This paper examines the problem of code-generation for expression trees on non-homogeneous register set architectures. It proposes and proves the optimality of an O(n) algorithm for the tasks of instruction selection, register allocation and scheduling on a class of architectures defined as the [1; 1] Model. Optimality is guaranteed by sufficient conditions derived from the Register Transfer Graph (RTG), a structural representation of the architecture which depends exclusively on the processor Instruction Set Architecture (ISA). Experimental results using the TMS320C25 as the target processor show the efficacy of the approach. 1 Introduction Non-homogeneous register architectures are frequently encountered in Application Specific Instruction Set Processors (ASIPs). These processors usually have a set of very specialized functional units, and associated registers, that are used to efficiently implement operations with hard performance requirements which frequently occur in the applica...

DSP algorithms in most cases are subject to hard real-time constraints. In case of programmable DSP processors, meeting those constraints must be ensured by appropriate code generation techniques. For processors offering instruction-level parallelism, the task of code generation includes code compaction. The exact timing behavior of a DSP program is only known after compaction. Therefore, real-time constraints should be taken into account during the compaction phase. While most known DSP code generators rely on rigid heuristics for that phase, this paper proposes a novel approach to local code compaction based on an Integer Programming model, which obeys exact timing constraints. Due to a general problem formulation, the model also obeys encoding restrictions and possible side effects. 1 1 Introduction & related work Design requirements for embedded systems including DSP functionality strongly differ from those for interactive environments such as workstations. While in the latter ca...

Besides high code quality, a primary issue in embedded code generation is retargetability of code generators. This paper presents techniques for automatic generation of code selectors from externally specified processor models. In contrast to previous work, our retargetable compiler Record does not require tool-specific modelling formalisms, but starts from general HDL processor models. From an HDL model, all processor aspects needed for code generation are automatically derived. As demonstrated by experimental results, short turnaround times for retargeting are achieved, which permits to study the HW/SW trade-off between processor architectures and program execution speed.

The role of software is becoming increasingly important in the implementation of DSP applications. As this trend intensifies, and the complexity of applications escalates, we are seeing an increased need for automated tools to aid in the development of DSP software. This paper reviews the state of the art in programming language and compiler technology for DSP software implementation. In particular, we review techniques for high level, block-diagram-based modeling of DSP applications; the translation of block diagram specifications into efficient C programs using global, target-independent optimization techniques; and the compilation of C programs into streamlined machine code for programmable DSP processors, using architecture-specific and retargetable back-end optimizations. In our review, we also point out some important directions for further investigation.

One important problem in code generation for embedded processors is the design of efficient compilers for ASIPs with application specific architectures. This paper outlines the design of a C compiler for an industrial ASIP for telecom applications. The target ASIP is a network processor with special instructions for bit-level access to data registers, which is required for packet-oriented communication protocol processing. From a practical viewpoint, we describe the main challenges in exploiting these application specific features in a C compiler, and we show how a compiler backend has been designed that accomodates these features by means of compiler intrinsics and a dedicated register allocator. The compiler is fully operational, and first experimental results indicate that C-level programming of the ASIP leads to good code quality without the need for time-consuming assembly programming.

The concept of retargetability enables compiler technology to keep pace with the increasing variety of domain-specific embedded processors. In order to achieve user retargetability, powerful processor modeling formalisms are required. Most of the recent modeling formalisms concentrate on horizontal, VLIWlike instruction formats. However, for encoded instruction formats with restricted instruction-level parallelism (ILP), a large number of ILP constraints might need to be specified, resulting in less concise processor models. This paper presents an HDL-based approach to processor modeling for retargetable compilation, in which ILP may be implicitly constrained. As a consequence, the formalism allows for concise models also for encoded instruction formats. The practical applicability of the modeling formalism is demonstrated by means of a case study for a complex DSP 1 1 Introduction As a result of the increasing diversity of embedded processors, retargetable compilers have received re...

One important problem in code generation for embedded processors is the design of efficient compilers for target machines with application specific architectures. This paper outlines the design of a C compiler for an industrial application specific processor (ASIP) for telecom applications. The target ASIP is a network processor with special instructions for bit-level access to data registers, which is required for packet oriented communication protocol processing. From a practical viewpoint, we describe the main challenges in exploiting these application specific features in a C compiler, and we show how a compiler backend has been designed that accommodates these features by means of compiler intrinsics and a dedicated register allocator. The compiler is fully operational, and first experimental results indicate that C-level programming of the ASIP leads to good code quality without the need for time-consuming assembly programming.

This paper presents a new code optimization technique for a class of embedded processors. Modern embedded processor architectures show deep instruction pipelines and highly parallel VLIW-like instruction sets. For such architectures, any change in the control flow of a machine program due to a conditional jump may cause a significant code performance penalty. Therefore, the instruction sets of recent VLIW machines offer support for branch-free execution of conditional statements in the form of so-called conditional instructions. Whether an if-then-else statement is implemented by a conditional jump scheme or by conditional instructions has a strong impact on its worst-case execution time. However, the optimal selection is difficult particularly for nested conditionals. We present a dynamic programming technique for selecting the fastest implementation for nested if-then-else statements based on estimations. The efficacy is demonstrated for a real-life VLIW DSP. 1 1 Introduction A maj...

In this paper, we present the application of dynamic trellis diagrams (DTDs) to automatic translation of data flow graphs (DFGs) into highly optimized programs for digital signal processors (DSPs). In contrast to static trellis diagrams (STDs), which may be precalculated, DTDs are built at runtime and adapted exactly to the local requirements. Therefore, DTDs are more flexible and need less program memory. Due to the significant reduction in memory size, the increase of compilation time is only moderate. At present, the concept of DTDs has been successfully applied to DFG compiler implementations for a variety of general purpose DSP families, including Motorola’s DSP56000 and Analog Devices ’ ADSP2100.