path: root/src/jdk/nashorn/internal/codegen/FoldConstants.java

/*
 * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package jdk.nashorn.internal.codegen;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import jdk.nashorn.internal.codegen.types.Type;
import jdk.nashorn.internal.ir.BinaryNode;
import jdk.nashorn.internal.ir.Block;
import jdk.nashorn.internal.ir.BlockStatement;
import jdk.nashorn.internal.ir.CaseNode;
import jdk.nashorn.internal.ir.EmptyNode;
import jdk.nashorn.internal.ir.Expression;
import jdk.nashorn.internal.ir.FunctionNode;
import jdk.nashorn.internal.ir.IfNode;
import jdk.nashorn.internal.ir.LiteralNode;
import jdk.nashorn.internal.ir.LiteralNode.ArrayLiteralNode;
import jdk.nashorn.internal.ir.Node;
import jdk.nashorn.internal.ir.Statement;
import jdk.nashorn.internal.ir.SwitchNode;
import jdk.nashorn.internal.ir.TernaryNode;
import jdk.nashorn.internal.ir.UnaryNode;
import jdk.nashorn.internal.ir.VarNode;
import jdk.nashorn.internal.ir.visitor.SimpleNodeVisitor;
import jdk.nashorn.internal.runtime.Context;
import jdk.nashorn.internal.runtime.JSType;
import jdk.nashorn.internal.runtime.ScriptRuntime;
import jdk.nashorn.internal.runtime.logging.DebugLogger;
import jdk.nashorn.internal.runtime.logging.Loggable;
import jdk.nashorn.internal.runtime.logging.Logger;

/**
 * Simple constant folding pass, executed before IR is starting to be lowered.
 */
@Logger(name="fold")
final class FoldConstants extends SimpleNodeVisitor implements Loggable {

    private final DebugLogger log;

    FoldConstants(final Compiler compiler) {
        this.log = initLogger(compiler.getContext());
    }

    @Override
    public DebugLogger getLogger() {
        return log;
    }

    @Override
    public DebugLogger initLogger(final Context context) {
        return context.getLogger(this.getClass());
    }

    @Override
    public Node leaveUnaryNode(final UnaryNode unaryNode) {
        final LiteralNode<?> literalNode = new UnaryNodeConstantEvaluator(unaryNode).eval();
        if (literalNode != null) {
            log.info("Unary constant folded ", unaryNode, " to ", literalNode);
            return literalNode;
        }
        return unaryNode;
    }

    @Override
    public Node leaveBinaryNode(final BinaryNode binaryNode) {
        final LiteralNode<?> literalNode = new BinaryNodeConstantEvaluator(binaryNode).eval();
        if (literalNode != null) {
            log.info("Binary constant folded ", binaryNode, " to ", literalNode);
            return literalNode;
        }
        return binaryNode;
    }

    @Override
    public Node leaveFunctionNode(final FunctionNode functionNode) {
        return functionNode;
    }

    @Override
    public Node leaveIfNode(final IfNode ifNode) {
        final Node test = ifNode.getTest();
        if (test instanceof LiteralNode.PrimitiveLiteralNode) {
            final boolean isTrue = ((LiteralNode.PrimitiveLiteralNode<?>)test).isTrue();
            final Block executed = isTrue ? ifNode.getPass() : ifNode.getFail();
            final Block dropped  = isTrue ? ifNode.getFail() : ifNode.getPass();
            final List<Statement> statements = new ArrayList<>();

            if (executed != null) {
                statements.addAll(executed.getStatements()); // Get statements form executed branch
            }
            if (dropped != null) {
                extractVarNodesFromDeadCode(dropped, statements); // Get var-nodes from non-executed branch
            }
            if (statements.isEmpty()) {
                return new EmptyNode(ifNode);
            }
            return BlockStatement.createReplacement(ifNode, ifNode.getFinish(), statements);
        }
        return ifNode;
    }

    @Override
    public Node leaveTernaryNode(final TernaryNode ternaryNode) {
        final Node test = ternaryNode.getTest();
        if (test instanceof LiteralNode.PrimitiveLiteralNode) {
            return (((LiteralNode.PrimitiveLiteralNode<?>)test).isTrue() ? ternaryNode.getTrueExpression() : ternaryNode.getFalseExpression()).getExpression();
        }
        return ternaryNode;
    }

    @Override
    public Node leaveSwitchNode(final SwitchNode switchNode) {
        return switchNode.setUniqueInteger(lc, isUniqueIntegerSwitchNode(switchNode));
    }

    private static boolean isUniqueIntegerSwitchNode(final SwitchNode switchNode) {
        final Set<Integer> alreadySeen = new HashSet<>();
        for (final CaseNode caseNode : switchNode.getCases()) {
            final Expression test = caseNode.getTest();
            if (test != null && !isUniqueIntegerLiteral(test, alreadySeen)) {
                return false;
            }
        }
        return true;
    }

    private static boolean isUniqueIntegerLiteral(final Expression expr, final Set<Integer> alreadySeen) {
        if (expr instanceof LiteralNode) {
            final Object value = ((LiteralNode<?>)expr).getValue();
            if (value instanceof Integer) {
                return alreadySeen.add((Integer)value);
            }
        }
        return false;
    }

    /**
     * Helper class to evaluate constant expressions at compile time This is
     * also a simplifier used by BinaryNode visits, UnaryNode visits and
     * conversions.
     */
    abstract static class ConstantEvaluator<T extends Node> {
        protected T            parent;
        protected final long   token;
        protected final int    finish;

        protected ConstantEvaluator(final T parent) {
            this.parent = parent;
            this.token  = parent.getToken();
            this.finish = parent.getFinish();
        }

        /**
         * Returns a literal node that replaces the given parent node, or null if replacement
         * is impossible
         * @return the literal node
         */
        protected abstract LiteralNode<?> eval();
    }

    /**
     * When we eliminate dead code, we must preserve var declarations as they are scoped to the whole
     * function. This method gathers var nodes from code passed to it, removing their initializers.
     *
     * @param deadCodeRoot the root node of eliminated dead code
     * @param statements a list that will be receiving the var nodes from the dead code, with their
     * initializers removed.
     */
    static void extractVarNodesFromDeadCode(final Node deadCodeRoot, final List<Statement> statements) {
        deadCodeRoot.accept(new SimpleNodeVisitor() {
            @Override
            public boolean enterVarNode(final VarNode varNode) {
                statements.add(varNode.setInit(null));
                return false;
            }

            @Override
            public boolean enterFunctionNode(final FunctionNode functionNode) {
                // Don't descend into nested functions
                return false;
            }
        });
    }

    private static class UnaryNodeConstantEvaluator extends ConstantEvaluator<UnaryNode> {
        UnaryNodeConstantEvaluator(final UnaryNode parent) {
            super(parent);
        }

        @Override
        protected LiteralNode<?> eval() {
            final Node rhsNode = parent.getExpression();

            if (!(rhsNode instanceof LiteralNode)) {
                return null;
            }

            if (rhsNode instanceof ArrayLiteralNode) {
                return null;
            }

            final LiteralNode<?> rhs = (LiteralNode<?>)rhsNode;
            final Type rhsType = rhs.getType();
            final boolean rhsInteger = rhsType.isInteger() || rhsType.isBoolean();

            LiteralNode<?> literalNode;

            switch (parent.tokenType()) {
            case ADD:
                if (rhsInteger) {
                    literalNode = LiteralNode.newInstance(token, finish, rhs.getInt32());
                } else if (rhsType.isLong()) {
                    literalNode = LiteralNode.newInstance(token, finish, rhs.getLong());
                } else {
                    literalNode = LiteralNode.newInstance(token, finish, rhs.getNumber());
                }
                break;
            case SUB:
                if (rhsInteger && rhs.getInt32() != 0) { // @see test/script/basic/minuszero.js
                    literalNode = LiteralNode.newInstance(token, finish, -rhs.getInt32());
                } else if (rhsType.isLong() && rhs.getLong() != 0L) {
                    literalNode = LiteralNode.newInstance(token, finish, -rhs.getLong());
                } else {
                    literalNode = LiteralNode.newInstance(token, finish, -rhs.getNumber());
                }
                break;
            case NOT:
                literalNode = LiteralNode.newInstance(token, finish, !rhs.getBoolean());
                break;
            case BIT_NOT:
                literalNode = LiteralNode.newInstance(token, finish, ~rhs.getInt32());
                break;
            default:
                return null;
            }

            return literalNode;
        }
    }

    //TODO add AND and OR with one constant parameter (bitwise)
    private static class BinaryNodeConstantEvaluator extends ConstantEvaluator<BinaryNode> {
        BinaryNodeConstantEvaluator(final BinaryNode parent) {
            super(parent);
        }

        @Override
        protected LiteralNode<?> eval() {
            LiteralNode<?> result;

            result = reduceTwoLiterals();
            if (result != null) {
                return result;
            }

            result = reduceOneLiteral();
            if (result != null) {
                return result;
            }

            return null;
        }

        @SuppressWarnings("static-method")
        private LiteralNode<?> reduceOneLiteral() {
            //TODO handle patterns like AND, OR, numeric ops that can be strength reduced but not replaced by a single literal node etc
            return null;
        }

        private LiteralNode<?> reduceTwoLiterals() {
            if (!(parent.lhs() instanceof LiteralNode && parent.rhs() instanceof LiteralNode)) {
                return null;
            }

            final LiteralNode<?> lhs = (LiteralNode<?>)parent.lhs();
            final LiteralNode<?> rhs = (LiteralNode<?>)parent.rhs();

            if (lhs instanceof ArrayLiteralNode || rhs instanceof ArrayLiteralNode) {
                return null;
            }

            final Type widest = Type.widest(lhs.getType(), rhs.getType());

            boolean isInteger = widest.isInteger();
            final double value;

            switch (parent.tokenType()) {
            case DIV:
                value = lhs.getNumber() / rhs.getNumber();
                break;
            case ADD:
                if ((lhs.isString() || rhs.isNumeric()) && (rhs.isString() || rhs.isNumeric())) {
                    final Object res = ScriptRuntime.ADD(lhs.getObject(), rhs.getObject());
                    if (res instanceof Number) {
                        value = ((Number)res).doubleValue();
                        break;
                    }
                    assert res instanceof CharSequence : res + " was not a CharSequence, it was a " + res.getClass();
                    return LiteralNode.newInstance(token, finish, res.toString());
                }
                return null;
            case MUL:
                value = lhs.getNumber() * rhs.getNumber();
                break;
            case MOD:
                value = lhs.getNumber() % rhs.getNumber();
                break;
            case SUB:
                value = lhs.getNumber() - rhs.getNumber();
                break;
            case SHR:
                final long result = JSType.toUint32(lhs.getInt32() >>> rhs.getInt32());
                return LiteralNode.newInstance(token, finish, JSType.toNarrowestNumber(result));
            case SAR:
                return LiteralNode.newInstance(token, finish, lhs.getInt32() >> rhs.getInt32());
            case SHL:
                return LiteralNode.newInstance(token, finish, lhs.getInt32() << rhs.getInt32());
            case BIT_XOR:
                return LiteralNode.newInstance(token, finish, lhs.getInt32() ^ rhs.getInt32());
            case BIT_AND:
                return LiteralNode.newInstance(token, finish, lhs.getInt32() & rhs.getInt32());
            case BIT_OR:
                return LiteralNode.newInstance(token, finish, lhs.getInt32() | rhs.getInt32());
            case GE:
                return LiteralNode.newInstance(token, finish, ScriptRuntime.GE(lhs.getObject(), rhs.getObject()));
            case LE:
                return LiteralNode.newInstance(token, finish, ScriptRuntime.LE(lhs.getObject(), rhs.getObject()));
            case GT:
                return LiteralNode.newInstance(token, finish, ScriptRuntime.GT(lhs.getObject(), rhs.getObject()));
            case LT:
                return LiteralNode.newInstance(token, finish, ScriptRuntime.LT(lhs.getObject(), rhs.getObject()));
            case NE:
                return LiteralNode.newInstance(token, finish, ScriptRuntime.NE(lhs.getObject(), rhs.getObject()));
            case NE_STRICT:
                return LiteralNode.newInstance(token, finish, ScriptRuntime.NE_STRICT(lhs.getObject(), rhs.getObject()));
            case EQ:
                return LiteralNode.newInstance(token, finish, ScriptRuntime.EQ(lhs.getObject(), rhs.getObject()));
            case EQ_STRICT:
                return LiteralNode.newInstance(token, finish, ScriptRuntime.EQ_STRICT(lhs.getObject(), rhs.getObject()));
            default:
                return null;
            }

            isInteger &= JSType.isStrictlyRepresentableAsInt(value);

            if (isInteger) {
                return LiteralNode.newInstance(token, finish, (int)value);
            }

            return LiteralNode.newInstance(token, finish, value);
        }
    }
}