This may not actually be a bug in GHC itself, but in the text library,
#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: 8.6.1 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 simonpj): particularly the fusion-related rules. Sounds plausible. Since there only very few such rules triggered in the trace you sent, you could disable them individually and see what happens. Then hand it off to the text library maintainers! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14519#comment:39 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler