#15938: Hadrian's recompilation check is extremely slow -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.8.1 Component: Build System | Version: 8.6.2 (Hadrian) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): I suspect to really solve this changes in Shake will be necessary. On quickly looking at the implementation a few things stood out: * paths are split on the directory separator every time we attempt to match it against a `FilePattern`. This is apparently how we end up with 180 million calls to `split`. * paths are represented as `ByteString`. Given the storage overhead and pinned nature of `ByteString`, I suspect there is a small amount of money on the table here -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15938#comment:17 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler