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package com.oracle.truffle.sl.runtime;
import java.util.logging.Level;
import com.oracle.truffle.api.Assumption;
import com.oracle.truffle.api.CallTarget;
import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
import com.oracle.truffle.api.RootCallTarget;
import com.oracle.truffle.api.TruffleLanguage;
import com.oracle.truffle.api.TruffleLogger;
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.interop.InteropLibrary;
import com.oracle.truffle.api.interop.TruffleObject;
import com.oracle.truffle.api.library.ExportLibrary;
import com.oracle.truffle.api.library.ExportMessage;
import com.oracle.truffle.api.nodes.DirectCallNode;
import com.oracle.truffle.api.nodes.IndirectCallNode;
import com.oracle.truffle.api.source.SourceSection;
import com.oracle.truffle.api.strings.TruffleString;
import com.oracle.truffle.api.utilities.CyclicAssumption;
import com.oracle.truffle.api.utilities.TriState;
import com.oracle.truffle.sl.SLLanguage;
import com.oracle.truffle.sl.nodes.SLUndefinedFunctionRootNode;
/**
* Represents a SL function. On the Truffle level, a callable element is represented by a
* {@link RootCallTarget call target}. This class encapsulates a call target, and adds version
* support: functions in SL can be redefined, i.e. changed at run time. When a function is
* redefined, the call target managed by this function object is changed (and {@link #callTarget} is
* therefore not a final field).
*
* Function redefinition is expected to be rare, therefore optimized call nodes want to speculate
* that the call target is stable. This is possible with the help of a Truffle {@link Assumption}: a
* call node can keep the call target returned by {@link #getCallTarget()} cached until the
* assumption returned by {@link #getCallTargetStable()} is valid.
*
* The {@link #callTarget} can be {@code null}. To ensure that only one {@link SLFunction} instance
* per name exists, the {@link SLFunctionRegistry} creates an instance also when performing name
* lookup. A function that has been looked up, i.e., used, but not defined, has a call target that
* encapsulates a {@link SLUndefinedFunctionRootNode}.
*/
@ExportLibrary(InteropLibrary.class)
@SuppressWarnings("static-method")
public final class SLFunction implements TruffleObject {
public static final int INLINE_CACHE_SIZE = 2;
private static final TruffleLogger LOG = TruffleLogger.getLogger(SLLanguage.ID, SLFunction.class);
/** The name of the function. */
private final TruffleString name;
/** The current implementation of this function. */
private RootCallTarget callTarget;
/**
* Manages the assumption that the {@link #callTarget} is stable. We use the utility class
* {@link CyclicAssumption}, which automatically creates a new {@link Assumption} when the old
* one gets invalidated.
*/
private final CyclicAssumption callTargetStable;
protected SLFunction(SLLanguage language, TruffleString name) {
this(name, language.getOrCreateUndefinedFunction(name));
}
protected SLFunction(TruffleString name, RootCallTarget callTarget) {
this.name = name;
this.callTargetStable = new CyclicAssumption(name.toJavaStringUncached());
setCallTarget(callTarget);
}
public TruffleString getName() {
return name;
}
protected void setCallTarget(RootCallTarget callTarget) {
boolean wasNull = this.callTarget == null;
this.callTarget = callTarget;
/*
* We have a new call target. Invalidate all code that speculated that the old call target
* was stable.
*/
LOG.log(Level.FINE, "Installed call target for: {0}", name);
if (!wasNull) {
callTargetStable.invalidate();
}
}
public RootCallTarget getCallTarget() {
return callTarget;
}
public Assumption getCallTargetStable() {
return callTargetStable.getAssumption();
}
/**
* This method is, e.g., called when using a function literal in a string concatenation. So
* changing it has an effect on SL programs.
*/
@Override
public String toString() {
return name.toJavaStringUncached();
}
@ExportMessage
boolean hasLanguage() {
return true;
}
@ExportMessage
Class> getLanguage() {
return SLLanguage.class;
}
/**
* {@link SLFunction} instances are always visible as executable to other languages.
*/
@SuppressWarnings("static-method")
@ExportMessage
@TruffleBoundary
SourceSection getSourceLocation() {
return getCallTarget().getRootNode().getSourceSection();
}
@SuppressWarnings("static-method")
@ExportMessage
boolean hasSourceLocation() {
return true;
}
/**
* {@link SLFunction} instances are always visible as executable to other languages.
*/
@ExportMessage
boolean isExecutable() {
return true;
}
@ExportMessage
boolean hasMetaObject() {
return true;
}
@ExportMessage
Object getMetaObject() {
return SLType.FUNCTION;
}
@ExportMessage
@SuppressWarnings("unused")
static final class IsIdenticalOrUndefined {
@Specialization
static TriState doSLFunction(SLFunction receiver, SLFunction other) {
/*
* SLFunctions are potentially identical to other SLFunctions.
*/
return receiver == other ? TriState.TRUE : TriState.FALSE;
}
@Fallback
static TriState doOther(SLFunction receiver, Object other) {
return TriState.UNDEFINED;
}
}
@ExportMessage
@TruffleBoundary
static int identityHashCode(SLFunction receiver) {
return System.identityHashCode(receiver);
}
@ExportMessage
Object toDisplayString(@SuppressWarnings("unused") boolean allowSideEffects) {
return name;
}
/**
* We allow languages to execute this function. We implement the interop execute message that
* forwards to a function dispatch.
*
* Since invocations are potentially expensive (result in an indirect call, which is expensive
* by itself but also limits function inlining which can hinder other optimisations) if the node
* turns megamorphic (i.e. cache limit is exceeded) we annotate it with
* {@link ReportPolymorphism}. This ensures that the runtime is notified when this node turns
* polymorphic. This, in turn, may, under certain conditions, cause the runtime to attempt to
* make node monomorphic again by duplicating the entire AST containing that node and
* specialising it for a particular call site.
*/
@ReportPolymorphism
@ExportMessage
abstract static class Execute {
/**
* 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 arguments the arguments to the function
* @param callTargetStable The assumption object assuming the function was not redefined.
* @param cachedTarget The call target we aim to invoke
* @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. */
Object returnValue = callNode.call(arguments);
return returnValue;
}
/**
* 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 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);
}
}
}