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Truffle SL is an example language implemented using the Truffle API.
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * The Universal Permissive License (UPL), Version 1.0
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 * person obtaining a copy of this software, associated documentation and/or
 * data (collectively the "Software"), free of charge and under any and all
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package com.oracle.truffle.sl.nodes.call;

import com.oracle.truffle.api.Assumption;
import com.oracle.truffle.api.CallTarget;
import com.oracle.truffle.api.RootCallTarget;
import com.oracle.truffle.api.dsl.Cached;
import com.oracle.truffle.api.dsl.Fallback;
import com.oracle.truffle.api.dsl.ReportPolymorphism;
import com.oracle.truffle.api.dsl.Specialization;
import com.oracle.truffle.api.dsl.TypeSystemReference;
import com.oracle.truffle.api.interop.ArityException;
import com.oracle.truffle.api.interop.ForeignAccess;
import com.oracle.truffle.api.interop.Message;
import com.oracle.truffle.api.interop.TruffleObject;
import com.oracle.truffle.api.interop.UnsupportedMessageException;
import com.oracle.truffle.api.interop.UnsupportedTypeException;
import com.oracle.truffle.api.nodes.DirectCallNode;
import com.oracle.truffle.api.nodes.IndirectCallNode;
import com.oracle.truffle.api.nodes.Node;
import com.oracle.truffle.sl.nodes.SLTypes;
import com.oracle.truffle.sl.nodes.interop.SLForeignToSLTypeNode;
import com.oracle.truffle.sl.nodes.interop.SLForeignToSLTypeNodeGen;
import com.oracle.truffle.sl.runtime.SLFunction;
import com.oracle.truffle.sl.runtime.SLUndefinedNameException;

@ReportPolymorphism
@TypeSystemReference(SLTypes.class)
public abstract class SLDispatchNode extends Node {

    public static final int INLINE_CACHE_SIZE = 2;

    public abstract Object executeDispatch(Object function, Object[] arguments);

    /**
     * Inline cached specialization of the dispatch.
     *
     * 
     * Since SL is a quite simple language, the benefit of the inline cache seems small: after
     * checking that the actual function to be executed is the same as the cachedFuntion, we can
     * safely execute the cached call target. You can reasonably argue that caching the call target
     * is overkill, since we could just retrieve it via {@code function.getCallTarget()}. However,
     * caching the call target and using a {@link DirectCallNode} allows Truffle to perform method
     * inlining. In addition, in a more complex language the lookup of the call target is usually
     * much more complicated than in SL.
     * 
     *
     * 
     * {@code limit = "INLINE_CACHE_SIZE"} Specifies the limit number of inline cache specialization
     * instantiations.
     * 
     * 
     * {@code guards = "function.getCallTarget() == cachedTarget"} The inline cache check. Note that
     * cachedTarget is a final field so that the compiler can optimize the check.
     * 
     * 
     * {@code assumptions = "callTargetStable"} Support for function redefinition: When a function
     * is redefined, the call target maintained by the SLFunction object is changed. To avoid a
     * check for that, we use an Assumption that is invalidated by the SLFunction when the change is
     * performed. Since checking an assumption is a no-op in compiled code, the assumption check
     * performed by the DSL does not add any overhead during optimized execution.
     * 
     *
     * @see Cached
     * @see Specialization
     *
     * @param function the dynamically provided function
     * @param cachedFunction the cached function of the specialization instance
     * @param callNode the {@link DirectCallNode} specifically created for the {@link CallTarget} in
     *            cachedFunction.
     */
    @Specialization(limit = "INLINE_CACHE_SIZE", //
                    guards = "function.getCallTarget() == cachedTarget", //
                    assumptions = "callTargetStable")
    @SuppressWarnings("unused")
    protected static Object doDirect(SLFunction function, Object[] arguments,
                    @Cached("function.getCallTargetStable()") Assumption callTargetStable,
                    @Cached("function.getCallTarget()") RootCallTarget cachedTarget,
                    @Cached("create(cachedTarget)") DirectCallNode callNode) {

        /* Inline cache hit, we are safe to execute the cached call target. */
        return callNode.call(arguments);
    }

    /**
     * Slow-path code for a call, used when the polymorphic inline cache exceeded its maximum size
     * specified in INLINE_CACHE_SIZE. Such calls are not optimized any further, e.g.,
     * no method inlining is performed.
     */
    @Specialization(replaces = "doDirect")
    protected static Object doIndirect(SLFunction function, Object[] arguments,
                    @Cached("create()") IndirectCallNode callNode) {
        /*
         * SL has a quite simple call lookup: just ask the function for the current call target, and
         * call it.
         */
        return callNode.call(function.getCallTarget(), arguments);
    }

    /**
     * When no specialization fits, the receiver is not an object (which is a type error).
     */
    @Fallback
    protected Object unknownFunction(Object function, @SuppressWarnings("unused") Object[] arguments) {
        throw SLUndefinedNameException.undefinedFunction(this, function);
    }

    /**
     * Language interoperability: If the function is a foreign value, i.e., not a SLFunction, we use
     * Truffle's interop API to execute the foreign function.
     */
    @Specialization(guards = "isForeignFunction(function)")
    protected Object doForeign(TruffleObject function, Object[] arguments,
                    // The child node to call the foreign function
                    @Cached("createCrossLanguageCallNode()") Node crossLanguageCallNode,
                    // The child node to convert the result of the foreign call to a SL value
                    @Cached("createToSLTypeNode()") SLForeignToSLTypeNode toSLTypeNode) {

        try {
            /* Perform the foreign function call. */
            Object res = ForeignAccess.sendExecute(crossLanguageCallNode, function, arguments);
            /* Convert the result to a SL value. */
            return toSLTypeNode.executeConvert(res);

        } catch (ArityException | UnsupportedTypeException | UnsupportedMessageException e) {
            /* Foreign access was not successful. */
            throw SLUndefinedNameException.undefinedFunction(this, function);
        }
    }

    protected static boolean isForeignFunction(TruffleObject function) {
        return !(function instanceof SLFunction);
    }

    protected static Node createCrossLanguageCallNode() {
        return Message.EXECUTE.createNode();
    }

    protected static SLForeignToSLTypeNode createToSLTypeNode() {
        return SLForeignToSLTypeNodeGen.create();
    }
}