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Opened by Simon Jakobi@sjakobiDeveloper

Performance regression in bytestring from 8.8 to 8.10

Summary

Many of the benchmarks in bytestring's bench-bytestring-builder benchmark suite run much slower with 8.10.1-alpha2 than with 8.8.

Here are the first lines of the benchmark diff (produced with criterion-compare), sorted by significance:

image

Full diff

Some of the results may be noisy, but at that magnitude it shouldn't matter much.

I also benchmarked with HEAD (923a1272), and got even worse results, but that might have been because that ghc was built with --flavour=Quick.

Note that the substrings/* benchmarks measure the findSubstrings function, which is deprecated. So the performance of the other benchmarks is actually more important.

Steps to reproduce

  1. Clone the branch from this PR which fixes building the benchmarks.
  2. cd bench
  3. cabal -O2 run bench-bytestring-builder

Expected behavior

The performance of these benchmarks should be no worse with 8.10 than with 8.8.

Environment

  • GHC versions used: 8.8.1 and 8.10.1-alpha2, both from hvr's PPA.
  • Operating System: Linux
  • System Architecture: x86_64
Edited by Simon Jakobi