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/*
* 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 static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSortedMap;
import com.google.javascript.jscomp.NodeTraversal.ScopedCallback;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Deque;
import java.util.List;
import javax.annotation.Nullable;
/**
* Optimization for functions that have {@code var_args} or access the
* arguments array.
*
* Example:
*
* function() { alert(arguments[0] + argument[1]) }
*
* to:
*
* function(a, b) { alert(a, b) }
*
*
* Each newly inserted variable name will be unique very much like the output
* of the AST found after the {@link Normalize} pass.
*/
class OptimizeArgumentsArray implements CompilerPass, ScopedCallback {
// The arguments object as described by ECMAScript version 3 section 10.1.8
private static final String ARGUMENTS = "arguments";
// To ensure that the newly introduced parameter names are unique. We will
// use this string as prefix unless the caller specifies a different prefix.
private static final String PARAMETER_PREFIX = "JSCompiler_OptimizeArgumentsArray_p";
// The prefix for the newly introduced parameter name.
private final String paramPrefix;
// To make each parameter name unique in the function we append a unique integer.
private int uniqueId = 0;
// Reference to the compiler object to notify any changes to source code AST.
private final AbstractCompiler compiler;
// A stack of arguments access list to the corresponding outer functions.
private final Deque> argumentsAccessStack = new ArrayDeque<>();
// The `arguments` access in the current scope.
//
// The elements are NAME nodes. This initial value is a error-detecting sentinel for the global
// scope, which is used because since `ArrayDeque` is null-hostile.
private List currentArgumentsAccesses = ImmutableList.of();
/**
* Construct this pass and use {@link #PARAMETER_PREFIX} as the prefix for
* all parameter names that it introduces.
*/
OptimizeArgumentsArray(AbstractCompiler compiler) {
this(compiler, PARAMETER_PREFIX);
}
/**
* @param paramPrefix the prefix to use for all parameter names that this
* pass introduces
*/
OptimizeArgumentsArray(AbstractCompiler compiler, String paramPrefix) {
this.compiler = checkNotNull(compiler);
this.paramPrefix = checkNotNull(paramPrefix);
}
@Override
public void process(Node externs, Node root) {
NodeTraversal.traverse(compiler, checkNotNull(root), this);
}
@Override
public void enterScope(NodeTraversal traversal) {
if (!definesArgumentsVar(traversal.getScopeRoot())) {
return;
}
// Introduces a new access list and stores the access list of the outer scope.
argumentsAccessStack.push(currentArgumentsAccesses);
currentArgumentsAccesses = new ArrayList<>();
}
@Override
public void exitScope(NodeTraversal traversal) {
if (!definesArgumentsVar(traversal.getScopeRoot())) {
return;
}
// Attempt to replace the argument access and if the AST has been change,
// report back to the compiler.
tryReplaceArguments(traversal.getScope());
currentArgumentsAccesses = argumentsAccessStack.pop();
}
private static boolean definesArgumentsVar(Node root) {
return root.isFunction() && !root.isArrowFunction();
}
@Override
public boolean shouldTraverse(NodeTraversal unused0, Node unused1, Node unused2) {
return true;
}
@Override
public void visit(NodeTraversal traversal, Node node, Node parent) {
if (traversal.inGlobalHoistScope()) {
return; // Do no rewriting in the global scope.
}
if (node.isName() && ARGUMENTS.equals(node.getString())) {
currentArgumentsAccesses.add(node); // Record all potential references to the arguments array.
}
}
/**
* Tries to optimize all the arguments array access in this scope by assigning a name to each
* element.
*
* @param scope scope of the function
*/
private void tryReplaceArguments(Scope scope) {
// Find the number of parameters that can be accessed without using `arguments`.
Node parametersList = NodeUtil.getFunctionParameters(scope.getRootNode());
checkState(parametersList.isParamList(), parametersList);
int numParameters = parametersList.getChildCount();
// Determine the highest index that is used to make an access on `arguments`. By default, assume
// that the value is the number of parameters to the function.
int highestIndex = getHighestIndex(numParameters - 1);
if (highestIndex < 0) {
return;
}
ImmutableSortedMap argNames =
assembleParamNames(parametersList, highestIndex + 1);
changeMethodSignature(argNames, parametersList);
changeBody(argNames);
}
/**
* Iterate through all the references to arguments array in the
* function to determine the real highestIndex. Returns -1 when we should not
* be replacing any arguments for this scope - we should exit tryReplaceArguments
*
* @param highestIndex highest index that has been accessed from the arguments array
*/
private int getHighestIndex(int highestIndex) {
for (Node ref : currentArgumentsAccesses) {
Node getElem = ref.getParent();
// Bail on anything but argument[c] access where c is a constant.
// TODO(user): We might not need to bail out all the time, there might
// be more cases that we can cover.
if (!getElem.isGetElem() || ref != getElem.getFirstChild()) {
return -1;
}
Node index = ref.getNext();
// We have something like arguments[x] where x is not a constant. That
// means at least one of the access is not known.
if (!index.isNumber() || index.getDouble() < 0) {
// TODO(user): Its possible not to give up just yet. The type
// inference did a 'semi value propagation'. If we know that string
// is never a subclass of the type of the index. We'd know that
// it is never 'callee'.
return -1; // Give up.
}
//We want to bail out if someone tries to access arguments[0.5] for example
if (index.getDouble() != Math.floor(index.getDouble())){
return -1;
}
Node getElemParent = getElem.getParent();
// When we have argument[0](), replacing it with a() is semantically
// different if argument[0] is a function call that refers to 'this'
if (getElemParent.isCall() && getElemParent.getFirstChild() == getElem) {
// TODO(user): We can consider using .call() if aliasing that
// argument allows shorter alias for other arguments.
return -1;
}
// Replace the highest index if we see an access that has a higher index
// than all the one we saw before.
int value = (int) index.getDouble();
if (value > highestIndex) {
highestIndex = value;
}
}
return highestIndex;
}
/**
* Inserts new formal parameters into the method's signature based on the given set of names.
*
* Example: function() --> function(r0, r1, r2)
*
* @param argNames maps param index to param name, if the param with that index has a name.
* @param paramList node representing the function signature
*/
private void changeMethodSignature(ImmutableSortedMap argNames, Node paramList) {
ImmutableSortedMap newParams = argNames.tailMap(paramList.getChildCount());
for (String name : newParams.values()) {
paramList.addChildToBack(IR.name(name).useSourceInfoIfMissingFrom(paramList));
}
if (!newParams.isEmpty()) {
compiler.reportChangeToEnclosingScope(paramList);
}
}
/**
* Performs the replacement of arguments[x] -> a if x is known.
*
* @param argNames maps param index to param name, if the param with that index has a name.
*/
private void changeBody(ImmutableMap argNames) {
for (Node ref : currentArgumentsAccesses) {
Node index = ref.getNext();
Node parent = ref.getParent();
int value = (int) index.getDouble(); // This was validated earlier.
@Nullable String name = argNames.get(value);
if (name == null) {
continue;
}
Node newName = IR.name(name).useSourceInfoIfMissingFrom(parent);
parent.replaceWith(newName);
// TODO(nickreid): See if we can do this fewer times. The accesses may be in different scopes.
compiler.reportChangeToEnclosingScope(newName);
}
}
/**
* Generates a {@link Map} from argument indices to parameter names.
*
* A {@link Map} is used because the sequence may be sparse in the case that there is an
* anonymous param, such as a destructuring param. There may also be fewer returned names than
* {@code maxCount} if there is a rest param, since no additional params may be synthesized.
*
* @param maxCount The maximum number of argument names in the returned map.
*/
private ImmutableSortedMap assembleParamNames(Node paramList, int maxCount) {
checkArgument(paramList.isParamList(), paramList);
ImmutableSortedMap.Builder builder = ImmutableSortedMap.naturalOrder();
int index = 0;
// Collect all existing param names first...
for (Node param = paramList.getFirstChild(); param != null; param = param.getNext()) {
switch (param.getToken()) {
case NAME:
builder.put(index, param.getString());
break;
case ITER_REST:
return builder.build();
case DEFAULT_VALUE:
// `arguments` doesn't consider default values. It holds exactly the provided args.
case OBJECT_PATTERN:
case ARRAY_PATTERN:
// Patterns have no names to substitute into the body.
break;
default:
throw new IllegalArgumentException(param.toString());
}
index++;
}
// ... then synthesize any additional param names.
for (; index < maxCount; index++) {
builder.put(index, paramPrefix + uniqueId++);
}
return builder.build();
}
}