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package com.oracle.truffle.api.dsl;
import com.oracle.truffle.api.Assumption;
import com.oracle.truffle.api.ExactMath;
import com.oracle.truffle.api.frame.Frame;
import com.oracle.truffle.api.frame.MaterializedFrame;
import com.oracle.truffle.api.frame.VirtualFrame;
import com.oracle.truffle.api.nodes.Node;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* <p>
* Defines a method of a node subclass to represent one specialization of an operation. Multiple
* specializations can be defined in a node representing an operation. A specialization defines
* which kind of input is expected using the method signature and the annotation attributes. The
* specialized semantics of the operation are defined using the body of the annotated Java method. A
* specialization method must be declared in a class that is derived from {@link Node} that
* references a {@link TypeSystem}. At least one specialization must be defined per operation. If no
* specialization is valid for the given set of input values then an
* {@link UnsupportedSpecializationException} is thrown instead of invoking any specialization
* method.
* </p>
* <p>
* A specialization must have at least as many parameters as there are {@link NodeChild} annotations
* declared for the enclosing operation node. These parameters are declared in the same order as the
* {@link NodeChild} annotations (linear execution order). We call such parameters dynamic input
* parameters. Every specialization that is declared within an operation must have an equal number
* of dynamic input parameters.
* </p>
* <p>
* The supported kind of input values for a specialization are declared using guards. A
* specialization may provide declarative specifications for four kinds of guards:
* <ul>
* <li><b>Type guards</b> optimistically assume the type of an input value. A value that matches the
* type is cast to its expected type automatically. Type guards are modeled using the parameter type
* of the specialization method. Types used for type guards must be defined in the
* {@link TypeSystem}. If the type of the parameter is {@link Object} then no type guard is used for
* the dynamic input parameter.</li>
*
* <li><b>Expression guards</b> optimistically assume the return value of a user-defined expression
* to be <code>true</code>. Expression guards are modeled using Java expressions that return a
* <code>boolean</code> value. If the guard expression returns <code>false</code>, the
* specialization is no longer applicable and the operation is re-specialized. Guard expressions are
* declared using the {@link #guards()} attribute.</li>
*
* <li><b>Event guards</b> trigger re-specialization in case an exception is thrown in the
* specialization body. The {@link #rewriteOn()} attribute can be used to declare a list of such
* exceptions. Guards of this kind are useful to avoid calculating a value twice when it is used in
* the guard and its specialization.</li>
*
* <li><b>Assumption guards</b> optimistically assume that the state of an {@link Assumption}
* remains <code>true</code>. Assumptions can be assigned to specializations using the
* {@link #assumptions()} attribute.</li>
* </ul>
* </p>
* <p>
* The enclosing {@link Node} of a specialization method must have at least one <code>public</code>
* and non-<code>final</code> execute method. An execute method is a method that starts with
* 'execute'. If all execute methods declare the first parameter type as {@link Frame},
* {@link VirtualFrame} or {@link MaterializedFrame} then the same frame type can be used as
* optional first parameter of the specialization. This parameter does not count to the number of
* dynamic parameters.
* </p>
* <p>
* A specialization method may declare multiple parameters annotated with {@link Cached}. Cached
* parameters are initialized and stored once per specialization instantiation. For consistency
* between specialization declarations cached parameters must be declared last in a specialization
* method.
* </p>
* <p>
* If the operation is re-specialized or if it is executed for the first time then all declared
* specializations of the operation are tried in declaration order until the guards of the first
* specialization accepts the current input values. The new specialization is then added to the
* chain of current specialization instances which might consist of one (monomorph) or multiple
* instances (polymorph). If an assumption of an instantiated specialization is violated then
* re-specialization is triggered again.
* </p>
* <p>
* With guards in combination with cached parameters it is possible that multiple instances of the
* same specialization are created. The {@link #limit()} attribute can be used to limit the number
* of instantiations per specialization.
* </p>
*
* @see NodeChild
* @see ShortCircuit
* @see Fallback
* @see Cached
* @see TypeSystem
* @see TypeSystemReference
* @see UnsupportedSpecializationException
* @since 0.8 or earlier
*/
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
public @interface Specialization {
/**
* References a specialization of a super class by its method name where this specialization is
* inserted before. The declaration order of a specialization is not usable for nodes where
* specializations are partly declared in the super class and partly declared in a derived
* class. By default all specializations declared in the derived class are appended to those in
* the super class. This attribute can be used to override the default behavior.
*/
String insertBefore() default "";
/**
* <p>
* Declares an event guards that trigger re-specialization in case an exception is thrown in the
* specialization body. This attribute can be used to declare a list of such exceptions. Guards
* of this kind are useful to avoid calculating a value twice when it is used in the guard and
* its specialization.
* </p>
*
* <p>
* If an event guard exception is triggered then all instantiations of this specialization are
* removed. If one of theses exceptions is thrown once then no further instantiations of this
* specialization are going to be created for this node. A specialization that rewrites on an
* exception must ensure that no non-repeatable side-effect is caused until the rewrite is
* triggered.
* </p>
*
* <b>Example usage:</b>
*
* <pre>
* @Specialization(rewriteOn = ArithmeticException.class)
* int doAddNoOverflow(int a, int b) {
* return ExactMath.addExact(a, b);
* }
* @Specialization
* long doAddWithOverflow(int a, int b) {
* return a + b;
* }
* ...
* Example executions:
* execute(Integer.MAX_VALUE - 1, 1) => doAddNoOverflow(Integer.MAX_VALUE - 1, 1)
* execute(Integer.MAX_VALUE, 1) => doAddNoOverflow(Integer.MAX_VALUE, 1)
* => throws ArithmeticException
* => doAddWithOverflow(Integer.MAX_VALUE, 1)
* execute(Integer.MAX_VALUE - 1, 1) => doAddWithOverflow(Integer.MAX_VALUE - 1, 1)
* </pre>
*
* </p>
*
* @see ExactMath#addExact(int, int)
*/
Class<? extends Throwable>[] rewriteOn() default {};
/**
* @see #replaces()
* @deprecated renamed to {@link #replaces()} since 0.22
*/
@Deprecated
String[] contains() default {};
/**
* <p>
* Declares other specializations of the same operation to be replaced by this specialization.
* Other specializations are referenced using their unique method name. If this specialization
* is instantiated then all replaced specialization instances are removed and never instantiated
* again for this node instance. Therefore this specialization should handle strictly more
* inputs than which were handled by the replaced specialization, otherwise the removal of the
* replaced specialization will lead to unspecialized types of input values. The replaces
* declaration is transitive for multiple involved specializations.
* </p>
* <b>Example usage:</b>
*
* <pre>
* @Specialization(guards = "b == 2")
* void doDivPowerTwo(int a, int b) {
* return a >> 1;
* }
* @Specialization(replaces ="doDivPowerTwo", guards = "b > 0")
* void doDivPositive(int a, int b) {
* return a / b;
* }
* ...
* Example executions with replaces="doDivPowerTwo":
* execute(4, 2) => doDivPowerTwo(4, 2)
* execute(9, 3) => doDivPositive(9, 3) // doDivPowerTwo instances get removed
* execute(4, 2) => doDivPositive(4, 2)
* Same executions without replaces="doDivPowerTwo"
* execute(4, 2) => doDivPowerTwo(4, 2)
* execute(9, 3) => doDivPositive(9, 3)
* execute(4, 2) => doDivPowerTwo(4, 2)
* </pre>
*
* </p>
*
* @see #guards()
* @since 0.22
*/
String[] replaces() default {};
/**
* <p>
* Declares <code>boolean</code> expressions that define whether or not input values are
* applicable to this specialization instance. Guard expressions must always return the same
* result for each combination of the enclosing node instance and the bound input values.
* </p>
* <p>
* If a guard expression does not bind any dynamic input parameters then the DSL assumes that
* the result will not change for this node after specialization instantiation. The DSL asserts
* this assumption if assertions are enabled (-ea).
* </p>
* <p>
* Guard expressions are defined using a subset of Java. This subset includes field/parameter
* accesses, function calls, type exact infix comparisons (==, !=, <, <=, >, >=), logical
* negation (!), logical disjunction (||) and integer literals. The return type of guard
* expressions must be <code>boolean</code>. Bound elements without receivers are resolved using
* the following order:
* <ol>
* <li>Dynamic and cached parameters of the enclosing specialization.</li>
* <li>Fields defined using {@link NodeField} for the enclosing node.</li>
* <li>Non-private, static or virtual methods or fields of enclosing node.</li>
* <li>Non-private, static or virtual methods or fields of super types of the enclosing node.
* </li>
* <li>Public and static methods or fields imported using {@link ImportStatic}.</li>
* </ol>
* </p>
* <p>
* <b>Example usage:</b>
*
* <pre>
* static boolean acceptOperand(int operand) { assert operand <= 42; return operand & 1 ==
* 1; } @Specialization(guards = {"operand <= 42", "acceptOperand(operand)"}) void
* doSpecialization(int operand) {...}
* </pre>
*
* </p>
*
* @see Cached
* @see ImportStatic
*/
String[] guards() default {};
/**
* <p>
* Declares assumption guards that optimistically assume that the state of an {@link Assumption}
* remains valid. Assumption expressions are cached once per specialization instantiation. If
* one of the returned assumptions gets invalidated then the specialization instance is removed.
* If the assumption expression returns an array of assumptions then all assumptions of the
* array are checked. This is limited to one-dimensional arrays.
* </p>
* <p>
* Assumption expressions are defined using a subset of Java. This subset includes
* field/parameter accesses, function calls, type exact infix comparisons (==, !=, <, <=, >,
* >=), logical negation (!), logical disjunction (||) and integer literals. The return type of
* the expression must be {@link Assumption} or an array of {@link Assumption} instances.
* Assumption expressions are not allowed to bind to dynamic parameter values of the
* specialization. Bound elements without receivers are resolved using the following order:
* <ol>
* <li>Cached parameters of the enclosing specialization.</li>
* <li>Fields defined using {@link NodeField} for the enclosing node.</li>
* <li>Non-private, static or virtual methods or fields of enclosing node.</li>
* <li>Non-private, static or virtual methods or fields of super types of the enclosing node.
* </li>
* <li>Public and static methods or fields imported using {@link ImportStatic}.</li>
* </ol>
* </p>
*
* <p>
* <b>Example usage:</b>
*
* <pre>
* static abstract class DynamicObject() { abstract Shape getShape(); ... } static
* abstract class Shape() { abstract Assumption getUnmodifiedAssuption(); ... }
* @Specialization(guards = "operand.getShape() == cachedShape", assumptions =
* "cachedShape.getUnmodifiedAssumption()") void doAssumeUnmodifiedShape(DynamicObject
* operand, @Cached("operand.getShape()") Shape cachedShape) {...}
* </pre>
*
* </p>
*
* @see Cached
* @see ImportStatic
*/
String[] assumptions() default {};
/**
* <p>
* Declares the expression that limits the number of specialization instantiations. The default
* limit for specialization instantiations is defined as <code>"3"</code>. If the limit is
* exceeded no more instantiations of the enclosing specialization method are created. Please
* note that the existing specialization instantiations are <b>not</b> removed from the
* specialization chain. You can use {@link #replaces()} to remove unnecessary specializations
* instances.
* </p>
* <p>
* The limit expression is defined using a subset of Java. This subset includes field/parameter
* accesses, function calls, type exact infix comparisons (==, !=, <, <=, >, >=), logical
* negation (!), logical disjunction (||) and integer literals. The return type of the limit
* expression must be <code>int</code>. Limit expressions are not allowed to bind to dynamic
* parameter values of the specialization. Bound elements without receivers are resolved using
* the following order:
* <ol>
* <li>Cached parameters of the enclosing specialization.</li>
* <li>Fields defined using {@link NodeField} for the enclosing node.</li>
* <li>Non-private, static or virtual methods or fields of enclosing node.</li>
* <li>Non-private, static or virtual methods or fields of super types of the enclosing node.
* </li>
* <li>Public and static methods or fields imported using {@link ImportStatic}.</li>
* </ol>
* </p>
*
* <p>
* <b>Example usage:</b>
*
* <pre>
* static int getCacheLimit() { return
* Integer.parseInt(System.getProperty("language.cacheLimit")); } @Specialization(guards =
* "operand == cachedOperand", limit = "getCacheLimit()") void doCached(Object
* operand, @Cached("operand") Object cachedOperand) {...}
* </pre>
*
* </p>
*
* @see #guards()
* @see #replaces()
* @see Cached
* @see ImportStatic
*/
String limit() default "";
}