#8763: forM_ [1..N] does not get fused (10 times slower than go function) -------------------------------------+------------------------------------- Reporter: nh2 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 7.6.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #7206 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by George): Your example seems to be different than mine in that when I compile yours with ghc 8.4.1 and -O there is no difference in allocation unlike mine. What flags did you compile with? {{{ ghc -O repro.hs +RTS [1 of 1] Compiling Main ( repro.hs, repro.o ) Linking repro ... bash-3.2$ ./repro 1 +RTS -s () 56,880 bytes allocated in the heap 3,480 bytes copied during GC 44,576 bytes maximum residency (1 sample(s)) 25,056 bytes maximum slop 2 MB total memory in use (0 MB lost due to fragmentation) Tot time (elapsed) Avg pause Max pause Gen 0 0 colls, 0 par 0.000s 0.000s 0.0000s 0.0000s Gen 1 1 colls, 0 par 0.000s 0.000s 0.0002s 0.0002s INIT time 0.000s ( 0.002s elapsed) MUT time 0.051s ( 0.052s elapsed) GC time 0.000s ( 0.000s elapsed) EXIT time 0.000s ( 0.003s elapsed) Total time 0.051s ( 0.057s elapsed) %GC time 0.3% (0.4% elapsed) Alloc rate 1,118,716 bytes per MUT second Productivity 99.3% of total user, 95.6% of total elapsed bash-3.2$ ./repro 2 +RTS -s () 56,880 bytes allocated in the heap 3,480 bytes copied during GC 44,576 bytes maximum residency (1 sample(s)) 25,056 bytes maximum slop 2 MB total memory in use (0 MB lost due to fragmentation) Tot time (elapsed) Avg pause Max pause Gen 0 0 colls, 0 par 0.000s 0.000s 0.0000s 0.0000s Gen 1 1 colls, 0 par 0.000s 0.000s 0.0002s 0.0002s INIT time 0.000s ( 0.002s elapsed) MUT time 0.051s ( 0.051s elapsed) GC time 0.000s ( 0.000s elapsed) EXIT time 0.000s ( 0.005s elapsed) Total time 0.051s ( 0.059s elapsed) %GC time 0.3% (0.3% elapsed) Alloc rate 1,120,655 bytes per MUT second Productivity 99.3% of total user, 95.7% of total elapsed }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8763#comment:47 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler