Code Generation for an Application-Specific VLIW Processor With Clustered, Addressable Register Files

Ivan Llopard 1, 2 Albert Cohen 1 Christian Fabre 2 Jérôme Martin 2 Henri-Pierre Charles 2 Christian Bernard 2
1 Parkas - Parallélisme de Kahn Synchrone
CNRS - Centre National de la Recherche Scientifique : UMR 8548, Inria Paris-Rocquencourt, DI-ENS - Département d'informatique de l'École normale supérieure
Abstract : Modern compilers integrate recent advances in compiler construction, intermediate representations, algorithms and programming language front-ends. Yet code generation for appli\-cation-specific architectures benefits only marginally from this trend, as most of the effort is oriented towards popular general-purpose architectures. Historically, non-orthogonal architectures have relied on custom compiler technologies, some retargettable, but largely decoupled from the evolution of mainstream tool flows. Very Long Instruction Word (VLIW) architectures have introduced a variety of interesting problems such as clusterization, packetization or bundling, instruction scheduling for exposed pipelines, long delay slots, software pipelining, etc. These have been addressed in the literature, with a focus on the exploitation of Instruction Level Parallelism (ILP). While these are well known solutions already embedded into existing compilers, they rely on common hardware functionalities that are expected to be present in a fairly large subset of VLIW architectures. This paper presents our work on back-end compiler for Mephisto, a high performance low-power application-specific processor, based on LLVM. Mephisto is specialized enough to challenge established code generation solutions for VLIW and DSP processors, calling for an innovative compilation flow. Conversely, even though Mephisto might be seen a somewhat exotic processor, its hardware characteristics such as addressable register files benefit from existing analyses and transformations in LLVM. We describe our model of the Mephisto architecture, the difficulties we encountered, and the associated compilation methods, some of them new and specific to Mephisto.
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Ivan Llopard, Albert Cohen, Christian Fabre, Jérôme Martin, Henri-Pierre Charles, et al.. Code Generation for an Application-Specific VLIW Processor With Clustered, Addressable Register Files. ODES'13 - 10th Workshop on Optimizations for DSP and Embedded Systems, associated with CGO, Feb 2013, Shenzhen, China. pp.11-19, ⟨10.1145/2443608.2443612⟩. ⟨hal-00911896⟩

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