diff options
| -rw-r--r-- | compiler/stranal/DmdAnal.hs | 22 |
1 files changed, 11 insertions, 11 deletions
diff --git a/compiler/stranal/DmdAnal.hs b/compiler/stranal/DmdAnal.hs index 14fd46a6a3..9a4c64bdbb 100644 --- a/compiler/stranal/DmdAnal.hs +++ b/compiler/stranal/DmdAnal.hs @@ -333,10 +333,7 @@ io_hack_reqd scrut con bndrs | (bndr:_) <- bndrs , con == tupleDataCon Unboxed 2 , idType bndr `eqType` realWorldStatePrimTy - , (fun, _) <- collectArgs scrut - = case fun of - Var f -> not (isPrimOpId f) - _ -> True + = not (exprOkForSpeculation scrut) | otherwise = False @@ -387,15 +384,18 @@ 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 made a material difference. -So if the scrutinee is a primop call, we *don't* apply the -state hack: +So if the scrutinee is ok-for-speculation, we *don't* apply the state hack, +because we are free to push evaluation of the scrutinee after evaluation of +expressions from the (single) case alternative. + +A few examples for different scrutinees: - If it 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 already discarded. + applying the hack would be over-conservative. + - If the primop is raise# then it returns bottom (so not ok-for-speculation), + but the result from the case alternatives are discarded anyway. - 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. + divide by zero (so not ok-for-speculation), then we are also bottoming out + anyway and don't mind evaluating 'x' first. Note [Demand on the scrutinee of a product case] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |