/*
* Copyright 2010 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.SourceInfo;
import com.google.gwt.dev.jjs.ast.Context;
import com.google.gwt.dev.jjs.ast.JBlock;
import com.google.gwt.dev.jjs.ast.JDeclarationStatement;
import com.google.gwt.dev.jjs.ast.JForStatement;
import com.google.gwt.dev.jjs.ast.JLocal;
import com.google.gwt.dev.jjs.ast.JLocalRef;
import com.google.gwt.dev.jjs.ast.JMethodBody;
import com.google.gwt.dev.jjs.ast.JModVisitor;
import com.google.gwt.dev.jjs.ast.JProgram;
import com.google.gwt.dev.jjs.ast.JStatement;
import com.google.gwt.dev.jjs.ast.JType;
import com.google.gwt.dev.jjs.ast.JVariable;
import com.google.gwt.dev.jjs.ast.JVisitor;
import com.google.gwt.dev.util.collect.HashSet;
import java.util.BitSet;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.Stack;
/**
* Utility base class for visitors that need to replace expressions with temp
* locals. This class specifically handles allocating temp locals, and inserting
* a {@link JDeclarationStatement} at the appropriate point. It tracks scopes
* and assigns any potentially conflicting uses with unique names. Subclasses
* are only allowed to use a temp within the {@link JBlock} within which it is
* allocated. Non-conflicting temp locals attempt to reuse as many names as
* possible in order to produce the most optimal output.
*
* <p>
* Subclasses must always visit a {@link JMethodBody} naturally, rather than
* individual blocks.
* </p>
*/
public abstract class TempLocalVisitor extends JModVisitor {
/*
* TODO(scottb): right now our handling of for statements is sub-optimal.
* Technically, a for statement creates an implicit scope that is not part of
* any block. This scope is a child of the block containing the for statement,
* and a parent of the for statement's action block. We don't presently model
* this scope, instead we just allow the for statement's top-level constructs
* to bleed up into the containing block, which is correct if sub-optimal for
* name reuse.
*/
/**
* Creates a Scope for each JBlock in the current method body.
*/
private static class CollectScopes extends JVisitor {
private Scope curScope = null;
private final Map<JBlock, Scope> scopes;
public CollectScopes(Map<JBlock, Scope> scopes) {
this.scopes = scopes;
}
@Override
public void endVisit(JBlock x, Context ctx) {
exit(x);
}
@Override
public void endVisit(JDeclarationStatement x, Context ctx) {
JVariable target = x.getVariableRef().getTarget();
if (target instanceof JLocal) {
String name = target.getName();
if (name.startsWith(PREFIX)) {
curScope.recordTempAllocated(Integer.parseInt(name.substring(PREFIX.length()), 10));
}
}
}
@Override
public boolean visit(JBlock x, Context ctx) {
enter(x);
return true;
}
private void enter(JBlock x) {
curScope = new Scope(curScope);
scopes.put(x, curScope);
}
private void exit(JBlock x) {
assert scopes.get(x) == curScope;
curScope = curScope.parent;
}
}
/**
* Represents a single logical scope (ie, JBlock), and tracks allocation and
* usage of any temps.
*/
private static class Scope {
/**
* My containing scope, will be <code>null</code> if this scope corresponds
* to the top-level method body block.
*/
public final Scope parent;
/**
* Caches which temps have been allocated both in this scope and all parent
* scopes.
*/
private transient BitSet allAllocated;
/**
* Caches the last temp allocated in this scope, for speedier lookup.
*/
private transient int lastTemp;
/**
* The set of all temps allocated by all my child blocks. This prevents me
* from allocating a temp one of my children already allocated; however it
* does not prevent my children from reusing temps also used by their
* siblings.
*/
private final BitSet myChildTemps = new BitSet();
/**
* The set of temps that have been directly allocated in this scope.
*/
private final BitSet myTemps = new BitSet();
public Scope(Scope parent) {
this.parent = parent;
}
/**
* Acquires the next free temp in this scope.
*/
public int allocateNextFreeTemp() {
if (allAllocated == null) {
allAllocated = new BitSet();
// Any temps already allocated by my parents are not available to me.
for (Scope it = this; it != null; it = it.parent) {
allAllocated.or(it.myTemps);
}
}
// Any temps already allocated by my children are not available to me.
allAllocated.or(myChildTemps);
// Find the next free temp.
lastTemp = allAllocated.nextClearBit(lastTemp);
recordTempAllocated(lastTemp);
return lastTemp;
}
/**
* Called when entering this scope, clears transient state.
*/
public void enter() {
// Assume dirty, lazy recompute.
allAllocated = null;
lastTemp = 0;
}
/**
* Called when exiting this scope.
*/
public void exit() {
// Free the memory.
allAllocated = null;
}
/**
* Record a temp as being allocated in this scope.
*/
public void recordTempAllocated(int tempNumber) {
assert !myTemps.get(tempNumber);
// Record my own usage.
myTemps.set(tempNumber);
if (allAllocated != null) {
allAllocated.set(tempNumber);
}
// Tell all my parents I'm now using this one.
for (Scope it = this.parent; it != null; it = it.parent) {
assert !it.myTemps.get(tempNumber);
it.myChildTemps.set(tempNumber);
}
}
}
/**
* Prefix for temp locals.
*/
private static final String PREFIX = "$t";
/**
* A set of statements we cannot insert declaration statements into. Currently
* this is just the "increments" list of a JForStatement.
*/
private final Set<JStatement> banList = new HashSet<JStatement>();
private JMethodBody curMethodBody = null;
private Scope curScope = null;
private final Stack<Context> insertionStack = new Stack<Context>();
private Map<JBlock, Scope> scopes = null;
@Override
public final void endVisit(JBlock x, Context ctx) {
exit(x);
super.endVisit(x, ctx);
}
@Override
public final void endVisit(JMethodBody x, Context ctx) {
curMethodBody = null;
scopes = null;
super.endVisit(x, ctx);
}
@Override
public final void endVisit(JStatement x, Context ctx) {
if (ctx.canInsert()) {
if (!banList.remove(x)) {
Context popped = insertionStack.pop();
assert popped == ctx;
}
}
super.endVisit(x, ctx);
}
@Override
public final boolean visit(JBlock x, Context ctx) {
enter(x);
return super.visit(x, ctx);
}
@Override
public final boolean visit(JMethodBody x, Context ctx) {
curMethodBody = x;
scopes = new HashMap<JBlock, Scope>();
new CollectScopes(scopes).accept(x);
return super.visit(x, ctx);
}
@Override
public final boolean visit(JStatement x, Context ctx) {
if (ctx.canInsert() && !banList.contains(x)) {
insertionStack.push(ctx);
}
if (x instanceof JForStatement) {
// Cannot add decl statements to a for statement increments list.
JForStatement forStmt = (JForStatement) x;
banList.addAll(forStmt.getIncrements());
}
return super.visit(x, ctx);
}
protected JLocal createTempLocal(SourceInfo info, JType type) {
int tempNum = curScope.allocateNextFreeTemp();
String name = PREFIX + tempNum;
JLocal local = JProgram.createLocal(info, name, type, false, curMethodBody);
JDeclarationStatement init = new JDeclarationStatement(info, new JLocalRef(info, local), null);
insertionStack.peek().insertBefore(init);
return local;
}
private boolean enter(JBlock x) {
Scope enterScope = scopes.get(x);
assert enterScope.parent == curScope;
curScope = enterScope;
enterScope.enter();
return true;
}
private void exit(JBlock x) {
assert scopes.get(x) == curScope;
curScope.exit();
curScope = curScope.parent;
}
}