/*

 * Copyright (c) 1999, 2006, 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 com.sun.tools.javac.comp;

import com.sun.tools.javac.code.*;

import com.sun.tools.javac.jvm.*;

import com.sun.tools.javac.util.*;

import com.sun.tools.javac.code.Type.*;

import static com.sun.tools.javac.code.TypeTags.*;

import static com.sun.tools.javac.jvm.ByteCodes.*;

/** Helper class for constant folding, used by the attribution phase.

 *  This class is marked strictfp as mandated by JLS 15.4.

 *

 *  <p><b>This is NOT part of any supported API.

 *  If you write code that depends on this, you do so at your own risk.

 *  This code and its internal interfaces are subject to change or

 *  deletion without notice.</b>

 */

strictfp class ConstFold {

    protected static final Context.Key<ConstFold> constFoldKey =

        new Context.Key<ConstFold>();

    private Symtab syms;

    public static ConstFold instance(Context context) {

        ConstFold instance = context.get(constFoldKey);

        if (instance == null)

            instance = new ConstFold(context);

        return instance;

    }

    private ConstFold(Context context) {

        context.put(constFoldKey, this);

        syms = Symtab.instance(context);

    }

    static Integer minusOne = -1;

    static Integer zero     = 0;

    static Integer one      = 1;

   /** Convert boolean to integer (true = 1, false = 0).

    */

    private static Integer b2i(boolean b) {

        return b ? one : zero;

    }

    private static int intValue(Object x) { return ((Number)x).intValue(); }

    private static long longValue(Object x) { return ((Number)x).longValue(); }

    private static float floatValue(Object x) { return ((Number)x).floatValue(); }

    private static double doubleValue(Object x) { return ((Number)x).doubleValue(); }

    /** Fold binary or unary operation, returning constant type reflecting the

     *  operations result. Return null if fold failed due to an

     *  arithmetic exception.

     *  @param opcode    The operation's opcode instruction (usually a byte code),

     *                   as entered by class Symtab.

     *  @param argtypes  The operation's argument types (a list of length 1 or 2).

     *                   Argument types are assumed to have non-null constValue's.

     */

    Type fold(int opcode, List<Type> argtypes) {

        int argCount = argtypes.length();

        if (argCount == 1)

            return fold1(opcode, argtypes.head);

        else if (argCount == 2)

            return fold2(opcode, argtypes.head, argtypes.tail.head);

        else

            throw new AssertionError();

    }

    /** Fold unary operation.

     *  @param opcode    The operation's opcode instruction (usually a byte code),

     *                   as entered by class Symtab.

     *                   opcode's ifeq to ifge are for postprocessing

     *                   xcmp; ifxx pairs of instructions.

     *  @param operand   The operation's operand type.

     *                   Argument types are assumed to have non-null constValue's.

     */

    Type fold1(int opcode, Type operand) {

        try {

            Object od = operand.constValue();

            switch (opcode) {

            case nop:

                return operand;

            case ineg: // unary -

                return syms.intType.constType(-intValue(od));

            case ixor: // ~

                return syms.intType.constType(~intValue(od));

            case bool_not: // !

                return syms.booleanType.constType(b2i(intValue(od) == 0));

            case ifeq:

                return syms.booleanType.constType(b2i(intValue(od) == 0));

            case ifne:

                return syms.booleanType.constType(b2i(intValue(od) != 0));

            case iflt:

                return syms.booleanType.constType(b2i(intValue(od) < 0));

            case ifgt:

                return syms.booleanType.constType(b2i(intValue(od) > 0));

            case ifle:

                return syms.booleanType.constType(b2i(intValue(od) <= 0));

            case ifge:

                return syms.booleanType.constType(b2i(intValue(od) >= 0));

            case lneg: // unary -

                return syms.longType.constType(new Long(-longValue(od)));

            case lxor: // ~

                return syms.longType.constType(new Long(~longValue(od)));

            case fneg: // unary -

                return syms.floatType.constType(new Float(-floatValue(od)));

            case dneg: // ~

                return syms.doubleType.constType(new Double(-doubleValue(od)));

            default:

                return null;

            }

        } catch (ArithmeticException e) {

            return null;

        }

    }

    /** Fold binary operation.

     *  @param opcode    The operation's opcode instruction (usually a byte code),

     *                   as entered by class Symtab.

     *                   opcode's ifeq to ifge are for postprocessing

     *                   xcmp; ifxx pairs of instructions.

     *  @param left      The type of the operation's left operand.

     *  @param right     The type of the operation's right operand.

     */

    Type fold2(int opcode, Type left, Type right) {

        try {

            if (opcode > ByteCodes.preMask) {

                // we are seeing a composite instruction of the form xcmp; ifxx.

                // In this case fold both instructions separately.

                Type t1 = fold2(opcode >> ByteCodes.preShift, left, right);

                return (t1.constValue() == null) ? t1

                    : fold1(opcode & ByteCodes.preMask, t1);

            } else {

                Object l = left.constValue();

                Object r = right.constValue();

                switch (opcode) {

                case iadd:

                    return syms.intType.constType(intValue(l) + intValue(r));

                case isub:

                    return syms.intType.constType(intValue(l) - intValue(r));

                case imul:

                    return syms.intType.constType(intValue(l) * intValue(r));

                case idiv:

                    return syms.intType.constType(intValue(l) / intValue(r));

                case imod:

                    return syms.intType.constType(intValue(l) % intValue(r));

                case iand:

                    return (left.tag == BOOLEAN

                      ? syms.booleanType : syms.intType)

                      .constType(intValue(l) & intValue(r));

                case bool_and:

                    return syms.booleanType.constType(b2i((intValue(l) & intValue(r)) != 0));

                case ior:

                    return (left.tag == BOOLEAN

                      ? syms.booleanType : syms.intType)

                      .constType(intValue(l) | intValue(r));

                case bool_or:

                    return syms.booleanType.constType(b2i((intValue(l) | intValue(r)) != 0));

                case ixor:

                    return (left.tag == BOOLEAN

                      ? syms.booleanType : syms.intType)

                      .constType(intValue(l) ^ intValue(r));

                case ishl: case ishll:

                    return syms.intType.constType(intValue(l) << intValue(r));

                case ishr: case ishrl:

                    return syms.intType.constType(intValue(l) >> intValue(r));

                case iushr: case iushrl:

                    return syms.intType.constType(intValue(l) >>> intValue(r));

                case if_icmpeq:

                    return syms.booleanType.constType(

                        b2i(intValue(l) == intValue(r)));

                case if_icmpne:

                    return syms.booleanType.constType(

                        b2i(intValue(l) != intValue(r)));

                case if_icmplt:

                    return syms.booleanType.constType(

                        b2i(intValue(l) < intValue(r)));

                case if_icmpgt:

                    return syms.booleanType.constType(

                        b2i(intValue(l) > intValue(r)));

                case if_icmple:

                    return syms.booleanType.constType(

                        b2i(intValue(l) <= intValue(r)));

                case if_icmpge:

                    return syms.booleanType.constType(

                        b2i(intValue(l) >= intValue(r)));

                case ladd:

                    return syms.longType.constType(

                        new Long(longValue(l) + longValue(r)));

                case lsub:

                    return syms.longType.constType(

                        new Long(longValue(l) - longValue(r)));

                case lmul:

                    return syms.longType.constType(

                        new Long(longValue(l) * longValue(r)));

                case ldiv:

                    return syms.longType.constType(

                        new Long(longValue(l) / longValue(r)));

                case lmod:

                    return syms.longType.constType(

                        new Long(longValue(l) % longValue(r)));

                case land:

                    return syms.longType.constType(

                        new Long(longValue(l) & longValue(r)));

                case lor:

                    return syms.longType.constType(

                        new Long(longValue(l) | longValue(r)));

                case lxor:

                    return syms.longType.constType(

                        new Long(longValue(l) ^ longValue(r)));

                case lshl: case lshll:

                    return syms.longType.constType(

                        new Long(longValue(l) << intValue(r)));

                case lshr: case lshrl:

                    return syms.longType.constType(

                        new Long(longValue(l) >> intValue(r)));

                case lushr:

                    return syms.longType.constType(

                        new Long(longValue(l) >>> intValue(r)));

                case lcmp:

                    if (longValue(l) < longValue(r))

                        return syms.intType.constType(minusOne);

                    else if (longValue(l) > longValue(r))

                        return syms.intType.constType(one);

                    else

                        return syms.intType.constType(zero);

                case fadd:

                    return syms.floatType.constType(

                        new Float(floatValue(l) + floatValue(r)));

                case fsub:

                    return syms.floatType.constType(

                        new Float(floatValue(l) - floatValue(r)));

                case fmul:

                    return syms.floatType.constType(

                        new Float(floatValue(l) * floatValue(r)));

                case fdiv:

                    return syms.floatType.constType(

                        new Float(floatValue(l) / floatValue(r)));

                case fmod:

                    return syms.floatType.constType(

                        new Float(floatValue(l) % floatValue(r)));

                case fcmpg: case fcmpl:

                    if (floatValue(l) < floatValue(r))

                        return syms.intType.constType(minusOne);

                    else if (floatValue(l) > floatValue(r))

                        return syms.intType.constType(one);

                    else if (floatValue(l) == floatValue(r))

                        return syms.intType.constType(zero);

                    else if (opcode == fcmpg)

                        return syms.intType.constType(one);

                    else

                        return syms.intType.constType(minusOne);

                case dadd:

                    return syms.doubleType.constType(

                        new Double(doubleValue(l) + doubleValue(r)));

                case dsub:

                    return syms.doubleType.constType(

                        new Double(doubleValue(l) - doubleValue(r)));

                case dmul:

                    return syms.doubleType.constType(

                        new Double(doubleValue(l) * doubleValue(r)));

                case ddiv:

                    return syms.doubleType.constType(

                        new Double(doubleValue(l) / doubleValue(r)));

                case dmod:

                    return syms.doubleType.constType(

                        new Double(doubleValue(l) % doubleValue(r)));

                case dcmpg: case dcmpl:

                    if (doubleValue(l) < doubleValue(r))

                        return syms.intType.constType(minusOne);

                    else if (doubleValue(l) > doubleValue(r))

                        return syms.intType.constType(one);

                    else if (doubleValue(l) == doubleValue(r))

                        return syms.intType.constType(zero);

                    else if (opcode == dcmpg)

                        return syms.intType.constType(one);

                    else

                        return syms.intType.constType(minusOne);

                case if_acmpeq:

                    return syms.booleanType.constType(b2i(l.equals(r)));

                case if_acmpne:

                    return syms.booleanType.constType(b2i(!l.equals(r)));

                case string_add:

                    return syms.stringType.constType(

                        left.stringValue() + right.stringValue());

                default:

                    return null;

                }

            }

        } catch (ArithmeticException e) {

            return null;

        }

    }

    /** Coerce constant type to target type.

     *  @param etype      The source type of the coercion,

     *                    which is assumed to be a constant type compatble with

     *                    ttype.

     *  @param ttype      The target type of the coercion.

     */

     Type coerce(Type etype, Type ttype) {

         // WAS if (etype.baseType() == ttype.baseType())

         if (etype.tsym.type == ttype.tsym.type)

             return etype;

         if (etype.tag <= DOUBLE) {

             Object n = etype.constValue();

             switch (ttype.tag) {

             case BYTE:

                 return syms.byteType.constType(0 + (byte)intValue(n));

             case CHAR:

                 return syms.charType.constType(0 + (char)intValue(n));

             case SHORT:

                 return syms.shortType.constType(0 + (short)intValue(n));

             case INT:

                 return syms.intType.constType(intValue(n));

             case LONG:

                 return syms.longType.constType(longValue(n));

             case FLOAT:

                 return syms.floatType.constType(floatValue(n));

             case DOUBLE:

                 return syms.doubleType.constType(doubleValue(n));

             }

         }

         return ttype;

     }

}