Design of a Two-Level Hot Path Detector for Path-based Loop Optimizations

T. Baba, T. Masuho, K. Ootsu, and T. Yokota (Japan)


hot path, hot loop, path profiling, path based loop opti mization, program behaviors


Aggressive execution-path-based compiler and architec ture optimizations require a path profiler that can specify several hottest paths at low overheads. Based on our ob servation that a limited number of paths are executed fre quently in hot loops, we have designed a two-level hot path detector to specify such hottest paths within hot loops. The detector consists of two tables: a filter table and an accu mulator table. The filter table captures the behavior of lo cally hot paths. This hot path information is then sent to the accumulator table to capture the behavior of globally hot paths. The path profiler also provides us with the in formation on hot loops as well as problematic instructions contained in the hot paths. They may be effectively utilized for the optimizations. We evaluate the profiler using SPEC CINT2000. The results show that the two-level organiza tion has an effect of filtering out less frequent paths, and that the top 5 frequent paths and their order can be ade quately detected.

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