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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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).
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package jdk.nashorn.internal.codegen;

import static jdk.nashorn.internal.codegen.CompilerConstants.SPLIT_PREFIX;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import jdk.nashorn.internal.ir.Block;
import jdk.nashorn.internal.ir.FunctionNode;
import jdk.nashorn.internal.ir.LiteralNode;
import jdk.nashorn.internal.ir.LiteralNode.ArrayLiteralNode;
import jdk.nashorn.internal.ir.Node;
import jdk.nashorn.internal.ir.ObjectNode;
import jdk.nashorn.internal.ir.PropertyNode;
import jdk.nashorn.internal.ir.SplitNode;
import jdk.nashorn.internal.ir.Splittable;
import jdk.nashorn.internal.ir.Statement;
import jdk.nashorn.internal.ir.VarNode;
import jdk.nashorn.internal.ir.visitor.SimpleNodeVisitor;
import jdk.nashorn.internal.runtime.Context;
import jdk.nashorn.internal.runtime.logging.DebugLogger;
import jdk.nashorn.internal.runtime.logging.Loggable;
import jdk.nashorn.internal.runtime.logging.Logger;
import jdk.nashorn.internal.runtime.options.Options;

Split the IR into smaller compile units.
/**
 * Split the IR into smaller compile units.
 */
@Logger(name="splitter")
final class Splitter extends SimpleNodeVisitor implements Loggable {
    
Current compiler. /** Current compiler. */
    private final Compiler compiler;

    
IR to be broken down. /** IR to be broken down. */
    private final FunctionNode outermost;

    
Compile unit for the main script. /** Compile unit for the main script. */
    private final CompileUnit outermostCompileUnit;

    
Cache for calculated block weights. /** Cache for calculated block weights. */
    private final Map<Node, Long> weightCache = new HashMap<>();

    
Weight threshold for when to start a split. /** Weight threshold for when to start a split. */
    public static final long SPLIT_THRESHOLD = Options.getIntProperty("nashorn.compiler.splitter.threshold", 32 * 1024);

    private final DebugLogger log;

    
Constructor.
Params:
compiler –              the compiler
functionNode –          function node to split
outermostCompileUnit –  compile unit for outermost function, if non-lazy this is the script's compile unit/**
     * Constructor.
     *
     * @param compiler              the compiler
     * @param functionNode          function node to split
     * @param outermostCompileUnit  compile unit for outermost function, if non-lazy this is the script's compile unit
     */
    public Splitter(final Compiler compiler, final FunctionNode functionNode, final CompileUnit outermostCompileUnit) {
        this.compiler             = compiler;
        this.outermost            = functionNode;
        this.outermostCompileUnit = outermostCompileUnit;
        this.log                  = initLogger(compiler.getContext());
    }

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

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

    
Execute the split.
Params:
fn – the function to split
top – whether this is the topmost compiled function (it's either a program, or we're doing a recompilation)./**
     * Execute the split.
     * @param fn the function to split
     * @param top whether this is the topmost compiled function (it's either a program, or we're doing a recompilation).
     */
    FunctionNode split(final FunctionNode fn, final boolean top) {
        FunctionNode functionNode = fn;

        log.fine("Initiating split of '", functionNode.getName(), "'");

        long weight = WeighNodes.weigh(functionNode);

        // We know that our LexicalContext is empty outside the call to functionNode.accept(this) below,
        // so we can pass null to all methods expecting a LexicalContext parameter.
        assert lc.isEmpty() : "LexicalContext not empty";

        if (weight >= SPLIT_THRESHOLD) {
            log.info("Splitting function '", functionNode.getName(), "' as its weight ", weight, " exceeds split threshold ", SPLIT_THRESHOLD);
            functionNode = (FunctionNode)functionNode.accept(this);

            if (functionNode.isSplit()) {
                // Weight has changed so weigh again, this time using block weight cache
                weight = WeighNodes.weigh(functionNode, weightCache);
                functionNode = functionNode.setBody(null, functionNode.getBody().setNeedsScope(null));
            }

            if (weight >= SPLIT_THRESHOLD) {
                functionNode = functionNode.setBody(null, splitBlock(functionNode.getBody(), functionNode));
                functionNode = functionNode.setFlag(null, FunctionNode.IS_SPLIT);
                weight = WeighNodes.weigh(functionNode.getBody(), weightCache);
            }
        }

        assert functionNode.getCompileUnit() == null : "compile unit already set for " + functionNode.getName();

