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/*
* Copyright 2009 Google Inc.
*
* 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.gwt.dev.js;
import com.google.gwt.dev.js.ast.JsBlock;
import com.google.gwt.dev.js.ast.JsContext;
import com.google.gwt.dev.js.ast.JsFunction;
import com.google.gwt.dev.js.ast.JsInvocation;
import com.google.gwt.dev.js.ast.JsModVisitor;
import com.google.gwt.dev.js.ast.JsName;
import com.google.gwt.dev.js.ast.JsNameOf;
import com.google.gwt.dev.js.ast.JsNameRef;
import com.google.gwt.dev.js.ast.JsProgram;
import com.google.gwt.dev.js.ast.JsVisitor;
import com.google.gwt.dev.util.collect.IdentityHashSet;
import java.util.HashMap;
import java.util.IdentityHashMap;
import java.util.Map;
import java.util.Set;
import java.util.Stack;
/**
* Replace references to functions which have post-obfuscation duplicate bodies
* by reference to a canonical one. Intended to run only when stack trace
* stripping is enabled.
*/
public class JsDuplicateFunctionRemover {
private class DuplicateFunctionBodyRecorder extends JsVisitor {
private final Set dontReplace = new IdentityHashSet();
private final Map duplicateOriginalMap = new IdentityHashMap();
private final Map duplicateMethodOriginalMap = new IdentityHashMap();
private final Stack invocationQualifiers = new Stack();
// static / global methods
private final Map uniqueBodies = new HashMap();
// vtable methods
private final Map uniqueMethodBodies = new HashMap();
public DuplicateFunctionBodyRecorder() {
// Add sentinel to stop Stack.peek() from throwing exception.
invocationQualifiers.add(null);
}
@Override
public void endVisit(JsInvocation x, JsContext ctx) {
if (x.getQualifier() instanceof JsNameRef) {
invocationQualifiers.pop();
}
}
@Override
public void endVisit(JsNameOf x, JsContext ctx) {
dontReplace.add(x.getName());
}
@Override
public void endVisit(JsNameRef x, JsContext ctx) {
if (x != invocationQualifiers.peek()) {
if (x.getName() != null) {
dontReplace.add(x.getName());
}
}
}
public Set getBlacklist() {
return dontReplace;
}
public Map getDuplicateMap() {
return duplicateOriginalMap;
}
public Map getDuplicateMethodMap() {
return duplicateMethodOriginalMap;
}
@Override
public boolean visit(JsFunction x, JsContext ctx) {
String fnSource = x.toSource();
String body = fnSource.substring(fnSource.indexOf("("));
/*
* Static function processed separate from virtual functions
*/
if (x.getName() != null) {
JsName original = uniqueBodies.get(body);
if (original != null) {
duplicateOriginalMap.put(x.getName(), original);
} else {
uniqueBodies.put(body, x.getName());
}
} else if (x.isFromJava()) {
JsFunction original = uniqueMethodBodies.get(body);
if (original != null) {
duplicateMethodOriginalMap.put(x, original);
} else {
uniqueMethodBodies.put(body, x);
}
}
return true;
}
@Override
public boolean visit(JsInvocation x, JsContext ctx) {
if (x.getQualifier() instanceof JsNameRef) {
invocationQualifiers.push((JsNameRef) x.getQualifier());
}
return true;
}
}
private class ReplaceDuplicateInvocationNameRefs extends JsModVisitor {
private final Set blacklist;
private final Map dupMethodMap;
private final Map hoistMap;
private final Map duplicateMap;
public ReplaceDuplicateInvocationNameRefs(Map duplicateMap,
Set blacklist, Map dupMethodMap,
Map hoistMap) {
this.duplicateMap = duplicateMap;
this.blacklist = blacklist;
this.dupMethodMap = dupMethodMap;
this.hoistMap = hoistMap;
}
@Override
public void endVisit(JsFunction x, JsContext ctx) {
if (dupMethodMap.containsKey(x)) {
ctx.replaceMe(hoistMap.get(dupMethodMap.get(x)).makeRef(x.getSourceInfo()));
} else if (hoistMap.containsKey(x)) {
ctx.replaceMe(hoistMap.get(x).makeRef(x.getSourceInfo()));
}
}
@Override
public void endVisit(JsNameRef x, JsContext ctx) {
JsName orig = duplicateMap.get(x.getName());
if (orig != null && x.getName() != null
&& x.getName().getEnclosing() == program.getScope()
&& !blacklist.contains(x.getName()) && !blacklist.contains(orig)) {
ctx.replaceMe(orig.makeRef(x.getSourceInfo()));
}
}
}
/**
* Entry point for the removeDuplicateFunctions optimization.
*
* This optimization will collapse functions whose JavaScript (output) code is identical. After
* collapsing duplicate functions it will remove functions that become unreferenced as a result.
*
* This pass is safe only for JavaScript functions generated from Java where references to
* local function variables can not be extruded by returning a function. E,g. in the next example
*
* function f1() {return a;}
*
* funcion f2() { var a; return function() {return a;}}
*
* f1() and the return of f2() are not duplicates even though the have a syntacticaly identical
* parameters and body. The reason is that a in f1() refers to some globally scoped variable a,
* whereas a in the return of f2() refers to the local variable a. It would be not correct to
* move the return of f2() to the global scope.
*
* This situation does NOT arise from functions that where generated from Java sources (non
* native)
*
* IMPORTANT NOTE: It is NOT safe to rename JsNames after this pass is performed. E.g.
*
* Consider an output JavaScript for two unrelated classes:
* defineSeed(...) //class A
* _.a
* _.m1 = function() { return this.a; }
*
* defineSeed(...) // class B
* _.a
* _.m2 = function() { return this.a; }
*
* Here m1() in class A and m2 in class B have identical parameters and bodies; hence the result
* will be
*
* defineSeed(...) //class A
* _.a
* _.m1 = g1
*
* defineSeed(...) // class B
* _.a
* _.m2 = g1
*
* function g1() { return this.a; }
*
* The reference to this.a in g1 will be to either A.a or B.a and as long as those names remain
* the same the removal was correct. However if A.a gets renamed then A.m1() and B.m2() would
* no longer have been identical hence the dedup that is already done is incorrect.
*
* @param program the program to optimize
* @param nameGenerator a freshNameGenerator to assign fresh names to deduped functions that are
* lifted to the global scope
* @return {@code true} if it made any changes; {@code false} otherwise.
*/
public static boolean exec(JsProgram program, FreshNameGenerator nameGenerator) {
return new JsDuplicateFunctionRemover(program, nameGenerator).execImpl();
}
private final JsProgram program;
/**
* A FreshNameGenerator instance to obtain fresh top scope names consistent with the
* naming strategy used.
*/
private FreshNameGenerator freshNameGenerator;
public JsDuplicateFunctionRemover(JsProgram program, FreshNameGenerator freshNameGenerator) {
this.program = program;
this.freshNameGenerator = freshNameGenerator;
}
private boolean execImpl() {
boolean changed = false;
for (int i = 0; i < program.getFragmentCount(); i++) {
JsBlock fragment = program.getFragmentBlock(i);
DuplicateFunctionBodyRecorder dfbr = new DuplicateFunctionBodyRecorder();
dfbr.accept(fragment);
Map newNamesByHoistedFunction = new HashMap();
// Hoist all anonymous duplicate functions.
Map dupMethodMap = dfbr.getDuplicateMethodMap();
for (JsFunction dupMethod : dupMethodMap.values()) {
if (newNamesByHoistedFunction.containsKey(dupMethod)) {
continue;
}
// move function to top scope and re-declaring it with a unique name
JsName newName = program.getScope().declareName(freshNameGenerator.getFreshName());
JsFunction newFunc = new JsFunction(dupMethod.getSourceInfo(),
program.getScope(), newName, dupMethod.isFromJava());
// we're not using the old function anymore, we can use reuse the body
// instead of cloning it
newFunc.setBody(dupMethod.getBody());
// also copy the parameters from the old function
newFunc.getParameters().addAll(dupMethod.getParameters());
// add the new function to the top level list of statements
fragment.getStatements().add(newFunc.makeStmt());
newNamesByHoistedFunction.put(dupMethod, newName);
}
ReplaceDuplicateInvocationNameRefs rdup = new ReplaceDuplicateInvocationNameRefs(
dfbr.getDuplicateMap(), dfbr.getBlacklist(), dupMethodMap, newNamesByHoistedFunction);
rdup.accept(fragment);
changed = changed || rdup.didChange();
}
if (changed) {
JsUnusedFunctionRemover.exec(program);
}
return changed;
}
}
