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 * 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
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 */

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.
/**
 * 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.
/**
     * 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
Returns:
the literal node/**
         * 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.
Params:
deadCodeRoot – the root node of eliminated dead code
statements – a list that will be receiving the var nodes from the dead code, with their
initializers removed./**
     * 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);
        }
    }
}