/*
* Copyright 2009 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.collect.HashMultimap;
import com.google.common.collect.Multimap;
import com.google.common.collect.Sets;
import com.google.javascript.jscomp.ControlFlowGraph.Branch;
import com.google.javascript.jscomp.Scope.Var;
import com.google.javascript.jscomp.graph.DiGraph.DiGraphEdge;
import com.google.javascript.jscomp.graph.GraphNode;
import com.google.javascript.jscomp.graph.LatticeElement;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
import java.util.Collection;
import java.util.List;
import java.util.Set;
/**
* Computes "may be" reaching use for all definitions of each variables.
*
* A use of {@code A} in {@code alert(A)} is a "may be" reaching use of
* the definition of {@code A} at {@code A = foo()} if at least one path from
* the use node reaches that definition and it is the last definition before
* the use on that path.
*
*/
class MaybeReachingVariableUse extends
DataFlowAnalysis<Node, MaybeReachingVariableUse.ReachingUses> {
// The scope of the function that we are analyzing.
private final Scope jsScope;
private final Set<Var> escaped;
MaybeReachingVariableUse(
ControlFlowGraph<Node> cfg, Scope jsScope, AbstractCompiler compiler) {
super(cfg, new ReachingUsesJoinOp());
this.jsScope = jsScope;
this.escaped = Sets.newHashSet();
// TODO(user): Maybe compute it somewhere else and re-use the escape
// local set here.
computeEscaped(jsScope, escaped, compiler);
}
/**
* May use definition lattice representation. It captures a product
* lattice for each local (non-escaped) variable. The sub-lattice is
* a n + 2 power set element lattice with all the Nodes in the program,
* TOP and BOTTOM. This is better explained with an example:
*
* Consider: A sub-lattice element representing the variable A represented
* by { N_4, N_5} where N_x is a Node in the program. This implies at
* that particular point in the program the content of A is "upward exposed"
* at point N_4 and N_5.
*
* Example:
*
* A = 1;
* ...
* N_3:
* N_4: print(A);
* N_5: y = A;
* N_6: A = 1;
* N_7: print(A);
*
* At N_3, reads of A in {N_4, N_5} are said to be upward exposed.
*/
static final class ReachingUses implements LatticeElement {
final Multimap<Var, Node> mayUseMap;
public ReachingUses() {
mayUseMap = HashMultimap.create();
}
/**
* Copy constructor.
*
* @param other The constructed object is a replicated copy of this element.
*/
public ReachingUses(ReachingUses other) {
mayUseMap = HashMultimap.create(other.mayUseMap);
}
@Override
public boolean equals(Object other) {
return (other instanceof ReachingUses) &&
((ReachingUses) other).mayUseMap.equals(this.mayUseMap);
}
@Override
public int hashCode() {
return mayUseMap.hashCode();
}
}
/**
* The join is a simple union because of the "may be" nature of the analysis.
*
* Consider: A = 1; if (x) { A = 2 }; alert(A);
*
* The read of A "may be" exposed to A = 1 in the beginning.
*/
private static class ReachingUsesJoinOp implements JoinOp<ReachingUses> {
@Override
public ReachingUses apply(List<ReachingUses> from) {
ReachingUses result = new ReachingUses();
for (ReachingUses uses : from) {
result.mayUseMap.putAll(uses.mayUseMap);
}
return result;
}
}
@Override
boolean isForward() {
return false;
}
@Override
ReachingUses createEntryLattice() {
return new ReachingUses();
}
@Override
ReachingUses createInitialEstimateLattice() {
return new ReachingUses();
}
@Override
ReachingUses flowThrough(Node n, ReachingUses input) {
ReachingUses output = new ReachingUses(input);
// If there's an ON_EX edge, this cfgNode may or may not get executed.
// We can express this concisely by just pretending this happens in
// a conditional.
boolean conditional = hasExceptionHandler(n);
computeMayUse(n, n, output, conditional);
return output;
}
private boolean hasExceptionHandler(Node cfgNode) {
List<DiGraphEdge<Node, Branch>> branchEdges = getCfg().getOutEdges(cfgNode);
for (DiGraphEdge<Node, Branch> edge : branchEdges) {
if (edge.getValue() == Branch.ON_EX) {
return true;
}
}
return false;
}
private void computeMayUse(
Node n, Node cfgNode, ReachingUses output, boolean conditional) {
switch (n.getType()) {
case Token.BLOCK:
case Token.FUNCTION:
return;
case Token.NAME:
addToUseIfLocal(n.getString(), cfgNode, output);
return;
case Token.WHILE:
case Token.DO:
case Token.IF:
computeMayUse(
NodeUtil.getConditionExpression(n), cfgNode, output, conditional);
return;
case Token.FOR:
if (!NodeUtil.isForIn(n)) {
computeMayUse(
NodeUtil.getConditionExpression(n), cfgNode, output, conditional);
} else {
// for(x in y) {...}
Node lhs = n.getFirstChild();
Node rhs = lhs.getNext();
if (lhs.isVar()) {
lhs = lhs.getLastChild(); // for(var x in y) {...}
}
if (lhs.isName() && !conditional) {
removeFromUseIfLocal(lhs.getString(), output);
}
computeMayUse(rhs, cfgNode, output, conditional);
}
return;
case Token.AND:
case Token.OR:
computeMayUse(n.getLastChild(), cfgNode, output, true);
computeMayUse(n.getFirstChild(), cfgNode, output, conditional);
return;
case Token.HOOK:
computeMayUse(n.getLastChild(), cfgNode, output, true);
computeMayUse(n.getFirstChild().getNext(), cfgNode, output, true);
computeMayUse(n.getFirstChild(), cfgNode, output, conditional);
return;
case Token.VAR:
Node varName = n.getFirstChild();
Preconditions.checkState(n.hasChildren(), "AST should be normalized");
if (varName.hasChildren()) {
computeMayUse(varName.getFirstChild(), cfgNode, output, conditional);
if (!conditional) {
removeFromUseIfLocal(varName.getString(), output);
}
}
return;
default:
if (NodeUtil.isAssignmentOp(n) && n.getFirstChild().isName()) {
Node name = n.getFirstChild();
if (!conditional) {
removeFromUseIfLocal(name.getString(), output);
}
// In case of a += "Hello". There is a read of a.
if (!n.isAssign()) {
addToUseIfLocal(name.getString(), cfgNode, output);
}
computeMayUse(name.getNext(), cfgNode, output, conditional);
} else {
/*
* We want to traverse in reverse order because we want the LAST
* definition in the sub-tree....
* But we have no better way to traverse in reverse other :'(
*/
for (Node c = n.getLastChild(); c != null; c = n.getChildBefore(c)) {
computeMayUse(c, cfgNode, output, conditional);
}
}
}
}
/**
* Sets the variable for the given name to the node value in the upward
* exposed lattice. Do nothing if the variable name is one of the escaped
* variable.
*/
private void addToUseIfLocal(String name, Node node, ReachingUses use) {
Var var = jsScope.getVar(name);
if (var == null || var.scope != jsScope) {
return;
}
if (!escaped.contains(var)) {
use.mayUseMap.put(var, node);
}
}
/**
* Removes the variable for the given name from the node value in the upward
* exposed lattice. Do nothing if the variable name is one of the escaped
* variable.
*/
private void removeFromUseIfLocal(String name, ReachingUses use) {
Var var = jsScope.getVar(name);
if (var == null || var.scope != jsScope) {
return;
}
if (!escaped.contains(var)) {
use.mayUseMap.removeAll(var);
}
}
/**
* Gets a list of nodes that may be using the value assigned to {@code name}
* in {@code defNode}. {@code defNode} must be one of the control flow graph
* nodes.
*
* @param name name of the variable. It can only be names of local variable
* that are not function parameters, escaped variables or variables
* declared in catch.
* @param defNode The list of upward exposed use for the variable.
*/
Collection<Node> getUses(String name, Node defNode) {
GraphNode<Node, Branch> n = getCfg().getNode(defNode);
Preconditions.checkNotNull(n);
FlowState<ReachingUses> state = n.getAnnotation();
return state.getOut().mayUseMap.get(jsScope.getVar(name));
}
}