/*
* 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.SourceInfo;
import com.google.gwt.dev.jjs.ast.JBinaryOperation;
import com.google.gwt.dev.jjs.ast.JBinaryOperator;
import com.google.gwt.dev.jjs.ast.JBlock;
import com.google.gwt.dev.jjs.ast.JBooleanLiteral;
import com.google.gwt.dev.jjs.ast.JCastOperation;
import com.google.gwt.dev.jjs.ast.JConditional;
import com.google.gwt.dev.jjs.ast.JExpression;
import com.google.gwt.dev.jjs.ast.JExpressionStatement;
import com.google.gwt.dev.jjs.ast.JIfStatement;
import com.google.gwt.dev.jjs.ast.JMethod;
import com.google.gwt.dev.jjs.ast.JNode;
import com.google.gwt.dev.jjs.ast.JPrefixOperation;
import com.google.gwt.dev.jjs.ast.JPrimitiveType;
import com.google.gwt.dev.jjs.ast.JReturnStatement;
import com.google.gwt.dev.jjs.ast.JStatement;
import com.google.gwt.dev.jjs.ast.JType;
import com.google.gwt.dev.jjs.ast.JUnaryOperation;
import com.google.gwt.dev.jjs.ast.JUnaryOperator;
import com.google.gwt.dev.jjs.ast.JValueLiteral;
import com.google.gwt.dev.jjs.ast.js.JMultiExpression;
import java.util.List;
/**
* Methods that both construct and try to simplify AST nodes. If simplification
* fails, then the methods will return an original, unmodified version of the
* node if one is supplied. The routines do not recurse into their arguments;
* the arguments are assumed to already be simplified as much as possible.
*/
public class Simplifier {
/**
* TODO: if the AST were normalized, we wouldn't need this.
*/
public static boolean isEmpty(JStatement stmt) {
if (stmt == null) {
return true;
}
return (stmt instanceof JBlock && ((JBlock) stmt).getStatements().isEmpty());
}
/**
* Negate the supplied expression if negating it makes the expression shorter.
* Otherwise, return null.
*/
private static JExpression maybeUnflipBoolean(JExpression expr) {
if (expr instanceof JUnaryOperation) {
JUnaryOperation unop = (JUnaryOperation) expr;
if (unop.getOp() == JUnaryOperator.NOT) {
return unop.getArg();
}
}
return null;
}
private static <T> List<T> allButLast(List<T> list) {
return list.subList(0, list.size() - 1);
}
private static <T> T last(List<T> list) {
return list.get(list.size() - 1);
}
/**
* This class provides only static methods. No instances will ever be created.
*/
private Simplifier() {
}
/**
* Simplify cast operations. Used when creating a cast in DeadCodeElimination. For simplifying
* casts that are actually in the AST, cast(JCastOperation) is used instead.
*
* <pre>
* (int) 1 -> 1
* (A) (a,b) -> (a, (A) b)
* </pre>
*
* @param type the Type to cast the expression <code>exp</code> to.
* @param exp the current JExpression under the cast as it is being simplified.
* @return the simplified expression.
*/
public static JExpression cast(JType type, JExpression exp) {
return castImpl(null, exp.getSourceInfo(), type, exp);
}
/**
* Simplify cast operations.
*
* <pre>
* (int) 1 -> 1
* (A) (a,b) -> (a, (A) b)
* </pre>
*
* @param exp a JCastOperation to be simplified.
* @return the simplified expression if a simplification was possible; <code>exp</code> otherwise.
*/
public static JExpression cast(JCastOperation exp) {
return castImpl(exp, exp.getSourceInfo(), exp.getCastType(), exp.getExpr());
}
private static JExpression castImpl(JExpression original, SourceInfo info, JType type,
JExpression exp) {
info = getBestSourceInfo(original, info, exp);
if (exp instanceof JMultiExpression) {
// (T)(a,b,c) -> a,b,(T) c
JMultiExpression expMulti = (JMultiExpression) exp;
JMultiExpression newMulti = new JMultiExpression(info);
newMulti.exprs.addAll(allButLast(expMulti.exprs));
newMulti.exprs.add(castImpl(null, info, type, last(expMulti.exprs)));
// TODO(rluble): immediately simplify the resulting multi.
// TODO(rluble): refactor common outward JMultiExpression movement.
return newMulti;
}
if (type == exp.getType()) {
return exp;
}
if ((type instanceof JPrimitiveType) && (exp instanceof JValueLiteral)) {
// Statically evaluate casting literals.
JPrimitiveType typePrim = (JPrimitiveType) type;
JValueLiteral expLit = (JValueLiteral) exp;
JValueLiteral casted = typePrim.coerceLiteral(expLit);
if (casted != null) {
return casted;
}
}
/*
* Discard casts from byte or short to int, because such casts are always
* implicit anyway. Cannot coerce char since that would change the semantics
* of concat.
*/
if (type == JPrimitiveType.INT) {
JType expType = exp.getType();
if ((expType == JPrimitiveType.SHORT)
|| (expType == JPrimitiveType.BYTE)) {
return exp;
}
}
// no simplification made
if (original != null) {
return original;
}
return new JCastOperation(info, type, exp);
}
/**
* Simplify conditional expressions.
*
* <pre>
* (a,b,c)?d:e -> a,b,(c?d:e)
* true ? then : else -> then
* false ? then : else -> else
* cond ? true : else) -> cond || else
* cond ? false : else -> !cond && else
* cond ? then : true -> !cond || then
* cond ? then : false -> cond && then
* !cond ? then : else -> cond ? else : then
* </pre>
*
* @param exp a JCondintional to be simplified.
* @return the simplified expression if a simplification was possible; <code>exp</code> otherwise.
*/
public static JExpression conditional(JConditional exp) {
return conditionalImpl(exp, exp.getSourceInfo(), exp.getType(), exp.getIfTest(),
exp.getThenExpr(), exp.getElseExpr());
}
private static JExpression conditionalImpl(JConditional original, SourceInfo info, JType type,
JExpression condExpr, JExpression thenExpr, JExpression elseExpr) {
info = getBestSourceInfo(original, info, condExpr);
if (condExpr instanceof JMultiExpression) {
// (a,b,c)?d:e -> a,b,(c?d:e)
// TODO(spoon): do this outward multi movement for all AST nodes
JMultiExpression condMulti = (JMultiExpression) condExpr;
JMultiExpression newMulti = new JMultiExpression(info);
newMulti.exprs.addAll(allButLast(condMulti.exprs));
newMulti.exprs.add(conditionalImpl(null, info, type, last(condMulti.exprs), thenExpr,
elseExpr));
// TODO(spoon): immediately simplify the resulting multi
return newMulti;
}
if (condExpr instanceof JBooleanLiteral) {
if (((JBooleanLiteral) condExpr).getValue()) {
// e.g. (true ? then : else) -> then
return thenExpr;
} else {
// e.g. (false ? then : else) -> else
return elseExpr;
}
} else if (thenExpr instanceof JBooleanLiteral) {
if (((JBooleanLiteral) thenExpr).getValue()) {
// e.g. (cond ? true : else) -> cond || else
return orImpl(null, info, condExpr, elseExpr);
} else {
// e.g. (cond ? false : else) -> !cond && else
JExpression notCondExpr = notImpl(null, condExpr.getSourceInfo(), condExpr);
return andImpl(null, info, notCondExpr, elseExpr);
}
} else if (elseExpr instanceof JBooleanLiteral) {
if (((JBooleanLiteral) elseExpr).getValue()) {
// e.g. (cond ? then : true) -> !cond || then
JExpression notCondExpr = notImpl(null, condExpr.getSourceInfo(), condExpr);
return orImpl(null, info, notCondExpr, thenExpr);
} else {
// e.g. (cond ? then : false) -> cond && then
return andImpl(null, info, condExpr, thenExpr);
}
} else {
// e.g. (!cond ? then : else) -> (cond ? else : then)
JExpression unflipped = maybeUnflipBoolean(condExpr);
if (unflipped != null) {
return new JConditional(info, type, unflipped, elseExpr, thenExpr);
}
}
// no simplification made
if (original != null) {
return original;
}
return new JConditional(info, type, condExpr, thenExpr, elseExpr);
}
/**
* Simplifies an ifthenelse statement.
*
* <pre>
* if(a,b,c) d [else e] -> {a; b; if(c) d [else e]; }
* if(true) a [else b] -> a
* if(false) a else b -> b
* if(notImpl(c)) a else b -> if(c) b else a
* if(true) ; else b -> true
* if(false) a [else ;] -> false
* if(c) ; [else ;] -> c
*</pre>
*
* @param stmt the statement to simplify.
* @param currentMethod the method where the statement resides
* @return the simplified statement if a simplification could be done and <code>stmt</code>
* otherwise.
*/
public static JStatement ifStatement(JIfStatement stmt, JMethod currentMethod) {
return ifStatementImpl(stmt, stmt.getSourceInfo(), stmt.getIfExpr(),
stmt.getThenStmt(), stmt.getElseStmt(), currentMethod);
}
private static JStatement ifStatementImpl(JIfStatement original, SourceInfo info,
JExpression condExpr, JStatement thenStmt,JStatement elseStmt, JMethod currentMethod) {
info = getBestSourceInfo(original, info, condExpr);
if (condExpr instanceof JMultiExpression) {
// if(a,b,c) d else e -> {a; b; if(c) d else e; }
JMultiExpression condMulti = (JMultiExpression) condExpr;
JBlock newBlock = new JBlock(info);
for (JExpression expr : allButLast(condMulti.exprs)) {
newBlock.addStmt(expr.makeStatement());
}
newBlock.addStmt(ifStatementImpl(null, info, last(condMulti.exprs), thenStmt, elseStmt,
currentMethod));
// TODO(spoon): immediately simplify the resulting block
return newBlock;
}
if (condExpr instanceof JBooleanLiteral) {
JBooleanLiteral booleanLiteral = (JBooleanLiteral) condExpr;
boolean boolVal = booleanLiteral.getValue();
if (boolVal && !isEmpty(thenStmt)) {
// If true, replace myself with then statement
return thenStmt;
} else if (!boolVal && !isEmpty(elseStmt)) {
// If false, replace myself with else statement
return elseStmt;
} else {
// just prune me
return condExpr.makeStatement();
}
}
if (isEmpty(thenStmt) && isEmpty(elseStmt)) {
return condExpr.makeStatement();
}
if (!isEmpty(elseStmt)) {
// if (!cond) foo else bar -> if (cond) bar else foo
JExpression unflipped = Simplifier.maybeUnflipBoolean(condExpr);
if (unflipped != null) {
// Force sub-parts to blocks, otherwise we break else-if chains.
// TODO: this goes away when we normalize the Java AST properly.
thenStmt = ensureBlock(thenStmt);
elseStmt = ensureBlock(elseStmt);
return ifStatementImpl(null, info, unflipped, elseStmt, thenStmt, currentMethod);
}
}
JStatement rewritenStatement =
rewriteIfIntoBoolean(info, condExpr, thenStmt, elseStmt, currentMethod);
if (rewritenStatement != null) {
return rewritenStatement;
}
// no simplification made
if (original != null) {
return original;
}
return new JIfStatement(info, condExpr, thenStmt, elseStmt);
}
/**
* Simplifies an negation expression.
*
* if(a,b,c) d else e -> {a; b; if(c) d else e; }
*
* @param expr the expression to simplify.
* @return the simplified expression if a simplification could be done and <code>expr</code>
* otherwise.
*/
public static JExpression not(JPrefixOperation expr) {
return notImpl(expr, expr.getSourceInfo(), expr.getArg());
}
private static JExpression notImpl(JPrefixOperation original, SourceInfo info, JExpression arg) {
info = getBestSourceInfo(original, info, arg);
if (arg instanceof JMultiExpression) {
// !(a,b,c) -> (a,b,!c)
JMultiExpression argMulti = (JMultiExpression) arg;
JMultiExpression newMulti = new JMultiExpression(info);
newMulti.exprs.addAll(allButLast(argMulti.exprs));
newMulti.exprs.add(notImpl(null, info, last(argMulti.exprs)));
// TODO(spoon): immediately simplify the newMulti
return newMulti;
}
if (arg instanceof JBinaryOperation) {
// try to invert the binary operator
JBinaryOperation argOp = (JBinaryOperation) arg;
JBinaryOperator op = argOp.getOp();
JBinaryOperator newOp = null;
if (op == JBinaryOperator.EQ) {
// e.g. !(x == y) -> x != y
newOp = JBinaryOperator.NEQ;
} else if (op == JBinaryOperator.NEQ) {
// e.g. !(x != y) -> x == y
newOp = JBinaryOperator.EQ;
} else if (op == JBinaryOperator.GT) {
// e.g. !(x > y) -> x <= y
newOp = JBinaryOperator.LTE;
} else if (op == JBinaryOperator.LTE) {
// e.g. !(x <= y) -> x > y
newOp = JBinaryOperator.GT;
} else if (op == JBinaryOperator.GTE) {
// e.g. !(x >= y) -> x < y
newOp = JBinaryOperator.LT;
} else if (op == JBinaryOperator.LT) {
// e.g. !(x < y) -> x >= y
newOp = JBinaryOperator.GTE;
}
if (newOp != null) {
JBinaryOperation newBinOp =
new JBinaryOperation(info, argOp.getType(), newOp, argOp.getLhs(), argOp.getRhs());
return newBinOp;
}
} else if (arg instanceof JPrefixOperation) {
// try to invert the unary operator
JPrefixOperation argOp = (JPrefixOperation) arg;
JUnaryOperator op = argOp.getOp();
// e.g. !!x -> x
if (op == JUnaryOperator.NOT) {
return argOp.getArg();
}
} else if (arg instanceof JBooleanLiteral) {
JBooleanLiteral booleanLit = (JBooleanLiteral) arg;
return JBooleanLiteral.get(!booleanLit.getValue());
}
// no simplification made
if (original != null) {
return original;
}
return new JPrefixOperation(info, JUnaryOperator.NOT, arg);
}
/**
* Simplify short circuit AND expressions.
*
* <pre>
* true && isWhatever() -> isWhatever()
* false && isWhatever() -> false
*
* isWhatever() && true -> isWhatever()
* isWhatever() && false -> false, unless side effects
*
* (a, b) && c -> (a, b && c)
* </pre>
*
* @param exp an AND JBinaryExpression to be simplified.
* @return the simplified expression if a simplification was possible; <code>exp</code> otherwise.
*
*/
public static JExpression and(JBinaryOperation exp) {
assert exp.getOp() == JBinaryOperator.AND : "Simplifier.and was called with " + exp;
return andImpl(exp, null, exp.getLhs(), exp.getRhs());
}
private static JExpression andImpl(JBinaryOperation original, SourceInfo info, JExpression lhs,
JExpression rhs) {
info = getBestSourceInfo(original, info, lhs);
if (lhs instanceof JMultiExpression) {
// (a,b,c)&&d -> a,b,(c&&d)
JMultiExpression lhsMulti = (JMultiExpression) lhs;
JMultiExpression newMulti = new JMultiExpression(info);
newMulti.exprs.addAll(allButLast(lhsMulti.exprs));
newMulti.exprs.add(andImpl(null, info, last(lhsMulti.exprs), rhs));
// TODO(rluble): immediately simplify the resulting multi.
// TODO(rluble): refactor common outward JMultiExpression movement.
return newMulti;
}
if (lhs instanceof JBooleanLiteral) {
JBooleanLiteral booleanLiteral = (JBooleanLiteral) lhs;
if (booleanLiteral.getValue()) {
return rhs;
} else {
return lhs;
}
} else if (rhs instanceof JBooleanLiteral) {
JBooleanLiteral booleanLiteral = (JBooleanLiteral) rhs;
if (booleanLiteral.getValue()) {
return lhs;
} else if (!lhs.hasSideEffects()) {
return rhs;
}
}
// no simplification made
if (original != null) {
return original;
}
return new JBinaryOperation(info, rhs.getType(), JBinaryOperator.AND, lhs, rhs);
}
/**
* Simplify short circuit OR expressions.
*
* <pre>
* true || isWhatever() -> true
* false || isWhatever() -> isWhatever()
*
* isWhatever() || false isWhatever()
* isWhatever() || true -> true, unless side effects
*
* (a, b) || c -> (a, b || c)
* </pre>
*
* @param exp an OR JBinaryExpression to be simplified.
* @return the simplified expression if a simplification was possible; <code>exp</code> otherwise.
*
*/
public static JExpression or(JBinaryOperation exp) {
assert exp.getOp() == JBinaryOperator.OR : "Simplifier.and was called with " + exp;
return orImpl(exp, null, exp.getLhs(), exp.getRhs());
}
private static JExpression orImpl(JBinaryOperation original, SourceInfo info, JExpression lhs,
JExpression rhs) {
info = getBestSourceInfo(original, info, lhs);
if (lhs instanceof JMultiExpression) {
// (a,b,c)|| d -> a,b,(c||d)
JMultiExpression lhsMulti = (JMultiExpression) lhs;
JMultiExpression newMulti = new JMultiExpression(info);
newMulti.exprs.addAll(allButLast(lhsMulti.exprs));
newMulti.exprs.add(orImpl(null, info, last(lhsMulti.exprs), rhs));
// TODO(rluble): immediately simplify the resulting multi.
// TODO(rluble): refactor common outward JMultiExpression movement.
return newMulti;
}
if (lhs instanceof JBooleanLiteral) {
JBooleanLiteral booleanLiteral = (JBooleanLiteral) lhs;
if (booleanLiteral.getValue()) {
return lhs;
} else {
return rhs;
}
} else if (rhs instanceof JBooleanLiteral) {
JBooleanLiteral booleanLiteral = (JBooleanLiteral) rhs;
if (!booleanLiteral.getValue()) {
return lhs;
} else if (!lhs.hasSideEffects()) {
return rhs;
}
}
// no simplification made
if (original != null) {
return original;
}
return new JBinaryOperation(info, rhs.getType(), JBinaryOperator.OR, lhs, rhs);
}
private static JStatement ensureBlock(JStatement stmt) {
if (stmt == null) {
return null;
}
if (!(stmt instanceof JBlock)) {
JBlock block = new JBlock(stmt.getSourceInfo());
block.addStmt(stmt);
stmt = block;
}
return stmt;
}
private static JExpression extractExpression(JStatement stmt) {
if (stmt instanceof JExpressionStatement) {
JExpressionStatement statement = (JExpressionStatement) stmt;
return statement.getExpr();
}
return null;
}
private static JStatement extractSingleStatement(JStatement stmt) {
if (stmt instanceof JBlock) {
JBlock block = (JBlock) stmt;
if (block.getStatements().size() == 1) {
return extractSingleStatement(block.getStatements().get(0));
}
}
return stmt;
}
/**
* Determine the best SourceInfo to use in a particular transformation.
*
* @param original the original node that is being transformed. Can be <code>null</code>.
* @param info an explicit SourceInfo that might be used, Can be <code>null</code>.
* @param defaultNode a node from where to obtain the SourceInfo.
* @return a SourceInfo chosen according to the following priority info>original>default.
*/
private static SourceInfo getBestSourceInfo(JNode original, SourceInfo info, JNode defaultNode) {
if (info == null) {
if (original == null) {
info = defaultNode.getSourceInfo();
} else {
info = original.getSourceInfo();
}
}
return info;
}
private static JStatement rewriteIfIntoBoolean(SourceInfo sourceInfo, JExpression condExpr,
JStatement thenStmt, JStatement elseStmt, JMethod currentMethod) {
thenStmt = extractSingleStatement(thenStmt);
elseStmt = extractSingleStatement(elseStmt);
if (thenStmt instanceof JReturnStatement && elseStmt instanceof JReturnStatement
&& currentMethod != null) {
// Special case
// if () { return ..; } else { return ..; } =>
// return ... ? ... : ...;
JExpression thenExpression = ((JReturnStatement) thenStmt).getExpr();
JExpression elseExpression = ((JReturnStatement) elseStmt).getExpr();
if (thenExpression == null || elseExpression == null) {
// empty returns are not supported.
return null;
}
JConditional conditional =
new JConditional(sourceInfo, currentMethod.getType(), condExpr, thenExpression,
elseExpression);
JReturnStatement returnStatement = new JReturnStatement(sourceInfo, conditional);
return returnStatement;
}
if (elseStmt != null) {
// if () { } else { } -> ... ? ... : ... ;
JExpression thenExpression = extractExpression(thenStmt);
JExpression elseExpression = extractExpression(elseStmt);
if (thenExpression != null && elseExpression != null) {
JConditional conditional =
new JConditional(sourceInfo, JPrimitiveType.VOID, condExpr, thenExpression,
elseExpression);
return conditional.makeStatement();
}
} else {
// if () { } -> ... && ...;
JExpression thenExpression = extractExpression(thenStmt);
if (thenExpression != null) {
JBinaryOperator binaryOperator = JBinaryOperator.AND;
JExpression unflipExpression = maybeUnflipBoolean(condExpr);
if (unflipExpression != null) {
condExpr = unflipExpression;
binaryOperator = JBinaryOperator.OR;
}
JBinaryOperation binaryOperation =
new JBinaryOperation(sourceInfo, JPrimitiveType.VOID, binaryOperator, condExpr,
thenExpression);
return binaryOperation.makeStatement();
}
}
return null;
}
}