Code Optimizations for a VLIW-Style Network Processing Unit

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The explosive growth in network bandwidth and Internet services such as QoS (quality of service) and SLA (service level agreement) monitoring have created the need for new networking hardware called a Network Processing Unit (NPU). In order to rapidly reconfigure the NPU for frequently varying Internet services and technologies, a high-performance C compiler is urgently needed. Several code generation techniques, which are intended to meet the high code quality demands of other types of application specific instruction-set processors (ASIPs) like digital signal processors (DSPs), have already been developed. However, these techniques are insufficient for NPUs due to striking architectural differences such as asymmetric data paths. The main purpose of this paper is to discuss our recent experience with the development of a commercial compiler for a new NPU called the Paion PPII, which is basically a packet engine for NPU to meet the growing need for new high-bandwidth communication equipment targeted for Internet routers and ethernet adapters. For this purpose, we will first show the architectural challenges posed by the target NPU. Then, we will describe several compiler techniques that we found to be effective for the target NPU with various unorthogonal architectural features. The current implementations of the PPII use a VLIW (Very Long Instruction Word) architecture. So, we handled this VLIW-style architecture by employing a simple code compaction scheme which packs multiple parallel instructions into one long instruction word. The experimental results show that our techniques are effective for significantly reducing the dynamic instruction count.