Scalable Optimization of Generic Java

Java程序员依赖于笨拙的“擦除”习惯用法来定义泛型操作：泛型类由常规类表示，其中对类型参数的所有引用都已被类型对象替换。依赖这一习惯用法的程序必须将泛型操作的结果反复强制转换为省略类型参数的类型。Java中的泛型操作比非泛型操作慢，因为这个习惯用法在表示实例化为基元类型的类型参数时引入了一定程度的间接性。研究人员最近完成了NexGen的原型编译器的构建，NexGen是由研究人员和Guy Steele设计的支持泛型的Java扩展。编译器依赖擦除习惯用法来实现泛型，因此不会提高涉及泛型类的计算的性能。要为泛型Java产生良好的性能，编译器必须消除泛型类实例表示中的间接性。必要的转换称为{\em整个程序分析}，因为如果任何程序操作依赖于内联对象的地址，则它是无效的。幸运的是，在具体类型分析研究人员之前的工作基础上，有一个近乎线性的算法可以确定给定的对象字段是否可以内联。该项目将为NextGen开发一个新的优化编译器，它使用具体类型分析来内联泛型类的参数字段。

Java programmers rely on clumsy "erasure" idiom to define generic operations: a generic class is represented by conventional classes where all references to type parameters have been replaced by the type Object. Programs that rely on this idiom must repeatedly cast the results of generic operations to the types of omitted type parameters. Generic operations in Java are slower than their non-generic counterparts because this idiom introduces a level of indirection in the representation of type parameters instantiated as primitive types.The investigator has recently completed the construction of a prototype compiler for NexGen, a Java extension supporting genericity designed by the investigator and Guy Steele. The compiler relies on the erasure idiom to implement genericity and hence does not improve the performance of computations involving generic classes.To produce good performance for generic Java, a compiler must eliminate indirection in the representation of generic class instances. The requisite transformation is called {\em whole program analysis} because it is invalid if any program operation depends on the address of an inlined object. Fortunately, there is a nearly linear algorithm based on previous work by the investigator on concrete type analysis that can determine if a given object field can be inlined.This project will develop a new optimizing compiler for NextGen that uses concrete type analysis to inline the parametric fields of generic classes.