#5075: CPR optimisation for sum types if only one constructor is used -------------------------------------+------------------------------------ Reporter: batterseapower | Owner: simonpj Type: feature request | Status: new Priority: normal | Milestone: 7.6.2 Component: Compiler | Version: 7.0.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Comment (by nomeata): In that case, let me add some numbers related to sum type CPR in local functions. With current master [4d70840d/ghc], enabling CPR for sum types has this effect: {{{ -------------------------------------------------------------------------------- Program Size Allocs Runtime Elapsed TotalMem -------------------------------------------------------------------------------- ansi +8.6% +0.5% 0.00 0.00 +0.0% awards +8.6% +0.2% 0.00 0.00 +0.0% cacheprof +8.0% +0.2% -3.1% -3.1% +0.0% calendar +8.6% +0.2% 0.00 0.00 +0.0% circsim +8.5% +1.1% -8.7% -8.7% -2.0% cryptarithm1 +8.7% -3.8% +0.5% +0.5% +0.0% cse +8.6% +0.2% 0.00 0.00 +0.0% fibheaps +8.6% -0.3% 0.02 0.02 +0.0% fluid +7.7% +3.4% 0.01 0.01 +0.0% fulsom +8.3% +0.1% 0.19 0.19 -31.2% hidden +8.3% +1.8% +3.4% +6.2% +0.0% kahan +8.1% +0.1% 0.17 0.17 +0.0% listcompr +8.6% +0.4% 0.06 0.05 +0.0% listcopy +8.6% +0.4% 0.07 0.06 +0.0% mandel +7.5% +0.3% 0.05 0.05 +0.0% mandel2 +8.7% +33.8% 0.00 0.00 +0.0% parser +8.1% +1.7% 0.02 0.02 +0.0% primetest +8.7% -0.2% 0.07 0.07 +0.0% reptile +8.5% +0.2% 0.01 0.01 +0.0% rewrite +8.5% +0.1% 0.02 0.02 +0.0% rfib +8.7% +0.6% 0.02 0.02 +0.0% spectral-norm +8.5% +0.7% -0.6% -0.6% +0.0% symalg +8.3% +0.2% 0.01 0.01 +0.0% tak +8.6% +1.3% 0.01 0.01 +0.0% transform +8.3% +0.1% +0.0% +0.0% +0.0% -------------------------------------------------------------------------------- Min +6.8% -3.8% -11.3% -11.3% -31.2% Max +8.7% +33.8% +3.9% +6.2% +6.1% Geometric Mean +8.4% +0.4% -1.8% -1.8% -0.4% }}} So one quite extreme degradation, and otherwise minor losses. If I make sure that join points do not get the CPR information unless the expression they are a join point for does, we get this change (relative to the same baseline): {{{ -------------------------------------------------------------------------------- Program Size Allocs Runtime Elapsed TotalMem -------------------------------------------------------------------------------- cacheprof +8.0% +0.3% -4.7% -4.7% +1.8% calendar +8.6% +0.1% 0.00 0.00 +0.0% circsim +8.5% +0.2% -8.4% -8.4% -2.0% cryptarithm1 +8.6% -3.8% +1.5% +1.5% +0.0% cse +8.6% +0.2% 0.00 0.00 +0.0% fibheaps +8.5% -0.3% 0.03 0.03 +0.0% fulsom +8.2% -3.7% 0.19 0.19 -31.2% kahan +8.1% -0.2% 0.17 0.17 +0.0% listcompr +8.6% +0.4% 0.07 0.06 +0.0% listcopy +8.6% +0.4% 0.07 0.06 +0.0% maillist +8.6% +0.0% 0.04 0.04 +16.0% mandel +7.4% +0.2% 0.05 0.05 +0.0% parser +8.1% +1.7% 0.02 0.02 +0.0% primetest +8.6% -0.2% 0.07 0.07 +0.0% rewrite +8.5% +0.1% 0.01 0.01 +0.0% -------------------------------------------------------------------------------- Min +6.8% -3.8% -8.4% -8.4% -31.2% Max +8.7% +1.7% +3.2% +3.4% +16.0% Geometric Mean +8.3% -0.0% -2.0% -1.9% -0.2% }}} This looks quite different now: A few losses, but much smaller than before. A mean of zero, and more gains than before. Unfortunately, the code size increase is still there... If it were not for the code size increase, I’d suggest to merge these changes: Fewer special cases in transformations is a good thing. But it is probably not worth the code size increase, is it? (Just for the record: In theory it is possible that CPR’ing a non-sum-type can destroy the join-point-property of a let. But it does not seem to happen: If I enable the cpr-join-point-fix, but keep CPR for sum types disabled, nofib does not record any change whatsoever.) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/5075#comment:19 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler