The performance of Very Long Instruction Word (VLIW) microprocessors depends on the close cooperation between the compiler and the architecture. This paper evaluates a set of important compilation techniques and related architectural features for VLIW machines. The evaluation is performed on a SPARC-based VLIW testbed where gcc-generated optimized SPARC code is scheduled into high-performance VLIW code. As a base scheduling compiler, we experiment with three core scheduling techniques including enhanced pipeline scheduling, all-path speculation, and renaming. We analyze the characteristics of the useful and useless ALUs in each cycle to see how many of those ALUs execute non-speculative operations, speculative operations, and copies, respectively. Then, we evaluate the following compilation techniques: software pipelining, loop unrolling, non-greedy enhanced pipeline scheduling, profile-based all-path speculation, trace-based speculation, renaming, restricted speculative loads, and memory disambiguation. Since we experiment on a uniform testbed based on a detailed analysis of ALUs, our evaluation provides an useful insight on the performance impact of these techniques.
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