> On Thu, 2024-02-08 at 16:35 +0100, Jose E. Marchesi wrote: > [...] > >> If the compiler generates assembly code the same code for profile2.c for >> before and after, that means that the loop does _not_ get unrolled when >> profiler.inc.h is built with -O2 but without #pragma unroll. >> >> But what if #pragma unroll is used? If it unrolls then, that would mean >> that the pragma does something more than -funroll-loops/-O2. >> >> Sorry if I am not making sense. Stuff like this confuses me to no end >> ;) > > Sorry, I messed up while switching branches :( > Here are the correct stats: > > | File | insn # | insn # | > | | before | after | > |-----------------+--------+--------| > | profiler1.bpf.o | 16716 | 4813 | This means: - With both `#pragma unroll' and -O2 we get 16716 instructions. - Without `#pragma unroll' and with -O2 we get 4813 instructions. Weird. > | profiler2.bpf.o | 2088 | 2050 | - Without `#pragma unroll' and with -O2 we get 2088 instructions. - With `#pragma loop unroll(disable)' and with -O2 we get 2050 instructions. Also surprising. > | profiler3.bpf.o | 4465 | 1690 |
