[0]; setValue(returnValue, updateValue); } _AbstractValue<T> lhs = getValue(node.receiver.definition); if (lhs.isUnknown) { // This may seem like a missed opportunity for evaluating short-circuiting // boolean operations; we are currently skipping these intentionally since // expressions such as `(new Foo() || true)` may introduce type errors // and thus evaluation to `true` would not be correct. // TODO(jgruber): Handle such cases while ensuring that new Foo() and // a type-check (in checked mode) are still executed. return; // And come back later. } else if (lhs.isNonConst) { setValues(nonConst()); return; } else if (!node.selector.isOperator) { // TODO(jgruber): Handle known methods on constants such as String.length. setValues(nonConst()); return; } // Calculate the resulting constant if possible. ConstantValue result; String opname = node.selector.name; if (node.selector.argumentCount == 0) { // Unary operator. if (opname == "unary-") { opname = "-"; } dart2js.UnaryOperation operation = constantSystem.lookupUnary(opname); if (operation != null) { result = operation.fold(lhs.constant); } } else if (node.selector.argumentCount == 1) { // Binary operator. _AbstractValue<T> rhs = getValue(node.arguments[0].definition); if (!rhs.isConstant) { setValues(rhs); return; } dart2js.BinaryOperation operation = constantSystem.lookupBinary(opname); if (operation != null) { result = operation.fold(lhs.constant, rhs.constant); } } // Update value of the continuation parameter. Again, this is effectively // a phi. if (result == null) { setValues(nonConst()); } else { T type = typeSystem.typeOf(result); setValues(new _AbstractValue<T>(result, type)); } } void visitInvokeMethodDirectly(InvokeMethodDirectly node) { Continuation cont = node.continuation.definition; setReachable(cont); assert(cont.parameters.length == 1); Parameter returnValue = cont.parameters[0]; // TODO(karlklose): lookup the function and get ites return type. setValue(returnValue, nonConst()); } void visitInvokeConstructor(InvokeConstructor node) { Continuation cont = node.continuation.definition; setReachable(cont); assert(cont.parameters.length == 1); Parameter returnValue = cont.parameters[0]; setValue(returnValue, nonConst()); } void visitConcatenateStrings(ConcatenateStrings node) { Continuation cont = node.continuation.definition; setReachable(cont); void setValues(_AbstractValue<T> updateValue) { setValue(node, updateValue); Parameter returnValue = cont.parameters[0]; setValue(returnValue, updateValue); } // TODO(jgruber): Currently we only optimize if all arguments are string // constants, but we could also handle cases such as "foo${42}". bool allStringConstants = node.arguments.every((Reference ref) { if (!(ref.definition is Constant)) { return false; } Constant constant = ref.definition; return constant != null && constant.value.isString; }); T type = typeSystem.stringType; assert(cont.parameters.length == 1); if (allStringConstants) { // All constant, we can concatenate ourselves. Iterable<String> allStrings = node.arguments.map((Reference ref) { Constant constant = ref.definition; StringConstantValue stringConstant = constant.value; return stringConstant.primitiveValue.slowToString(); }); LiteralDartString dartString = new LiteralDartString(allStrings.join()); ConstantValue constant = new StringConstantValue(dartString); setValues(new _AbstractValue<T>(constant, type)); } else { setValues(nonConst(type)); } } void visitBranch(Branch node) { IsTrue isTrue = node.condition; _AbstractValue<T> conditionCell = getValue(isTrue.value.definition); if (conditionCell.isUnknown) { return; // And come back later. } else if (conditionCell.isNonConst) { setReachable(node.trueContinuation.definition); setReachable(node.falseContinuation.definition); } else if (conditionCell.isConstant && !(conditionCell.constant.isBool)) { // Treat non-bool constants in condition as non-const since they result // in type errors in checked mode. // TODO(jgruber): Default to false in unchecked mode. setReachable(node.trueContinuation.definition); setReachable(node.falseContinuation.definition); setValue(isTrue.value.definition, nonConst(typeSystem.boolType)); } else if (conditionCell.isConstant && conditionCell.constant.isBool) { BoolConstantValue boolConstant = conditionCell.constant; setReachable((boolConstant.isTrue) ? node.trueContinuation.definition : node.falseContinuation.definition); } } void visitTypeOperator(TypeOperator node) { Continuation cont = node.continuation.definition; setReachable(cont); void setValues(_AbstractValue<T> updateValue) { setValue(node, updateValue); Parameter returnValue = cont.parameters[0]; setValue(returnValue, updateValue); } if (node.isTypeCast) { // TODO(jgruber): Add support for `as` casts. setValues(nonConst()); } _AbstractValue<T> cell = getValue(node.receiver.definition); if (cell.isUnknown) { return; // And come back later. } else if (cell.isNonConst) { setValues(nonConst(cell.type)); } else if (node.type.kind == types.TypeKind.INTERFACE) { // Receiver is a constant, perform is-checks at compile-time. types.InterfaceType checkedType = node.type; ConstantValue constant = cell.constant; // TODO(karlklose): remove call to computeType. types.DartType constantType = constant.getType(_dartTypes.coreTypes); T type = typeSystem.boolType; _AbstractValue<T> result; if (constant.isNull && checkedType != _dartTypes.coreTypes.nullType && checkedType != _dartTypes.coreTypes.objectType) { // `(null is Type)` is true iff Type is in { Null, Object }. result = constantValue(new FalseConstantValue(), type); } else { // Otherwise, perform a standard subtype check. result = constantValue( constantSystem.isSubtype(_dartTypes, constantType, checkedType) ? new TrueConstantValue() : new FalseConstantValue(), type); } setValues(result); } } void visitSetMutableVariable(SetMutableVariable node) { setValue(node.variable.definition, getValue(node.value.definition)); setReachable(node.body); } void visitDeclareFunction(DeclareFunction node) { setReachable(node.definition); setReachable(node.body); } // Definitions. void visitLiteralList(LiteralList node) { // Constant lists are translated into (Constant ListConstant(...)) IR nodes, // and thus LiteralList nodes are NonConst. setValue(node, nonConst(typeSystem.listType)); } void visitLiteralMap(LiteralMap node) { // Constant maps are translated into (Constant MapConstant(...)) IR nodes, // and thus LiteralMap nodes are NonConst. setValue(node, nonConst(typeSystem.mapType)); } void visitConstant(Constant node) { ConstantValue value = node.value; setValue(node, constantValue(value, typeSystem.typeOf(value))); } void visitReifyTypeVar(ReifyTypeVar node) { setValue(node, nonConst(typeSystem.typeType)); } void visitCreateFunction(CreateFunction node) { setReachable(node.definition); ConstantValue constant = new FunctionConstantValue(node.definition.element); setValue(node, constantValue(constant, typeSystem.functionType)); } void visitGetMutableVariable(GetMutableVariable node) { setValue(node, getValue(node.variable.definition)); } void visitMutableVariable(MutableVariable node) { // [MutableVariable]s are bound either as parameters to // [FunctionDefinition]s, by [LetMutable], or by [DeclareFunction]. if (node.parent is RootNode) { // Just like immutable parameters, the values of mutable parameters are // never constant. // TODO(karlklose): remove reference to the element model. Entity source = node.hint; T type = (source is ParameterElement) ? typeSystem.getParameterType(source) : typeSystem.dynamicType; setValue(node, nonConst(type)); } else if (node.parent is LetMutable || node.parent is DeclareFunction) { // Mutable values bound by LetMutable or DeclareFunction could have // known values. } else { internalError(node.hint, "Unexpected parent of MutableVariable"); } } void visitParameter(Parameter node) { Entity source = node.hint; // TODO(karlklose): remove reference to the element model. T type = (source is ParameterElement) ? typeSystem.getParameterType(source) : typeSystem.dynamicType; if (node.parent is RootNode) { // Functions may escape and thus their parameters must be non-constant. setValue(node, nonConst(type)); } else if (node.parent is Continuation) { // Continuations on the other hand are local, and parameters can have // some other abstract value than non-constant. } else { internalError(node.hint, "Unexpected parent of Parameter: ${node.parent}"); } } void visitContinuation(Continuation node) { node.parameters.forEach(visit); if (node.body != null) { setReachable(node.body); } } // Conditions. void visitIsTrue(IsTrue node) { Branch branch = node.parent; visitBranch(branch); } // JavaScript specific nodes. void visitIdentical(Identical node) { _AbstractValue<T> leftConst = getValue(node.left.definition); _AbstractValue<T> rightConst = getValue(node.right.definition); ConstantValue leftValue = leftConst.constant; ConstantValue rightValue = rightConst.constant; if (leftConst.isUnknown || rightConst.isUnknown) { // Come back later. return; } else if (!leftConst.isConstant || !rightConst.isConstant) { T leftType = leftConst.type; T rightType = rightConst.type; if (!typeSystem.areAssignable(leftType, rightType)) { setValue(node, constantValue(new FalseConstantValue(), typeSystem.boolType)); } else { setValue(node, nonConst(typeSystem.boolType)); } } else if (leftValue.isPrimitive && rightValue.isPrimitive) { assert(leftConst.isConstant && rightConst.isConstant); PrimitiveConstantValue left = leftValue; PrimitiveConstantValue right = rightValue; ConstantValue result = new BoolConstantValue(left.primitiveValue == right.primitiveValue); setValue(node, new _AbstractValue<T>(result, typeSystem.boolType)); } } void visitInterceptor(Interceptor node) { setReachable(node.input.definition); } void visitGetField(GetField node) { setValue(node, nonConst()); } void visitSetField(SetField node) { setReachable(node.body); } void visitCreateBox(CreateBox node) { setValue(node, nonConst()); } void visitCreateInstance(CreateInstance node) { setValue(node, nonConst()); } void visitReifyRuntimeType(ReifyRuntimeType node) { setValue(node, nonConst(typeSystem.typeType)); } void visitReadTypeVariable(ReadTypeVariable node) { // TODO(karlklose): come up with a type marker for JS entities or switch to // real constants of type [Type]. setValue(node, nonConst()); } @override visitTypeExpression(TypeExpression node) { // TODO(karlklose): come up with a type marker for JS entities or switch to // real constants of type [Type]. setValue(node, nonConst()); } } /// Represents the abstract value of a primitive value at some point in the /// program. Abstract values of all kinds have a type [T]. /// /// The different kinds of abstract values represents the knowledge about the /// constness of the value: /// UNKNOWN: may be some as yet undetermined constant. /// CONSTANT: is a constant as stored in the local field. /// NONCONST: not a constant. class _AbstractValue<T> { static const int UNKNOWN = 0; static const int CONSTANT = 1; static const int NONCONST = 2; final int kind; final ConstantValue constant; final T type; _AbstractValue._internal(this.kind, this.constant, this.type) { assert(kind != CONSTANT || constant != null); assert(type != null); } _AbstractValue(ConstantValue constant, T type) : this._internal(CONSTANT, constant, type); _AbstractValue.unknown(T type) : this._internal(UNKNOWN, null, type); _AbstractValue.nonConst(T type) : this._internal(NONCONST, null, type); bool get isUnknown => (kind == UNKNOWN); bool get isConstant => (kind == CONSTANT); bool get isNonConst => (kind == NONCONST); int get hashCode { return kind | (constant.hashCode * 5) | type.hashCode * 7; } bool operator ==(_AbstractValue that) { return that.kind == this.kind && that.constant == this.constant && that.type == this.type; } String toString() { switch (kind) { case UNKNOWN: return "Unknown"; case CONSTANT: return "Constant: $constant: $type"; case NONCONST: return "Non-constant: $type"; default: assert(false); } return null; } /// Compute the join of two values in the lattice. _AbstractValue join(_AbstractValue that, TypeSystem typeSystem) { assert(that != null); if (this.isUnknown) { return that; } else if (that.isUnknown) { return this; } else if (this.isConstant && that.isConstant && this.constant == that.constant) { return this; } else { return new _AbstractValue.nonConst(typeSystem.join(this.type, that.type)); } } }