Bother. It seems like a good improvement to SpecConstr anyway. But it's disappointing that it doesn't hit this case. In fact it seems that it should. It's not ok to discard a 'touch' but it's fine to move it around. Maybe what we want is primOpIsCheap? Which is currently defined to be the same as primOpOkForSpeculation, but perhaps it should not be. Simon | -----Original Message----- | From: Roman Leshchinskiy [mailto:rl@cse.unsw.edu.au] | Sent: 23 April 2010 07:55 | To: Simon Peyton-Jones | Cc: Haskell Libraries | Subject: Re: Storable and constant memory | | Simon, | | On 23/04/2010, at 16:49, Simon Peyton-Jones wrote: | | > | foo v x = ... case readIntOffAddr# p# i# realWorld# of { (# s#, n# #) -> | > | case touch# fp s# of { _ -> | > foo v (Just (I# n# }})) ... | > | > I'll implement that fix. It should catch cases like this where the primops | involves are | > - ok-for-speculation | > - have just one result (ie only one case alternative | | I don't think touch# is ok-for-speculation. | | primop TouchOp "touch#" GenPrimOp | o -> State# RealWorld -> State# RealWorld | with | has_side_effects = True | | Note the has_side_effects part. In fact, wouldn't it be eliminated altogether | in this case if it was ok-for-speculation? | | Roman | |