Compiling Esterel into Static Discrete-Event Code

Executing concurrent specifications on sequential hardware is important for both simulation of systems that are eventually implemented on concurrent hardware and for those most conveniently described as a set of concurrent processes. As with most forms of simulation, this is easy to do correctly but difficult to do efficiently. Solutions such as preemptive operating systems and discrete-event simulators present significant overhead. In this paper, we present a technique for compiling the concurrent language Esterel into very efficient C code. Our technique minimizes runtime overhead by making most scheduling decisions at compile time and using a very simple linked-list-based event queue at runtime. While these techniques work particularly well for Esterel with its high-level concurrent semantics, the same technique could also be applied to efficiently execute other concurrent specifications

Removing Cycles in Esterel Programs

Programs written in the synchronous programming language Esterel may contain statically cyclic dependencies of signals, which inhibits the application of certain compilation approaches that rely on static scheduling. This talk proposes an algorithm which, given a constructive synchronous program, performs a semantics-preserving source-level code transformation that removes cyclic signal dependencies. The transformation exploits the monotonicity of constructive programs, and is illustrated in the context of Esterel, but should be applicable to other synchronous languages as well

A Concurrent Reactive Esterel Processor based on Multi-Threading

The synchronous language Esterel is well-suited for programming control-dominated reactive systems at the system level. It provides non-traditional control structures, in particular concurrency and various forms of preemption, which allow to concisely express reactive behavior. As these control structures cannot be mapped easily onto traditional, sequential processors, an alternative approach that has emerged recently makes use of special-purpose reactive processors. However, the designs proposed so far have limitations regarding completeness of the language support, and did not really take advantage of compile-time knowledge to optimize resource usage. This paper presents a reactive processor, the Kiel Esterel Processor 3a (KEP3a), and its compiler. The KEP3a improves on earlier designs in several areas; most notable are the support for exception handling and the provision of context-dependent preemption handling instructions. The KEP3a compiler presented here is to our knowledge the first for multi-threaded reactive processors. The translation of Esterel's preemption constructs onto KEP3a assembler is straightforward; however, a challenge is the correct and efficient representation of Esterel's concurrency. The compiler generates code that respects data and control dependencies using the KEP3a priority-based scheduling mechanism. We present a priority assignment approach that makes use of a novel concurrent control flow graph and has a complexity that in practice tends to be linear in the size of the program. Unlike earlier Esterel compilation schemes, this approach avoids unnecessary context switches by considering each thread's actual execution state at run time. Furthermore, it avoids code replication present in other approaches

Efficient Compilation of Cyclic Synchronous Programs

Synchronous programs may contain cyclic signal interdependencies. This prohibits a static scheduling, which limits the choice of available compilation techniques for such programs. This paper proposes an algorithm which, given a constructive synchronous program, performs a semantics-preserving source-level code transformation that removes cyclic signal dependencies, and also exposes opportunities for further optimization. The transformation exploits the monotonicity of constructive programs, and is illustrated in the context of Esterel; however, it should be applicable to other synchronous languages as well. Experimental results indicate the efficacy of this approach, resulting in reduced run times and/or smaller code sizes, and potentially reduced compilation times as well. Furthermore, experiments with generating hardware indicate that here as well the synthesis results can be improved

Generating Fast Code from Concurrent Program Dependence Graphs

While concurrency in embedded systems is most often supplied by real-time operating systems, this approach can be unpredictable and difficult to debug. Synchronous concurrency, in which a system marches in lockstep to a global clock, is conceptually easier and potentially more efficient because it can be statically scheduled beforehand. We present an algorithm for generating efficient sequential code from such synchronous concurrent specifications. Starting from a concurrent program dependence graph generated from the synchronous, concurrent language Esterel, we generate efficient, statically scheduled sequential code while adding a minimal amount of runtime scheduling overhead. Experimentally, we obtain speedups as high as six times over existing techniques. While we applied our technique to Esterel, it should be applicable to other synchronous, concurrent languages

Towards Coq-verified Esterel Semantics and Compiling

This paper focuses on semantics of the Esterel synchronous programming language. In particular, in addition to the usual behavioral (CBS) and state (CSS) semantics, it introduces a novel microstep semantics which does not need the Can potential function. Formal proofs in Coq of the equivalence between the CBS and CSS semantics and of the refinement between the CSS and microstep semantics are also provided

Efficient Code Generation from SHIM Models

Programming concurrent systems is substantially more difficult than programming sequential systems, yet most embedded systems need concurrency. We believe this should be addressed through higher-level models of concurrency that eliminate many of the usual challenges, such as nondeterminism arising from races. The shim model of computation provides deterministic concurrency, and there already exist ways of implementing it in hardware and software. In this work, we describe how to produce more efficient C code from shim systems. We propose two techniques: a largely mechanical one that produces tail-recursive code for simulating concurrency, and a more clever one that statically analyzes the communication pattern of multiple processes to produce code with far less overhead. Experimentally, we find our tail-recursive technique produces code that runs roughly twice as fast as a baseline; our statically-scheduled code can run up to twelve times faster

A sequentially constructive circuit semantics for Esterel

Static Single Assignment (SSA) is an established concept that facilitates various program optimizations. However, it is typically restricted to sequential programming. We present an approach that extends SSA for concurrent, reactive programming, specifically for the synchronous language Esterel. This extended SSA transformation expands the class of programs that can be compiled by existing Esterel compilers without causality problems. It also offers a new, efficient solution for the well-studied signal reincarnation problem. Finally, our approach rules out speculation/backtracking, unlike the recently proposed sequentially constructive model of computation

Code Generation in the Columbia Esterel Compiler

The synchronous language Esterel provides deterministic concurrency by adopting a semantics in which threads march in step with a global clock and communicate in a very disciplined way. Its expressive power comes at a cost, however: it is a difficult language to compile into machine code for standard von Neumann processors. The open-source Columbia Esterel Compiler is a research vehicle for experimenting with new code generation techniques for the language. Providing a front-end and a fairly generic concurrent intermediate representation, a variety of back-ends have been developed. We present three of the most mature ones, which are based on program dependence graphs, dynamic lists, and a virtual machine. After describing the very different algorithms used in each of these techniques, we present experimental results that compares twenty-four benchmarks generated by eight different compilation techniques running on seven different processors