Move dart2js from sdk/lib/_internal/compiler to pkg/compiler

sdk/lib/_internal/compiler/implementation/cps_ir/constant_propagation.dart

Index: sdk/lib/_internal/compiler/implementation/cps_ir/constant_propagation.dart
diff --git a/sdk/lib/_internal/compiler/implementation/cps_ir/constant_propagation.dart b/sdk/lib/_internal/compiler/implementation/cps_ir/constant_propagation.dart
deleted file mode 100644
index 985cd279b8153b3c396327869f3f6a48c1013c5b..0000000000000000000000000000000000000000
--- a/sdk/lib/_internal/compiler/implementation/cps_ir/constant_propagation.dart
+++ /dev/null
@@ -1,666 +0,0 @@
-// 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.optimizers;
-
-/**
- * Propagates 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 ConstantPropagator implements Pass {
-
-  // Required for type determination in analysis of TypeOperator expressions.
-  final dart2js.Compiler _compiler;
-
-  // The constant system is used for evaluation of expressions with constant
-  // arguments.
-  final dart2js.ConstantSystem _constantSystem;
-
-  ConstantPropagator(this._compiler, this._constantSystem);
-
-  void rewrite(FunctionDefinition root) {
-    if (root.isAbstract) return;
-
-    // Set all parent pointers.
-
-    new _ParentVisitor().visit(root);
-
-    // Analyze. In this phase, the entire term is analyzed for reachability
-    // and the constant status of each expression.
-
-    _ConstPropagationVisitor analyzer =
-        new _ConstPropagationVisitor(_compiler, _constantSystem);
-    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.node2value);
-    transformer.transform(root);
-  }
-}
-
-/**
- * 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, _ConstnessLattice> node2value;
-
-  _TransformingVisitor(this.reachable, this.node2value);
-
-  void transform(FunctionDefinition root) {
-    visitFunctionDefinition(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()) {
-    _ConstnessLattice cell = node2value[node];
-    if (cell == null || !cell.isConstant) {
-      return null;
-    }
-
-    assert(continuation.parameters.length == 1);
-
-    // Set up the replacement structure.
-
-    PrimitiveConstantValue primitiveConstant = cell.constant;
-    ConstantExpression constExp =
-        new PrimitiveConstantExpression(primitiveConstant);
-    Constant constant = new Constant(constExp);
-    LetPrim letPrim = new LetPrim(constant);
-    InvokeContinuation invoke =
-        new InvokeContinuation(continuation, <Definition>[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, <Definition>[]);
-
-    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 _ConstPropagationVisitor extends 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.Compiler compiler;
-  final dart2js.ConstantSystem constantSystem;
-
-  // 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, _ConstnessLattice> node2value = <Node, _ConstnessLattice>{};
-
-  _ConstPropagationVisitor(this.compiler, this.constantSystem);
-
-  void analyze(FunctionDefinition 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.
-  _ConstnessLattice getValue(Node node) {
-    _ConstnessLattice value = node2value[node];
-    return (value == null) ? _ConstnessLattice.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, _ConstnessLattice updateValue) {
-    _ConstnessLattice oldValue = getValue(node);
-    _ConstnessLattice newValue = updateValue.join(oldValue);
-    if (oldValue == newValue) {
-      return;
-    }
-
-    // Values may only move in the direction UNKNOWN -> CONSTANT -> NONCONST.
-    assert(newValue.kind >= oldValue.kind);
-
-    node2value[node] = newValue;
-    if (node is Definition) {
-      defWorkset.add(node);
-    }
-  }
-
-  // -------------------------- Visitor overrides ------------------------------
-
-  void visitNode(Node node) {
-    compiler.internalError(NO_LOCATION_SPANNABLE,
-        "_ConstPropagationVisitor is stale, add missing visit overrides");
-  }
-
-  void visitFunctionDefinition(FunctionDefinition node) {
-    node.parameters.forEach(visitParameter);
-    setReachable(node.body);
-  }
-
-  // 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 visitInvokeStatic(InvokeStatic node) {
-    Continuation cont = node.continuation.definition;
-    setReachable(cont);
-
-    assert(cont.parameters.length == 1);
-    Parameter returnValue = cont.parameters[0];
-    setValue(returnValue, _ConstnessLattice.NonConst);
-  }
-
-  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;
-      _ConstnessLattice 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(_ConstnessLattice updateValue) {
-      setValue(node, updateValue);
-      Parameter returnValue = cont.parameters[0];
-      setValue(returnValue, updateValue);
-    }
-
-    _ConstnessLattice 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(_ConstnessLattice.NonConst);
-      return;
-    } else if (!node.selector.isOperator) {
-      // TODO(jgruber): Handle known methods on constants such as String.length.
-      setValues(_ConstnessLattice.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.
-
-      _ConstnessLattice 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.
-
-    setValues((result == null) ?
-        _ConstnessLattice.NonConst : new _ConstnessLattice(result));
-   }
-
-  void visitInvokeSuperMethod(InvokeSuperMethod node) {
-    Continuation cont = node.continuation.definition;
-    setReachable(cont);
-
-    assert(cont.parameters.length == 1);
-    Parameter returnValue = cont.parameters[0];
-    setValue(returnValue, _ConstnessLattice.NonConst);
-  }
-
-  void visitInvokeConstructor(InvokeConstructor node) {
-    Continuation cont = node.continuation.definition;
-    setReachable(cont);
-
-    assert(cont.parameters.length == 1);
-    Parameter returnValue = cont.parameters[0];
-    setValue(returnValue, _ConstnessLattice.NonConst);
-  }
-
-  void visitConcatenateStrings(ConcatenateStrings node) {
-    Continuation cont = node.continuation.definition;
-    setReachable(cont);
-
-    void setValues(_ConstnessLattice 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;
-    });
-
-    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 _ConstnessLattice(constant));
-    } else {
-      setValues(_ConstnessLattice.NonConst);
-    }
-  }
-
-  void visitBranch(Branch node) {
-    IsTrue isTrue = node.condition;
-    _ConstnessLattice 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, _ConstnessLattice.NonConst);
-    } 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(_ConstnessLattice updateValue) {
-      setValue(node, updateValue);
-      Parameter returnValue = cont.parameters[0];
-      setValue(returnValue, updateValue);
-    }
-
-    if (node.isTypeCast) {
-      // TODO(jgruber): Add support for `as` casts.
