diff options
| -rw-r--r-- | compiler/basicTypes/Demand.hs | 2 | ||||
| -rw-r--r-- | compiler/stranal/DmdAnal.hs | 6 |
2 files changed, 4 insertions, 4 deletions
diff --git a/compiler/basicTypes/Demand.hs b/compiler/basicTypes/Demand.hs index bd2924af22..8ee0f13e72 100644 --- a/compiler/basicTypes/Demand.hs +++ b/compiler/basicTypes/Demand.hs @@ -1214,7 +1214,7 @@ splitDmdTy ty@(DmdType _ [] res_ty) = (resTypeArgDmd res_ty, ty) -- what of this demand should we consider, given that the IO action can cleanly -- exit? -- * We have to kill all strictness demands (i.e. lub with a lazy demand) --- * We can keep demand information (i.e. lub with an absent deman) +-- * We can keep demand information (i.e. lub with an absent demand) -- * We have to kill definite divergence -- * We can keep CPR information. -- See Note [IO hack in the demand analyser] diff --git a/compiler/stranal/DmdAnal.hs b/compiler/stranal/DmdAnal.hs index 8b97b6be98..5836bfd6af 100644 --- a/compiler/stranal/DmdAnal.hs +++ b/compiler/stranal/DmdAnal.hs @@ -342,7 +342,7 @@ dmdAnalAlt env dmd case_bndr (con,bndrs,rhs) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ There's a hack here for I/O operations. Consider case foo x s of { (# s, r #) -> y } -Is this strict in 'y'. Normally yes, but what if 'foo' is an I/O +Is this strict in 'y'? Normally yes, but what if 'foo' is an I/O operation that simply terminates the program (not in an erroneous way)? In that case we should not evaluate 'y' before the call to 'foo'. Hackish solution: spot the IO-like situation and add a virtual branch, @@ -365,14 +365,14 @@ However, consider Here it is terribly sad to make 'f' lazy in 's'. After all, getMaskingState# is not going to diverge or throw an exception! This situation actually arises in GHC.IO.Handle.Internals.wantReadableHandle -(on an MVar not an Int), and make a material difference. +(on an MVar not an Int), and made a material difference. So if the scrutinee is a primop call, we *don't* apply the state hack: - If is a simple, terminating one like getMaskingState, applying the hack is over-conservative. - If the primop is raise# then it returns bottom, so - the case alternatives are alraedy discarded. + the case alternatives are already discarded. - If the primop can raise a non-IO exception, like divide by zero or seg-fault (eg writing an array out of bounds) then we don't mind evaluating 'x' first. |