The current level of circuit integration led to complex designs encompassing full systems on a single chip, known as System-on-a-Chip (SoC). In order to predict the best design options and reduce the design costs, designers are required to perform a large design space exploration on early stages of the design. To speed up this process, Electronic Design Automation (EDA) tools are employed to model and experiment with the system. ArchC is an "Architecture Description Language" (ADL) and a set of tools that can be leveraged to automatically build SoC simulators based on high-level system models, enabling easy and fast design space exploration in early stages of the design. Currently, ArchC is capable of automatically generating hardware simulators, assemblers, and linkers for a given architecture model. In this work, we present ACCGen, an automatic Compiler Generator for ArchC, the missing link on the automatic generation of compiler tool chains for ArchC. Our experimental results show that compilers generated by ACCGen are correct for Mibench applications. They compare, as well, the generated code quality with LLVM and gcc, two well-known open-source compilers. We also show that ACCGen is fast and has little impact on the design space exploration turnaround time, allowing the designer to, using an easy and fully automated workflow, completely assess the outcome of architectural changes in less than 2 minutes.

The shift towards multicore processors and the well-known drawbacks imposed by lock-based synchronization have forced researchers to devise new alternatives for building concurrent software, of which transactional memory is a promising one. This work presents a comprehensive study on the energy consumption of a state-of-the-art STM (Software Transactional Memory) implementation using STAMP, a representative set of transactional workloads, comparing it to its lock-based counterpart. Our results show that STM can be up to 22x (~3x on average) more energy-inefficient when compared to locks. This work is a novel step towards a better understanding of the energy behavior of STM systems.

RISC processors can be used to face the ever increasing demand for performance required by embedded systems. Nevertheless, this solution comes with the cost of poor code density. Alternative encodings for instruction sets, such as MIPS16 and Thumb, represent an effective approach to deal with this drawback. This article proposes to apply a new encoding to the SPARCv8 architecture. Through extensive analysis of a program mix from the Mibench and Mediabench benchmark suites, we suggest a new 16-bit instruction set, easily translated to its 32-bit counterpart during execution time. Using the aforementioned program mix to infer how code could be represented in the proposed 16-bit ISA, compression ratios as low as 56% can be obtained. We also evaluated the cache behavior and showed reductions of 42% on cache misses that can increase performance up to 28% (for patricia program with 2KB cache).

Due to the advent of multi-core processors and the consequent need for better concurrent programming abstractions, new synchronization paradigms have emerged. A promising one, known as software transactional memory (STM), aims to use transactions as the key synchronization mechanism to ease program development as well as increase its performance. Many (if not all) of the current STM implementations target homogeneous architectures. In this paper we describe an implementation of an STM system for an asymmetric architecture, the Cell BE. We evaluated our Transactional Software Cache (TSC) mechanism using a well-known micro-benchmark (IntSet) and the Genome application from STAMP. The results show that an STM implementation for the Cell architecture is feasible if the shared-memory programming model is adopted. When compared to a conventional lock-based implementation, the STM version of Genome obtained a performance gain of 84% and 24% with large and small input sets, respectively.

Electronic system level (ESL) modeling allows early hardware-dependent software (HDS) development. Due to broad CPU diversity and shrinking time-to-market, HDS development can neither rely on hand-retargeting binary tools, nor can it rely on pre-existent tools within standard packages. As a consequence, binary utilities which can be easily adapted to new CPU targets are of increasing interest. We present in this article a framework for automatic generation of binary utilities. It relies on two innovative ideas: platform-aware modeling and more inclusive relocation handling. Generated assemblers, linkers, disassemblers and debuggers were validated for MIPS, SPARC, PowerPC, i8051 and PIC16F84. An open-source prototype generator is available for download.

In this paper, we extend the ArchC language with new constructs to describe the assembly language syntax and operand encoding of an instruction set architecture. Based on the extended language we have created a tool which can automatically generate assemblers. Our tool uses the GNU Binutils framework in order to produce the assembler, generating the architecture dependent files necessary to retarget the GNU assembler and the Binutils libraries. We have generated assemblers for the MIPS-I and SPARC-V8 architectures based on ArchC models using our tool. The assemblers generated for both architectures were compared with the default gas assemblers for a set of files taken from the MiBench benchmark, and the ELF object files generated by each pair of assemblers were equivalent in both cases.

Code compression has been shown to be an effective technique to reduce code size in memory constrained embedded systems. It has also been used as a way to increase cache hit ratio, thus reducing power consumption and improving performance. This paper proposes an approach to mix static/dynamic instruction profiling in dictionary construction, so as to best exploit trade-offs in compression ratio/performance. Compressed instructions are stored as variable-size indices into fixed-size codewords, eliminating compressed code misalignments. Experimental results, using the Leon (SPARCv8) processor and a program mix from MiBench and Mediabench, show that our approach halves the number of cache accesses and power consumption while produces compression ratios as low as 56%.

Code compression has been used to minimize the memory area requirement of embedded systems. Recently, performance improvement and energy consumption reduction are observed as a by-product of compression. In this paper we propose a novel technique for efficiently exploring the trade-offs involved in code compression. Our multiprofile approach to build dictionaries combines the best features of both static and dynamic program behaviors. The experiments with Mediabench and MiBench suites and the Leon (SPARCv8) processor reveal a compression ratio as low as 71% while performance speed-up reaches 1.5.

In this paper we describe a design exploration methodology for clustered VLIW architectures. The central idea of this work is a set of three techniques aimed at reducing the cost of expensive inter-cluster copy operations. Instruction scheduling is performed using a list-scheduling algorithm that stores operand chains into the same register file. Functional units are assigned to clusters based on the application inter-cluster communication pattern. Finally, a careful insertion of pipeline bypasses is used to increase the number of data-dependencies that can be satisfied by pipeline register operands. Experimental results, using the SPEC95 benchmark and the IMPACT compiler, reveal a substantial reduction in the number of copies between clusters.

Reducing program size has become an important goal in the design of modern embedded systems targeted to mass production. This problem has driven efforts aimed at designing processors with shorter instruction formats (e.g., ARM Thumb and MIPS16) or able to execute compressed code (e.g., IBM PowerPC 405), This paper proposes three code compression algorithms for embedded RISC architectures. In all algorithms, the encoded symbols are extracted from program expression trees. The algorithms differ on the granularity of the encoded symbol, which are selected from whole trees, parts of trees, or single instructions. Dictionary-based decompression engines are proposed for each compression algorithm. Experimental results, based on SPEC CINT95 programs running on the MIPS R4000 processor, reveal an average compression ratio of 53.6% (31.5%) if the area of the decompression engine is (not) considered.

This paper proposes a code compression technique called operand factorization. The central idea of operand factorization is the separation of program expression trees into sequences of tree-patterns (opcodes) and operand patterns (registers and immediates). Using this technique, we show that tree and operand patterns have exponential frequency distributions. A set of experiments were designed to explore this feature. They reveal an average compression ratio of 43% for SPECInt95 programs. A decompression engine is proposed, which assembles tree and operand patterns into uncompressed instruction sequences. An encoding that improves the design of the decompression engine results in a 48% compression ratio. Compression ratio numbers take into consideration an estimate of the decompression engine size.