-      setValues(_ConstnessLattice.NonConst);
-    }
-
-    _ConstnessLattice cell = getValue(node.receiver.definition);
-    if (cell.isUnknown) {
-      return;  // And come back later.
-    } else if (cell.isNonConst) {
-      setValues(_ConstnessLattice.NonConst);
-    } 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;
-      types.DartType constantType = constant.computeType(compiler);
-
-      _ConstnessLattice result = _ConstnessLattice.NonConst;
-      if (constant.isNull &&
-          checkedType.element != compiler.nullClass &&
-          checkedType.element != compiler.objectClass) {
-        // `(null is Type)` is true iff Type is in { Null, Object }.
-        result = new _ConstnessLattice(new FalseConstantValue());
-      } else {
-        // Otherwise, perform a standard subtype check.
-        result = new _ConstnessLattice(
-            constantSystem.isSubtype(compiler, constantType, checkedType)
-            ? new TrueConstantValue()
-            : new FalseConstantValue());
-      }
-
-      setValues(result);
-    }
-  }
-
-  void visitSetClosureVariable(SetClosureVariable node) {
-    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, _ConstnessLattice.NonConst);
-  }
-
-  void visitLiteralMap(LiteralMap node) {
-    // Constant maps are translated into (Constant MapConstant(...)) IR nodes,
-    // and thus LiteralMap nodes are NonConst.
-    setValue(node, _ConstnessLattice.NonConst);
-  }
-
-  void visitConstant(Constant node) {
-    setValue(node, new _ConstnessLattice(node.value));
-  }
-
-  void visitThis(This node) {
-    setValue(node, _ConstnessLattice.NonConst);
-  }
-
-  void visitReifyTypeVar(ReifyTypeVar node) {
-    setValue(node, _ConstnessLattice.NonConst);
-  }
-
-  void visitCreateFunction(CreateFunction node) {
-    setReachable(node.definition);
-    ConstantValue constant =
-        new FunctionConstantValue(node.definition.element);
-    setValue(node, new _ConstnessLattice(constant));
-  }
-
-  void visitGetClosureVariable(GetClosureVariable node) {
-    setValue(node, _ConstnessLattice.NonConst);
-  }
-
-  void visitParameter(Parameter node) {
-    if (node.parent is FunctionDefinition) {
-      // Functions may escape and thus their parameters must be initialized to
-      // NonConst.
-      setValue(node, _ConstnessLattice.NonConst);
-    } else if (node.parent is Continuation) {
-      // Continuations on the other hand are local, and parameters are
-      // initialized to Unknown.
-      setValue(node, _ConstnessLattice.Unknown);
-    } else {
-      compiler.internalError(node.hint, "Unexpected parent of Parameter");
-    }
-  }
-
-  void visitContinuation(Continuation node) {
-    node.parameters.forEach((Parameter p) {
-      setValue(p, _ConstnessLattice.Unknown);
-      defWorkset.add(p);
-    });
-
-    if (node.body != null) {
-      setReachable(node.body);
-    }
-  }
-
-  // Conditions.
-
-  void visitIsTrue(IsTrue node) {
-    Branch branch = node.parent;
-    visitBranch(branch);
-  }
-}
-
-/// Represents the constant-state of a variable at some point in the program.
-/// UNKNOWN: may be some as yet undetermined constant.
-/// CONSTANT: is a constant as stored in the local field.
-/// NONCONST: not a constant.
-class _ConstnessLattice {
-  static const int UNKNOWN  = 0;
-  static const int CONSTANT = 1;
-  static const int NONCONST = 2;
-
-  final int kind;
-  final ConstantValue constant;
-
-  static final _ConstnessLattice Unknown =
-      new _ConstnessLattice._internal(UNKNOWN, null);
-  static final _ConstnessLattice NonConst =
-      new _ConstnessLattice._internal(NONCONST, null);
-
-  _ConstnessLattice._internal(this.kind, this.constant);
-  _ConstnessLattice(this.constant) : kind = CONSTANT {
-    assert(this.constant != null);
-  }
-
-  bool get isUnknown  => (kind == UNKNOWN);
-  bool get isConstant => (kind == CONSTANT);
-  bool get isNonConst => (kind == NONCONST);
-
-  int get hashCode => kind | (constant.hashCode << 2);
-  bool operator==(_ConstnessLattice that) =>
-      (that.kind == this.kind && that.constant == this.constant);
-
-  String toString() {
-    switch (kind) {
-      case UNKNOWN: return "Unknown";
-      case CONSTANT: return "Constant: $constant";
-      case NONCONST: return "Non-constant";
-      default: assert(false);
-    }
-    return null;
-  }
-
-  /// Compute the join of two values in the lattice.
-  _ConstnessLattice join(_ConstnessLattice that) {
-    assert(that != null);
-
-    if (this.isNonConst || that.isUnknown) {
-      return this;
-    }
-
-    if (this.isUnknown || that.isNonConst) {
-      return that;
-    }
-
-    if (this.constant == that.constant) {
-      return this;
-    }
-
-    return NonConst;
-  }
-}