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...-- (2) FE-based Instr 201.658 250.8% 65238880 (3) late Instr 103.662 129.0% 14860144 (4) (3) + w/o pre-inline 199.924 248.7% 70762720 (5) (4) + Silva 119.904 149.2% 24499528 Config(5) used the simple heuristic that Sean Silva proposed: not instrumenting single BB functions that contain less than 10 instructions (excluding debug and phi stmts). We can see: 1) Simple heuristic of not instrumenting small single BB functions improves instrumentation performance as expect...

...-based Instr 201.658 250.8% 65238880 > (3) late Instr 103.662 129.0% 14860144 > (4) (3) + w/o pre-inline 199.924 248.7% 70762720 > (5) (4) + Silva 119.904 149.2% 24499528 > > Config(5) used the simple heuristic that Sean Silva proposed: not > instrumenting single BB functions that contain less than 10 instructions > (excluding debug and phi stmts). > > We can see: > 1) Simple heuristic of not instrumenting small single BB functions > improves...

One aspect of this that I have not seen discussed is that middle-end instrumentation enables PGO optimizations to front-ends other than Clang. While I agree that FE instrumentation could be improved, it still requires every FE to implement essentially the same common functionality. Having PGO instrumentation generated in the middle-end, allows us every FE to automatically take advantage of PGO.