com.google.javascript.jscomp.MustBeReachingVariableDef Maven / Gradle / Ivy
/*
* Copyright 2008 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 static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkState;
import com.google.javascript.jscomp.ControlFlowGraph.AbstractCfgNodeTraversalCallback;
import com.google.javascript.jscomp.ControlFlowGraph.Branch;
import com.google.javascript.jscomp.graph.GraphNode;
import com.google.javascript.jscomp.graph.LatticeElement;
import com.google.javascript.rhino.Node;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import javax.annotation.Nullable;
/**
* Computes must-be-reaching definition for all uses of each variable.
*
* A definition of {@code A} in {@code A = foo()} is a must-be-reaching definition of the use of
* {@code A} in {@code alert(A)} if all paths from entry node to the use pass through that
* definition and it is the last definition before the use.
*
*
By definition, a must-be-reaching definition for a given use is always a single definition and
* it "dominates" that use (i.e. always must execute before that use).
*/
final class MustBeReachingVariableDef
extends DataFlowAnalysis {
// The scope of the function that we are analyzing.
private final AbstractCompiler compiler;
private final Set escaped;
private final Map allVarsInFn;
MustBeReachingVariableDef(
ControlFlowGraph cfg,
AbstractCompiler compiler,
Set escaped,
Map allVarsInFn) {
super(cfg, new MustDefJoin());
this.compiler = compiler;
this.escaped = escaped;
this.allVarsInFn = allVarsInFn;
}
/**
* Abstraction of a local variable definition. It represents the node which
* a local variable is defined as well as a set of other local variables that
* this definition reads from. For example N: a = b + foo.bar(c). The
* definition node will be N, the depending set would be {b,c}.
*/
static class Definition {
final Node node;
final Set depends = new HashSet<>();
private boolean unknownDependencies = false;
Definition(Node node) {
this.node = node;
}
@Override
public boolean equals(Object other) {
if (!(other instanceof Definition)) {
return false;
}
Definition otherDef = (Definition) other;
// If the var has the same definition node we can assume they have the
// same depends set.
return otherDef.node == node;
}
@Override
public String toString() {
return "Definition@" + node;
}
@Override
public int hashCode() {
return node.hashCode();
}
}
/**
* Must reaching definition lattice representation. It captures a product
* lattice for each local (non-escaped) variable. The sub-lattice is
* a n + 2 element lattice with all the {@link Definition} in the program,
* TOP and BOTTOM.
*
* Since this is a Must-Define analysis, BOTTOM represents the case where
* there might be more than one reaching definition for the variable.
*
*
* (TOP)
* / | | \
* N1 N2 N3 ....Nn
* \ | | /
* (BOTTOM)
*
*/
static final class MustDef implements LatticeElement {
// TODO(user): Use bit vector instead of maps might get better
// performance. Change it after this is tested to be fully functional.
// When a Var "A" = "TOP", "A" does not exist in reachingDef's keySet.
// When a Var "A" = Node N, "A" maps to that node.
// When a Var "A" = "BOTTOM", "A" maps to null.
final Map reachingDef;
public MustDef() {
reachingDef = new HashMap<>();
}
public MustDef(Collection vars) {
this();
for (Var var : vars) {
reachingDef.put(var, new Definition(var.getScope().getRootNode()));
}
}
/**
* Copy constructor.
*
* @param other The constructed object is a replicated copy of this element.
*/
public MustDef(MustDef other) {
reachingDef = new HashMap<>(other.reachingDef);
}
@Override
public boolean equals(Object other) {
return (other instanceof MustDef) && ((MustDef) other).reachingDef.equals(this.reachingDef);
}
@Override
public int hashCode() {
return reachingDef.hashCode();
}
}
private static class MustDefJoin extends JoinOp.BinaryJoinOp {
@Override
public MustDef apply(MustDef a, MustDef b) {
MustDef result = new MustDef();
Map resultMap = result.reachingDef;
// Take the join of all variables that are not TOP in this.
for (Map.Entry varEntry : a.reachingDef.entrySet()) {
Var var = varEntry.getKey();
Definition aDef = varEntry.getValue();
if (aDef == null) {
// "a" is BOTTOM implies that the variable has more than one possible
// definition. We set the join of this to be BOTTOM regardless of what
// "b" might be.
resultMap.put(var, null);
continue;
}
if (b.reachingDef.containsKey(var)) {
Definition bDef = b.reachingDef.get(var);
if (aDef.equals(bDef)) {
resultMap.put(var, aDef);
} else {
resultMap.put(var, null);
}
} else {
resultMap.put(var, aDef);
}
}
// Take the join of all variables that are not TOP in other but it is TOP
// in this.
for (Map.Entry entry : b.reachingDef.entrySet()) {
Var var = entry.getKey();
if (!a.reachingDef.containsKey(var)) {
resultMap.put(var, entry.getValue());
}
}
return result;
}
}
@Override
boolean isForward() {
return true;
}
@Override
MustDef createEntryLattice() {
return new MustDef(allVarsInFn.values());
}
@Override
MustDef createInitialEstimateLattice() {
return new MustDef();
}
@Override
MustDef flowThrough(Node n, MustDef input) {
// TODO(user): We are doing a straight copy from input to output. There
// might be some opportunities to cut down overhead.
MustDef output = new MustDef(input);
// TODO(user): This must know about ON_EX edges but it should handle
// it better than what we did in liveness. Because we are in a forward mode,
// we can used the branched forward analysis.
computeMustDef(n, n, output, false);
return output;
}
/**
* @param n The node in question.
* @param cfgNode The node to add
* @param conditional true if the definition is not always executed.
*/
private void computeMustDef(
Node n, Node cfgNode, MustDef output, boolean conditional) {
switch (n.getToken()) {
case BLOCK:
case ROOT:
case FUNCTION:
return;
case WHILE:
case DO:
case IF:
case FOR:
computeMustDef(
NodeUtil.getConditionExpression(n), cfgNode, output, conditional);
return;
case FOR_IN:
case FOR_OF:
case FOR_AWAIT_OF:
// for(x in y) {...}
Node lhs = n.getFirstChild();
Node rhs = lhs.getNext();
if (NodeUtil.isNameDeclaration(lhs)) {
lhs = lhs.getLastChild(); // for(var x in y) {...}
}
if (lhs.isName()) {
// TODO(lharker): This doesn't seem right - given for (x in y), the value set to x isn't y
addToDefIfLocal(lhs.getString(), cfgNode, rhs, output);
} else if (lhs.isDestructuringLhs()) {
lhs = lhs.getFirstChild();
}
if (lhs.isDestructuringPattern()) {
computeMustDef(lhs, cfgNode, output, true);
}
return;
case OPTCHAIN_GETPROP:
computeMustDef(n.getFirstChild(), cfgNode, output, conditional);
return;
case AND:
case OR:
case COALESCE:
case OPTCHAIN_GETELEM:
computeMustDef(n.getFirstChild(), cfgNode, output, conditional);
computeMustDef(n.getLastChild(), cfgNode, output, true);
return;
case OPTCHAIN_CALL:
computeMustDef(n.getFirstChild(), cfgNode, output, conditional);
for (Node c = n.getSecondChild(); c != null; c = c.getNext()) {
computeMustDef(c, cfgNode, output, true);
}
return;
case HOOK:
computeMustDef(n.getFirstChild(), cfgNode, output, conditional);
computeMustDef(n.getSecondChild(), cfgNode, output, true);
computeMustDef(n.getLastChild(), cfgNode, output, true);
return;
case LET:
case CONST:
case VAR:
for (Node c = n.getFirstChild(); c != null; c = c.getNext()) {
if (c.hasChildren()) {
if (c.isName()) {
computeMustDef(c.getFirstChild(), cfgNode, output, conditional);
addToDefIfLocal(c.getString(), conditional ? null : cfgNode,
c.getFirstChild(), output);
} else {
checkState(c.isDestructuringLhs(), c);
computeMustDef(c.getSecondChild(), cfgNode, output, conditional);
computeMustDef(c.getFirstChild(), cfgNode, output, conditional);
}
}
}
return;
case DEFAULT_VALUE:
if (n.getFirstChild().isDestructuringPattern()) {
computeMustDef(n.getSecondChild(), cfgNode, output, true);
computeMustDef(n.getFirstChild(), cfgNode, output, conditional);
} else if (n.getFirstChild().isName()) {
computeMustDef(n.getSecondChild(), cfgNode, output, true);
addToDefIfLocal(
n.getFirstChild().getString(), conditional ? null : cfgNode, null, output);
} else {
computeMustDef(n.getFirstChild(), cfgNode, output, conditional);
computeMustDef(n.getSecondChild(), cfgNode, output, true);
}
break;
case NAME:
if (NodeUtil.isLhsByDestructuring(n)) {
addToDefIfLocal(n.getString(), conditional ? null : cfgNode, null, output);
} else if ("arguments".equals(n.getString())) {
escapeParameters(output);
}
return;
default:
if (NodeUtil.isAssignmentOp(n)) {
if (n.getFirstChild().isName()) {
Node name = n.getFirstChild();
computeMustDef(name.getNext(), cfgNode, output, conditional);
addToDefIfLocal(
name.getString(), conditional ? null : cfgNode, n.getLastChild(), output);
return;
} else if (NodeUtil.isNormalGet(n.getFirstChild())) {
// Treat all assignments to arguments as redefining the
// parameters itself.
Node obj = n.getFirstFirstChild();
if (obj.isName() && "arguments".equals(obj.getString())) {
// TODO(user): More accuracy can be introduced
// i.e. We know exactly what arguments[x] is if x is a constant
// number.
escapeParameters(output);
}
} else if (n.getFirstChild().isDestructuringPattern()) {
computeMustDef(n.getSecondChild(), cfgNode, output, conditional);
computeMustDef(n.getFirstChild(), cfgNode, output, conditional);
return;
}
}
// DEC and INC actually defines the variable.
if (n.isDec() || n.isInc()) {
Node target = n.getFirstChild();
if (target.isName()) {
addToDefIfLocal(target.getString(), conditional ? null : cfgNode, null, output);
return;
}
}
for (Node c = n.getFirstChild(); c != null; c = c.getNext()) {
computeMustDef(c, cfgNode, output, conditional);
}
}
}
/**
* Set the variable lattice for the given name to the node value in the def
* lattice. Do nothing if the variable name is one of the escaped variable.
*
* @param node The CFG node where the definition should be record to.
* {@code null} if this is a conditional define.
*/
private void addToDefIfLocal(String name, @Nullable Node node,
@Nullable Node rValue, MustDef def) {
Var var = allVarsInFn.get(name);
// var might be null if the variable is defined in the externs
if (var == null) {
return;
}
for (Var other : def.reachingDef.keySet()) {
Definition otherDef = def.reachingDef.get(other);
if (otherDef == null) {
continue;
}
if (otherDef.depends.contains(var)) {
def.reachingDef.put(other, null);
}
}
if (!escaped.contains(var)) {
if (node == null) {
def.reachingDef.put(var, null);
} else {
Definition definition = new Definition(node);
if (rValue != null) {
computeDependence(definition, rValue);
}
def.reachingDef.put(var, definition);
}
}
}
private void escapeParameters(MustDef output) {
for (Var v : allVarsInFn.values()) {
if (isParameter(v)) {
// Assume we no longer know where the parameter comes from
// anymore.
output.reachingDef.put(v, null);
}
}
// Also, assume we no longer know anything that depends on a parameter.
for (Entry pair : output.reachingDef.entrySet()) {
Definition value = pair.getValue();
if (value == null) {
continue;
}
for (Var dep : value.depends) {
if (isParameter(dep)) {
output.reachingDef.put(pair.getKey(), null);
}
}
}
}
private static boolean isParameter(Var v) {
return v.isParam();
}
/**
* Computes all the local variables that rValue reads from and store that
* in the def's depends set.
*/
private void computeDependence(final Definition def, Node rValue) {
NodeTraversal.traverse(
compiler,
rValue,
new AbstractCfgNodeTraversalCallback() {
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
if (n.isName()) {
Var dep = allVarsInFn.get(n.getString());
if (dep == null) {
def.unknownDependencies = true;
} else {
def.depends.add(dep);
}
}
}
});
}
/**
* Gets the must-be-reaching definition of a given use node.
*
* @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 useNode the location of the use where the definition reaches.
*/
Definition getDef(String name, Node useNode) {
checkArgument(getCfg().hasNode(useNode));
GraphNode n = getCfg().getNode(useNode);
FlowState state = n.getAnnotation();
return state.getIn().reachingDef.get(allVarsInFn.get(name));
}
Node getDefNode(String name, Node useNode) {
Definition def = getDef(name, useNode);
return def == null ? null : def.node;
}
boolean dependsOnOuterScopeVars(Definition def) {
if (def.unknownDependencies) {
return true;
}
for (Var s : def.depends) {
// Don't inline try catch
if (s.getScope().isCatchScope()) {
return true;
}
}
return false;
}
}