diff options
Diffstat (limited to 'compiler/stranal/DmdAnal.hs')
| -rw-r--r-- | compiler/stranal/DmdAnal.hs | 19 |
1 files changed, 17 insertions, 2 deletions
diff --git a/compiler/stranal/DmdAnal.hs b/compiler/stranal/DmdAnal.hs index 9a4c64bdbb..afde951e60 100644 --- a/compiler/stranal/DmdAnal.hs +++ b/compiler/stranal/DmdAnal.hs @@ -603,8 +603,8 @@ dmdAnalRhsLetDown top_lvl rec_flag env let_dmd id rhs rhs_arity = idArity id rhs_dmd -- See Note [Demand analysis for join points] - -- See Note [idArity for join points] in SimplUtils - -- rhs_arity matches the join arity of the join point + -- See Note [Invariants on join points] invariant 2b, in CoreSyn + -- rhs_arity matches the join arity of the join point | isJoinId id = mkCallDmds rhs_arity let_dmd | otherwise @@ -727,6 +727,21 @@ let_dmd here). Another win for join points! #13543. +However, note that the strictness signature for a join point can +look a little puzzling. E.g. + + (join j x = \y. error "urk") + (in case v of ) + ( A -> j 3 ) x + ( B -> j 4 ) + ( C -> \y. blah ) + +The entire thing is in a C(S) context, so j's strictness signature +will be [A]b +meaning one absent argument, returns bottom. That seems odd because +there's a \y inside. But it's right because when consumed in a C(1) +context the RHS of the join point is indeed bottom. + Note [Demand signatures are computed for a threshold demand based on idArity] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We compute demand signatures assuming idArity incoming arguments to approximate |