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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.JsArrayLiteral;
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.JsLiteral;
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.JsNumberLiteral;
import com.google.gwt.dev.js.ast.JsObjectLiteral;
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.JsRegExp;
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 com.google.gwt.thirdparty.guava.common.base.Preconditions;
import com.google.gwt.thirdparty.guava.common.collect.HashMultiset;
import com.google.gwt.thirdparty.guava.common.collect.Maps;
import com.google.gwt.thirdparty.guava.common.collect.Multiset;
import com.google.gwt.thirdparty.guava.common.collect.Sets;
import java.util.Collection;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
/**
* Interns conditionally either all literals in a JsProgram, or literals
* which exceed a certain usage count. Each unique literal will be assigned to a
* variable in an appropriate program fragment and the JsLiteral will be
* replaced with a JsNameRef. This optimization is complete in a single pass,
*
* It is not safe to run the interner multiple times on the same tree as the names that are
* assigned to interned literals will collide.
*/
public class JsLiteralInterner {
/**
* Counts occurrences of each potentially internable literal.
*/
private static class OccurrenceCounterVisitor extends JsVisitor {
private Multiset countByLiteral = HashMultiset.create();
public Multiset getLiteralCounts() {
return countByLiteral;
}
/**
* Implement visit(Js*Literal,...) in a general way as there is no visit(JsLiteral, JsContext)
* to override in Js*Visitor.
*/
private boolean doVisitLiteral(JsLiteral x) {
if (x.isInternable()) {
countByLiteral.add(x);
// Literal was internable and counted, do not count its internal literals.
return false;
}
// The literal was not internable but might have some internable constants inside,
// so count them.
return true;
}
@Override
public boolean visit(JsBinaryOperation x, JsContext ctx) {
if (!hasLhsLiteral(x)) {
// Literal l-values should not arise from valid code, but they are excluded
// anyway so that errors are not masked away by interning.
accept(x.getArg1());
}
accept(x.getArg2());
return false;
}
/**
* Prevents 'fixing' an otherwise illegal operation.
*/
@Override
public boolean visit(JsPostfixOperation x, JsContext ctx) {
return !(x.getArg() instanceof JsLiteral);
}
/**
* Prevents 'fixing' an otherwise illegal operation.
*/
@Override
public boolean visit(JsPrefixOperation x, JsContext ctx) {
return !(x.getArg() instanceof JsLiteral);
}
/**
* 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) {
return doVisitLiteral(x);
}
/**
* Count occurences of Object literal.
*/
@Override
public boolean visit(JsObjectLiteral x, JsContext ctx) {
return doVisitLiteral(x);
}
@Override
public boolean visit(JsRegExp x, JsContext ctx) {
return doVisitLiteral(x);
}
@Override
public boolean visit(JsNumberLiteral x, JsContext ctx) {
return doVisitLiteral(x);
}
/**
* Count occurences of Array literal.
*/
@Override
public boolean visit(JsArrayLiteral x, JsContext ctx) {
return doVisitLiteral(x);
}
/**
* 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 internable JsLiterals with JsNameRefs, creating new JsName allocations
* on the fly.
*/
private static class LiteralInterningVisitor extends JsModVisitor {
/**
* The average length of an obfuscated id. It is OK to overestimate it.
*/
private static final int AVERAGE_ID_LENGTH = 3;
/**
* The number of characters needed to declare an interned literal. As there are many literals we
* only count the equal sign and the comma.
* It is OK to overestimate the overhead.
*/
private static final int INTERNED_LITERAL_DECLARATION_OVERHEAD = AVERAGE_ID_LENGTH + 2;
/*
* Minimum number of times a literal must occur to be interned.
*/
private static final Integer MINIMUM_NUMBER_OF_OCCURRENCES_TO_INTERN = Integer.parseInt(
System.getProperty("gwt.jjs.literalInternerThreshold", "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 Map fragmentAssignment = Maps.newLinkedHashMap();
/**
* A counter used for assigning ids to literals. Even though it's unlikely
* that someone would actually have two billion literals in their
* application, it doesn't hurt to think ahead.
*/
private long lastId = 0;
/**
* Count of # of occurences of each literal, or null if
* count-sensitive interning is off.
*/
private Multiset occurrencesPerLiteral;
/**
* Only used to get fragment load order so literals used in multiple
* fragments are placed in the right fragment.
*/
private final JProgram program;
/**
* Records the scope in which the interned identifiers are declared.
*/
private final JsScope scope;
/**
* Whether to intern all literals without considering occurrence count and profitability.
*/
private final boolean alwaysIntern;
/**
* Maps a literal to be interned to its interned variable name.
*/
private final Map variableNameForInternedLiteral = Maps.newLinkedHashMap();
/**
* This is a set of flags indicating what types of literals are to be interned.
*/
private final byte whatToIntern;
/**
* Constructor.
*
* @param scope specifies the scope in which the interned literals should be.
* @param alwaysIntern whether to intern all literals without considering occurrence count and
* profitability
* @param occurrencesPerLiteral a multiset representing the literal counts.
* @param whatToIntern what types of literals are to be interned.
*/
public LiteralInterningVisitor(JProgram program, JsScope scope, boolean alwaysIntern,
Multiset occurrencesPerLiteral, byte whatToIntern) {
assert alwaysIntern || (occurrencesPerLiteral != null);
this.program = program;
this.scope = scope;
this.occurrencesPerLiteral = occurrencesPerLiteral;
this.whatToIntern = whatToIntern;
this.alwaysIntern = alwaysIntern;
}
@Override
public void endVisit(JsProgramFragment x, JsContext ctx) {
currentFragment++;
}
/**
* Replace JsArrayLiteral instances with JsNameRefs.
*/
@Override
public boolean visit(JsArrayLiteral x, JsContext ctx) {
boolean interned = false;
if ((whatToIntern & INTERN_ARRAY_LITERALS) != 0) {
interned = maybeInternLiteral(x, ctx);
}
// If the array literal is interned do not try to intern any of its contents.
return !interned;
}
/**
* Prevents 'fixing' an otherwise illegal operation.
*/
@Override
public boolean visit(JsBinaryOperation x, JsContext ctx) {
if (!hasLhsLiteral(x)) {
// Literal l-values should not arise from valid code, but they are excluded
// anyway so that errors are not masked away by interning.
x.setArg1(accept(x.getArg1()));
}
x.setArg2(accept(x.getArg2()));
return false;
}
/**
* Prevents 'fixing' an otherwise illegal operation.
*/
@Override
public boolean visit(JsPostfixOperation x, JsContext ctx) {
return !(x.getArg() instanceof JsLiteral);
}
/**
* Prevents 'fixing' an otherwise illegal operation.
*/
@Override
public boolean visit(JsPrefixOperation x, JsContext ctx) {
return !(x.getArg() instanceof JsLiteral);
}
/**
* 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 ((whatToIntern & INTERN_STRINGS) != 0) {
maybeInternLiteral(x, ctx);
}
return false;
}
/**
* Replace JsObjectLiteral instances with JsNameRefs.
*/
@Override
public boolean visit(JsObjectLiteral x, JsContext ctx) {
boolean interned = false;
if ((whatToIntern & INTERN_OBJECT_LITERALS) != 0) {
interned = maybeInternLiteral(x, ctx);
}
// If the object literal is interned do not try to intern any of its contents.
return !interned;
}
/**
* Replace JsRegExp instances with JsNameRefs.
*/
@Override
public boolean visit(JsRegExp x, JsContext ctx) {
if ((whatToIntern & INTERN_REGEXES) != 0) {
maybeInternLiteral(x, ctx);
}
return false;
}
/**
* Replace JsNumberLiteral instances with JsNameRefs.
*/
@Override
public boolean visit(JsNumberLiteral x, JsContext ctx) {
if ((whatToIntern & INTERN_NUMBERS) != 0) {
maybeInternLiteral(x, ctx);
}
return false;
}
/**
* Returns true if interning {@code literal} will most likely reduce code size.
*/
private boolean isProfitableToIntern(JsLiteral literal, int occurrences) {
int literalSize = literal.toSource().length();
int internedSize = occurrences * AVERAGE_ID_LENGTH + INTERNED_LITERAL_DECLARATION_OVERHEAD +
literalSize;
int uninternedSize = occurrences * literalSize;
return internedSize < uninternedSize;
}
/**
* Interns a literal if deemed profitable or {@code alwaysIntern} is {@code true}.
*/
private boolean maybeInternLiteral(JsLiteral x, JsContext ctx) {
if (!x.isInternable()) {
return false;
}
if (!alwaysIntern) {
int occurrences = occurrencesPerLiteral.count(x);
if (occurrences < MINIMUM_NUMBER_OF_OCCURRENCES_TO_INTERN) {
return false;
}
boolean alreadyInterned = variableNameForInternedLiteral.containsKey(x);
if (!alreadyInterned && !isProfitableToIntern(x, occurrences)) {
return false;
}
}
JsName name = variableNameForInternedLiteral.get(x);
if (name == null) {
String ident = PREFIX + lastId++;
name = scope.declareName(ident);
variableNameForInternedLiteral.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
Preconditions.checkState(program != null, "JsLiteralInterner cannot be used with "
+ "fragmented JsProgram without an accompanying JProgram");
int newAssignment = program.getCommonAncestorFragmentId(currentAssignment, currentFragment);
if (newAssignment != currentAssignment) {
// Assign the JsName to the common ancestor.
fragmentAssignment.put(x, newAssignment);
}
}
ctx.replaceMe(name.makeRef(x.getSourceInfo().makeChild()));
return true;
}
/**
* 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));
}
}
/**
* Flags to control what type of literals to intern.
*/
public static final byte INTERN_ARRAY_LITERALS = 0x01;
public static final byte INTERN_NUMBERS = 0x02;
public static final byte INTERN_OBJECT_LITERALS = 0x04;
public static final byte INTERN_REGEXES = 0x08;
public static final byte INTERN_STRINGS = 0x10;
public static final byte INTERN_ALL = INTERN_ARRAY_LITERALS | INTERN_NUMBERS |
INTERN_OBJECT_LITERALS | INTERN_REGEXES | INTERN_STRINGS;
private static final String PREFIX = "$intern_";
/**
* Apply interning of literals to a JsProgram. The symbol names for the
* interned literals 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 {@code program}
* @param program the JsProgram
* @param whatToIntern a byte mask indicating what types of literals are interned.
* @return a map describing the interning that occurred
*/
public static Map exec(JProgram jprogram, JsProgram program,
byte whatToIntern) {
LiteralInterningVisitor v = new LiteralInterningVisitor(jprogram, program.getScope(), false,
computeOccurrenceCounts(program), whatToIntern);
v.accept(program);
Map> bins = Maps.newHashMap();
for (int i = 0, j = program.getFragmentCount(); i < j; i++) {
bins.put(i, Sets.newLinkedHashSet());
}
for (Map.Entry entry : v.fragmentAssignment.entrySet()) {
Set 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.variableNameForInternedLiteral);
}
return reverse(v.variableNameForInternedLiteral);
}
/**
* Intern 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 whether to intern all literals regardless of their occurrence count.
* @return {@code true} if any changes were made to the block.
*/
public static boolean exec(JsProgram program, JsBlock block, JsScope scope,
boolean alwaysIntern) {
Multiset occurrencesPerLiteral = null;
if (!alwaysIntern) {
occurrencesPerLiteral = computeOccurrenceCounts(block);
}
LiteralInterningVisitor v = new LiteralInterningVisitor(null, scope, alwaysIntern,
occurrencesPerLiteral, INTERN_ALL);
v.accept(block);
createVars(program, block, v.variableNameForInternedLiteral.keySet(),
v.variableNameForInternedLiteral);
return v.didChange();
}
/**
* Create variable declarations in {@code block} for literals
* {@code variableNameForInternedLiteral} using the variable map {@code 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(JsLiteralInterner.class);
JsVars vars = new JsVars(sourceInfo);
for (JsLiteral literal : toCreate) {
JsVar var = new JsVar(sourceInfo, names.get(literal));
var.setInitExpr(literal);
vars.add(var);
}
block.getStatements().add(0, vars);
}
}
private static Multiset computeOccurrenceCounts(JsNode node) {
OccurrenceCounterVisitor oc = new OccurrenceCounterVisitor();
oc.accept(node);
return oc.getLiteralCounts();
}
private static Map reverse(Map
variableNameForInternedLiteral) {
Map reversed = Maps.newLinkedHashMap();
for (Entry entry : variableNameForInternedLiteral.entrySet()) {
reversed.put(entry.getValue(), entry.getKey());
}
return reversed;
}
private static boolean hasLhsLiteral(JsBinaryOperation x) {
return x.getOperator().isAssignment()
&& (x.getArg1() instanceof JsLiteral);
}
/**
* Utility class.
*/
private JsLiteralInterner() {
}
}
