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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.SourceInfo;
import com.google.gwt.dev.jjs.ast.Context;
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.JBreakStatement;
import com.google.gwt.dev.jjs.ast.JCaseStatement;
import com.google.gwt.dev.jjs.ast.JCastOperation;
import com.google.gwt.dev.jjs.ast.JCharLiteral;
import com.google.gwt.dev.jjs.ast.JClassType;
import com.google.gwt.dev.jjs.ast.JConditional;
import com.google.gwt.dev.jjs.ast.JContinueStatement;
import com.google.gwt.dev.jjs.ast.JDeclarationStatement;
import com.google.gwt.dev.jjs.ast.JDeclaredType;
import com.google.gwt.dev.jjs.ast.JDoStatement;
import com.google.gwt.dev.jjs.ast.JDoubleLiteral;
import com.google.gwt.dev.jjs.ast.JEnumField;
import com.google.gwt.dev.jjs.ast.JExpression;
import com.google.gwt.dev.jjs.ast.JExpressionStatement;
import com.google.gwt.dev.jjs.ast.JField;
import com.google.gwt.dev.jjs.ast.JFieldRef;
import com.google.gwt.dev.jjs.ast.JFloatLiteral;
import com.google.gwt.dev.jjs.ast.JForStatement;
import com.google.gwt.dev.jjs.ast.JIfStatement;
import com.google.gwt.dev.jjs.ast.JInstanceOf;
import com.google.gwt.dev.jjs.ast.JIntLiteral;
import com.google.gwt.dev.jjs.ast.JLiteral;
import com.google.gwt.dev.jjs.ast.JLocalRef;
import com.google.gwt.dev.jjs.ast.JLongLiteral;
import com.google.gwt.dev.jjs.ast.JMethod;
import com.google.gwt.dev.jjs.ast.JMethodCall;
import com.google.gwt.dev.jjs.ast.JNewInstance;
import com.google.gwt.dev.jjs.ast.JNode;
import com.google.gwt.dev.jjs.ast.JParameterRef;
import com.google.gwt.dev.jjs.ast.JPostfixOperation;
import com.google.gwt.dev.jjs.ast.JPrefixOperation;
import com.google.gwt.dev.jjs.ast.JPrimitiveType;
import com.google.gwt.dev.jjs.ast.JProgram;
import com.google.gwt.dev.jjs.ast.JReferenceType;
import com.google.gwt.dev.jjs.ast.JStatement;
import com.google.gwt.dev.jjs.ast.JStringLiteral;
import com.google.gwt.dev.jjs.ast.JSwitchStatement;
import com.google.gwt.dev.jjs.ast.JTryStatement;
import com.google.gwt.dev.jjs.ast.JType;
import com.google.gwt.dev.jjs.ast.JUnaryOperator;
import com.google.gwt.dev.jjs.ast.JValueLiteral;
import com.google.gwt.dev.jjs.ast.JVariableRef;
import com.google.gwt.dev.jjs.ast.JVisitor;
import com.google.gwt.dev.jjs.ast.JWhileStatement;
import com.google.gwt.dev.jjs.ast.RuntimeConstants;
import com.google.gwt.dev.jjs.ast.js.JMultiExpression;
import com.google.gwt.dev.util.Ieee754_64_Arithmetic;
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.annotations.VisibleForTesting;
import com.google.gwt.thirdparty.guava.common.collect.ImmutableMap;
import com.google.gwt.thirdparty.guava.common.collect.Lists;
import com.google.gwt.thirdparty.guava.common.collect.Sets;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
/**
* Removes certain kinds of dead code, and simplifies certain expressions. This
* pass focuses on intraprocedural optimizations, that is, optimizations that
* can be performed inside of a single method body (and usually a single
* expression) rather than global transformations. Global optimizations done in
* other passes will feed into this, however.
*/
public class DeadCodeElimination {
/**
* Eliminates dead or unreachable code when possible, and makes local
* simplifications like changing "x || true" to "x".
*
* This visitor should perform all of its optimizations in a single pass.
* Except in rare cases, running this pass multiple times should produce no
* changes after the first pass. The only currently known exception to this
* rule is in {@link #endVisit(JNewInstance, Context)}, where the target
* constructor may be non-empty at the beginning of DCE and become empty
* during the run, which potentially unlocks optimizations at call sites.
*
* TODO: leverage ignoring expression output more to remove intermediary
* operations in favor of pure side effects.
*
* TODO: move more simplifications into methods like
* {@link #cast(JExpression, SourceInfo, JType, JExpression) simplifyCast}, so
* that more simplifications can be made on a single pass through a tree.
*/
public class DeadCodeVisitor extends JChangeTrackingVisitor {
public DeadCodeVisitor(OptimizerContext optimizerCtx) {
super(optimizerCtx);
}
/**
* Expressions whose result does not matter. A parent node should add any
* children whose result does not matter to this set during the parent's
* visit() method. It should then remove those children during
* its own endVisit().
*
* TODO: there's a latent bug here: some immutable nodes (such as literals)
* can be multiply referenced in the AST. In theory, one reference to that
* node could be put into this set while another reference actually contains
* a result that is needed. In practice this is okay at the moment since the
* existing uses of ignoringExpressionOutput are with mutable
* nodes.
*/
private final Set ignoringExpressionOutput = Sets.newHashSet();
/**
* Expressions being used as lvalues.
*/
private final Set lvalues = Sets.newHashSet();
private final Set switchBlocks = Sets.newHashSet();
private final JMethod isScriptMethod = program.getIndexedMethod(RuntimeConstants.GWT_IS_SCRIPT);
private final JMethod enumOrdinalMethod =
program.getIndexedMethod(RuntimeConstants.ENUM_ORDINAL);
private final JField enumOrdinalField =
program.getIndexedField(RuntimeConstants.ENUM_ORDINAL);
/**
* Short circuit binary operations.
*/
@Override
public void endVisit(JBinaryOperation x, Context ctx) {
JBinaryOperator op = x.getOp();
JExpression lhs = x.getLhs();
JExpression rhs = x.getRhs();
// If either parameter is a multiexpression, restructure if possible.
if (isNonEmptyMultiExpression(lhs)) {
// Push the operation inside the multiexpression. This exposes other optimization
// opportunities for latter passes e.g:
//
// (a(), b(), 1) + 2 ==> (a(), b(), 1 + 2) ==> (a(), b(), 3)
//
// There is no need to consider the symmetric case as it requires that all expression in the
// rhs (except the last one) to be side effect free, in which case they will end up being
// removed anyway.
List expressions = ((JMultiExpression) lhs).getExpressions();
JMultiExpression result = new JMultiExpression(lhs.getSourceInfo(),
expressions.subList(0, expressions.size() - 1));
result.addExpressions(new JBinaryOperation(x.getSourceInfo(), x.getType(), x.getOp(),
expressions.get(expressions.size() - 1), rhs));
ctx.replaceMe(result);
return;
}
if (isNonEmptyMultiExpression(rhs) && lhs instanceof JValueLiteral &&
op != JBinaryOperator.AND && op != JBinaryOperator.OR) {
// Push the operation inside the multiexpression if the lhs is a value literal.
// This exposes other optimization opportunities for latter passes e.g:
//
// 2 + (a(), b(), 1) ==> (a(), b(), 2 + 1) ==> (a(), b(), 3)
//
// And exception must be made for || and &&, as these operations might not evaluate the
// rhs due to shortcutting.
List expressions = ((JMultiExpression) rhs).getExpressions();
JMultiExpression result = new JMultiExpression(rhs.getSourceInfo(),
expressions.subList(0, expressions.size() - 1));
result.addExpressions(new JBinaryOperation(x.getSourceInfo(), x.getType(), x.getOp(),
lhs, expressions.get(expressions.size() - 1)));
ctx.replaceMe(result);
return;
}
if ((lhs instanceof JValueLiteral) && (rhs instanceof JValueLiteral)) {
if (evalOpOnLiterals(op, (JValueLiteral) lhs, (JValueLiteral) rhs, ctx)) {
return;
}
}
switch (op) {
case AND:
maybeReplaceMe(x, Simplifier.and(x), ctx);
break;
case OR:
maybeReplaceMe(x, Simplifier.or(x), ctx);
break;
case BIT_XOR:
simplifyXor(lhs, rhs, ctx);
break;
case EQ:
simplifyEq(lhs, rhs, ctx, false);
break;
case NEQ:
simplifyEq(lhs, rhs, ctx, true);
break;
case ADD:
simplifyAdd(lhs, rhs, ctx, x.getType());
break;
case CONCAT:
evalConcat(x.getSourceInfo(), lhs, rhs, ctx);
break;
case SUB:
simplifySub(lhs, rhs, ctx, x.getType());
break;
case MUL:
simplifyMul(lhs, rhs, ctx, x.getType());
break;
case DIV:
simplifyDiv(lhs, rhs, ctx, x.getType());
break;
case SHL:
case SHR:
case SHRU:
if (isLiteralZero(rhs)) {
ctx.replaceMe(lhs);
}
break;
default:
if (op.isAssignment()) {
lvalues.remove(lhs);
}
break;
}
}
private boolean isNonEmptyMultiExpression(JExpression expression) {
return expression instanceof JMultiExpression &&
!((JMultiExpression) expression).getExpressions().isEmpty();
}
/**
* Prune dead statements and empty blocks.
*/
@Override
public void endVisit(JBlock x, Context ctx) {
// Switch blocks require special optimization code
if (switchBlocks.contains(x)) {
return;
}
/*
* Remove any dead statements after an abrupt change in code flow and
* promote safe statements within nested blocks to this block.
*/
for (int i = 0; i < x.getStatements().size(); i++) {
JStatement stmt = x.getStatements().get(i);
if (stmt instanceof JBlock) {
/*
* Promote a sub-block's children to the current block, unless the
* sub-block contains local declarations as children.
*/
JBlock block = (JBlock) stmt;
if (canPromoteBlock(block)) {
x.removeStmt(i);
x.addStmts(i, block.getStatements());
i--;
madeChanges();
continue;
}
}
if (stmt instanceof JExpressionStatement) {
JExpressionStatement stmtExpr = (JExpressionStatement) stmt;
if (stmtExpr.getExpr() instanceof JMultiExpression) {
// Promote a multi's expressions to the current block
x.removeStmt(i);
int start = i;
JMultiExpression multi = ((JMultiExpression) stmtExpr.getExpr());
for (JExpression expr : multi.getExpressions()) {
x.addStmt(i++, expr.makeStatement());
}
i = start - 1;
continue;
}
}
if (stmt.unconditionalControlBreak()) {
// Abrupt change in flow, chop the remaining items from this block
for (int j = i + 1; j < x.getStatements().size();) {
x.removeStmt(j);
madeChanges();
}
}
}
if (ctx.canRemove() && x.getStatements().size() == 0) {
// Remove blocks with no effect
ctx.removeMe();
}
}
@Override
public void endVisit(JCastOperation x, Context ctx) {
maybeReplaceMe(x, Simplifier.cast(x), ctx);
}
@Override
public void endVisit(JConditional x, Context ctx) {
maybeReplaceMe(x, Simplifier.conditional(x), ctx);
}
@Override
public void endVisit(JDeclarationStatement x, Context ctx) {
JVariableRef variableRef = x.getVariableRef();
lvalues.remove(variableRef);
}
/**
* Convert do { } while (false); into a block.
*/
@Override
public void endVisit(JDoStatement x, Context ctx) {
JExpression expression = x.getTestExpr();
if (expression instanceof JBooleanLiteral) {
JBooleanLiteral booleanLiteral = (JBooleanLiteral) expression;
// If false, replace do with do's body
if (!booleanLiteral.getValue()) {
if (Simplifier.isEmpty(x.getBody())) {
ctx.removeMe();
} else { // Unless it contains break/continue statements
FindBreakContinueStatementsVisitor visitor = new FindBreakContinueStatementsVisitor();
visitor.accept(x.getBody());
if (!visitor.hasBreakContinueStatements()) {
ctx.replaceMe(x.getBody());
}
}
}
}
}
@Override
public void endVisit(JExpressionStatement x, Context ctx) {
ignoringExpressionOutput.remove(x.getExpr());
if (!x.getExpr().hasSideEffects()) {
removeMe(x, ctx);
}
}
@Override
public void endVisit(JFieldRef x, Context ctx) {
if (x.getField() == enumOrdinalField) {
maybeReplaceWithOrdinalValue(x.getInstance(), ctx);
return;
}
JLiteral literal = tryGetConstant(x);
if (literal == null && !ignoringExpressionOutput.contains(x)) {
return;
}
/*
* At this point, either we have a constant replacement, or our value is
* irrelevant. We can inline the constant, if any, but we might also need
* to evaluate an instance and run a clinit.
*/
// We can inline the constant, but we might also need to evaluate an
// instance and run a clinit.
List exprs = Lists.newArrayList();
JExpression instance = x.getInstance();
if (instance != null) {
exprs.add(instance);
}
if (x.hasClinit() && !x.getField().isCompileTimeConstant()) {
// Access to compile time constants do not trigger class initialization (JLS 12.4.1).
exprs.add(createClinitCall(x.getSourceInfo(), x.getField().getEnclosingType()));
}
if (literal != null) {
exprs.add(literal);
}
JExpression replacement;
if (exprs.size() == 1) {
replacement = exprs.get(0);
} else {
replacement = new JMultiExpression(x.getSourceInfo(), exprs);
}
ctx.replaceMe(this.accept(replacement));
}
/**
* Prune for (X; false; Y) statements, but make sure X is run.
*/
@Override
public void endVisit(JForStatement x, Context ctx) {
JExpression expression = x.getCondition();
if (expression instanceof JBooleanLiteral) {
JBooleanLiteral booleanLiteral = (JBooleanLiteral) expression;
// If false, replace the for statement with its initializers
if (!booleanLiteral.getValue()) {
JBlock block = new JBlock(x.getSourceInfo());
block.addStmts(x.getInitializers());
replaceMe(block, ctx);
}
}
}
/**
* Simplify if statements.
*/
@Override
public void endVisit(JIfStatement x, Context ctx) {
maybeReplaceMe(x, Simplifier.ifStatement(x, getCurrentMethod()), ctx);
}
/**
* Simplify JInstanceOf expression whose output is ignored.
*/
@Override
public void endVisit(JInstanceOf x, Context ctx) {
if (ignoringExpressionOutput.contains(x)) {
ctx.replaceMe(x.getExpr());
ignoringExpressionOutput.remove(x);
return;
}
if (!(x.getExpr().getType() instanceof JReferenceType)) {
return;
}
AnalysisResult analysisResult =
staticallyEvaluateInstanceOf((JReferenceType) x.getExpr().getType(), x.getTestType());
switch (analysisResult) {
case TRUE:
// replace with a simple null test: (expr != null).
ctx.replaceMe(
JjsUtils.createOptimizedNotNullComparison(program, x.getSourceInfo(), x.getExpr()));
break;
case FALSE:
// replace with a false literal
ctx.replaceMe(JjsUtils.createOptimizedMultiExpression(x.getExpr(),
program.getLiteralBoolean(false)));
break;
case UNKNOWN:
default:
}
}
@Override
public void endVisit(JLocalRef x, Context ctx) {
JLiteral literal = tryGetConstant(x);
if (literal != null) {
assert (!x.hasSideEffects());
ctx.replaceMe(literal);
}
}
/**
* Resolve method calls that can be computed statically.
*/
@Override
public void endVisit(JMethodCall x, Context ctx) {
// Restore ignored expressions.
JMethod target = x.getTarget();
JExpression instance = x.getInstance();
if (target.isStatic() && instance != null) {
ignoringExpressionOutput.remove(instance);
}
// Normal optimizations.
JDeclaredType targetType = target.getEnclosingType();
if (targetType == program.getTypeJavaLangString() ||
(instance != null &&
instance.getType().getUnderlyingType() == program.getTypeJavaLangString())) {
tryOptimizeStringCall(x, ctx, target);
} else if (JProgram.isClinit(target)) {
// Eliminate the call if the target is now empty.
if (!targetType.hasClinit()) {
ctx.replaceMe(program.getLiteralNull());
} else if (targetType != targetType.getClinitTarget()) {
// Tighten the target.
ctx.replaceMe(createClinitCall(x.getSourceInfo(), targetType.getClinitTarget()));
}
} else if (target == isScriptMethod) {
// optimize out in draftCompiles that don't do inlining
ctx.replaceMe(JBooleanLiteral.TRUE);
} else if (target == enumOrdinalMethod) {
maybeReplaceWithOrdinalValue(instance, ctx);
}
}
/**
* Remove any parts of JMultiExpression that have no side-effect.
*/
@Override
public void endVisit(JMultiExpression x, Context ctx) {
List exprs = x.getExpressions();
if (exprs.size() > 0) {
if (ignoringExpressionOutput.contains(x)) {
// Remove all my children we previously added.
ignoringExpressionOutput.removeAll(exprs);
} else {
// Remove the non-final children we previously added.
List nonFinalChildren = exprs.subList(0, exprs.size() - 1);
ignoringExpressionOutput.removeAll(nonFinalChildren);
}
}
HashSet clinitsCalled = new HashSet();
for (int i = 0; i < numRemovableExpressions(x); ++i) {
JExpression expr = x.getExpression(i);
if (!expr.hasSideEffects()) {
x.removeExpression(i);
--i;
madeChanges();
continue;
}
// Remove nested JMultiExpressions
if (expr instanceof JMultiExpression) {
x.removeExpression(i);
x.addExpressions(i, ((JMultiExpression) expr).getExpressions());
i--;
madeChanges();
continue;
}
// Remove redundant clinits
if (expr instanceof JMethodCall && JProgram.isClinit(((JMethodCall) expr).getTarget())) {
JDeclaredType enclosingType = ((JMethodCall) expr).getTarget().getEnclosingType();
// If a clinit of enclosingType or a subclass of enclosingType has already been
// called as part of this JMultiExpression then this clinit call is noop at runtime
// and can be statically removed.
if (enclosingType.findSubtype(clinitsCalled) != null) {
x.removeExpression(i);
--i;
madeChanges();
continue;
} else {
clinitsCalled.add(enclosingType);
}
}
}
if (x.getNumberOfExpressions() == 1) {
maybeReplaceMe(x, x.getExpressions().get(0), ctx);
}
}
@Override
public void endVisit(JNewInstance x, Context ctx) {
super.endVisit(x, ctx);
/*
* If the result of a new operation is ignored, we can remove it, provided
* it has no side effects.
*/
if (ignoringExpressionOutput.contains(x)) {
if (!x.getTarget().isEmpty()) {
return;
}
JMultiExpression multi = new JMultiExpression(x.getSourceInfo());
multi.addExpressions(x.getArgs());
// Determine whether a new Blah() in this method needs a clinit.
if (getCurrentMethod().getEnclosingType().checkClinitTo(x.getTarget().getEnclosingType())) {
multi.addExpressions(
createClinitCall(x.getSourceInfo(), x.getTarget().getEnclosingType()));
}
ignoringExpressionOutput.add(multi);
ctx.replaceMe(this.accept(multi));
ignoringExpressionOutput.remove(multi);
}
}
@Override
public void endVisit(JParameterRef x, Context ctx) {
JLiteral literal = tryGetConstant(x);
if (literal != null) {
assert (!x.hasSideEffects());
ctx.replaceMe(literal);
}
}
/**
* Replace post-inc/dec with pre-inc/dec if the result doesn't matter.
*/
@Override
public void endVisit(JPostfixOperation x, Context ctx) {
if (x.getOp().isModifying()) {
lvalues.remove(x.getArg());
}
if (isNonEmptyMultiExpression(x.getArg())) {
List expressions = ((JMultiExpression) x.getArg()).getExpressions();
JMultiExpression result = new JMultiExpression(x.getArg().getSourceInfo(),
expressions.subList(0, expressions.size() - 1));
result.addExpressions(new JPostfixOperation(x.getSourceInfo(), x.getOp(),
expressions.get(expressions.size() - 1)));
ctx.replaceMe(result);
return;
}
if (ignoringExpressionOutput.contains(x)) {
JPrefixOperation newOp = new JPrefixOperation(x.getSourceInfo(), x.getOp(), x.getArg());
ctx.replaceMe(newOp);
}
}
/**
* Simplify the ! operator if possible.
*/
@Override
public void endVisit(JPrefixOperation x, Context ctx) {
if (x.getOp().isModifying()) {
lvalues.remove(x.getArg());
}
// If the argument is a multiexpression restructure it if possible.
if (isNonEmptyMultiExpression(x.getArg())) {
List expressions = ((JMultiExpression) x.getArg()).getExpressions();
JMultiExpression result = new JMultiExpression(x.getArg().getSourceInfo(),
expressions.subList(0, expressions.size() - 1));
result.addExpressions(new JPrefixOperation(x.getSourceInfo(), x.getOp(),
expressions.get(expressions.size() - 1)));
ctx.replaceMe(result);
return;
}
if (x.getArg() instanceof JValueLiteral) {
if (evalOpOnLiteral(x.getOp(), (JValueLiteral) x.getArg(), ctx)) {
return;
}
}
if (x.getOp() == JUnaryOperator.NOT) {
maybeReplaceMe(x, Simplifier.not(x), ctx);
return;
} else if (x.getOp() == JUnaryOperator.NEG) {
maybeReplaceMe(x, simplifyNegate(x, x.getArg()), ctx);
}
}
/**
* Optimize switch statements.
*/
@Override
public void endVisit(JSwitchStatement x, Context ctx) {
switchBlocks.remove(x.getBody());
// If it returns true, it was reduced to nothing
if (tryReduceSwitchWithConstantInput(x, ctx)) {
return;
}
if (hasNoDefaultCase(x)) {
removeEmptyCases(x);
}
removeDoubleBreaks(x);
tryRemoveSwitch(x, ctx);
}
/**
* 1) Remove catch blocks whose exception type is not instantiable. 2) Prune
* try statements with no body. 3) Hoist up try statements with no catches
* and an empty finally.
*/
@Override
public void endVisit(JTryStatement x, Context ctx) {
// 1) Remove catch blocks whose exception type is not instantiable.
List catchClauses = x.getCatchClauses();
Iterator itClauses = catchClauses.iterator();
while (itClauses.hasNext()) {
JTryStatement.CatchClause clause = itClauses.next();
// Go over the types in the multiexception and remove the ones that are not instantiable.
Iterator itTypes = clause.getTypes().iterator();
while (itTypes.hasNext()) {
JReferenceType type = (JReferenceType) itTypes.next();
if (!program.typeOracle.isInstantiatedType(type) || type.isNullType()) {
itTypes.remove();
madeChanges();
}
}
// if all exception types are gone then remove whole clause.
if (clause.getTypes().isEmpty()) {
itClauses.remove();
madeChanges();
}
}
// Compute properties regarding the state of this try statement
boolean noTry = Simplifier.isEmpty(x.getTryBlock());
boolean noCatch = catchClauses.size() == 0;
boolean noFinally = Simplifier.isEmpty(x.getFinallyBlock());
if (noTry) {
// 2) Prune try statements with no body.
if (noFinally) {
// if there's no finally, prune the whole thing
removeMe(x, ctx);
} else {
// replace the try statement with just the contents of the finally
replaceMe(x.getFinallyBlock(), ctx);
}
} else if (noCatch && noFinally) {
// 3) Hoist up try statements with no catches and an empty finally.
// If there's no catch or finally, there's no point in this even being
// a try statement, replace myself with the try block
replaceMe(x.getTryBlock(), ctx);
}
}
/**
* Prune while (false) statements.
*/
@Override
public void endVisit(JWhileStatement x, Context ctx) {
JExpression expression = x.getTestExpr();
if (expression instanceof JBooleanLiteral) {
JBooleanLiteral booleanLiteral = (JBooleanLiteral) expression;
// If false, prune the while statement
if (!booleanLiteral.getValue()) {
removeMe(x, ctx);
}
}
}
@Override
public boolean visit(JBinaryOperation x, Context ctx) {
if (x.getOp().isAssignment()) {
lvalues.add(x.getLhs());
}
return true;
}
@Override
public boolean visit(JClassType x, Context ctx) {
// We can't eliminate code from an external type
return !x.isExternal();
}
@Override
public boolean visit(JDeclarationStatement x, Context ctx) {
lvalues.add(x.getVariableRef());
return true;
}
@Override
public boolean visit(JExpressionStatement x, Context ctx) {
ignoringExpressionOutput.add(x.getExpr());
return true;
}
@Override
public boolean visit(JMethodCall x, Context ctx) {
JMethod target = x.getTarget();
if (target.isStatic() && x.getInstance() != null) {
ignoringExpressionOutput.add(x.getInstance());
}
return true;
}
@Override
public boolean visit(JMultiExpression x, Context ctx) {
List exprs = x.getExpressions();
if (exprs.size() > 0) {
if (ignoringExpressionOutput.contains(x)) {
// None of my children matter.
ignoringExpressionOutput.addAll(exprs);
} else {
// Only my final child matters.
List nonFinalChildren = exprs.subList(0, exprs.size() - 1);
ignoringExpressionOutput.addAll(nonFinalChildren);
}
}
return true;
}
@Override
public boolean visit(JPostfixOperation x, Context ctx) {
if (x.getOp().isModifying()) {
lvalues.add(x.getArg());
}
return true;
}
@Override
public boolean visit(JPrefixOperation x, Context ctx) {
if (x.getOp().isModifying()) {
lvalues.add(x.getArg());
}
return true;
}
@Override
public boolean visit(JSwitchStatement x, Context ctx) {
switchBlocks.add(x.getBody());
return true;
}
/**
* Returns true if a block can be merged into its parent block. This is true
* when the block contains no local declarations.
*/
private boolean canPromoteBlock(JBlock block) {
for (JStatement nestedStmt : block.getStatements()) {
if (nestedStmt instanceof JDeclarationStatement) {
JDeclarationStatement decl = (JDeclarationStatement) nestedStmt;
if (decl.getVariableRef() instanceof JLocalRef) {
return false;
}
}
}
return true;
}
private JMethodCall createClinitCall(SourceInfo sourceInfo, JDeclaredType targetType) {
JMethod clinit = targetType.getClinitTarget().getClinitMethod();
assert (JProgram.isClinit(clinit));
return new JMethodCall(sourceInfo, null, clinit);
}
private void evalConcat(SourceInfo info, JExpression lhs, JExpression rhs, Context ctx) {
if (lhs instanceof JValueLiteral && rhs instanceof JValueLiteral) {
Object lhsObj = ((JValueLiteral) lhs).getValueObj();
Object rhsObj = ((JValueLiteral) rhs).getValueObj();
ctx.replaceMe(program.getStringLiteral(info, String.valueOf(lhsObj)
+ String.valueOf(rhsObj)));
}
}
/**
* Evaluate lhs == rhs.
*
* @param lhs Any literal.
* @param rhs Any literal.
* @return Whether lhs == rhs will evaluate to
* true at run time; string literal comparisons use .equals() semantics.
*/
private boolean evalEq(JValueLiteral lhs, JValueLiteral rhs) {
if (isTypeNull(lhs)) {
return isTypeNull(rhs);
}
if (isTypeString(lhs)) {
return isTypeString(rhs) &&
((JStringLiteral) lhs).getValue().equals(((JStringLiteral) rhs).getValue());
}
if (isTypeBoolean(lhs)) {
return toBoolean(lhs) == toBoolean(rhs);
}
if (isTypeFloatingPoint(lhs) || isTypeFloatingPoint(rhs)) {
return Ieee754_64_Arithmetic.eq(toDouble(lhs), toDouble(rhs));
}
if (isTypeLong(lhs) || isTypeLong(rhs)) {
return toLong(lhs) == toLong(rhs);
}
return toInt(lhs) == toInt(rhs);
}
/**
* Static evaluation of a unary operation on a literal.
*
* @return Whether a change was made
*/
private boolean evalOpOnLiteral(JUnaryOperator op, JValueLiteral exp, Context ctx) {
switch (op) {
case BIT_NOT: {
long value = toLong(exp);
long res = ~value;
if (isTypeLong(exp)) {
ctx.replaceMe(program.getLiteralLong(res));
} else {
ctx.replaceMe(program.getLiteralInt((int) res));
}
return true;
}
case NEG:
if (isTypeLong(exp)) {
ctx.replaceMe(program.getLiteralLong(-toLong(exp)));
return true;
}
if (isTypeIntegral(exp)) {
ctx.replaceMe(program.getLiteralInt(-toInt(exp)));
return true;
}
if (isTypeDouble(exp)) {
ctx.replaceMe(program.getLiteralDouble(Ieee754_64_Arithmetic.neg(toDouble(exp))));
return true;
}
if (isTypeFloat(exp)) {
ctx.replaceMe(program.getLiteralFloat(Ieee754_64_Arithmetic.neg(toDouble(exp))));
return true;
}
return false;
case NOT: {
JBooleanLiteral booleanLit = (JBooleanLiteral) exp;
ctx.replaceMe(program.getLiteralBoolean(!booleanLit.getValue()));
return true;
}
default:
return false;
}
}
/**
* Static evaluation of a binary operation on two literals.
*
* @return Whether a change was made
*/
private boolean evalOpOnLiterals(JBinaryOperator op, JValueLiteral lhs, JValueLiteral rhs,
Context ctx) {
switch (op) {
case EQ: {
ctx.replaceMe(program.getLiteralBoolean(evalEq(lhs, rhs)));
return true;
}
case NEQ: {
ctx.replaceMe(program.getLiteralBoolean(!evalEq(lhs, rhs)));
return true;
}
case ADD:
case SUB:
case MUL:
case DIV:
case MOD: {
if (isTypeFloatingPoint(lhs) || isTypeFloatingPoint(rhs)) {
// do the op on doubles and cast back
double left = toDouble(lhs);
double right = toDouble(rhs);
double res;
switch (op) {
case ADD:
res = Ieee754_64_Arithmetic.add(left, right);
break;
case SUB:
res = Ieee754_64_Arithmetic.subtract(left, right);
break;
case MUL:
res = Ieee754_64_Arithmetic.multiply(left, right);
break;
case DIV:
res = Ieee754_64_Arithmetic.divide(left, right);
break;
case MOD:
res = Ieee754_64_Arithmetic.mod(left, right);
break;
default:
assert false;
return false;
}
if (isTypeDouble(lhs) || isTypeDouble(rhs)) {
ctx.replaceMe(program.getLiteralDouble(res));
} else {
ctx.replaceMe(program.getLiteralFloat(res));
}
return true;
} else if (isTypeIntegral(lhs) && isTypeIntegral(rhs)) {
// do the op on longs and cast to the correct
// result type at the end
long left = toLong(lhs);
long right = toLong(rhs);
long res;
switch (op) {
case ADD:
res = left + right;
break;
case SUB:
res = left - right;
break;
case MUL:
res = left * right;
break;
case DIV:
if (right == 0) {
// Don't divide by zero
return false;
}
res = left / right;
break;
case MOD:
if (right == 0) {
// Don't divide by zero
return false;
}
res = left % right;
break;
default:
assert false;
return false;
}
if (isTypeLong(lhs) || isTypeLong(rhs)) {
ctx.replaceMe(program.getLiteralLong(res));
} else {
ctx.replaceMe(program.getLiteralInt((int) res));
}
return true;
}
return false;
}
case LT:
case LTE:
case GT:
case GTE: {
if (isTypeFloatingPoint(lhs) || isTypeFloatingPoint(rhs)) {
// operate on doubles
double left = toDouble(lhs);
double right = toDouble(rhs);
boolean res;
switch (op) {
case LT:
res = Ieee754_64_Arithmetic.lt(left, right);
break;
case LTE:
res = Ieee754_64_Arithmetic.le(left, right);
break;
case GT:
res = Ieee754_64_Arithmetic.gt(left, right);
break;
case GTE:
res = Ieee754_64_Arithmetic.ge(left, right);
break;
default:
assert false;
return false;
}
ctx.replaceMe(program.getLiteralBoolean(res));
return true;
} else if (isTypeIntegral(lhs) && isTypeIntegral(rhs)) {
// operate on longs
long left = toLong(lhs);
long right = toLong(rhs);
boolean res;
switch (op) {
case LT:
res = left < right;
break;
case LTE:
res = left <= right;
break;
case GT:
res = left > right;
break;
case GTE:
res = left >= right;
break;
default:
assert false;
return false;
}
ctx.replaceMe(program.getLiteralBoolean(res));
return true;
}
return false;
}
case BIT_AND:
case BIT_OR:
case BIT_XOR:
if (isTypeBoolean(lhs)) {
// TODO: maybe eval non-short-circuit boolean operators.
return false;
} else if (isTypeIntegral(lhs) && isTypeIntegral(rhs)) {
// operate on longs and then cast down
long left = toLong(lhs);
long right = toLong(rhs);
long res;
switch (op) {
case BIT_AND:
res = left & right;
break;
case BIT_OR:
res = left | right;
break;
case BIT_XOR:
res = left ^ right;
break;
default:
assert false;
return false;
}
if (isTypeLong(lhs) || isTypeLong(rhs)) {
ctx.replaceMe(program.getLiteralLong(res));
} else {
ctx.replaceMe(program.getLiteralInt((int) res));
}
return true;
}
return false;
case SHL:
case SHR:
case SHRU: {
if (isTypeLong(lhs)) {
long left = toLong(lhs);
int right = toInt(rhs);
long res;
switch (op) {
case SHL:
res = left << right;
break;
case SHR:
res = left >> right;
break;
case SHRU:
res = left >>> right;
break;
default:
assert false;
return false;
}
ctx.replaceMe(program.getLiteralLong(res));
return true;
} else if (isTypeIntegral(lhs) && isTypeIntegral(rhs)) {
int left = toInt(lhs);
int right = toInt(rhs);
int res;
switch (op) {
case SHL:
res = left << right;
break;
case SHR:
res = left >> right;
break;
case SHRU:
res = left >>> right;
break;
default:
assert false;
return false;
}
ctx.replaceMe(program.getLiteralInt(res));
return true;
}
return false;
}
default:
return false;
}
}
/**
* If the effect of statement is to immediately do a break,
* then return the {@link JBreakStatement} corresponding to that break.
*/
private JBreakStatement findUnconditionalBreak(JStatement statement) {
if (statement instanceof JBreakStatement) {
return (JBreakStatement) statement;
} else if (statement instanceof JBlock) {
JBlock block = (JBlock) statement;
List blockStmts = block.getStatements();
if (blockStmts.size() > 0 && isUnconditionalBreak(blockStmts.get(0))) {
return (JBreakStatement) blockStmts.get(0);
}
}
return null;
}
/**
* Tries to removes cases and statements from switches whose expression is a
* constant value.
*
* @return true, if the switch was completely eliminated
*/
private boolean tryReduceSwitchWithConstantInput(JSwitchStatement s, Context ctx) {
if (!(s.getExpr() instanceof JValueLiteral)) {
// the input is not a constant
return false;
}
JValueLiteral targetValue = (JValueLiteral) s.getExpr();
// Find the matching case
JCaseStatement matchingCase = null;
for (JStatement subStatement : s.getBody().getStatements()) {
if (subStatement instanceof JCaseStatement) {
JCaseStatement caseStatement = (JCaseStatement) subStatement;
if (caseStatement.getExpr() == null) {
// speculatively put the default case into the matching case
matchingCase = caseStatement;
} else if (caseStatement.getExpr() instanceof JValueLiteral) {
JValueLiteral caseValue = (JValueLiteral) caseStatement.getExpr();
if (caseValue.getValueObj().equals(targetValue.getValueObj())) {
matchingCase = caseStatement;
break;
}
}
}
}
if (matchingCase == null) {
// the switch has no default and no matching cases
// the expression is a value literal, so it can go away completely
removeMe(s, ctx);
return true;
}
Iterator it = s.getBody().getStatements().iterator();
// Remove things until we find the matching case
while (it.hasNext() && (it.next() != matchingCase)) {
it.remove();
madeChanges();
}
// Until an unconditional control break, preserve everything that isn't a case
// or default.
while (it.hasNext()) {
JStatement statement = it.next();
if (statement.unconditionalControlBreak()) {
break;
} else if (statement instanceof JCaseStatement) {
it.remove();
}
}
// having found a break or return (or reached the end), remove all remaining
while (it.hasNext()) {
it.next();
it.remove();
madeChanges();
}
return false;
}
private boolean hasNoDefaultCase(JSwitchStatement x) {
JBlock body = x.getBody();
boolean inDefault = false;
for (JStatement statement : body.getStatements()) {
if (statement instanceof JCaseStatement) {
JCaseStatement caseStmt = (JCaseStatement) statement;
if (caseStmt.getExpr() == null) {
inDefault = true;
}
} else if (isUnconditionalUnlabeledBreak(statement)) {
inDefault = false;
} else {
// We have some code to execute other than a break.
if (inDefault) {
// We have a default case with real code.
return false;
}
}
}
// We found no default case that wasn't empty.
return true;
}
private boolean isLiteralNegativeOne(JExpression exp) {
if (!(exp instanceof JValueLiteral)) {
return false;
}
JValueLiteral lit = (JValueLiteral) exp;
if (isTypeIntegral(lit) && toLong(lit) == -1) {
return true;
}
if (isTypeFloatingPoint(lit) && toDouble(lit) == -1.0) {
return true;
}
return false;
}
private boolean isLiteralOne(JExpression exp) {
if (!(exp instanceof JValueLiteral)) {
return false;
}
JValueLiteral lit = (JValueLiteral) exp;
if (isTypeIntegral(lit) && toLong(lit) == 1) {
return true;
}
return isTypeFloatingPoint(lit) && toDouble(lit) == 1.0;
}
private boolean isLiteralZero(JExpression exp) {
if (exp instanceof JValueLiteral) {
JValueLiteral lit = (JValueLiteral) exp;
if (toDouble(lit) == 0.0) {
// Using toDouble only is safe even for integer types. All types but
// long will keep full precision. Longs will lose precision, but
// it will not affect whether the resulting double is zero or not.
return true;
}
}
return false;
}
private boolean isTypeBoolean(JExpression lhs) {
return lhs.getType() == program.getTypePrimitiveBoolean();
}
private boolean isTypeDouble(JExpression exp) {
return isTypeDouble(exp.getType());
}
private boolean isTypeDouble(JType type) {
return type == program.getTypePrimitiveDouble();
}
private boolean isTypeFloat(JExpression exp) {
return isTypeFloat(exp.getType());
}
private boolean isTypeFloat(JType type) {
return type == program.getTypePrimitiveFloat();
}
/**
* Return whether the type of the expression is float or double.
*/
private boolean isTypeFloatingPoint(JExpression exp) {
return isTypeFloatingPoint(exp.getType());
}
private boolean isTypeFloatingPoint(JType type) {
return ((type == program.getTypePrimitiveDouble()) || (type == program
.getTypePrimitiveFloat()));
}
/**
* Return whether the type of the expression is byte, char, short, int, or
* long.
