#13745: Investigate compile-time regressions in regex-tdfa-1.2.2 -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: task | Status: new Priority: high | Milestone: 8.2.3 Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by ntc2): I'm observing an apparently **exponential run time performance regression** when combining GHC 8.2.1, `Data.Text.Lazy`, and `Text.RE.TDFA`. Here's my repo with simple test code illustrating the regression and timing stats: https://github.com/ntc2/ghc-8.2.1-regex-lazy- text-bug. In summary, for the problematic combination of GHC version and libraries, the run times are 3s, 10s, 22s, and 40s for counting regex matches in files with 10000, 20000, 30000, and 40000 lines, respectively. For all of the unproblematic combinations -- i.e. GHC 8.0.2, `String`, strict `Data.Text`, or building with profiling -- the run time is always about 1s! And this is a Heisenbug, in that the performance problem goes away if I build with profiling support! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13745#comment:18 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler