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/*
* Copyright 2010 The Closure Compiler Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.javascript.jscomp;
import com.google.common.base.Preconditions;
import com.google.common.base.Predicate;
import com.google.common.collect.Iterables;
import com.google.javascript.jscomp.NodeTraversal.AbstractShallowCallback;
import com.google.javascript.jscomp.ReferenceCollectingCallback.Reference;
import com.google.javascript.jscomp.ReferenceCollectingCallback.ReferenceCollection;
import com.google.javascript.jscomp.VariableVisibilityAnalysis.VariableVisibility;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
/**
* A pass that analyzes side effects to determine when it is safe to move
* code from one program point to another.
*
* In its current form, SideEffectsAnalysis is very incomplete; this is
* mostly a sketch to prototype the interface and the broad strokes of
* a possible implementation based on flow-insensitive MOD and REF sets.
*
* See:
*
* Banning, John. "An efficient way to find the side effects of procedure
* calls and the aliases of variables." POPL '79.
*
* For an introduction to MOD and REF sets.
*
* @author [email protected] (Devin Coughlin)
*/
class SideEffectsAnalysis implements CompilerPass {
/**
* The type of location abstraction to use for this analysis.
*/
enum LocationAbstractionMode {
/** See {@link DegenerateLocationAbstraction} for details. */
DEGENERATE,
/** See {@link VisibilityLocationAbstraction} for details. */
VISIBILITY_BASED
}
private static final Predicate NOT_FUNCTION_PREDICATE =
new Predicate() {
@Override
public boolean apply(Node input) {
return !input.isFunction();
}
};
private AbstractCompiler compiler;
/** The location abstraction used to calculate the effects of code */
private LocationAbstraction locationAbstraction;
/** The kind of location abstraction to use */
private final LocationAbstractionMode locationAbstractionIdentifier;
/**
* Constructs a new SideEffectsAnalysis with the given location abstraction.
*
* @param compiler A compiler instance
* @param locationAbstractionMode The location abstraction to use. {@code
* DEGENERATE} will use {@link DegenerateLocationAbstraction} while
* {@code VISIBILITY_BASED} will use {@link VisibilityLocationAbstraction}
*
*/
public SideEffectsAnalysis(AbstractCompiler compiler,
LocationAbstractionMode locationAbstractionMode) {
this.compiler = compiler;
this.locationAbstractionIdentifier = locationAbstractionMode;
}
public SideEffectsAnalysis(AbstractCompiler compiler) {
this(compiler, LocationAbstractionMode.DEGENERATE);
}
@Override
public void process(Node externs, Node root) {
switch(locationAbstractionIdentifier) {
case DEGENERATE:
locationAbstraction = new DegenerateLocationAbstraction();
break;
case VISIBILITY_BASED:
locationAbstraction = createVisibilityAbstraction(externs, root);
break;
default:
throw new IllegalStateException("Unrecognized location abstraction " +
"identifier: " + locationAbstractionIdentifier);
}
// In the future, this method
// will construct a callgraph and calculate side effects summaries
// for all functions.
// TODO(dcc): Add per-function side effects summaries.
}
private LocationAbstraction createVisibilityAbstraction(Node externs,
Node root) {
VariableVisibilityAnalysis variableVisibility =
new VariableVisibilityAnalysis(compiler);
variableVisibility.process(externs, root);
VariableUseDeclarationMap variableMap =
new VariableUseDeclarationMap(compiler);
variableMap.mapUses(root);
return new VisibilityLocationAbstraction(compiler,
variableVisibility, variableMap);
}
/**
* Determines whether it is safe to move code ({@code source}) across
* an environment to another program point (immediately preceding
* {@code destination}).
*
* The notion of "environment" is optimization-specific, but it should
* include any code that could be executed between the source program point
* and the destination program point.
*
* {@code destination} must not be a descendant of {@code source}.
*
* @param source The node that would be moved
* @param environment An environment representing the code across which
* the source will be moved.
* @param destination The node before which the source would be moved
* @return Whether it is safe to move the source to the destination
*/
public boolean safeToMoveBefore(Node source,
AbstractMotionEnvironment environment,
Node destination) {
Preconditions.checkNotNull(locationAbstraction);
Preconditions.checkArgument(!nodeHasAncestor(destination, source));
// It is always safe to move pure code.
if (isPure(source)) {
return true;
}
// Don't currently support interprocedural analysis
if (nodeHasCall(source)) {
return false;
}
LocationSummary sourceLocationSummary =
locationAbstraction.calculateLocationSummary(source);
EffectLocation sourceModSet = sourceLocationSummary.getModSet();
// If the source has side effects, then we require that the source
// is executed exactly as many times as the destination.
if (!sourceModSet.isEmpty() &&
!nodesHaveSameControlFlow(source, destination)) {
return false;
}
EffectLocation sourceRefSet = sourceLocationSummary.getRefSet();
Set environmentNodes = environment.calculateEnvironment();
for (Node environmentNode : environmentNodes) {
if (nodeHasCall(environmentNode)) {
return false;
}
}
LocationSummary environmentLocationSummary =
locationAbstraction.calculateLocationSummary(environmentNodes);
EffectLocation environmentModSet = environmentLocationSummary.getModSet();
EffectLocation environmentRefSet = environmentLocationSummary.getRefSet();
// If MOD(environment) intersects REF(source) then moving the
// source across the environment could cause the source
// to read an incorrect value.
// If REF(environment) intersects MOD(source) then moving the
// source across the environment could cause the environment
// to read an incorrect value.
// If MOD(environment) intersects MOD(source) then moving the
// source across the environment could cause some later code that reads
// a modified location to get an incorrect value.
return !environmentModSet.intersectsLocation(sourceRefSet)
&& !environmentRefSet.intersectsLocation(sourceModSet)
&& !environmentModSet.intersectsLocation(sourceModSet);
}
/**
* Returns true if the node is pure, that is it side effect free and does it
* not depend on its environment?
* @param node node to check.
*/
private static boolean isPure(Node node) {
// For now, we conservatively assume all code is not pure.
// TODO(dcc): Implement isPure().
return false;
}
/**
* Returns true if the two nodes have the same control flow properties,
* that is, is node1 be executed every time node2 is executed and vice versa?
*/
private static boolean nodesHaveSameControlFlow(Node node1, Node node2) {
/*
* We conservatively approximate this with the following criteria:
*
* Define the "deepest control dependent block" for a node to be the
* closest ancestor whose *parent* is a control structure and where that
* ancestor may or may be executed depending on the parent.
*
* So, for example, in:
* if (a) {
* b;
* } else {
* c;
* }
*
* a has not deepest control dependent block.
* b's deepest control dependent block is the "then" block of the IF.
* c's deepest control dependent block is the "else" block of the IF.
*
* We'll say two nodes have the same control flow if
*
* 1) they have the same deepest control dependent block
* 2) that block is either a CASE (which can't have early exits) or it
* doesn't have any early exits (e.g. breaks, continues, returns.)
*
*/
Node node1DeepestControlDependentBlock =
closestControlDependentAncestor(node1);
Node node2DeepestControlDependentBlock =
closestControlDependentAncestor(node2);
if (node1DeepestControlDependentBlock ==
node2DeepestControlDependentBlock) {
if (node2DeepestControlDependentBlock != null) {
// CASE is complicated because we have to deal with fall through and
// because some BREAKs are early exits and some are not.
// For now, we don't allow movement within a CASE.
//
// TODO(dcc): be less conservative about movement within CASE
if (node2DeepestControlDependentBlock.isCase()) {
return false;
}
// Don't allow breaks, continues, returns in control dependent
// block because we don't actually create a control-flow graph
// and so don't know if early exits site between the source
// and the destination.
//
// This is overly conservative as it doesn't allow, for example,
// moving in the following case:
// while (a) {
// source();
//
// while(b) {
// break;
// }
//
// destination();
// }
//
// To fully support this kind of movement, we'll probably have to use
// a CFG-based analysis rather than just looking at the AST.
//
// TODO(dcc): have nodesHaveSameControlFlow() use a CFG
Predicate isEarlyExitPredicate =
new Predicate() {
@Override
public boolean apply(Node input) {
Token nodeType = input.getToken();
return nodeType == Token.RETURN
|| nodeType == Token.BREAK
|| nodeType == Token.CONTINUE;
}
};
return !NodeUtil.has(node2DeepestControlDependentBlock,
isEarlyExitPredicate, NOT_FUNCTION_PREDICATE);
} else {
return true;
}
} else {
return false;
}
}
/**
* Returns true if the number of times the child executes depends on the
* parent.
*
* For example, the guard of an IF is not control dependent on the
* IF, but its two THEN/ELSE blocks are.
*
* Also, the guard of WHILE and DO are control dependent on the parent
* since the number of times it executes depends on the parent.
*/
private static boolean isControlDependentChild(Node child) {
Node parent = child.getParent();
if (parent == null) {
return false;
}
ArrayList siblings = new ArrayList<>();
Iterables.addAll(siblings, parent.children());
int indexOfChildInParent = siblings.indexOf(child);
switch (parent.getToken()) {
case IF:
case HOOK:
return (indexOfChildInParent == 1 || indexOfChildInParent == 2);
case FOR:
case FOR_IN:
// Only initializer is not control dependent
return indexOfChildInParent != 0;
case SWITCH:
return indexOfChildInParent > 0;
case WHILE:
case DO:
case AND:
case OR:
case FUNCTION:
return true;
default:
return false;
}
}
private static Node closestControlDependentAncestor(Node node) {
if (isControlDependentChild(node)) {
return node;
}
// Note: node is not considered one of its ancestors
for (Node ancestor : node.getAncestors()) {
if (isControlDependentChild(ancestor)) {
return ancestor;
}
}
return null;
}
/**
* Returns true if {@code possibleAncestor} is an ancestor of{@code node}.
* A node is not considered to be an ancestor of itself.
*/
private static boolean nodeHasAncestor(Node node, Node possibleAncestor) {
// Note node is not in node.getAncestors()
for (Node ancestor : node.getAncestors()) {
if (ancestor == possibleAncestor) {
return true;
}
}
return false;
}
/**
* Returns true if a node has a CALL or a NEW descendant.
*/
private static boolean nodeHasCall(Node node) {
return NodeUtil.has(node, new Predicate() {
@Override
public boolean apply(Node input) {
return input.isCall() || input.isNew() || input.isTaggedTemplateLit();
}},
NOT_FUNCTION_PREDICATE);
}
/**
* Represents an environment across which code might be moved, i.e. the set
* of code that could be run in between the source and the destination.
*
* SideEffectAnalysis characterizes the code to be moved and the environment
* in order to determine if they interact in such a way as to make the move
* unsafe.
*
* Since determining the environment for an optimization can be tricky,
* we provide several concrete subclasses that common classes of optimizations
* may be able to reuse.
*/
public abstract static class AbstractMotionEnvironment {
/**
* Calculates the set of nodes that this environment represents.
*/
public abstract Set calculateEnvironment();
}
/**
* An environment for motion within a function. Given a
* control flow graph and a source and destination node in the control
* flow graph, instances of this object will calculate the environment between
* the source and destination.
*/
public static class IntraproceduralMotionEnvironment
extends AbstractMotionEnvironment {
/**
* Creates an intraprocedural motion environment.
*
* @param controlFlowGraph A control flow graph for function in which
* code will be moved
* @param cfgSource The code to be moved
* @param cfgDestination The node immediately before which cfgSource
* will be moved
*/
public IntraproceduralMotionEnvironment(
ControlFlowGraph controlFlowGraph,
Node cfgSource,
Node cfgDestination) {
}
@Override
public Set calculateEnvironment() {
// TODO(dcc): Implement IntraproceduralMotionEnvironment
return null;
}
}
/**
* An environment for motion between modules. Given a
* module graph and as well as source and destination nodes and modules,
* instances of this object will calculate the environment between the source
* and destination.
*/
public static class CrossModuleMotionEnvironment
extends AbstractMotionEnvironment {
/**
* Creates a cross module code motion environment.
*
* @param sourceNode The code to be moved
* @param sourceModule The module for the code to be moved
* @param destinationNode The node before which sourceNode will be inserted
* @param destinationModule The module that destination is in
* @param moduleGraph The module graph of the entire program
*/
public CrossModuleMotionEnvironment(Node sourceNode,
JSModule sourceModule,
Node destinationNode,
JSModule destinationModule,
JSModuleGraph moduleGraph) {
}
@Override
public Set calculateEnvironment() {
// TODO(dcc): Implement CrossModuleMotionEnvironment
return null;
}
}
/**
* A low-level concrete environment that allows the client to specify
* the environment nodes directly. Clients may wish to use this environment
* if none of the higher-level environments fit their needs.
*/
public static class RawMotionEnvironment
extends AbstractMotionEnvironment {
Set environment;
public RawMotionEnvironment(Set environment) {
this.environment = environment;
}
@Override
public Set calculateEnvironment() {
return environment;
}
}
/*
* A combined representation for location set summaries.
*
* Basically, it is often easier to shuffle MOD/REF around together; this is
* a value class for that purpose.
*/
private static class LocationSummary {
private EffectLocation modSet;
private EffectLocation refSet;
public LocationSummary(EffectLocation modSet, EffectLocation refSet) {
this.modSet = modSet;
this.refSet = refSet;
}
public EffectLocation getModSet() {
return modSet;
}
public EffectLocation getRefSet() {
return refSet;
}
}
/**
* Interface representing the notion of an effect location -- an abstract
* location that can be modified or referenced.
*
* Since there are an infinite number of possible concrete locations
* in a running program, this abstraction must be imprecise (i.e. there
* will be some distinct concrete locations that are indistinguishable
* under the abstraction).
*
*
Different location abstractions will provide their
* own implementations of this interface, based on the level and kind
* of precision they provide.
*/
private static interface EffectLocation {
/**
* Does the receiver's effect location intersect a given effect location?
* That is, could any of the concrete storage locations (fields, variables,
* etc.) represented by the receiver be contained in the set of concrete
* storage locations represented by the given abstract effect location.
*/
public boolean intersectsLocation(EffectLocation otherLocation);
/**
* Returns the result of merging the given effect location with
* the receiver. The concrete locations represented by the result must
* include all the concrete locations represented by each of the merged
* locations and may also possibly include more (i.e., a join may
* introduce a loss of precision).
*/
public EffectLocation join(EffectLocation otherLocation);
/**
* Does the effect location represent any possible concrete locations?
*/
public boolean isEmpty();
}
/**
* An abstract class representing a location abstraction. (Here "abstraction"
* means an imprecise representation of concrete side effects.)
*
*
Implementations of this class will each provide own their
* implementation(s) of SideEffectLocation and methods to determine the side
* effect locations of a given piece of code.
*/
private abstract static class LocationAbstraction {
/** Calculates the abstraction-specific side effects
* for the node.
*/
abstract LocationSummary calculateLocationSummary(Node node);
/**
* Returns an abstraction-specific EffectLocation representing
* no location.
*
*
The bottom location joined with any location should return
* that location.
*/
abstract EffectLocation getBottomLocation();
/**
* Calculates the abstraction-specific side effects
* for the node.
*/
public LocationSummary calculateLocationSummary(Set nodes) {
EffectLocation modAccumulator = getBottomLocation();
EffectLocation refAccumulator = getBottomLocation();
for (Node node : nodes) {
LocationSummary nodeLocationSummary = calculateLocationSummary(node);
modAccumulator = modAccumulator.join(nodeLocationSummary.getModSet());
refAccumulator = refAccumulator.join(nodeLocationSummary.getRefSet());
}
return new LocationSummary(modAccumulator, refAccumulator);
}
}
/**
* A very imprecise location abstraction in which there are only two abstract
* locations: one representing all concrete locations and one for bottom
* (no concrete locations).
*
* This implementation is a thin wrapper on NodeUtil.mayHaveSideEffects()
* and NodeUtil.canBeSideEffected() -- it doesn't add any real value other
* than to prototype the LocationAbstraction interface.
*/
private static class DegenerateLocationAbstraction
extends LocationAbstraction {
private static final EffectLocation EVERY_LOCATION =
new DegenerateEffectLocation();
private static final EffectLocation NO_LOCATION =
new DegenerateEffectLocation();
@Override
EffectLocation getBottomLocation() {
return NO_LOCATION;
}
@Override
public LocationSummary calculateLocationSummary(Node node) {
return new LocationSummary(calculateModSet(node), calculateRefSet(node));
}
static EffectLocation calculateRefSet(Node node) {
if (NodeUtil.canBeSideEffected(node)) {
return EVERY_LOCATION;
} else {
return NO_LOCATION;
}
}
static EffectLocation calculateModSet(Node node) {
if (NodeUtil.mayHaveSideEffects(node)) {
return EVERY_LOCATION;
} else {
return NO_LOCATION;
}
}
private static class DegenerateEffectLocation implements EffectLocation {
@Override
public EffectLocation join(EffectLocation otherLocation) {
if (otherLocation == EVERY_LOCATION) {
return otherLocation;
} else {
return this;
}
}
@Override
public boolean intersectsLocation(EffectLocation otherLocation) {
return this == EVERY_LOCATION && otherLocation == EVERY_LOCATION;
}
@Override
public boolean isEmpty() {
return this == NO_LOCATION;
}
}
}
/**
* A location abstraction based on the visibility of concrete locations.
*
* A global variables are treated as one common location, as are all heap
* storage locations.
*
* Local variables are broken up into two classes, one for truly local
* variables and one for local variables captured by an inner scope. Each
* of these classes has their own separate location representing the
* variables in the class.
*
* Parameter variables are considered to be heap locations since they
* can be accessed via the arguments object which itself can be aliased.
*
* A more precise analysis could:
* 1) put parameters on the heap only when "arguments" is actually used
* in a method
* 2) recognize that GETPROPs cannot access or modify parameters, only
* GETELEMs
*
* TODO(dcc): Don't merge parameters with the heap unless necessary.
*
* Internally, abstract locations are represented as integers
* with bits set (masks) representing the storage classes in the location, so
* that joining is bit-wise ORing and intersection is bitwise AND.
*/
private static class VisibilityLocationAbstraction
extends LocationAbstraction {
/** The "bottom" location. Used to signify an empty location set */
private static final int VISIBILITY_LOCATION_NONE = 0;
/** The "top" location. Used to signify the set containing all locations */
private static final int UNKNOWN_LOCATION_MASK = 0xFFFFFFFF;
private static final int LOCAL_VARIABLE_LOCATION_MASK = 1 << 1;
private static final int CAPTURED_LOCAL_VARIABLE_LOCATION_MASK = 1 << 2;
private static final int GLOBAL_VARIABLE_LOCATION_MASK = 1 << 3;
private static final int HEAP_LOCATION_MASK = 1 << 4;
AbstractCompiler compiler;
VariableVisibilityAnalysis variableVisibilityAnalysis;
VariableUseDeclarationMap variableUseMap;
private VisibilityLocationAbstraction(AbstractCompiler compiler,
VariableVisibilityAnalysis variableVisibilityAnalysis,
VariableUseDeclarationMap variableUseMap) {
this.compiler = compiler;
this.variableVisibilityAnalysis = variableVisibilityAnalysis;
this.variableUseMap = variableUseMap;
}
/**
* Calculates the MOD/REF summary for the given node.
*/
@Override
LocationSummary calculateLocationSummary(Node node) {
int visibilityRefLocations = VISIBILITY_LOCATION_NONE;
int visibilityModLocations = VISIBILITY_LOCATION_NONE;
for (Node reference : findStorageLocationReferences(node)) {
int effectMask;
if (reference.isName()) {
// Variable access
effectMask = effectMaskForVariableReference(reference);
} else {
// Heap access
effectMask = HEAP_LOCATION_MASK;
}
if (storageNodeIsLValue(reference)) {
visibilityModLocations |= effectMask;
}
if (storageNodeIsRValue(reference)) {
visibilityRefLocations |= effectMask;
}
}
VisibilityBasedEffectLocation modSet =
new VisibilityBasedEffectLocation(visibilityModLocations);
VisibilityBasedEffectLocation refSet =
new VisibilityBasedEffectLocation(visibilityRefLocations);
return new LocationSummary(modSet, refSet);
}
/**
* Returns the set of references to storage locations (both variables
* and the heap) under {@code root}.
*/
private Set findStorageLocationReferences(Node root) {
final Set references = new HashSet<>();
NodeTraversal.traverseEs6(compiler, root, new AbstractShallowCallback() {
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
if (NodeUtil.isGet(n)
|| (n.isName() && !parent.isFunction())) {
references.add(n);
}
}
});
return references;
}
/**
* Calculates the effect mask for a variable reference.
*/
private int effectMaskForVariableReference(Node variableReference) {
Preconditions.checkArgument(variableReference.isName());
int effectMask = VISIBILITY_LOCATION_NONE;
Node declaringNameNode =
variableUseMap.findDeclaringNameNodeForUse(variableReference);
if (declaringNameNode != null) {
VariableVisibility visibility =
variableVisibilityAnalysis.getVariableVisibility(declaringNameNode);
switch (visibility) {
case LOCAL:
effectMask = LOCAL_VARIABLE_LOCATION_MASK;
break;
case CAPTURED_LOCAL:
effectMask = CAPTURED_LOCAL_VARIABLE_LOCATION_MASK;
break;
case PARAMETER:
// Parameters are considered to be on the heap since they
// can be accessed via the arguments object.
effectMask = HEAP_LOCATION_MASK;
break;
case GLOBAL:
effectMask = GLOBAL_VARIABLE_LOCATION_MASK;
break;
default:
throw new IllegalStateException("Unrecognized variable" +
" visibility: " + visibility);
}
} else {
// Couldn't find a variable for the reference
effectMask = UNKNOWN_LOCATION_MASK;
}
return effectMask;
}
@Override
EffectLocation getBottomLocation() {
return new VisibilityBasedEffectLocation(VISIBILITY_LOCATION_NONE);
}
/**
* Returns true if the node is a storage node.
*
* Only NAMEs, GETPROPs, and GETELEMs are storage nodes.
*/
private static boolean isStorageNode(Node node) {
return node.isName() || NodeUtil.isGet(node);
}
/**
* Return true if the storage node is an r-value.
*/
private static boolean storageNodeIsRValue(Node node) {
Preconditions.checkArgument(isStorageNode(node));
// We consider all names to be r-values unless
// LHS of Token.ASSIGN
// LHS of of for in expression
// Child of VAR
Node parent = node.getParent();
if (storageNodeIsLValue(node)) {
// Assume l-value is NOT an r-value
// unless it is a non-simple assign
// or an increment/decrement
boolean nonSimpleAssign =
NodeUtil.isAssignmentOp(parent) && !parent.isAssign();
return (nonSimpleAssign
|| parent.isDec()
|| parent.isInc());
}
return true;
}
/**
* Return true if the storage node is an l-value.
*/
private static boolean storageNodeIsLValue(Node node) {
Preconditions.checkArgument(isStorageNode(node));
return NodeUtil.isLValue(node);
}
/**
* An abstract effect location based the visibility of the
* concrete storage location.
*
* See {@link VisibilityLocationAbstraction} for deeper description
* of this abstraction.
*
* The effect locations are stored as bits set on an integer, so
* intersect, join, etc. are the standard bitwise operations.
*/
private static class VisibilityBasedEffectLocation
implements EffectLocation {
int visibilityMask = VISIBILITY_LOCATION_NONE;
public VisibilityBasedEffectLocation(int visibilityMask) {
this.visibilityMask = visibilityMask;
}
@Override
public boolean intersectsLocation(EffectLocation otherLocation) {
Preconditions.checkArgument(otherLocation instanceof
VisibilityBasedEffectLocation);
int otherMask =
((VisibilityBasedEffectLocation) otherLocation).visibilityMask;
return (visibilityMask & otherMask) > 0;
}
@Override
public boolean isEmpty() {
return visibilityMask == VISIBILITY_LOCATION_NONE;
}
@Override
public EffectLocation join(EffectLocation otherLocation) {
Preconditions.checkArgument(otherLocation instanceof
VisibilityBasedEffectLocation);
int otherMask =
((VisibilityBasedEffectLocation) otherLocation).visibilityMask;
int joinedMask = visibilityMask | otherMask;
return new VisibilityBasedEffectLocation(joinedMask);
}
}
}
/**
* Maps NAME nodes that refer to variables to the NAME
* nodes that declared them.
*/
private static class VariableUseDeclarationMap {
private AbstractCompiler compiler;
// Maps a using name to its declaring name
private Map referencesByNameNode;
public VariableUseDeclarationMap(AbstractCompiler compiler) {
this.compiler = compiler;
}
/**
* Adds a map from each use NAME in {@code root} to its corresponding
* declaring name, *provided the declaration is also under root*.
*
* If the declaration is not under root, then the reference will
* not be added to the map.
*/
public void mapUses(Node root) {
referencesByNameNode = new HashMap<>();
ReferenceCollectingCallback callback =
new ReferenceCollectingCallback(
compiler,
ReferenceCollectingCallback.DO_NOTHING_BEHAVIOR,
new Es6SyntacticScopeCreator(compiler));
callback.process(root);
for (Var variable : callback.getAllSymbols()) {
ReferenceCollection referenceCollection =
callback.getReferences(variable);
for (Reference reference : referenceCollection.references) {
Node referenceNameNode = reference.getNode();
// Note that this counts a declaration as a reference to itself
referencesByNameNode.put(referenceNameNode, variable.getNameNode());
}
}
}
/**
* Returns the NAME node for the declaration of the variable
* that {@code usingNameNode} refers to, if it is in the map,
* or {@code null} otherwise.
*/
public Node findDeclaringNameNodeForUse(Node usingNameNode) {
Preconditions.checkArgument(usingNameNode.isName());
return referencesByNameNode.get(usingNameNode);
}
}
}