#14052: Significant GHCi speed regression with :module and `let` in GHC 8.2.1 -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: GHCi | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by phadej): I added two time profiles, running the variants of ryan's test-case, with and without ":m *Foo". They look similar, but in bad behaviour withCleanupSession does something, which takes half of the time. {{{ individual inherited COST CENTRE MODULE no. entries %time %alloc WITH :m *Foo, BAD behaviour withCleanupSession GHC 1501 1 50.2 90.2 99.9 99.9 hscStmtWithLocation HscMain 2406 1201 0.0 0.0 16.5 9.4 hscParseStmtWithLocation HscMain 2407 1201 0.0 0.0 0.1 0.1 hscParseThingWithLocation HscMain 2408 1201 0.0 0.0 0.1 0.1 Parser HscMain 2409 1201 0.1 0.1 0.1 0.1 logWarningsReportErrors HscMain 2410 1201 0.0 0.0 0.0 0.0 logWarnings HscMain 2411 1201 0.0 0.0 0.0 0.0 hscParsedStmt HscMain 2412 1201 1.4 1.7 16.4 9.3 ioMsgMaybe HscMain 2413 2402 8.7 4.3 10.9 5.2 Digraph.topSort Digraph 2414 7508 0.0 0.0 0.0 0.0 solveSimples TcInteract 2424 6307 0.1 0.0 2.0 0.9 solve_loop TcInteract 2426 0 1.5 0.7 1.9 0.9 canEvVar TcCanonical 2427 8108 0.4 0.2 0.4 0.2 canClass TcCanonical 2428 901 0.0 0.0 0.0 0.0 WITHOUT :m *Foo, GOOD behaviour withCleanupSession GHC 1501 1 6.4 16.8 99.8 99.3 hscStmtWithLocation HscMain 2406 1201 0.0 0.0 30.9 81.2 hscParseStmtWithLocation HscMain 2407 1201 0.0 0.0 0.3 1.0 hscParseThingWithLocation HscMain 2408 1201 0.0 0.0 0.3 1.0 Parser HscMain 2409 1201 0.3 0.9 0.3 0.9 logWarningsReportErrors HscMain 2410 1201 0.0 0.0 0.0 0.0 logWarnings HscMain 2411 1201 0.0 0.0 0.0 0.0 hscParsedStmt HscMain 2412 1201 2.8 14.4 30.5 80.2 ioMsgMaybe HscMain 2413 2402 16.3 37.2 20.2 45.2 Digraph.topSort Digraph 2414 7508 0.0 0.1 0.0 0.1 solveSimples TcInteract 2424 6307 0.2 0.1 3.6 7.6 solve_loop TcInteract 2426 0 2.7 5.7 3.4 7.5 canEvVar TcCanonical 2427 8108 0.8 1.7 0.8 1.7 canClass TcCanonical 2428 901 0.0 0.1 0.0 0.1 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14052#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler