#10069: CPR related performance issue -------------------------------------+------------------------------------- Reporter: pacak | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1-rc2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by simonpj): Thanks for the `-ddump-simpl` output. I can see what is happening. The trouble is that `a1`, `a2` etc are marked `NOINLINE`, but their strictness information is still visible. That makes `fa` strict too. So the original code looks like this (I have decreased the number of selectors to make it easy to read): {{{ --------- Before strictness analysis ------------- fa a = case a1 a of I# i1 -> case a2 a of I# i2 -> I# (i1 +# i2) --------- After strictness analysis and worker/wrapper ------------- fa a = case a of A _ _ _ _ i1 _ _ _ _ i2 _ _ _ _ -> $wfa i1 i2 $wfa i1 i2 = let a = A bot bot bot bot i1 bot bot bot bot i2 bot bot bot bot in case a1 a of I# i1 -> case a2 a of I# i2 -> I# (i1 +# i2) }}} The worker `$wfa` would normally collapse into nice tight code, when the workers for `a1` and `a2` are inlined. But here they are not! So `$wfa` does reboxing which is terrible. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10069#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler