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Move isBlock/isBarrier optimisation into findBacktrackSteps

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This makes dependent ==> dependent'
This commit is contained in:
Michael Walker 2017-10-30 19:24:24 +00:00
parent 03ca3c978e
commit 5bc3eb2773
1 changed files with 10 additions and 16 deletions
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26
dejafu/Test/DejaFu/SCT/Internal.hs
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@ -277,7 +277,14 @@ findBacktrackSteps memtype backtrack boundKill = go initialDepState S.empty init
_ -> False
{-# INLINE isDependent #-}
isDependent b = dependent' memtype (bcktState b) (bcktThreadid b) (bcktAction b) u n
isDependent b
-- Don't impose a dependency if the other thread will
-- immediately block already. This is safe because a
-- context switch will occur anyway so there's no point
-- pre-empting the action UNLESS the pre-emption would
-- possibly allow for a different relaxed memory stage.
| isBlock (bcktAction b) && isBarrier (simplifyLookahead n) = False
| otherwise = dependent' memtype (bcktState b) (bcktThreadid b) (bcktAction b) u n
in backtrack bs idxs
-- | Add new backtracking points, if they have not already been
@ -603,15 +610,8 @@ dependent memtype ds t1 a1 t2 a2 = case (a1, a2) of
(BlockedSTM _, STM _ _) -> not . S.null $ tvarsOf a1 `S.intersection` tvarsOf a2
(BlockedSTM _, BlockedSTM _) -> not . S.null $ tvarsOf a1 `S.intersection` tvarsOf a2
-- The @isBlock@ / @isBarrier@ case in 'dependent'' is NOT a sound
-- optimisation when dealing with a 'ThreadAction' that has been
-- converted to a 'Lookahead'. I'm not entirely sure why, which
-- makes me question whether the \"optimisation\" is sound as it is.
_ -> case (,) <$> rewind a1 <*> rewind a2 of
Just (l1, l2)
| not (isBlock a1 && isBarrier (simplifyLookahead l2)) &&
not (isBlock a2 && isBarrier (simplifyLookahead l1)) ->
dependent' memtype ds t1 a1 t2 l2 && dependent' memtype ds t2 a2 t1 l1
Just (l1, l2) -> dependent' memtype ds t1 a1 t2 l2 && dependent' memtype ds t2 a2 t1 l1
_ -> dependentActions memtype ds (simplifyAction a1) (simplifyAction a2)
-- | Variant of 'dependent' to handle 'Lookahead'.
@ -642,13 +642,7 @@ dependent' memtype ds t1 a1 t2 l2 = case (a1, l2) of
(SetNumCapabilities _, WillGetNumCapabilities) -> True
(SetNumCapabilities a, WillSetNumCapabilities b) -> a /= b
-- Don't impose a dependency if the other thread will immediately
-- block already. This is safe because a context switch will occur
-- anyway so there's no point pre-empting the action UNLESS the
-- pre-emption would possibly allow for a different relaxed memory
-- stage.
_ | isBlock a1 && isBarrier (simplifyLookahead l2) -> False
| otherwise -> dependentActions memtype ds (simplifyAction a1) (simplifyLookahead l2)
_ -> dependentActions memtype ds (simplifyAction a1) (simplifyLookahead l2)
-- | Check if two 'ActionType's are dependent. Note that this is not
-- sufficient to know if two 'ThreadAction's are dependent, without