/*
 * Copyright (c) 2015, 2018, 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.jvm;

import com.sun.tools.javac.code.*;
import com.sun.tools.javac.code.Symbol.MethodSymbol;
import com.sun.tools.javac.comp.Resolve;
import com.sun.tools.javac.jvm.PoolConstant.LoadableConstant;
import com.sun.tools.javac.tree.JCTree;
import com.sun.tools.javac.tree.TreeInfo;
import com.sun.tools.javac.tree.TreeMaker;
import com.sun.tools.javac.util.*;

import static com.sun.tools.javac.code.Kinds.Kind.MTH;
import static com.sun.tools.javac.code.TypeTag.*;
import static com.sun.tools.javac.jvm.ByteCodes.*;
import static com.sun.tools.javac.tree.JCTree.Tag.PLUS;
import com.sun.tools.javac.jvm.Items.*;

import java.util.HashMap;
import java.util.Map;

This lowers the String concatenation to something that JVM can understand.
 
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.
/** This lowers the String concatenation to something that JVM can understand.
 *
 *  <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>
 */
public abstract class StringConcat {

    
Maximum number of slots for String Concat call.
JDK's StringConcatFactory does not support more than that.
/**
     * Maximum number of slots for String Concat call.
     * JDK's StringConcatFactory does not support more than that.
     */
    private static final int MAX_INDY_CONCAT_ARG_SLOTS = 200;
    private static final char TAG_ARG   = '\u0001';
    private static final char TAG_CONST = '\u0002';

    protected final Gen gen;
    protected final Symtab syms;
    protected final Names names;
    protected final TreeMaker make;
    protected final Types types;
    protected final Map<Type, Symbol> sbAppends;
    protected final Resolve rs;

    protected static final Context.Key<StringConcat> concatKey = new Context.Key<>();

    public static StringConcat instance(Context context) {
        StringConcat instance = context.get(concatKey);
        if (instance == null) {
            instance = makeConcat(context);
        }
        return instance;
    }

    private static StringConcat makeConcat(Context context) {
        Target target = Target.instance(context);
        String opt = Options.instance(context).get("stringConcat");
        if (target.hasStringConcatFactory()) {
            if (opt == null) {
                opt = "indyWithConstants";
            }
        } else {
            if (opt != null && !"inline".equals(opt)) {
                Assert.error("StringConcatFactory-based string concat is requested on a platform that does not support it.");
            }
            opt = "inline";
        }

        switch (opt) {
            case "inline":
                return new Inline(context);
            case "indy":
                return new IndyPlain(context);
            case "indyWithConstants":
                return new IndyConstants(context);
            default:
                Assert.error("Unknown stringConcat: " + opt);
                throw new IllegalStateException("Unknown stringConcat: " + opt);
        }
    }

    protected StringConcat(Context context) {
        context.put(concatKey, this);
        gen = Gen.instance(context);
        syms = Symtab.instance(context);
        types = Types.instance(context);
        names = Names.instance(context);
        make = TreeMaker.instance(context);
        rs = Resolve.instance(context);
        sbAppends = new HashMap<>();
    }

    public abstract Item makeConcat(JCTree.JCAssignOp tree);
    public abstract Item makeConcat(JCTree.JCBinary tree);

    protected List<JCTree> collectAll(JCTree tree) {
        return collect(tree, List.nil());
    }

    protected List<JCTree> collectAll(JCTree.JCExpression lhs, JCTree.JCExpression rhs) {
        return List.<JCTree>nil()
                .appendList(collectAll(lhs))
                .appendList(collectAll(rhs));
    }

    private List<JCTree> collect(JCTree tree, List<JCTree> res) {
        tree = TreeInfo.skipParens(tree);
        if (tree.hasTag(PLUS) && tree.type.constValue() == null) {
            JCTree.JCBinary op = (JCTree.JCBinary) tree;
            if (op.operator.kind == MTH && op.operator.opcode == string_add) {
                return res
                        .appendList(collect(op.lhs, res))
                        .appendList(collect(op.rhs, res));
            }
        }
        return res.append(tree);
    }

    
If the type is not accessible from current context, try to figure out the
sharpest accessible supertype.
Params:
originalType – type to sharpen
Returns:
sharped type/**
     * If the type is not accessible from current context, try to figure out the
     * sharpest accessible supertype.
     *
     * @param originalType type to sharpen
     * @return sharped type
     */
    Type sharpestAccessible(Type originalType) {
        if (originalType.hasTag(ARRAY)) {
            return types.makeArrayType(sharpestAccessible(types.elemtype(originalType)));
        }

        Type type = originalType;
        while (!rs.isAccessible(gen.getAttrEnv(), type.asElement())) {
            type = types.supertype(type);
        }
        return type;
    }

    
"Legacy" bytecode flavor: emit the StringBuilder.append chains for string
concatenation.
/**
     * "Legacy" bytecode flavor: emit the StringBuilder.append chains for string
     * concatenation.
     */
    private static class Inline extends StringConcat {
        public Inline(Context context) {
            super(context);
        }

        @Override
        public Item makeConcat(JCTree.JCAssignOp tree) {
            // Generate code to make a string builder
            JCDiagnostic.DiagnosticPosition pos = tree.pos();

            // Create a string builder.
            newStringBuilder(tree);

            // Generate code for first string, possibly save one
            // copy under builder
            Item l = gen.genExpr(tree.lhs, tree.lhs.type);
            if (l.width() > 0) {
                gen.getCode().emitop0(dup_x1 + 3 * (l.width() - 1));
            }

            // Load first string and append to builder.
            l.load();
            appendString(tree.lhs);

            // Append all other strings to builder.
            List<JCTree> args = collectAll(tree.rhs);
            for (JCTree t : args) {
                gen.genExpr(t, t.type).load();
                appendString(t);
            }

            // Convert builder to string.
            builderToString(pos);

            return l;
        }

        @Override
        public Item makeConcat(JCTree.JCBinary tree) {
            JCDiagnostic.DiagnosticPosition pos = tree.pos();

            // Create a string builder.
            newStringBuilder(tree);

            // Append all strings to builder.
            List<JCTree> args = collectAll(tree);
            for (JCTree t : args) {
                gen.genExpr(t, t.type).load();
                appendString(t);
            }

            // Convert builder to string.
            builderToString(pos);

            return gen.getItems().makeStackItem(syms.stringType);
        }

        private JCDiagnostic.DiagnosticPosition newStringBuilder(JCTree tree) {
            JCDiagnostic.DiagnosticPosition pos = tree.pos();
            gen.getCode().emitop2(new_, gen.makeRef(pos, syms.stringBuilderType), syms.stringBuilderType);
            gen.getCode().emitop0(dup);
            gen.callMethod(pos, syms.stringBuilderType, names.init, List.nil(), false);
            return pos;
        }

        private void appendString(JCTree tree) {
            Type t = tree.type.baseType();
            if (!t.isPrimitive() && t.tsym != syms.stringType.tsym) {
                t = syms.objectType;
            }

            Assert.checkNull(t.constValue());
            Symbol method = sbAppends.get(t);
            if (method == null) {
                method = rs.resolveInternalMethod(tree.pos(), gen.getAttrEnv(), syms.stringBuilderType, names.append, List.of(t), null);
                sbAppends.put(t, method);
            }

            gen.getItems().makeMemberItem(method, false).invoke();
        }

        private void builderToString(JCDiagnostic.DiagnosticPosition pos) {
            gen.callMethod(pos, syms.stringBuilderType, names.toString, List.nil(), false);
        }
    }

    
Base class for indified concatenation bytecode flavors.
/**
     * Base class for indified concatenation bytecode flavors.
     */
    private static abstract class Indy extends StringConcat {
        public Indy(Context context) {
            super(context);
        }

        @Override
        public Item makeConcat(JCTree.JCAssignOp tree) {
            List<JCTree> args = collectAll(tree.lhs, tree.rhs);
            Item l = gen.genExpr(tree.lhs, tree.lhs.type);
            l.duplicate();
            l.load();
            emit(tree.pos(), args, false, tree.type);
            return l;
        }

        @Override
        public Item makeConcat(JCTree.JCBinary tree) {
            List<JCTree> args = collectAll(tree.lhs, tree.rhs);
            emit(tree.pos(), args, true, tree.type);
            return gen.getItems().makeStackItem(syms.stringType);
        }

        protected abstract void emit(JCDiagnostic.DiagnosticPosition pos, List<JCTree> args, boolean generateFirstArg, Type type);

        
Peel the argument list into smaller chunks. /** Peel the argument list into smaller chunks. */
        protected List<List<JCTree>> split(List<JCTree> args) {
            ListBuffer<List<JCTree>> splits = new ListBuffer<>();

            int slots = 0;

            // Need to peel, so that neither call has more than acceptable number
            // of slots for the arguments.
            ListBuffer<JCTree> cArgs = new ListBuffer<>();
            for (JCTree t : args) {
                int needSlots = (t.type.getTag() == LONG || t.type.getTag() == DOUBLE) ? 2 : 1;
                if (slots + needSlots >= MAX_INDY_CONCAT_ARG_SLOTS) {
                    splits.add(cArgs.toList());
                    cArgs.clear();
                    slots = 0;
                }
                cArgs.add(t);
                slots += needSlots;
            }

            // Flush the tail slice
            if (!cArgs.isEmpty()) {
                splits.add(cArgs.toList());
            }

            return splits.toList();
        }
    }

    
Emits the invokedynamic call to JDK java.lang.invoke.StringConcatFactory,
without handling constants specially.
We bypass empty strings, because they have no meaning at this level. This
captures the Java language trick to force String concat with e.g. ("" + int)-like
expression. Down here, we already know we are in String concat business, and do
not require these markers.
/**
     * Emits the invokedynamic call to JDK java.lang.invoke.StringConcatFactory,
     * without handling constants specially.
     *
     * We bypass empty strings, because they have no meaning at this level. This
     * captures the Java language trick to force String concat with e.g. ("" + int)-like
     * expression. Down here, we already know we are in String concat business, and do
     * not require these markers.
     */
    private static class IndyPlain extends Indy {
        public IndyPlain(Context context) {
            super(context);
        }

        
Emit the indy concat for all these arguments, possibly peeling along the way /** Emit the indy concat for all these arguments, possibly peeling along the way */
        protected void emit(JCDiagnostic.DiagnosticPosition pos, List<JCTree> args, boolean generateFirstArg, Type type) {
            List<List<JCTree>> split = split(args);

            boolean first = true;
            for (List<JCTree> t : split) {
                Assert.check(!t.isEmpty(), "Arguments list is empty");

                ListBuffer<Type> dynamicArgs = new ListBuffer<>();
                for (JCTree arg : t) {
                    Object constVal = arg.type.constValue();
                    if ("".equals(constVal)) continue;
                    if (arg.type == syms.botType) {
                        dynamicArgs.add(types.boxedClass(syms.voidType).type);
                    } else {
                        dynamicArgs.add(sharpestAccessible(arg.type));
                    }
                    if (!first || generateFirstArg) {
                        gen.genExpr(arg, arg.type).load();
                    }
                    first = false;
                }
                doCall(type, pos, dynamicArgs.toList());
            }

            // More that one peel slice produced: concatenate the results
            if (split.size() > 1) {
                ListBuffer<Type> argTypes = new ListBuffer<>();
                for (int c = 0; c < split.size(); c++) {
                    argTypes.append(syms.stringType);
                }
                doCall(type, pos, argTypes.toList());
            }
        }

        
Produce the actual invokedynamic call to StringConcatFactory /** Produce the actual invokedynamic call to StringConcatFactory */
        private void doCall(Type type, JCDiagnostic.DiagnosticPosition pos, List<Type> dynamicArgTypes) {
            Type.MethodType indyType = new Type.MethodType(dynamicArgTypes,
                    type,
                    List.nil(),
                    syms.methodClass);

            int prevPos = make.pos;
            try {
                make.at(pos);

                List<Type> bsm_staticArgs = List.of(syms.methodHandleLookupType,
                        syms.stringType,
                        syms.methodTypeType);

                Symbol bsm = rs.resolveInternalMethod(pos,
                        gen.getAttrEnv(),
                        syms.stringConcatFactory,
                        names.makeConcat,
                        bsm_staticArgs,
                        null);

                Symbol.DynamicMethodSymbol dynSym = new Symbol.DynamicMethodSymbol(names.makeConcat,
                        syms.noSymbol,
                        ((MethodSymbol)bsm).asHandle(),
                        indyType,
                        List.nil().toArray(new LoadableConstant[0]));

                Items.Item item = gen.getItems().makeDynamicItem(dynSym);
                item.invoke();
            } finally {
                make.at(prevPos);
            }
        }
    }

    
Emits the invokedynamic call to JDK java.lang.invoke.StringConcatFactory.
This code concatenates all known constants into the recipe, possibly escaping
some constants separately.
We also bypass empty strings, because they have no meaning at this level. This
captures the Java language trick to force String concat with e.g. ("" + int)-like
expression. Down here, we already know we are in String concat business, and do
not require these markers.
/**
     * Emits the invokedynamic call to JDK java.lang.invoke.StringConcatFactory.
     * This code concatenates all known constants into the recipe, possibly escaping
     * some constants separately.
     *
     * We also bypass empty strings, because they have no meaning at this level. This
     * captures the Java language trick to force String concat with e.g. ("" + int)-like
     * expression. Down here, we already know we are in String concat business, and do
     * not require these markers.
     */
    private static final class IndyConstants extends Indy {
        public IndyConstants(Context context) {
            super(context);
        }

        @Override
        protected void emit(JCDiagnostic.DiagnosticPosition pos, List<JCTree> args, boolean generateFirstArg, Type type) {
            List<List<JCTree>> split = split(args);

            boolean first = true;
            for (List<JCTree> t : split) {
                Assert.check(!t.isEmpty(), "Arguments list is empty");

                StringBuilder recipe = new StringBuilder(t.size());
                ListBuffer<Type> dynamicArgs = new ListBuffer<>();
                ListBuffer<LoadableConstant> staticArgs = new ListBuffer<>();

                for (JCTree arg : t) {
                    Object constVal = arg.type.constValue();
                    if ("".equals(constVal)) continue;
                    if (arg.type == syms.botType) {
                        // Concat the null into the recipe right away
                        recipe.append((String) null);
                    } else if (constVal != null) {
                        // Concat the String representation of the constant, except
                        // for the case it contains special tags, which requires us
                        // to expose it as detached constant.
                        String a = arg.type.stringValue();
                        if (a.indexOf(TAG_CONST) != -1 || a.indexOf(TAG_ARG) != -1) {
                            recipe.append(TAG_CONST);
                            staticArgs.add(LoadableConstant.String(a));
                        } else {
                            recipe.append(a);
                        }
                    } else {
                        // Ordinary arguments come through the dynamic arguments.
                        recipe.append(TAG_ARG);
                        dynamicArgs.add(sharpestAccessible(arg.type));
                        if (!first || generateFirstArg) {
                            gen.genExpr(arg, arg.type).load();
                        }
                        first = false;
                    }
                }

                doCall(type, pos, recipe.toString(), staticArgs.toList(), dynamicArgs.toList());
            }

            // More that one peel slice produced: concatenate the results
            // All arguments are assumed to be non-constant Strings.
            if (split.size() > 1) {
                ListBuffer<Type> argTypes = new ListBuffer<>();
                StringBuilder recipe = new StringBuilder();
                for (int c = 0; c < split.size(); c++) {
                    argTypes.append(syms.stringType);
                    recipe.append(TAG_ARG);
                }
                doCall(type, pos, recipe.toString(), List.nil(), argTypes.toList());
            }
        }

        
Produce the actual invokedynamic call to StringConcatFactory /** Produce the actual invokedynamic call to StringConcatFactory */
        private void doCall(Type type, JCDiagnostic.DiagnosticPosition pos, String recipe, List<LoadableConstant> staticArgs, List<Type> dynamicArgTypes) {
            Type.MethodType indyType = new Type.MethodType(dynamicArgTypes,
                    type,
                    List.nil(),
                    syms.methodClass);

            int prevPos = make.pos;
            try {
                make.at(pos);

                ListBuffer<Type> constTypes = new ListBuffer<>();
                ListBuffer<LoadableConstant> constants = new ListBuffer<>();
                for (LoadableConstant t : staticArgs) {
                    constants.add(t);
                    constTypes.add(syms.stringType);
                }

                List<Type> bsm_staticArgs = List.of(syms.methodHandleLookupType,
                        syms.stringType,
                        syms.methodTypeType)
                        .append(syms.stringType)
                        .appendList(constTypes);

                Symbol bsm = rs.resolveInternalMethod(pos,
                        gen.getAttrEnv(),
                        syms.stringConcatFactory,
                        names.makeConcatWithConstants,
                        bsm_staticArgs,
                        null);

                Symbol.DynamicMethodSymbol dynSym = new Symbol.DynamicMethodSymbol(names.makeConcatWithConstants,
                        syms.noSymbol,
                        ((MethodSymbol)bsm).asHandle(),
                        indyType,
                        List.of(LoadableConstant.String(recipe))
                                .appendList(constants).toArray(new LoadableConstant[constants.size()]));

                Items.Item item = gen.getItems().makeDynamicItem(dynSym);
                item.invoke();
            } finally {
                make.at(prevPos);
            }
        }
    }

}