#5996: fix for CSE ---------------------------------+------------------------------------------ Reporter: michalt | Owner: simonpj Type: bug | Status: patch Priority: normal | Milestone: 7.8.1 Component: Compiler | Version: 7.5 Keywords: | Os: Unknown/Multiple Architecture: Unknown/Multiple | Failure: Runtime performance bug Difficulty: Unknown | Testcase: Blockedby: | Blocking: Related: | ---------------------------------+------------------------------------------ Comment(by igloo): I get very different nofib (mode=slow) results to you, using recent HEAD: {{{ -------------------------------------------------------------------------------- Program Size Allocs Runtime Elapsed TotalMem -------------------------------------------------------------------------------- [...] ansi -1.1% +9.4% +10.1% +10.1% +0.0% [...] compress -0.5% -0.0% 0.10 0.10 -33.3% [...] Min -2.2% -1.3% -6.6% -7.1% -33.3% Max -0.4% +9.4% +10.1% +10.1% +1.7% Geometric Mean -0.6% +0.1% +0.5% +0.5% -0.4% }}} I took a look at the ansi test. `Main.hs` is a boiled down version of it. Compiling with {{{ ghc -O2 -rtsopts --make Main -fforce-recomp }}} and running with {{{ time ./Main 1400 +RTS -t < /dev/null > out }}} I get {{{ <<ghc: 15797996408 bytes, 24864 GCs, 512598/945104 avg/max bytes residency (70 samples), 3M in use, 0.00 INIT (0.00 elapsed), 1.82 MUT (1.82 elapsed), 2.08 GC (2.08 elapsed) :ghc>> ./Main 1400 +RTS -t < /dev/null > out 3.88s user 0.03s system 99% cpu 3.907 total }}} for HEAD, and {{{ <<ghc: 16996446952 bytes, 27034 GCs, 536827/955856 avg/max bytes residency (75 samples), 3M in use, 0.00 INIT (0.00 elapsed), 1.95 MUT (1.95 elapsed), 2.64 GC (2.64 elapsed) :ghc>> ./Main 1400 +RTS -t < /dev/null > out 4.56s user 0.03s system 99% cpu 4.594 total }}} with this patch. I believe the difference is ultimately caused by the expression {{{ loop 0 "" }}} which appears in the program twice. -- Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5996#comment:8> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler