Porting GCC to Exposed Pipeline VLIW Processors

EVP and TriMedia are embedded application processors targeted at mobile communication and multimedia domains. Both architectures originate from Philips Semiconductors and are currently developed by ST-Ericsson and NXP Semiconductors, respectively. Both processors have a VLIWarchitecture with an exposed pipeline. Such architectures impose different requirements on a compiler than the majority of existing GCC targets, which are scalar or superscalar machines with interlocked pipelines. First, the exposed pipeline organization requires a compiler to schedule operations such that all data and resource hazards are avoided. Second, a compiler for a VLIW machine has to provide stronger capabilities for discovering and exposing the instruction level parallelism (ILP), as it can not rely on the hardware ILP mechanisms employed in superscalar processors. We have ported GCC to EVP and TriMedia and provided extensions to support code generation for an exposed pipeline VLIW. To increase the amount of exploitable ILP, we have also enhanced the current GCC mechanisms such as loop unrolling and the alias analysis. The ports were benchmarked against the existing production compilers and encouraging results in terms of cycle counts and code size have been achieved.Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc