#16335: Make CPR Analysis more aggressive for inductive cases -------------------------------------+------------------------------------- Reporter: sgraf | Owner: (none) Type: task | Status: new Priority: normal | Milestone: ⊥ Component: Compiler | Version: 8.6.3 Resolution: | Keywords: CPRAnalysis Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by sgraf): To expand on the "Return pattern specialisation" thing: ||=SpecConstr=||= CPR+WW =|| ||Multiple specialisations||One specialisation|| ||Looks at how much the definition scrutinises its arguments in ''any'' of its case expressions||Looks at how deep the constructed products are in ''all'' its return branches (mostly since we only do one specialisation)|| ||Compares that to how the function is called and only allows matching specialisations (unless `-fspec-constr-keen`||Doesn't look at calls, but only provides the most conservative specialisation anyway|| Put another way: If we allowed multiple specialisations, we could have the following two specialisations, no reboxing happening (no promises made on correctness): {{{ Foo.$weval = \ (w_s1cn :: Expr) -> case w_s1cn of { Lit dt_d11b -> case dt_d11b { I# ds_abcd -> ds_abcd }; Plus a_aXf b_aXg -> case Foo.$weval a_aXf of ww_s1cq { __DEFAULT -> case Foo.$weval b_aXg of ww1_X1dh { __DEFAULT -> GHC.Prim.+# ww_s1cq ww1_X1dh } } } eval = \ (ds_d112 :: Expr) -> case ds_d112 of { Lit n_aXf -> n_aXf; Plus a_aXg b_aXh -> case $weval a_aXg of { __DEFAULT -> case $weval b_aXh of { __DEFAULT -> GHC.Types.I# (GHC.Prim.+# a_aXg b_aXh) } } } }}} Note that we were able to rewrite both inductive calls in terms of `$weval`, but still have the vanilla version around if we ever need the boxed result of `eval`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16335#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler