Tracing tools are used widely to help analyze, design, and tune both hardware and software systems. This paper describes a tool called Shade which combines efficient instruction-set simulation with a flexible, extensible trace generation capability. Efficiency is achieved by dynamically compiling and caching code to simulate and trace the application program. The user may control the extent of tracing in a variety of ways; arbitrarily detailed application state information may be collected during the simulation, but tracing less translates directly into greater efficiency. Current Shade implementations run on SPARC systems and simulate the SPARC (Versions 8 and 9) and MIPS I instruction sets. This paper describes the capabilities, design, implementation, and performance of Shade, and discusses instruction set emulation in general.

This paper introduces superoperators, an optimization technique for bytecoded interpreters. Superoperators are virtual machine operations automatically synthesized from smaller operations to avoid costly per-operation overheads. Superoperators decrease executable size and can double or triple the speed of interpreted programs. The paper describes a simple and effective heuristic for inferring powerful superoperators from the usage patterns of simple operators. The paper describes the design and implementation of a hybrid translator/interpreter that employs superoperators. From a specification of the superoperators (either automatically inferred or manually chosen), the system builds an efficient implementation of the virtual machine in assembly language. The system is easily retargetable and currently runs on the MIPS R3000 and the SPARC.

This paper introduces the idea of dynamically moving functionality in a network---between clients and servers, and between hosts at the edge of the network and nodes inside the network. At the heart of moving functionality is the ability to support mobile code---code that is not tied to any single machine, but instead can easily move from one machine to another. Mobile code has been studied mostly for application-level code. This paper explores its use for all facets of the network, and in a much more general way. Issues of efficiency, interface design, security, and resource allocation, among others, are addressed. We use the term liquid software to describe the complete picture---liquidsoftware is an entire infrastructure for dynamically moving functionality throughout a network. We expect liquid software to enble new paradigms, such as active networks that allow users and applications to customize the network by interjecting code into it. Department of Computer Science The Univers...

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Languages with programmer-visible stacks (stack-based languages) are used widely, as intermediate languages (e.g., JavaVM, FCode), and as languages for human programmers (e.g., Forth, PostScript). However, the prevalent computer architecture is the register machine. This poses the problem of efficiently implementing stack-based languages on register machines. A straight-forward implementation of the stack consists of a memory area that contains the stack items, and a pointer to the top-of-stack item. The basic

Interpreters designed for high general-purpose performance typically perform a large number of indirect branches (3.2%-13% of all executed instructions in our benchmarks). These branches consume...

Presentation conversion is a key operation in any development environment for distributed applications, such as Corba, Java-RMI, DCE or ASN.1-based environments. It is also well-known performance bottleneck in high-speed network communication. Presentation conversion code is usually generated by an automatic code generation tool referred to as stub compiler. The quality of the code generated by a stub compiler is often very low. The code is either very slow, or has a large code size, or both. This paper describes the design and experimental evaluation of an optimization stage for a stub compiler. The optimization stage automates the trade-off between code size and execution speed of the code generated by the compiler. This is achieved by using a hybrid of two implementation alternatives for presentation conversion routines (interpreted and procedure-driven code). The optimization problem is modeled as a Knapsack problem. A Markov model in combination with a heuristic branch predictor is used for...

Many advantages have been given for using formal specifications in the design and implementation of communication systems. Performance is usually not among them. It is commonly believed that code generated by an automatic tool from a formal specification is inherently slower than code implemented manually. This paper gives experimental evidence that this contention might be false. The key idea is to integrate heuristics used by a human programmer when optimizing code into the code generation tool. This way, the tool can generate code that is competitive with code written by a human programmer, and even better for specications of sufficient complexity. Experiments were conducted using the presentation conversion routines generated by an ASN.1 compiler. The paper describes the design and implementation of an optimisation stage that automates the trade-off between code size and execution speed in these routines. For this purpose, a heuristic method to predict the frequency of type usage is dev...

Presentation conversion is a key operation in any development environment for distributed applications, such as Corba, Java-RMI, DCE or ASN.1-based environments. It is also well-known performance bottleneck in high-speed network communication. Presentation conversion code is usually generated by an automatic code generation tool referred to as stub compiler. The quality of the code generated by a stub compiler is often very low. The code is either very slow, or has a large code size, or both. This paper describes the design and experimental evaluation of an optimization stage for a stub compiler. The optimization stage automates the trade-off between code size and execution speed of the code generated by the compiler. This is achieved by using a hybrid of two implementation alternatives for presentation conversion routines (interpreted and procedure-driven code). The optimization problem is modeled as a Knapsack problem. A Markov model in combination with a heuristic branch predictor...