#7450: Regression in optimisation time of functions with many patterns (6.12 to 7.4)? -------------------------------------+------------------------------------- Reporter: iustin | Owner: bgamari Type: bug | Status: patch Priority: normal | Milestone: 7.12.1 Component: Compiler | Version: 7.6.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: Phab:D1012 -------------------------------------+------------------------------------- Comment (by Ben Gamari <ben@…>): In [changeset:"b29633f5cf310824f3e34716e9261162ced779d3/ghc"]: {{{ #!CommitTicketReference repository="ghc" revision="b29633f5cf310824f3e34716e9261162ced779d3" Bitmap: Fix thunk explosion Previously we would build up another `map (-N)` thunk for every word in the bitmap. Now we strictly accumulate the position and carry out a single ``map (`subtract` accum)``. `Bitmap.intsToBitmap` showed up in the profile while compiling a testcase of #7450 (namely a program containing a record type with large number of fields which derived `Read`). The culprit was `CmmBuildInfoTables.procpointSRT.bitmap`. On the testcase (with 4096 fields), the profile previously looked like, ``` total time = 307.94 secs (307943 ticks @ 1000 us, 1 processor) total alloc = 336,797,868,056 bytes (excludes profiling overheads) COST CENTRE MODULE %time %alloc lintAnnots CoreLint 17.2 25.8 procpointSRT.bitmap CmmBuildInfoTables 11.3 25.2 FloatOutwards SimplCore 7.5 1.6 flatten.lookup CmmBuildInfoTables 4.0 3.9 ... ``` After this fix it looks like, ``` total time = 256.88 secs (256876 ticks @ 1000 us, 1 processor) total alloc = 255,033,667,448 bytes (excludes profiling overheads) COST CENTRE MODULE %time %alloc lintAnnots CoreLint 20.3 34.1 FloatOutwards SimplCore 9.1 2.1 flatten.lookup CmmBuildInfoTables 4.8 5.2 pprNativeCode AsmCodeGen 3.7 4.3 simplLetUnfolding Simplify 3.6 2.2 StgCmm HscMain 3.6 2.1 ``` Signed-off-by: Ben Gamari <ben@smart-cactus.org> Test Plan: Validate Reviewers: austin, simonpj Reviewed By: simonpj Subscribers: thomie Differential Revision: https://phabricator.haskell.org/D1041 GHC Trac Issues: #7450 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7450#comment:26> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler