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package com.oracle.truffle.sl.nodes.expression;
import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
import com.oracle.truffle.api.dsl.Fallback;
import com.oracle.truffle.api.dsl.ImplicitCast;
import com.oracle.truffle.api.dsl.Specialization;
import com.oracle.truffle.api.nodes.NodeInfo;
import com.oracle.truffle.sl.SLException;
import com.oracle.truffle.sl.nodes.SLBinaryNode;
import com.oracle.truffle.sl.nodes.SLTypes;
import com.oracle.truffle.sl.runtime.SLBigNumber;
/**
* SL node that performs the "+" operation, which performs addition on arbitrary precision numbers,
* as well as String concatenation if one of the operands is a String.
*
* Type specialization on the input values is essential for the performance. This is achieved via
* node rewriting: specialized subclasses handle just a single type, so that the generic node that
* can handle all types is used only in cases where different types were encountered. The subclasses
* are automatically generated by the Truffle DSL. In addition, a {@link SLAddNodeGen factory class}
* is generated that provides, e.g., {@link SLAddNodeGen#create node creation}.
*/
@NodeInfo(shortName = "+")
public abstract class SLAddNode extends SLBinaryNode {
/**
* Specialization for primitive {@code long} values. This is the fast path of the
* arbitrary-precision arithmetic. We need to check for overflows of the addition, and switch to
* the {@link #add(SLBigNumber, SLBigNumber) slow path}. Therefore, we use an
* {@link Math#addExact(long, long) addition method that throws an exception on overflow}. The
* {@code rewriteOn} attribute on the {@link Specialization} annotation automatically triggers
* the node rewriting on the exception.
*
* In compiled code, {@link Math#addExact(long, long) addExact} is compiled to efficient machine
* code that uses the processor's overflow flag. Therefore, this method is compiled to only two
* machine code instructions on the fast path.
*
* This specialization is automatically selected by the Truffle DSL if both the left and right
* operand are {@code long} values.
*/
@Specialization(rewriteOn = ArithmeticException.class)
protected long add(long left, long right) {
return Math.addExact(left, right);
}
/**
* This is the slow path of the arbitrary-precision arithmetic. The {@link SLBigNumber} type of
* Java is doing everything we need.
*
* This specialization is automatically selected by the Truffle DSL if both the left and right
* operand are {@link SLBigNumber} values. Because the type system defines an
* {@link ImplicitCast implicit conversion} from {@code long} to {@link SLBigNumber} in
* {@link SLTypes#castBigNumber(long)}, this specialization is also taken if the left or the
* right operand is a {@code long} value. Because the {@link #add(long, long) long}
* specialization} has the {@code rewriteOn} attribute, this specialization is also taken if
* both input values are {@code long} values but the primitive addition overflows.
*/
@Specialization
@TruffleBoundary
protected SLBigNumber add(SLBigNumber left, SLBigNumber right) {
return new SLBigNumber(left.getValue().add(right.getValue()));
}
/**
* Specialization for String concatenation. The SL specification says that String concatenation
* works if either the left or the right operand is a String. The non-string operand is
* converted then automatically converted to a String.
*
* To implement these semantics, we tell the Truffle DSL to use a custom guard. The guard
* function is defined in {@link #isString this class}, but could also be in any superclass.
*/
@Specialization(guards = "isString(left, right)")
@TruffleBoundary
protected String add(Object left, Object right) {
return left.toString() + right.toString();
}
/**
* Guard for String concatenation: returns true if either the left or the right operand is a
* {@link String}.
*/
protected boolean isString(Object a, Object b) {
return a instanceof String || b instanceof String;
}
@Fallback
protected Object typeError(Object left, Object right) {
throw SLException.typeError(this, left, right);
}
}