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package com.oracle.truffle.sl.nodes.call;

import com.oracle.truffle.api.CallTarget;
import com.oracle.truffle.api.dsl.Cached;
import com.oracle.truffle.api.dsl.Specialization;
import com.oracle.truffle.api.frame.VirtualFrame;
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.runtime.SLFunction;

public abstract class SLDispatchNode extends Node {

    protected static final int INLINE_CACHE_SIZE = 2;

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

    @Specialization(guards = "function.getCallTarget() == null")
    protected Object doUndefinedFunction(SLFunction function, @SuppressWarnings("unused") Object[] arguments) {
        throw new SLUndefinedFunctionException(function.getName());
    }

    /**
     * Inline cached specialization of the dispatch.
     *
     * <p>
     * Since SL is a quite simple language, the benefit of the inline cache is quite 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,
     * in a more complex language the lookup of the call target is usually much more complicated
     * than in SL. In addition, caching the call target allows method inlining.
     * </p>
     *
     * <p>
     * {@code limit = "INLINE_CACHE_SIZE"} Specifies the limit number of inline cache specialization
     * instantiations.
     * </p>
     * <p>
     * {@code guards = "function == cachedFunction"} The inline cache check. Note that
     * cachedFunction is a final field so that the compiler can optimize the check.
     * </p>
     * <p>
     * {@code assumptions = "cachedFunction.getCallTargetStable()"} Support for function
     * redefinition: When a function is redefined, the call target maintained by the SLFunction
     * object is change. 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.
     * </p>
     *
     * @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 == cachedFunction", assumptions = "cachedFunction.getCallTargetStable()")
    protected static Object doDirect(VirtualFrame frame, SLFunction function, Object[] arguments,   //
                    @Cached("function") SLFunction cachedFunction,   //
                    @Cached("create(cachedFunction.getCallTarget())") DirectCallNode callNode) {
        /* Inline cache hit, we are safe to execute the cached call target. */
        return callNode.call(frame, arguments);
    }

    /**
     * Slow-path code for a call, used when the polymorphic inline cache exceeded its maximum size
     * specified in <code>INLINE_CACHE_SIZE</code>. Such calls are not optimized any further, e.g.,
     * no method inlining is performed.
     */
    @Specialization(contains = "doDirect")
    protected static Object doIndirect(VirtualFrame frame, 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(frame, function.getCallTarget(), arguments);
    }

}