From 071a58c673054d170320bdc8ef222c0f67d22497 Mon Sep 17 00:00:00 2001 From: Sebastian Graf Date: Mon, 13 Jan 2020 11:07:28 +0100 Subject: Revert "`exprOkForSpeculation` for Note [IO hack in the demand analyser]" This reverts commit ce64b397777408731c6dd3f5c55ea8415f9f565b on the grounds of the regression it would introduce in a couple of packages. Fixes #17653. Also undoes a slight metric increase in #13701 introduced by that commit that we didn't see prior to !1983. Metric Decrease: T13701 --- compiler/stranal/DmdAnal.hs | 22 +++++++++++----------- 1 file changed, 11 insertions(+), 11 deletions(-) diff --git a/compiler/stranal/DmdAnal.hs b/compiler/stranal/DmdAnal.hs index b1601f2fed..6faf668067 100644 --- a/compiler/stranal/DmdAnal.hs +++ b/compiler/stranal/DmdAnal.hs @@ -333,7 +333,10 @@ io_hack_reqd scrut con bndrs | (bndr:_) <- bndrs , con == tupleDataCon Unboxed 2 , idType bndr `eqType` realWorldStatePrimTy - = not (exprOkForSpeculation scrut) + , (fun, _) <- collectArgs scrut + = case fun of + Var f -> not (isPrimOpId f) + _ -> True | otherwise = False @@ -384,18 +387,15 @@ 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 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: +So if the scrutinee is a primop call, we *don't* apply the +state hack: - If it is a simple, terminating one like getMaskingState, - 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. + applying the hack is over-conservative. + - If the primop is raise# then it returns bottom, so + the case alternatives are already discarded. - If the primop can raise a non-IO exception, like - divide by zero (so not ok-for-speculation), then we are also bottoming out - anyway and don't mind evaluating 'x' first. + divide by zero or seg-fault (eg writing an array + out of bounds) then we don't mind evaluating 'x' first. Note [Demand on the scrutinee of a product case] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- cgit v1.2.1