#14519: Exponential runtime performance regression in GHC 8.2 + Data.Text.Lazy + Text.RE.TDFA -------------------------------------+------------------------------------- Reporter: ntc2 | Owner: tdammers Type: bug | Status: new Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 8.2.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Runtime | Test Case: performance bug | https://github.com/ntc2/ghc-8.2.1 | -regex-lazy-text- | bug/tree/07b7bb32c6e90e8f2d2eada4b59943f37e632d53 Blocked By: | Blocking: Related Tickets: #13745, #14564 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by tdammers):
I would urge you to build the program and libraries with -ticky and see which function is getting executed a lot. The advantage of -ticky is that it's guaranteed not to affect optimisation or indeed anything. It just logs what happens.
That's actually exactly what I'm doing right now. A comparison of running two regular expressions such that one is fast (`^[^.]d`) and the other is slow (`^def`) shows that all the metrics are the same, or nearly the same, except for ALLOC_PRIM_gds (from 669 up to 1801526) and ALLOC_PRIM_ctr (from 371392 up to 9325581456). I should probably dig a bit deeper from here. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14519#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler