Fix <bitset> benchmark correctness
#4817
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AlexGuteniev
changed the title
<bitset> binchmark correctness<bitset> benchmark correctness
StephanTLavavej
approved these changes
Jul 8, 2024
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I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed. |
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Thanks for improving how we benchmark all of these bits! 🚀 💻 ⏱️ |
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I see more things to do with
bitsetregarding performance, but first let's fix the current benchmark.Fortunately, the discovered issues didn't have impact on results, and on performance decisions.
Add
DoNotOptimizeto inputShould use this to prevent compiler making the benchmarked function or its part constant.
Currently the compiler doesn't do this, but it might improve in the future
Make 512 case as large
Small cases were initialized with
uint64_twhich was not enough to initialize 512 bit bitset.The 512 rows in the benchmark improved, but it is gooseberries vs watermelons: small cases have inner loop whereas large doesn't.
(The loop in small cases is to defeat branch prediction for the cases of branchy implementation activation. It is not needed for larger bitsets, as these would be vectorized, and if they wouldn't, the amount of bits should be enough to overflow the branch prediction)