*/
private boolean isTypeIntegral(JExpression exp) {
return isTypeIntegral(exp.getType());
}
private boolean isTypeIntegral(JType type) {
return ((type == program.getTypePrimitiveInt()) || (type == program.getTypePrimitiveLong())
|| (type == program.getTypePrimitiveChar()) || (type == program.getTypePrimitiveByte())
|| (type == program.getTypePrimitiveShort()));
}
private boolean isTypeLong(JExpression exp) {
return isTypeLong(exp.getType());
}
private boolean isTypeLong(JType type) {
return type == program.getTypePrimitiveLong();
}
private boolean isTypeNull(JExpression exp) {
return isTypeNull(exp.getType());
}
private boolean isTypeNull(JType type) {
return type.isNullType();
}
private boolean isTypeString(JExpression exp) {
return program.isJavaLangString(exp.getType());
}
private boolean isUnconditionalBreak(JStatement statement) {
return findUnconditionalBreak(statement) != null;
}
private boolean isUnconditionalUnlabeledBreak(JStatement statement) {
JBreakStatement breakStat = findUnconditionalBreak(statement);
return (breakStat != null) && (breakStat.getLabel() == null);
}
private T last(List statements) {
return statements.get(statements.size() - 1);
}
private Class classObjectForType(JType type) {
return classObjectsByType.get(type);
}
/**
* Replace me only if the updated expression is different.
*/
private void maybeReplaceMe(JExpression x, JExpression updated, Context ctx) {
if (updated != x) {
ctx.replaceMe(updated);
}
}
private void maybeReplaceMe(JStatement x, JStatement updated, Context ctx) {
if (updated != x) {
replaceMe(updated, ctx);
}
}
private void maybeReplaceWithOrdinalValue(JExpression instanceExpr, Context ctx) {
if (!(instanceExpr instanceof JFieldRef)) {
return;
}
JFieldRef fieldRef = (JFieldRef) instanceExpr;
if (!(fieldRef.getField() instanceof JEnumField)) {
return;
}
assert fieldRef.getInstance() == null;
JEnumField enumField = (JEnumField) fieldRef.getField();
ctx.replaceMe(program.getLiteralInt(enumField.ordinal()));
}
private int numRemovableExpressions(JMultiExpression x) {
if (ignoringExpressionOutput.contains(x)) {
// The result doesn't matter: all expressions can be removed.
return x.getNumberOfExpressions();
} else {
// The last expression cannot be removed.
return x.getNumberOfExpressions() - 1;
}
}
/**
* Removes any break statements that appear one after another.
*/
private void removeDoubleBreaks(JSwitchStatement x) {
JBlock body = x.getBody();
boolean lastWasBreak = true;
for (int i = 0; i < body.getStatements().size(); ++i) {
JStatement statement = body.getStatements().get(i);
boolean isBreak = isUnconditionalBreak(statement);
if (isBreak && lastWasBreak) {
body.removeStmt(i--);
madeChanges();
}
lastWasBreak = isBreak;
}
// Remove a trailing break statement from a case block
if (body.getStatements().size() > 0
&& isUnconditionalUnlabeledBreak(last(body.getStatements()))) {
body.removeStmt(body.getStatements().size() - 1);
madeChanges();
}
}
/**
* A switch with no default case can have its empty cases pruned.
*/
private void removeEmptyCases(JSwitchStatement x) {
JBlock body = x.getBody();
List noOpCaseStatements = new ArrayList();
List potentialNoOpCaseStatements = new ArrayList();
/*
* A case statement has no effect if there is no code between it and
* either an unconditional break or the end of the switch.
*/
for (JStatement statement : body.getStatements()) {
if (statement instanceof JCaseStatement) {
potentialNoOpCaseStatements.add(statement);
} else if (isUnconditionalUnlabeledBreak(statement)) {
// If we have any potential no-ops, they now become real no-ops.
noOpCaseStatements.addAll(potentialNoOpCaseStatements);
potentialNoOpCaseStatements.clear();
} else {
// Any other kind of statement makes these case statements are useful.
potentialNoOpCaseStatements.clear();
}
}
// None of the remaining case statements have any effect
noOpCaseStatements.addAll(potentialNoOpCaseStatements);
if (noOpCaseStatements.size() > 0) {
for (JStatement statement : noOpCaseStatements) {
body.removeStmt(body.getStatements().indexOf(statement));
madeChanges();
}
}
}
/**
* Call this instead of directly calling ctx.removeMe() for
* Statements.
*/
private void removeMe(JStatement stmt, Context ctx) {
if (ctx.canRemove()) {
ctx.removeMe();
} else {
// empty block statement
ctx.replaceMe(new JBlock(stmt.getSourceInfo()));
}
}
/**
*
* Call this instead of directly calling ctx.replaceMe() for
* Statements.
*/
private void replaceMe(JStatement stmt, Context ctx) {
stmt = this.accept(stmt, ctx.canRemove());
if (stmt == null) {
ctx.removeMe();
} else {
ctx.replaceMe(stmt);
}
}
private boolean simplifyAdd(JExpression lhs, JExpression rhs, Context ctx, JType type) {
if (isLiteralZero(rhs)) {
ctx.replaceMe(Simplifier.cast(type, lhs));
return true;
}
if (isLiteralZero(lhs)) {
ctx.replaceMe(Simplifier.cast(type, rhs));
return true;
}
return false;
}
/**
* Simplify exp == bool, where bool is a boolean
* literal.
*/
private void simplifyBooleanEq(JExpression exp, boolean bool, Context ctx) {
if (bool) {
ctx.replaceMe(exp);
} else {
ctx.replaceMe(new JPrefixOperation(exp.getSourceInfo(), JUnaryOperator.NOT, exp));
}
}
/**
* Simplify lhs == rhs, where lhs and
* rhs are known to be boolean. If negate is
* true, then treat it as lhs != rhs instead of
* lhs == rhs. Assumes that the case where both sides are
* literals has already been checked.
*/
private void simplifyBooleanEq(JExpression lhs, JExpression rhs, Context ctx, boolean negate) {
if (lhs instanceof JBooleanLiteral) {
boolean left = ((JBooleanLiteral) lhs).getValue();
simplifyBooleanEq(rhs, left ^ negate, ctx);
return;
}
if (rhs instanceof JBooleanLiteral) {
boolean right = ((JBooleanLiteral) rhs).getValue();
simplifyBooleanEq(lhs, right ^ negate, ctx);
return;
}
}
private boolean simplifyDiv(JExpression lhs, JExpression rhs, Context ctx, JType type) {
if (isLiteralOne(rhs)) {
ctx.replaceMe(Simplifier.cast(type, lhs));
return true;
}
if (isLiteralNegativeOne(rhs)) {
ctx.replaceMe(simplifyNegate(Simplifier.cast(type, lhs)));
return true;
}
return false;
}
private AnalysisResult staticallyEvaluateEq(JExpression lhs, JExpression rhs) {
JType lhsType = lhs.getType();
JType rhsType = rhs.getType();
if (lhsType.isNullType() && rhsType.isNullType()) {
return AnalysisResult.TRUE;
}
if (lhsType.isNullType() && !rhsType.canBeNull() ||
rhsType.isNullType() && !lhsType.canBeNull()) {
return AnalysisResult.FALSE;
}
if (!lhsType.canBeSubclass() && !rhsType.canBeSubclass() &&
!lhsType.canBeNull() && !rhsType.canBeNull() && lhsType instanceof JReferenceType &&
lhsType.getUnderlyingType() != rhsType.getUnderlyingType()) {
// We can conclude that lhs != rhs via type compatibility. If both lhs and rhs are typed
// as exact and not null then if the underlying types are different the comparison clearly
// fails.
return AnalysisResult.FALSE;
}
return AnalysisResult.UNKNOWN;
}
/**
* Tries to statically evaluate the instanceof operation. Returning TRUE if it can be determined
* statically that it is true when not null, FALSE if it can be determined that is false and
* UNKNOWN if the* result can not be determined statically.
*/
private AnalysisResult staticallyEvaluateInstanceOf(JReferenceType fromType,
JReferenceType toType) {
if (fromType.isNullType()) {
// null is never instanceof anything
return AnalysisResult.FALSE;
} else if (program.typeOracle.castSucceedsTrivially(fromType, toType)) {
return AnalysisResult.TRUE;
} else if (!program.typeOracle.isInstantiatedType(toType)) {
return AnalysisResult.FALSE;
} else if (program.typeOracle.castFailsTrivially(fromType, toType)) {
return AnalysisResult.FALSE;
}
return AnalysisResult.UNKNOWN;
}
/**
* Simplify lhs == rhs. If negate is true, then
* it's actually static evaluation of lhs != rhs.
