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Diffstat (limited to 'compiler/GHC/Core/Opt/DmdAnal.hs')
| -rw-r--r-- | compiler/GHC/Core/Opt/DmdAnal.hs | 20 |
1 files changed, 19 insertions, 1 deletions
diff --git a/compiler/GHC/Core/Opt/DmdAnal.hs b/compiler/GHC/Core/Opt/DmdAnal.hs index e5d9c9a0d9..7f4327591e 100644 --- a/compiler/GHC/Core/Opt/DmdAnal.hs +++ b/compiler/GHC/Core/Opt/DmdAnal.hs @@ -1179,8 +1179,26 @@ type DFunFlag = Bool -- indicates if the lambda being considered is in the notArgOfDfun :: DFunFlag notArgOfDfun = False +{- Note [dmdAnalEnv performance] + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +It's tempting to think that removing the dynflags from AnalEnv would improve +performance. After all when analysing recursive groups we end up allocating +a lot of environments. However this is not the case. + +We do get some performance by making AnalEnv smaller. However very often we +defer computation which means we have to capture the dynflags in the thunks +we allocate. Doing this naively in practice causes more allocation than the +removal of DynFlags saves us. + +In theory it should be possible to make this better if we are stricter in +the analysis and therefore allocate fewer thunks. But I couldn't get there +in a few hours and overall the impact on GHC here is small, and there are +bigger fish to fry. So for new the env will keep a reference to the flags. +-} + data AnalEnv - = AE { ae_dflags :: DynFlags + = AE { ae_dflags :: DynFlags -- See Note [dmdAnalEnv performance] , ae_sigs :: SigEnv , ae_virgin :: Bool -- True on first iteration only -- See Note [Initialising strictness] |