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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.jjs.impl;
import com.google.gwt.dev.jjs.InternalCompilerException;
import com.google.gwt.dev.jjs.SourceInfo;
import com.google.gwt.dev.jjs.ast.CanBeStatic;
import com.google.gwt.dev.jjs.ast.Context;
import com.google.gwt.dev.jjs.ast.HasEnclosingType;
import com.google.gwt.dev.jjs.ast.HasName;
import com.google.gwt.dev.jjs.ast.JArrayType;
import com.google.gwt.dev.jjs.ast.JBinaryOperation;
import com.google.gwt.dev.jjs.ast.JBinaryOperator;
import com.google.gwt.dev.jjs.ast.JClassType;
import com.google.gwt.dev.jjs.ast.JConstructor;
import com.google.gwt.dev.jjs.ast.JDeclarationStatement;
import com.google.gwt.dev.jjs.ast.JDeclaredType;
import com.google.gwt.dev.jjs.ast.JExpression;
import com.google.gwt.dev.jjs.ast.JField;
import com.google.gwt.dev.jjs.ast.JFieldRef;
import com.google.gwt.dev.jjs.ast.JLocal;
import com.google.gwt.dev.jjs.ast.JMethod;
import com.google.gwt.dev.jjs.ast.JMethodBody;
import com.google.gwt.dev.jjs.ast.JMethodCall;
import com.google.gwt.dev.jjs.ast.JNameOf;
import com.google.gwt.dev.jjs.ast.JNewInstance;
import com.google.gwt.dev.jjs.ast.JNode;
import com.google.gwt.dev.jjs.ast.JParameter;
import com.google.gwt.dev.jjs.ast.JProgram;
import com.google.gwt.dev.jjs.ast.JReferenceType;
import com.google.gwt.dev.jjs.ast.JRuntimeTypeReference;
import com.google.gwt.dev.jjs.ast.JType;
import com.google.gwt.dev.jjs.ast.JVariable;
import com.google.gwt.dev.jjs.ast.JVariableRef;
import com.google.gwt.dev.jjs.ast.js.JMultiExpression;
import com.google.gwt.dev.jjs.ast.js.JsniFieldRef;
import com.google.gwt.dev.jjs.ast.js.JsniMethodRef;
import com.google.gwt.dev.util.collect.Stack;
import com.google.gwt.dev.util.log.speedtracer.CompilerEventType;
import com.google.gwt.dev.util.log.speedtracer.SpeedTracerLogger;
import com.google.gwt.dev.util.log.speedtracer.SpeedTracerLogger.Event;
import com.google.gwt.thirdparty.guava.common.base.Predicate;
import com.google.gwt.thirdparty.guava.common.base.Predicates;
import com.google.gwt.thirdparty.guava.common.collect.ArrayListMultimap;
import com.google.gwt.thirdparty.guava.common.collect.ImmutableList;
import com.google.gwt.thirdparty.guava.common.collect.Iterables;
import com.google.gwt.thirdparty.guava.common.collect.ListMultimap;
import com.google.gwt.thirdparty.guava.common.collect.Sets;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
/**
* Remove globally unreferenced classes, interfaces, methods, parameters, and
* fields from the AST. This algorithm is based on having known "entry points"
* into the application which serve as the root(s) from which reachability is
* determined and everything else is rescued. Pruner determines reachability at
* a global level based on method calls and new operations; it does not perform
* any local code flow analysis. But, a local code flow optimization pass that
* can eliminate method calls would allow Pruner to prune additional nodes.
*
* Note: references to pruned types may still exist in the tree after this pass
* runs, however, it should only be in contexts that do not rely on any code
* generation for the pruned type. For example, it's legal to have a variable of
* a pruned type, or to try to cast to a pruned type. These will cause natural
* failures at run time; or later optimizations might be able to hard-code
* failures at compile time.
*
* Note: this class is limited to pruning parameters of static methods only.
*/
public class Pruner {
/**
* Remove assignments to pruned fields, locals and params. Nullify the return
* type of methods declared to return a globally uninstantiable type. Replace
* references to pruned variables and methods by references to the null field
* and null method, assignments to pruned variables, and nullify the type of
* variable whose type is a pruned type.
*/
private class CleanupRefsVisitor extends JModVisitorWithTemporaryVariableCreation {
private final Stack lValues = new Stack();
private final ListMultimap priorParametersByMethod;
private final Set referencedNonTypes;
{
// Initialize a sentinel value to avoid having to check for empty stack.
lValues.push(null);
}
public CleanupRefsVisitor(Set referencedNodes,
ListMultimap priorParametersByMethod,
OptimizerContext optimizerCtx) {
super(optimizerCtx);
this.referencedNonTypes = referencedNodes;
this.priorParametersByMethod = priorParametersByMethod;
}
@Override
public void endVisit(JBinaryOperation x, Context ctx) {
if (x.getOp() != JBinaryOperator.ASG) {
return;
}
// The LHS of assignments may have been pruned.
lValues.pop();
JExpression lhs = x.getLhs();
if (!(lhs instanceof JVariableRef)) {
return;
}
JVariableRef variableRef = (JVariableRef) lhs;
if (isVariablePruned(variableRef.getTarget())) {
// TODO: better null tracking; we might be missing some NPEs here.
JExpression replacement =
makeReplacementForAssignment(x.getSourceInfo(), variableRef, x.getRhs());
ctx.replaceMe(replacement);
}
}
@Override
public void endVisit(JDeclarationStatement x, Context ctx) {
super.endVisit(x, ctx);
lValues.pop();
// The variable may have been pruned.
if (isVariablePruned(x.getVariableRef().getTarget())) {
JExpression replacement =
makeReplacementForAssignment(x.getSourceInfo(), x.getVariableRef(), x.getInitializer());
ctx.replaceMe(replacement.makeStatement());
}
}
@Override
public void endVisit(JFieldRef x, Context ctx) {
// Handle l-values at a higher level.
if (lValues.peek() == x) {
return;
}
if (isPruned(x.getField())) {
// The field is gone; replace x by a null field reference.
JFieldRef fieldRef = transformToNullFieldRef(x, program);
ctx.replaceMe(fieldRef);
}
}
@Override
public void exit(JMethod x, Context ctx) {
JType type = x.getType();
if (type instanceof JReferenceType &&
!program.typeOracle.isInstantiatedType((JReferenceType) type)) {
x.setType(JReferenceType.NULL_TYPE);
}
Predicate isPruned = new Predicate() {
@Override
public boolean apply(JMethod method) {
return isPruned(method);
}
};
Iterables.removeIf(x.getOverriddenMethods(), isPruned);
Iterables.removeIf(x.getOverridingMethods(), isPruned);
}
@Override
public void endVisit(JMethodCall x, Context ctx) {
JMethod method = x.getTarget();
// Is the method pruned entirely?
if (isPruned(method)) {
/*
* We assert that method must be non-static, otherwise it would have
* been rescued.
*/
ctx.replaceMe(transformToNullMethodCall(x, program));
return;
}
maybeReplaceForPrunedParameters(x, ctx);
}
@Override
public void endVisit(JNameOf x, Context ctx) {
HasName node = x.getNode();
boolean pruned;
if (node instanceof JField) {
pruned = isPruned((JField) node);
} else if (node instanceof JMethod) {
pruned = isPruned((JMethod) node);
} else if (node instanceof JReferenceType) {
pruned = !program.typeOracle.isInstantiatedType((JReferenceType) node);
} else {
throw new InternalCompilerException("Unhandled JNameOf node: " + node);
}
if (pruned) {
ctx.replaceMe(program.getLiteralNull());
}
}
@Override
public void endVisit(JNewInstance x, Context ctx) {
maybeReplaceForPrunedParameters(x, ctx);
}
@Override
public void endVisit(JRuntimeTypeReference x, Context ctx) {
if (!program.typeOracle.isInstantiatedType(x.getReferredType())) {
ctx.replaceMe(program.getLiteralNull());
}
}
@Override
public void endVisit(JsniFieldRef x, Context ctx) {
if (isPruned(x.getField())) {
String ident = x.getIdent();
JField nullField = program.getNullField();
JsniFieldRef nullFieldRef =
new JsniFieldRef(x.getSourceInfo(), ident, nullField, x.getEnclosingType(), x
.isLvalue());
ctx.replaceMe(nullFieldRef);
}
}
@Override
public void endVisit(JsniMethodRef x, Context ctx) {
// Redirect JSNI refs to uninstantiable types to the null method.
if (isPruned(x.getTarget())) {
String ident = x.getIdent();
JMethod nullMethod = program.getNullMethod();
JsniMethodRef nullMethodRef =
new JsniMethodRef(x.getSourceInfo(), ident, nullMethod, program.getJavaScriptObject());
ctx.replaceMe(nullMethodRef);
}
}
@Override
public void exit(JVariable x, Context ctx) {
JType type = x.getType();
if (type instanceof JReferenceType &&
!program.typeOracle.isInstantiatedType((JReferenceType) type)) {
x.setType(JReferenceType.NULL_TYPE);
madeChanges();
}
}
@Override
public boolean visit(JBinaryOperation x, Context ctx) {
if (x.getOp() == JBinaryOperator.ASG) {
lValues.push(x.getLhs());
}
return true;
}
@Override
public boolean visit(JDeclarationStatement x, Context ctx) {
super.visit(x, ctx);
lValues.push(x.getVariableRef());
return true;
}
private boolean isPruned(T node) {
if (!referencedNonTypes.contains(node)) {
return true;
}
JReferenceType enclosingType = node.getEnclosingType();
return !node.isStatic() && enclosingType != null
&& !program.typeOracle.isInstantiatedType(enclosingType);
}
private boolean isVariablePruned(JVariable variable) {
if (variable instanceof JField) {
return isPruned((JField) variable);
}
return !referencedNonTypes.contains(variable);
}
private JExpression makeReplacementForAssignment(SourceInfo info, JVariableRef variableRef,
JExpression rhs) {
// Replace with a multi, which may wind up empty.
JMultiExpression multi = new JMultiExpression(info);
// If the lhs is a field ref, evaluate it first.
if (variableRef instanceof JFieldRef) {
JFieldRef fieldRef = (JFieldRef) variableRef;
JExpression instance = fieldRef.getInstance();
if (instance != null) {
multi.addExpressions(instance);
}
}
// If there is an rhs, evaluate it second.
if (rhs != null) {
multi.addExpressions(rhs);
}
if (multi.getNumberOfExpressions() == 1) {
return multi.getExpression(0);
} else {
return multi;
}
}
// Arguments for pruned parameters will be pushed right into a multiexpression that will be
// evaluated with the next arg, e.g. m(arg1, (prunnedArg2, prunnedArg3, arg4)).
private void maybeReplaceForPrunedParameters(JMethodCall x, Context ctx) {
if (!priorParametersByMethod.containsKey(x.getTarget())) {
// No parameter was pruned.
return;
}
JMethodCall replacementCall = x.cloneWithoutParameters();
assert !x.getTarget().canBePolymorphic();
List originalParams = priorParametersByMethod.get(x.getTarget());
// The method and the call agree in the number of parameters.
assert originalParams.size() == x.getArgs().size();
// Traverse the call arguments left to right.
SourceInfo sourceInfo = x.getSourceInfo();
JMultiExpression unevaluatedArgumentsForPrunedParameters =
new JMultiExpression(sourceInfo);
List args = x.getArgs();
for (int currentArgumentIndex = 0; currentArgumentIndex < args.size();
++currentArgumentIndex) {
JExpression arg = args.get(currentArgumentIndex);
// If the parameter was not pruned .
if (referencedNonTypes.contains(originalParams.get(currentArgumentIndex))) {
// Add the current argument to the list of unevaluated arguments and pass the multi
// expression to the call.
unevaluatedArgumentsForPrunedParameters.addExpressions(arg);
replacementCall.addArg(unevaluatedArgumentsForPrunedParameters);
// Reset the accumulating multi expression.
unevaluatedArgumentsForPrunedParameters = new JMultiExpression(sourceInfo);
} else if (arg.hasSideEffects()) {
// If the argument was pruned and has sideffects accumulate it; otherwise discard.
unevaluatedArgumentsForPrunedParameters.addExpressions(arg);
}
}
if (unevaluatedArgumentsForPrunedParameters.isEmpty()) {
// We are done, all (side effectful) parameters have been evaluated.
ctx.replaceMe(replacementCall);
return;
}
// If the last few parameters where pruned, we need to evaluate the (side effectful) arguments
// for those parameters.
if (replacementCall.getArgs().isEmpty()) {
// All parameters have been pruned, replace by (prunedArg1, ..., prunedArgn, m()).
unevaluatedArgumentsForPrunedParameters.addExpressions(replacementCall);
ctx.replaceMe(unevaluatedArgumentsForPrunedParameters);
return;
}
// Some parameters have been pruned from the end, replace by
// m(arg1,..., (lastArg = lastUnprunedArg, remainingArgs, lastArg))
JExpression lastArg = Iterables.getLast(replacementCall.getArgs());
JLocal tempVar =
createTempLocal(sourceInfo, Iterables.getLast(
Iterables.filter(originalParams, Predicates.in(referencedNonTypes))).getType(), "lastArg");
unevaluatedArgumentsForPrunedParameters.addExpressions(0, JProgram.createAssignment(
lastArg.getSourceInfo(), tempVar.makeRef(sourceInfo), lastArg));
unevaluatedArgumentsForPrunedParameters.addExpressions(tempVar.makeRef(sourceInfo));
replacementCall.setArg(replacementCall.getArgs().size() - 1, unevaluatedArgumentsForPrunedParameters);
ctx.replaceMe(replacementCall);
}
}
/**
* Remove any unreferenced classes and interfaces from JProgram. Remove any
* unreferenced methods and fields from their containing classes.
*/
private class PruneVisitor extends JChangeTrackingVisitor {
private final ListMultimap priorParametersByMethod =
ArrayListMultimap.create();
private final Set referencedNonTypes;
private final Set referencedTypes;
public PruneVisitor(Set referencedTypes,
Set referencedNodes, OptimizerContext optimizerCtx) {
super(optimizerCtx);
this.referencedTypes = referencedTypes;
this.referencedNonTypes = referencedNodes;
}
public ListMultimap getPriorParametersByMethod() {
return priorParametersByMethod;
}
@Override
public boolean visit(JDeclaredType type, Context ctx) {
assert referencedTypes.contains(type);
Predicate notReferenced = Predicates.not(Predicates.in(referencedNonTypes));
removeFields(notReferenced, type);
removeMethods(notReferenced, type);
for (JMethod method : type.getMethods()) {
accept(method);
}
return false;
}
@Override
public boolean enter(JMethod x, Context ctx) {
if (!x.canBePolymorphic()) {
/*
* Don't prune parameters on unreferenced methods. The methods might not
* be reachable through the current method traversal routines, but might
* be used or checked elsewhere.
*
* Basically, if we never actually checked if the method parameters were
* used or not, don't prune them. Doing so would leave a number of
* dangling JParameterRefs that blow up in later optimizations.
*/
if (!referencedNonTypes.contains(x)) {
return true;
}
/*
* We cannot prune parameters from staticImpls that still have a live
* instance method, because doing so would screw up any subsequent
* devirtualizations. If the instance method has been pruned, then it's
* okay. Also, it's okay on the final pass (saveCodeTypes == false)
* since no more devirtualizations will occur.
*
* TODO: prune params; MakeCallsStatic smarter to account for it.
*/
JMethod instanceMethod = program.instanceMethodForStaticImpl(x);
// Unless the instance method has already been pruned, of course.
if (saveCodeGenTypes && instanceMethod != null &&
referencedNonTypes.contains(instanceMethod)) {
// instance method is still live
return true;
}
List originalParameters = ImmutableList.copyOf(x.getParams());
for (int i = 0; i < x.getParams().size(); ++i) {
JParameter param = x.getParams().get(i);
if (!referencedNonTypes.contains(param)) {
x.removeParam(i);
madeChanges();
--i;
}
}
if (x.getParams().size() != originalParameters.size()) {
// Parameters were pruned. record the original parameters for the cleanup pass.
priorParametersByMethod.putAll(x, originalParameters);
}
}
return true;
}
@Override
public boolean visit(JMethodBody x, Context ctx) {
for (int i = 0; i < x.getLocals().size(); ++i) {
if (!referencedNonTypes.contains(x.getLocals().get(i))) {
x.removeLocal(i--);
madeChanges();
}
}
return false;
}
@Override
public boolean visit(JProgram program, Context ctx) {
for (Iterator it = program.getDeclaredTypes().iterator(); it.hasNext();) {
JDeclaredType type = it.next();
if (referencedTypes.contains(type)) {
accept(type);
} else {
prunedMethods.addAll(type.getMethods());
methodsWereRemoved(type.getMethods());
fieldsWereRemoved(type.getFields());
it.remove();
madeChanges();
}
}
return false;
}
private void removeFields(Predicate shouldRemove, JDeclaredType type) {
for (int i = 0; i < type.getFields().size(); ++i) {
JField field = type.getFields().get(i);
if (!shouldRemove.apply(field)) {
continue;
}
wasRemoved(field);
type.removeField(i);
madeChanges();
--i;
}
}
private void removeMethods(Predicate shouldRemove, JDeclaredType type) {
// Skip method 0 which is clinit and is assumed to exist.
assert type.getMethods().get(0) == type.getClinitMethod();
for (int i = 1; i < type.getMethods().size(); ++i) {
JMethod method = type.getMethods().get(i);
if (!shouldRemove.apply(method)) {
continue;
}
prunedMethods.add(method);
wasRemoved(method);
type.removeMethod(i);
program.removeStaticImplMapping(method);
madeChanges();
--i;
}
}
}
private static final String NAME = Pruner.class.getSimpleName();
public static OptimizerStats exec(JProgram program, boolean noSpecialTypes,
OptimizerContext optimizerCtx) {
Event optimizeEvent = SpeedTracerLogger.start(CompilerEventType.OPTIMIZE, "optimizer", NAME);
OptimizerStats stats = new Pruner(program, noSpecialTypes).execImpl(optimizerCtx);
optimizeEvent.end("didChange", "" + stats.didChange());
return stats;
}
public static OptimizerStats exec(JProgram program, boolean noSpecialTypes) {
return exec(program, noSpecialTypes, OptimizerContext.NULL_OPTIMIZATION_CONTEXT);
}
/**
* Transform a reference to a pruned instance field into a reference to the
* null field, which will be used to replace x.
*/
public static JFieldRef transformToNullFieldRef(JFieldRef x, JProgram program) {
JExpression instance = x.getInstance();
/*
* We assert that field must be non-static if it's an rvalue, otherwise it
* would have been rescued.
*/
// assert !x.getField().isStatic();
/*
* HACK HACK HACK: ControlFlowAnalyzer has special hacks for dealing with
* ClassLiterals, which causes the body of ClassLiteralHolder's clinit to
* never be rescured. This in turn causes invalid references to static
* methods, which violates otherwise good assumptions about compiler
* operation.
*
* TODO: Remove this when ControlFlowAnalyzer doesn't special-case
* CLH.clinit().
*/
if (x.getField().isStatic() && instance == null) {
instance = program.getLiteralNull();
}
assert instance != null;
if (!instance.hasSideEffects()) {
instance = program.getLiteralNull();
}
JFieldRef fieldRef =
new JFieldRef(x.getSourceInfo(), instance, program.getNullField(), x.getEnclosingType(),
primitiveTypeOrNullTypeOrArray(program, x.getType()));
return fieldRef;
}
/**
* Transform a call to a pruned instance method (or static impl) into a call
* to the null method, which will be used to replace x.
*/
public static JMethodCall transformToNullMethodCall(JMethodCall x, JProgram program) {
JExpression instance = x.getInstance();
List args = x.getArgs();
if (program.isStaticImpl(x.getTarget())) {
instance = args.get(0);
args = args.subList(1, args.size());
} else {
/*
* We assert that method must be non-static, otherwise it would have been
* rescued.
*/
// assert !x.getTarget().isStatic();
/*
* HACK HACK HACK: ControlFlowAnalyzer has special hacks for dealing with
* ClassLiterals, which causes the body of ClassLiteralHolder's clinit to
* never be rescured. This in turn causes invalid references to static
* methods, which violates otherwise good assumptions about compiler
* operation.
*
* TODO: Remove this when ControlFlowAnalyzer doesn't special-case
* CLH.clinit().
*/
if (x.getTarget().isStatic() && instance == null) {
instance = program.getLiteralNull();
}
}
assert (instance != null);
if (!instance.hasSideEffects()) {
instance = program.getLiteralNull();
}
JMethodCall newCall = new JMethodCall(x.getSourceInfo(), instance, program.getNullMethod());
newCall.overrideReturnType(primitiveTypeOrNullTypeOrArray(program, x.getType()));
// Retain the original arguments, they will be evaluated for side effects.
for (JExpression arg : args) {
if (arg.hasSideEffects()) {
newCall.addArg(arg);
}
}
return newCall;
}
/**
* Return the smallest type that is is a subtype of the argument.
*/
static JType primitiveTypeOrNullTypeOrArray(JProgram program, JType type) {
if (type instanceof JArrayType) {
JType leafType = primitiveTypeOrNullTypeOrArray(program, ((JArrayType) type).getLeafType());
return program.getOrCreateArrayType(leafType, ((JArrayType) type).getDims());
}
if (type.isPrimitiveType()) {
return type;
}
return JReferenceType.NULL_TYPE;
}
private final JProgram program;
private final boolean saveCodeGenTypes;
private final Set prunedMethods = Sets.newLinkedHashSet();
private Pruner(JProgram program, boolean saveCodeGenTypes) {
this.program = program;
this.saveCodeGenTypes = saveCodeGenTypes;
}
private OptimizerStats execImpl(OptimizerContext optimizerCtx) {
OptimizerStats stats = new OptimizerStats(NAME);
ControlFlowAnalyzer livenessAnalyzer = new ControlFlowAnalyzer(program);
livenessAnalyzer.setForPruning();
// SPECIAL: Immortal codegen types are never pruned
traverseTypes(livenessAnalyzer, program.immortalCodeGenTypes);
if (saveCodeGenTypes) {
/*
* SPECIAL: Some classes contain methods used by code generation later.
* Unless those transforms have already been performed, we must rescue all
* contained methods for later user.
*/
traverseTypes(livenessAnalyzer, program.codeGenTypes);
}
livenessAnalyzer.traverseEverything();
program.typeOracle.setInstantiatedTypes(livenessAnalyzer.getInstantiatedTypes());
PruneVisitor pruner =
new PruneVisitor(livenessAnalyzer.getReferencedTypes(), livenessAnalyzer
.getLiveFieldsAndMethods(), optimizerCtx);
pruner.accept(program);
stats.recordModified(pruner.getNumMods());
if (!pruner.didChange()) {
return stats;
}
CleanupRefsVisitor cleaner =
new CleanupRefsVisitor(livenessAnalyzer.getLiveFieldsAndMethods(), pruner
.getPriorParametersByMethod(), optimizerCtx);
cleaner.accept(program.getDeclaredTypes());
optimizerCtx.incOptimizationStep();
optimizerCtx.syncDeletedSubCallGraphsSince(optimizerCtx.getLastStepFor(NAME) + 1,
prunedMethods);
JavaAstVerifier.assertProgramIsConsistent(program);
return stats;
}
/**
* Traverse from all methods starting from a set of types.
*/
private void traverseTypes(ControlFlowAnalyzer livenessAnalyzer,
List types) {
for (JClassType type : types) {
livenessAnalyzer.traverseFromReferenceTo(type);
for (JMethod method : type.getMethods()) {
if (method instanceof JConstructor) {
livenessAnalyzer.traverseFromInstantiationOf(type);
}
livenessAnalyzer.traverseFrom(method);
}
}
}
}