*/
private void simplifyEq(JExpression lhs, JExpression rhs, Context ctx, boolean negate) {
// simplify: null == null -> true
AnalysisResult analysisResult = staticallyEvaluateEq(lhs, rhs);
if (analysisResult != AnalysisResult.UNKNOWN) {
ctx.replaceMe(JjsUtils.createOptimizedMultiExpression(
lhs, rhs, program.getLiteralBoolean(negate ^ (analysisResult == AnalysisResult.TRUE))));
return;
}
if (isTypeBoolean(lhs) && isTypeBoolean(rhs)) {
simplifyBooleanEq(lhs, rhs, ctx, negate);
return;
}
}
private boolean simplifyMul(JExpression lhs, JExpression rhs, Context ctx, JType type) {
if (isLiteralOne(rhs)) {
ctx.replaceMe(Simplifier.cast(type, lhs));
return true;
}
if (isLiteralOne(lhs)) {
ctx.replaceMe(Simplifier.cast(type, rhs));
return true;
}
if (isLiteralNegativeOne(rhs)) {
ctx.replaceMe(simplifyNegate(Simplifier.cast(type, lhs)));
return true;
}
if (isLiteralNegativeOne(lhs)) {
ctx.replaceMe(simplifyNegate(Simplifier.cast(type, rhs)));
return true;
}
if (isLiteralZero(rhs) && !lhs.hasSideEffects()) {
ctx.replaceMe(Simplifier.cast(type, rhs));
return true;
}
if (isLiteralZero(lhs) && !rhs.hasSideEffects()) {
ctx.replaceMe(Simplifier.cast(type, lhs));
return true;
}
return false;
}
private JExpression simplifyNegate(JExpression exp) {
return simplifyNegate(null, exp);
}
/**
* Simplify the expression -exp.
*
* @param original An expression equivalent to -exp.
* @param exp The expression to negate.
*
* @return A simplified expression equivalent to - exp.
*/
private JExpression simplifyNegate(JExpression original, JExpression exp) {
// - -x -> x
if (exp instanceof JPrefixOperation) {
JPrefixOperation prefarg = (JPrefixOperation) exp;
if (prefarg.getOp() == JUnaryOperator.NEG) {
return prefarg.getArg();
}
}
// no change
if (original != null) {
return original;
}
return new JPrefixOperation(exp.getSourceInfo(), JUnaryOperator.NEG, exp);
}
private boolean simplifySub(JExpression lhs, JExpression rhs, Context ctx, JType type) {
if (isLiteralZero(rhs)) {
ctx.replaceMe(Simplifier.cast(type, lhs));
return true;
}
if (isLiteralZero(lhs) && !isTypeFloatingPoint(type)) {
ctx.replaceMe(simplifyNegate(Simplifier.cast(type, rhs)));
return true;
}
return false;
}
private void simplifyXor(JExpression lhs, JBooleanLiteral rhs, Context ctx) {
if (rhs.getValue()) {
ctx.replaceMe(new JPrefixOperation(lhs.getSourceInfo(), JUnaryOperator.NOT, lhs));
} else {
ctx.replaceMe(lhs);
}
}
/**
* Simplify XOR expressions.
*
*
* true ^ x -> !x
* false ^ x -> x
* y ^ true -> !y
* y ^ false -> y
*
*/
private void simplifyXor(JExpression lhs, JExpression rhs, Context ctx) {
if (lhs instanceof JBooleanLiteral) {
JBooleanLiteral booleanLiteral = (JBooleanLiteral) lhs;
simplifyXor(rhs, booleanLiteral, ctx);
} else if (rhs instanceof JBooleanLiteral) {
JBooleanLiteral booleanLiteral = (JBooleanLiteral) rhs;
simplifyXor(lhs, booleanLiteral, ctx);
}
}
private boolean toBoolean(JValueLiteral x) {
return ((JBooleanLiteral) x).getValue();
}
/**
* Cast a Java wrapper class (Integer, Double, Float, etc.) to a double.
*/
private double toDouble(JValueLiteral literal) {
Object valueObj = literal.getValueObj();
if (valueObj instanceof Number) {
return ((Number) valueObj).doubleValue();
} else {
return ((Character) valueObj).charValue();
}
}
/**
* Cast a Java wrapper class (Integer, Double, Float, etc.) to a long.
*/
private int toInt(JValueLiteral literal) {
Object valueObj = literal.getValueObj();
if (valueObj instanceof Number) {
return ((Number) valueObj).intValue();
} else {
return ((Character) valueObj).charValue();
}
}
/**
* Cast a Java wrapper class (Integer, Double, Float, etc.) to a long.
*/
private long toLong(JValueLiteral literal) {
Object valueObj = literal.getValueObj();
if (valueObj instanceof Number) {
return ((Number) valueObj).longValue();
} else {
return ((Character) valueObj).charValue();
}
}
private JLiteral tryGetConstant(JVariableRef x) {
if (!lvalues.contains(x)) {
JLiteral lit = x.getTarget().getConstInitializer();
if (lit != null) {
/*
* Upcast the initializer so that the semantics of any arithmetic on
* this value is not changed.
*/
// TODO(spoon): use Simplifier.cast to shorten this
if (x.getType().isPrimitiveType() && (lit instanceof JValueLiteral)) {
JPrimitiveType xTypePrim = (JPrimitiveType) x.getType();
lit = xTypePrim.coerce((JValueLiteral) lit);
}
return lit;
}
}
return null;
}
/**
* Replace String methods having literal args with the static result.
*/
private void tryOptimizeStringCall(JMethodCall x, Context ctx, JMethod method) {
if (method.getType() == program.getTypeVoid()) {
return;
}
if (method.getOriginalParamTypes().size() != method.getParams().size()) {
// One or more parameters were pruned, abort.
return;
}
if (method.getName().endsWith("hashCode")) {
// This cannot be computed at compile time because our implementation
// differs from the JRE.
// TODO: actually, I think it DOES match now, so we can remove this?
return;
}
boolean isStaticImplMethod = program.isStaticImpl(method);
JExpression instance = isStaticImplMethod ? x.getArgs().get(0) : x.getInstance();
// drop the instance argument if the call was devirtualized as the compile time evaluation
// will use the real Java String class.
List arguments = isStaticImplMethod
? x.getArgs().subList(1, x.getArgs().size())
: x.getArgs();
// Handle toString specially to make sure it is a noop on non null string objects.
if (method.getName().endsWith("toString")) {
// replaces s.toString() with s
if (!instance.getType().canBeNull()) {
// Only replace when it known to be non null, otherwise it should follow the normal path
// and throw an NPE if null at runtime.
ctx.replaceMe(instance);
}
return;
}
Object instanceLiteral = tryTranslateLiteral(instance, String.class);
method = isStaticImplMethod ? program.instanceMethodForStaticImpl(method) : method;
if (instanceLiteral == null && !method.isStatic()) {
// Instance method on an instance that was not a literal.
return;
}
// Extract constant values from arguments or bail out if not possible, and also extract the
// declared parameter types that will be used to get the correct override.
int numberOfParameters = method.getOriginalParamTypes().size();
Object[] argumentConstantValues = new Object[numberOfParameters];
Class[] parametersClasses = new Class[numberOfParameters];
for (int i = 0; i < numberOfParameters; i++) {
parametersClasses[i] = classObjectForType(method.getOriginalParamTypes().get(i));
argumentConstantValues[i] = tryTranslateLiteral(arguments.get(i), parametersClasses[i]);
if (parametersClasses[i] == null || argumentConstantValues[i] == null) {
// not a literal, cannot evaluate statically.
return;
}
}
// Finally invoke the method statically.
JLiteral resultValue = staticallyInvokeStringMethod(
method.getName(), instanceLiteral, parametersClasses, argumentConstantValues);
if (resultValue != null) {
ctx.replaceMe(resultValue);
}
}
private JLiteral staticallyInvokeStringMethod(
String methodName, Object instance, Class[] parameterClasses, Object[] argumentValues) {
Method actualMethod = getMethod(methodName, String.class, parameterClasses);
if (actualMethod == null) {
// Convert all parameters types to Object to find a more generic applicable method.
Arrays.fill(parameterClasses, Object.class);
actualMethod = getMethod(methodName, String.class, parameterClasses);
}
if (actualMethod == null) {
return null;
}
try {
return program.getLiteral(actualMethod.invoke(instance, argumentValues));
} catch (Exception e) {
// couldn't evaluate statically or convert the result to a JLiteral
return null;
}
}
private Method getMethod(String name, Class enclosingClass, Class[] parameterTypes) {
try {
return enclosingClass.getMethod(name, parameterTypes);
} catch (NoSuchMethodException e) {
return null;
}
}
private void tryRemoveSwitch(JSwitchStatement x, Context ctx) {
JBlock body = x.getBody();
if (body.getStatements().size() == 0) {
// Empty switch; just run the switch condition.
replaceMe(x.getExpr().makeStatement(), ctx);
} else if (body.getStatements().size() == 2) {
/*
* If there are only two statements, we know it's a case statement and
* something with an effect.
*
* TODO: make this more sophisticated; what we should really care about
* is how many case statements it contains, not how many statements:
*
* switch(i) { default: a(); b(); c(); }
*
* becomes { a(); b(); c(); }
*
* switch(i) { case 1: a(); b(); c(); }
*
* becomes if (i == 1) { a(); b(); c(); }
*
* switch(i) { case 1: a(); b(); break; default: c(); d(); }
*
* becomes if (i == 1) { a(); b(); } else { c(); d(); }
*/
JCaseStatement caseStatement = (JCaseStatement) body.getStatements().get(0);
JStatement statement = body.getStatements().get(1);
FindBreakContinueStatementsVisitor visitor = new FindBreakContinueStatementsVisitor();
visitor.accept(statement);
if (visitor.hasBreakContinueStatements()) {
// Cannot optimize.
return;
}
if (caseStatement.getExpr() != null) {
// Create an if statement equivalent to the single-case switch.
JBinaryOperation compareOperation =
new JBinaryOperation(x.getSourceInfo(), program.getTypePrimitiveBoolean(),
JBinaryOperator.EQ, x.getExpr(), caseStatement.getExpr());
JBlock block = new JBlock(x.getSourceInfo());
block.addStmt(statement);
JIfStatement ifStatement =
new JIfStatement(x.getSourceInfo(), compareOperation, block, null);
replaceMe(ifStatement, ctx);
} else {
// All we have is a default case; convert to a JBlock.
JBlock block = new JBlock(x.getSourceInfo());
block.addStmt(x.getExpr().makeStatement());
block.addStmt(statement);
replaceMe(block, ctx);
}
}
}
private Object tryTranslateLiteral(JExpression maybeLiteral, Class type) {
if (!(maybeLiteral instanceof JValueLiteral)) {
return null;
}
// TODO: make this way better by a mile
if (type == boolean.class && maybeLiteral instanceof JBooleanLiteral) {
return Boolean.valueOf(((JBooleanLiteral) maybeLiteral).getValue());
}
if (type == char.class && maybeLiteral instanceof JCharLiteral) {
return Character.valueOf(((JCharLiteral) maybeLiteral).getValue());
}
if (type == double.class && maybeLiteral instanceof JFloatLiteral) {
return new Double(((JFloatLiteral) maybeLiteral).getValue());
}
if (type == double.class && maybeLiteral instanceof JDoubleLiteral) {
return new Double(((JDoubleLiteral) maybeLiteral).getValue());
}
if (type == int.class && maybeLiteral instanceof JIntLiteral) {
return Integer.valueOf(((JIntLiteral) maybeLiteral).getValue());
}
if (type == long.class && maybeLiteral instanceof JLongLiteral) {
return Long.valueOf(((JLongLiteral) maybeLiteral).getValue());
}
if (type == String.class && maybeLiteral instanceof JStringLiteral) {
return ((JStringLiteral) maybeLiteral).getValue();
}
if (type == Object.class) {
// We already know it is a JValueLiteral instance
return ((JValueLiteral) maybeLiteral).getValueObj();
}
return null;
}
}
/**
* Examines code to find out whether it contains any break or continue
* statements.
*
* TODO: We could be more sophisticated with this. A nested while loop with an
* unlabeled break should not cause this visitor to return false. Nor should a
* labeled break break to another context.
*/
public static class FindBreakContinueStatementsVisitor extends JVisitor {
private boolean hasBreakContinueStatements = false;
@Override
public void endVisit(JBreakStatement x, Context ctx) {
hasBreakContinueStatements = true;
}
@Override
public void endVisit(JContinueStatement x, Context ctx) {
hasBreakContinueStatements = true;
}
protected boolean hasBreakContinueStatements() {
return hasBreakContinueStatements;
}
}
public static final String NAME = DeadCodeElimination.class.getSimpleName();
@VisibleForTesting
public static OptimizerStats exec(JProgram program) {
return new DeadCodeElimination(program).execImpl(Collections.singleton(program),
OptimizerContext.NULL_OPTIMIZATION_CONTEXT);
}
// TODO(leafwang): Mark this as @VisibleForTesting eventually; this code path is also used
// by DataflowOptimizer for now.
public static OptimizerStats exec(JProgram program, JMethod method) {
return new DeadCodeElimination(program).execImpl(Collections.singleton(method),
OptimizerContext.NULL_OPTIMIZATION_CONTEXT);
}
/**
* Apply DeadCodeElimination on the set of newly modified methods (obtained from the optimzer
* context).
*/
public static OptimizerStats exec(JProgram program, OptimizerContext optimizerCtx) {
Set affectedMethods = affectedMethods(optimizerCtx);
OptimizerStats stats = new DeadCodeElimination(program).execImpl(affectedMethods, optimizerCtx);
optimizerCtx.setLastStepFor(NAME, optimizerCtx.getOptimizationStep());
optimizerCtx.incOptimizationStep();
JavaAstVerifier.assertProgramIsConsistent(program);
return stats;
}
/**
* Return the set of methods affected (because they are or callers of) by the modifications to the
* given set functions.
*/
private static Set affectedMethods(OptimizerContext optimizerCtx) {
Set modifiedMethods =
optimizerCtx.getModifiedMethodsSince(optimizerCtx.getLastStepFor(NAME));
Set affectedMethods = Sets.newLinkedHashSet();
affectedMethods.addAll(modifiedMethods);
affectedMethods.addAll(optimizerCtx.getCallers(modifiedMethods));
affectedMethods.addAll(optimizerCtx.getMethodsByReferencedFields(
optimizerCtx.getModifiedFieldsSince(optimizerCtx.getLastStepFor(NAME))));
return affectedMethods;
}
private final JProgram program;
private final Map> classObjectsByType;
public DeadCodeElimination(JProgram program) {
this.program = program;
classObjectsByType = new ImmutableMap.Builder()
.put(program.getTypeJavaLangObject(), Object.class)
.put(program.getTypeJavaLangString(), String.class)
.put(program.getTypePrimitiveBoolean(), boolean.class)
.put(program.getTypePrimitiveByte(), byte.class)
.put(program.getTypePrimitiveChar(), char.class)
.put(program.getTypePrimitiveDouble(), double.class)
.put(program.getTypePrimitiveFloat(), float.class)
.put(program.getTypePrimitiveInt(), int.class)
.put(program.getTypePrimitiveLong(), long.class)
.put(program.getTypePrimitiveShort(), short.class)
.build();
}
private OptimizerStats execImpl(Iterable nodes, OptimizerContext optimizerCtx) {
OptimizerStats stats = new OptimizerStats(NAME);
Event optimizeEvent = SpeedTracerLogger.start(CompilerEventType.OPTIMIZE, "optimizer", NAME);
DeadCodeVisitor deadCodeVisitor = new DeadCodeVisitor(optimizerCtx);
for (JNode node : nodes) {
deadCodeVisitor.accept(node);
}
stats.recordModified(deadCodeVisitor.getNumMods());
optimizeEvent.end("didChange", "" + stats.didChange());
return stats;
}
private enum AnalysisResult { TRUE, FALSE, UNKNOWN }
}
