diff options
| -rw-r--r-- | compiler/stranal/DmdAnal.lhs | 13 | ||||
| -rw-r--r-- | compiler/stranal/WwLib.lhs | 25 |
2 files changed, 22 insertions, 16 deletions
diff --git a/compiler/stranal/DmdAnal.lhs b/compiler/stranal/DmdAnal.lhs index 0bfd025410..167debfb55 100644 --- a/compiler/stranal/DmdAnal.lhs +++ b/compiler/stranal/DmdAnal.lhs @@ -592,7 +592,7 @@ mkSigTy top_lvl rec_flag id rhs dmd_ty maybe_id_dmd = idDemandInfo_maybe id -- Is Nothing the first time round - thunk_cpr_ok + thunk_cpr_ok -- See Note [CPR for thunks] | isTopLevel top_lvl = False -- Top level things don't get -- their demandInfo set at all | isRec rec_flag = False -- Ditto recursive things @@ -601,8 +601,8 @@ mkSigTy top_lvl rec_flag id rhs dmd_ty -- See notes below \end{code} -The thunk_cpr_ok stuff [CPR-AND-STRICTNESS] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Note [CPR for thunks] +~~~~~~~~~~~~~~~~~~~~~ If the rhs is a thunk, we usually forget the CPR info, because it is presumably shared (else it would have been inlined, and so we'd lose sharing if w/w'd it into a function). E.g. @@ -662,8 +662,8 @@ have a CPR in it or not. Simple solution: NB: strictly_demanded is never true of a top-level Id, or of a recursive Id. -The Nothing case in thunk_cpr_ok [CPR-AND-STRICTNESS] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Note [Optimistic in the Nothing case] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Demand info now has a 'Nothing' state, just like strictness info. The analysis works from 'dangerous' towards a 'safe' state; so we start with botSig for 'Nothing' strictness infos, and we start with @@ -1010,8 +1010,7 @@ extendSigsWithLam :: AnalEnv -> Id -> AnalEnv extendSigsWithLam env id = case idDemandInfo_maybe id of Nothing -> extendAnalEnv NotTopLevel env id cprSig - -- Optimistic in the Nothing case; - -- See notes [CPR-AND-STRICTNESS] + -- See Note [Optimistic in the Nothing case] Just (Eval (Prod _)) -> extendAnalEnv NotTopLevel env id cprSig _ -> env \end{code} diff --git a/compiler/stranal/WwLib.lhs b/compiler/stranal/WwLib.lhs index 4b18b8ba7d..5a82b8ad9e 100644 --- a/compiler/stranal/WwLib.lhs +++ b/compiler/stranal/WwLib.lhs @@ -133,15 +133,10 @@ mkWwBodies fun_ty demands res_info one_shots ; (wrap_args, wrap_fn_args, work_fn_args, res_ty) <- mkWWargs emptyTvSubst fun_ty arg_info ; (work_args, wrap_fn_str, work_fn_str) <- mkWWstr wrap_args - -- Don't do CPR if the worker doesn't have any value arguments - -- Then the worker is just a constant, so we don't want to unbox it. - ; (wrap_fn_cpr, work_fn_cpr, _cpr_res_ty) - <- if any isId work_args then - mkWWcpr res_ty res_info - else - return (id, id, res_ty) - - ; let (work_lam_args, work_call_args) = mkWorkerArgs work_args res_ty + -- Do CPR w/w. See Note [Always do CPR w/w] + ; (wrap_fn_cpr, work_fn_cpr, cpr_res_ty) <- mkWWcpr res_ty res_info + + ; let (work_lam_args, work_call_args) = mkWorkerArgs work_args cpr_res_ty ; return ([idDemandInfo v | v <- work_call_args, isId v], wrap_fn_args . wrap_fn_cpr . wrap_fn_str . applyToVars work_call_args . Var, mkLams work_lam_args. work_fn_str . work_fn_cpr . work_fn_args) } @@ -154,6 +149,18 @@ mkWwBodies fun_ty demands res_info one_shots -- fw from being inlined into f's RHS \end{code} +Note [Always do CPR w/w] +~~~~~~~~~~~~~~~~~~~~~~~~ +At one time we refrained from doing CPR w/w for thunks, on the grounds that +we might duplicate work. But that is already handled by the demand analyser, +which doesn't give the CPR proprety if w/w might waste work: see +Note [CPR for thunks] in DmdAnal. + +And if something *has* been given the CPR property and we don't w/w, it's +a disaster, because then the enclosing function might say it has the CPR +property, but now doesn't and there a cascade of disaster. A good example +is Trac #5920. + %************************************************************************ %* * |