        if (top) {
            assert outermostCompileUnit != null : "outermost compile unit is null";
            functionNode = functionNode.setCompileUnit(null, outermostCompileUnit);
            outermostCompileUnit.addWeight(weight + WeighNodes.FUNCTION_WEIGHT);
        } else {
            functionNode = functionNode.setCompileUnit(null, findUnit(weight));
        }

        final Block body = functionNode.getBody();
        final List<FunctionNode> dc = directChildren(functionNode);

        final Block newBody = (Block)body.accept(new SimpleNodeVisitor() {
            @Override
            public boolean enterFunctionNode(final FunctionNode nestedFunction) {
                return dc.contains(nestedFunction);
            }

            @Override
            public Node leaveFunctionNode(final FunctionNode nestedFunction) {
                final FunctionNode split = new Splitter(compiler, nestedFunction, outermostCompileUnit).split(nestedFunction, false);
                lc.replace(nestedFunction, split);
                return split;
            }
        });
        functionNode = functionNode.setBody(null, newBody);

        assert functionNode.getCompileUnit() != null;

        return functionNode;
    }

    private static List<FunctionNode> directChildren(final FunctionNode functionNode) {
        final List<FunctionNode> dc = new ArrayList<>();
        functionNode.accept(new SimpleNodeVisitor() {
            @Override
            public boolean enterFunctionNode(final FunctionNode child) {
                if (child == functionNode) {
                    return true;
                }
                if (lc.getParentFunction(child) == functionNode) {
                    dc.add(child);
                }
                return false;
            }
        });
        return dc;
    }

    
Override this logic to look up compile units in a different way
Params:
weight – weight needed
Returns:
compile unit/**
     * Override this logic to look up compile units in a different way
     * @param weight weight needed
     * @return compile unit
     */
    protected CompileUnit findUnit(final long weight) {
        return compiler.findUnit(weight);
    }

    
Split a block into sub methods.
Params:
block – Block or function to split.
Returns:
new weight for the resulting block./**
     * Split a block into sub methods.
     *
     * @param block Block or function to split.
     *
     * @return new weight for the resulting block.
     */
    private Block splitBlock(final Block block, final FunctionNode function) {

        final List<Statement> splits = new ArrayList<>();
        List<Statement> statements = new ArrayList<>();
        long statementsWeight = 0;

        for (final Statement statement : block.getStatements()) {
            final long weight = WeighNodes.weigh(statement, weightCache);
            final boolean isBlockScopedVarNode = isBlockScopedVarNode(statement);

            if (statementsWeight + weight >= SPLIT_THRESHOLD || statement.isTerminal() || isBlockScopedVarNode) {
                if (!statements.isEmpty()) {
                    splits.add(createBlockSplitNode(block, function, statements, statementsWeight));
                    statements = new ArrayList<>();
                    statementsWeight = 0;
                }
            }

            if (statement.isTerminal() || isBlockScopedVarNode) {
                splits.add(statement);
            } else {
                statements.add(statement);
                statementsWeight += weight;
            }
        }

        if (!statements.isEmpty()) {
            splits.add(createBlockSplitNode(block, function, statements, statementsWeight));
        }

        return block.setStatements(lc, splits);
    }

    
Create a new split node from statements contained in a parent block.
Params:
parent –     Parent block.
statements – Statements to include.
Returns:
New split node./**
     * Create a new split node from statements contained in a parent block.
     *
     * @param parent     Parent block.
     * @param statements Statements to include.
     *
     * @return New split node.
     */
    private SplitNode createBlockSplitNode(final Block parent, final FunctionNode function, final List<Statement> statements, final long weight) {
        final long   token      = parent.getToken();
        final int    finish     = parent.getFinish();
        final String name       = function.uniqueName(SPLIT_PREFIX.symbolName());

        final Block newBlock = new Block(token, finish, statements);

        return new SplitNode(name, newBlock, compiler.findUnit(weight + WeighNodes.FUNCTION_WEIGHT));
    }

    private boolean isBlockScopedVarNode(final Statement statement) {
        return statement instanceof VarNode && ((VarNode) statement).isBlockScoped();
    }

    @Override
    public boolean enterBlock(final Block block) {
        if (block.isCatchBlock()) {
            return false;
        }

        final long weight = WeighNodes.weigh(block, weightCache);

        if (weight < SPLIT_THRESHOLD) {
            weightCache.put(block, weight);
            return false;
        }

        return true;
    }

    @Override
    public Node leaveBlock(final Block block) {
        assert !block.isCatchBlock();

        Block newBlock = block;

        // Block was heavier than SLIT_THRESHOLD in enter, but a sub-block may have
        // been split already, so weigh again before splitting.
        long weight = WeighNodes.weigh(block, weightCache);
        if (weight >= SPLIT_THRESHOLD) {
            final FunctionNode currentFunction = lc.getCurrentFunction();
            newBlock = splitBlock(block, currentFunction);
            weight   = WeighNodes.weigh(newBlock, weightCache);
            lc.setFlag(currentFunction, FunctionNode.IS_SPLIT);
        }
        weightCache.put(newBlock, weight);
        return newBlock;
    }

    @SuppressWarnings("rawtypes")
    @Override
    public Node leaveLiteralNode(final LiteralNode literal) {
        final long weight = WeighNodes.weigh(literal);

        if (weight < SPLIT_THRESHOLD) {
            return literal;
        }

        final FunctionNode functionNode = lc.getCurrentFunction();

        lc.setFlag(functionNode, FunctionNode.IS_SPLIT);

        if (literal instanceof ArrayLiteralNode) {
            final ArrayLiteralNode arrayLiteralNode = (ArrayLiteralNode) literal;
            final Node[]           value            = arrayLiteralNode.getValue();
            final int[]            postsets         = arrayLiteralNode.getPostsets();
            final List<Splittable.SplitRange> ranges = new ArrayList<>();

            long totalWeight = 0;
            int  lo          = 0;

            for (int i = 0; i < postsets.length; i++) {
                final int  postset = postsets[i];
                final Node element = value[postset];

                final long elementWeight = WeighNodes.weigh(element);
                totalWeight += WeighNodes.AASTORE_WEIGHT + elementWeight;

                if (totalWeight >= SPLIT_THRESHOLD) {
                    final CompileUnit unit = compiler.findUnit(totalWeight - elementWeight);
                    ranges.add(new Splittable.SplitRange(unit, lo, i));
                    lo = i;
                    totalWeight = elementWeight;
                }
            }

            if (lo != postsets.length) {
                final CompileUnit unit = compiler.findUnit(totalWeight);
                ranges.add(new Splittable.SplitRange(unit, lo, postsets.length));
            }

            log.info("Splitting array literal in '", functionNode.getName(), "' as its weight ", weight, " exceeds split threshold ", SPLIT_THRESHOLD);

            return arrayLiteralNode.setSplitRanges(lc, ranges);
        }

        return literal;
    }

    @Override
    public Node leaveObjectNode(final ObjectNode objectNode) {
        final long weight = WeighNodes.weigh(objectNode);

        if (weight < SPLIT_THRESHOLD) {
            return objectNode;
        }

        final FunctionNode functionNode = lc.getCurrentFunction();
        lc.setFlag(functionNode, FunctionNode.IS_SPLIT);

        final List<Splittable.SplitRange> ranges        = new ArrayList<>();
        final List<PropertyNode>          properties    = objectNode.getElements();
        final boolean                     isSpillObject = properties.size() > CodeGenerator.OBJECT_SPILL_THRESHOLD;
        long totalWeight = 0;
        int  lo          = 0;

        for (int i = 0; i < properties.size(); i++) {

            final PropertyNode property = properties.get(i);
            final boolean isConstant = LiteralNode.isConstant(property.getValue());

            if (!isConstant || !isSpillObject) {
                final long propertyWeight = isConstant ? 0 : WeighNodes.weigh(property.getValue());
                totalWeight += WeighNodes.AASTORE_WEIGHT + propertyWeight;

                if (totalWeight >= SPLIT_THRESHOLD) {
                    final CompileUnit unit = compiler.findUnit(totalWeight - propertyWeight);
                    ranges.add(new Splittable.SplitRange(unit, lo, i));
                    lo = i;
                    totalWeight = propertyWeight;
                }
            }
        }

        if (lo != properties.size()) {
            final CompileUnit unit = compiler.findUnit(totalWeight);
            ranges.add(new Splittable.SplitRange(unit, lo, properties.size()));
        }

        log.info("Splitting object node in '", functionNode.getName(), "' as its weight ", weight, " exceeds split threshold ", SPLIT_THRESHOLD);

        return objectNode.setSplitRanges(lc, ranges);
    }

    @Override
    public boolean enterFunctionNode(final FunctionNode node) {
        //only go into the function node for this splitter. any subfunctions are rejected
        return node == outermost;
    }
}