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/*
* Copyright 2008 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.jjs.SourceInfo;
import com.google.gwt.dev.jjs.ast.JProgram;
import com.google.gwt.dev.js.ast.JsBinaryOperation;
import com.google.gwt.dev.js.ast.JsBlock;
import com.google.gwt.dev.js.ast.JsContext;
import com.google.gwt.dev.js.ast.JsModVisitor;
import com.google.gwt.dev.js.ast.JsName;
import com.google.gwt.dev.js.ast.JsNode;
import com.google.gwt.dev.js.ast.JsPostfixOperation;
import com.google.gwt.dev.js.ast.JsPrefixOperation;
import com.google.gwt.dev.js.ast.JsProgram;
import com.google.gwt.dev.js.ast.JsProgramFragment;
import com.google.gwt.dev.js.ast.JsPropertyInitializer;
import com.google.gwt.dev.js.ast.JsScope;
import com.google.gwt.dev.js.ast.JsStringLiteral;
import com.google.gwt.dev.js.ast.JsVars;
import com.google.gwt.dev.js.ast.JsVars.JsVar;
import com.google.gwt.dev.js.ast.JsVisitor;
import java.util.Collection;
import java.util.Comparator;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.SortedMap;
import java.util.SortedSet;
import java.util.TreeMap;
import java.util.TreeSet;
/**
* Interns conditionally either all String literals in a JsProgram, or Strings
* which exceed a certain usage count. Each unique String will be assigned to a
* variable in an appropriate program fragment and the JsStringLiteral will be
* replaced with a JsNameRef. This optimization is complete in a single pass,
* although it may be performed multiple times without duplicating the intern
* pool.
*/
public class JsStringInterner {
/**
* Counts occurences of each potentially internable String literal.
*/
private static class OccurenceCounter extends JsVisitor {
private Map occurenceMap = new HashMap();
public Map buildOccurenceMap() {
return occurenceMap;
}
/**
* Prevents 'fixing' an otherwise illegal operation.
*/
@Override
public boolean visit(JsBinaryOperation x, JsContext ctx) {
return !x.getOperator().isAssignment()
|| !(x.getArg1() instanceof JsStringLiteral);
}
/**
* Prevents 'fixing' an otherwise illegal operation.
*/
@Override
public boolean visit(JsPostfixOperation x, JsContext ctx) {
return !(x.getArg() instanceof JsStringLiteral);
}
/**
* Prevents 'fixing' an otherwise illegal operation.
*/
@Override
public boolean visit(JsPrefixOperation x, JsContext ctx) {
return !(x.getArg() instanceof JsStringLiteral);
}
/**
* We ignore property initializer labels in object literals, but do process
* the expression. This is because the LHS is always treated as a string,
* and never evaluated as an expression.
*/
@Override
public boolean visit(JsPropertyInitializer x, JsContext ctx) {
accept(x.getValueExpr());
return false;
}
/**
* Count occurences of String literal.
*/
@Override
public boolean visit(JsStringLiteral x, JsContext ctx) {
String literal = x.getValue();
Integer occurs = occurenceMap.get(literal);
if (occurs == null) {
occurs = 0;
}
occurenceMap.put(literal, ++occurs);
return false;
}
/**
* This prevents duplicating the intern pool by not traversing JsVar
* declarations that look like they were created by the interner.
*/
@Override
public boolean visit(JsVar x, JsContext ctx) {
return !(x.getName().getIdent().startsWith(PREFIX));
}
}
/**
* Replaces JsStringLiterals with JsNameRefs, creating new JsName allocations
* on the fly.
*/
private static class StringVisitor extends JsModVisitor {
/*
* Minimum number of times a string must occur to be interned.
*/
private static final Integer INTERN_THRESHOLD = Integer.parseInt(
System.getProperty("gwt.jjs.stringInternerThreshold", "2"));
/**
* The current fragment being visited.
*/
private int currentFragment = 0;
/**
* This map records which program fragment the variable for this JsName
* should be created in.
*/
private final SortedMap fragmentAssignment = new TreeMap(
LITERAL_COMPARATOR);
/**
* A counter used for assigning ids to Strings. Even though it's unlikely
* that someone would actually have two billion strings in their
* application, it doesn't hurt to think ahead.
*/
private long lastId = 0;
/**
* Count of # of occurences of each String literal, or null if
* count-sensitive interning is off.
*/
private Map occurenceMap;
/**
* Only used to get fragment load order so strings used in multiple
* fragments need only be downloaded once.
*/
private final JProgram program;
/**
* Records the scope in which the interned identifiers are declared.
*/
private final JsScope scope;
/**
* This is a TreeMap to ensure consistent iteration order, based on the
* lexicographical ordering of the string constant.
*/
private final SortedMap toCreate = new TreeMap(
LITERAL_COMPARATOR);
/**
* Constructor.
*
* @param scope specifies the scope in which the interned strings should be
* @param occurenceMap
*/
public StringVisitor(JProgram program, JsScope scope,
Map occurenceMap) {
this.program = program;
this.scope = scope;
this.occurenceMap = occurenceMap;
}
@Override
public void endVisit(JsProgramFragment x, JsContext ctx) {
currentFragment++;
}
/**
* Prevents 'fixing' an otherwise illegal operation.
*/
@Override
public boolean visit(JsBinaryOperation x, JsContext ctx) {
return !x.getOperator().isAssignment()
|| !(x.getArg1() instanceof JsStringLiteral);
}
/**
* Prevents 'fixing' an otherwise illegal operation.
*/
@Override
public boolean visit(JsPostfixOperation x, JsContext ctx) {
return !(x.getArg() instanceof JsStringLiteral);
}
/**
* Prevents 'fixing' an otherwise illegal operation.
*/
@Override
public boolean visit(JsPrefixOperation x, JsContext ctx) {
return !(x.getArg() instanceof JsStringLiteral);
}
/**
* We ignore property initializer labels in object literals, but do process
* the expression. This is because the LHS is always treated as a string,
* and never evaluated as an expression.
*/
@Override
public boolean visit(JsPropertyInitializer x, JsContext ctx) {
x.setValueExpr(accept(x.getValueExpr()));
return false;
}
/**
* Replace JsStringLiteral instances with JsNameRefs.
*/
@Override
public boolean visit(JsStringLiteral x, JsContext ctx) {
if (occurenceMap != null) {
Integer occurences = occurenceMap.get(x.getValue());
assert occurences != null;
if (occurences < INTERN_THRESHOLD) {
return false;
}
}
JsName name = toCreate.get(x);
if (name == null) {
String ident = PREFIX + lastId++;
name = scope.declareName(ident);
toCreate.put(x, name);
}
Integer currentAssignment = fragmentAssignment.get(x);
if (currentAssignment == null) {
// Assign the JsName to the current program fragment
fragmentAssignment.put(x, currentFragment);
} else if (currentAssignment != currentFragment) {
// See if we need to move the assignment to a common ancestor
assert program != null : "JsStringInterner cannot be used with "
+ "fragmented JsProgram without an accompanying JProgram";
int newAssignment = program.lastFragmentLoadingBefore(currentFragment,
currentAssignment);
if (newAssignment != currentAssignment) {
// Assign the JsName to the common ancestor
fragmentAssignment.put(x, newAssignment);
}
}
ctx.replaceMe(name.makeRef(x.getSourceInfo().makeChild()));
return false;
}
/**
* This prevents duplicating the intern pool by not traversing JsVar
* declarations that look like they were created by the interner.
*/
@Override
public boolean visit(JsVar x, JsContext ctx) {
return !(x.getName().getIdent().startsWith(PREFIX));
}
}
public static final String PREFIX = "$intern_";
private static final Comparator LITERAL_COMPARATOR = new Comparator() {
public int compare(JsStringLiteral o1, JsStringLiteral o2) {
return o1.getValue().compareTo(o2.getValue());
}
};
/**
* Apply interning of String literals to a JsProgram. The symbol names for the
* interned strings will be defined within the program's top scope and the
* symbol declarations will be added as the first statement in the program's
* global block.
*
* @param jprogram the JProgram that has fragment dependency data for
* program
* @param program the JsProgram
* @param alwaysIntern true for browsers like IE which must always intern literals
* @return a map describing the interning that occurred
*/
public static Map exec(JProgram jprogram, JsProgram program,
boolean alwaysIntern) {
StringVisitor v = new StringVisitor(jprogram, program.getScope(), alwaysIntern ? null :
getOccurenceMap(program));
v.accept(program);
Map> bins = new HashMap>();
for (int i = 0, j = program.getFragmentCount(); i < j; i++) {
bins.put(i, new TreeSet(LITERAL_COMPARATOR));
}
for (Map.Entry entry : v.fragmentAssignment.entrySet()) {
SortedSet set = bins.get(entry.getValue());
assert set != null;
set.add(entry.getKey());
}
for (Map.Entry> entry : bins.entrySet()) {
createVars(program, program.getFragmentBlock(entry.getKey()),
entry.getValue(), v.toCreate);
}
return reverse(v.toCreate);
}
/**
* Intern String literals that occur within a JsBlock. The symbol declarations
* will be added as the first statement in the block.
*
* @param block the block to visit
* @param scope the JsScope in which to reserve the new identifiers
* @param alwaysIntern true for browsers like IE which must always intern literals
* @return true if any changes were made to the block
*/
public static boolean exec(JsProgram program, JsBlock block, JsScope scope,
boolean alwaysIntern) {
StringVisitor v = new StringVisitor(null, scope, alwaysIntern ? null :
getOccurenceMap(block));
v.accept(block);
createVars(program, block, v.toCreate.keySet(), v.toCreate);
return v.didChange();
}
/**
* Create variable declarations in block for literal strings
* toCreate using the variable map names.
*/
private static void createVars(JsProgram program, JsBlock block,
Collection toCreate, Map names) {
if (toCreate.size() > 0) {
// Create the pool of variable names.
SourceInfo sourceInfo = program.createSourceInfoSynthetic(JsStringInterner.class);
JsVars vars = new JsVars(sourceInfo);
for (JsStringLiteral literal : toCreate) {
JsVar var = new JsVar(sourceInfo, names.get(literal));
var.setInitExpr(literal);
vars.add(var);
}
block.getStatements().add(0, vars);
}
}
private static Map getOccurenceMap(JsNode node) {
OccurenceCounter oc = new OccurenceCounter();
oc.accept(node);
return oc.buildOccurenceMap();
}
private static Map reverse(
SortedMap toCreate) {
Map reversed = new LinkedHashMap(
toCreate.size());
for (Entry entry : toCreate.entrySet()) {
reversed.put(entry.getValue(), entry.getKey().getValue());
}
return reversed;
}
/**
* Utility class.
*/
private JsStringInterner() {
}
}
