Alp,
Is this related to #15570. If so, it'd be good to make that connection.
S
| -----Original Message-----
| From: ghc-commits On Behalf Of
| git@git.haskell.org
| Sent: 02 September 2018 22:16
| To: ghc-commits@haskell.org
| Subject: [commit: ghc] master: make iToBase62's inner loop stricter in
| one of its arguments (ed78951)
|
| Repository : ssh://git@git.haskell.org/ghc
|
| On branch : master
| Link :
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| 08d6111955e2%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636715197856324
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| ed=0
|
| >---------------------------------------------------------------
|
| commit ed789516e201e4fad771e5588da47a62e53b42b8
| Author: Alp Mestanogullari
| Date: Sun Sep 2 22:06:55 2018 +0200
|
| make iToBase62's inner loop stricter in one of its arguments
|
| Summary:
| hadrian's support for dynamic ways is currently broken (see
| hadrian#641 [1]).
| The stage 1 GHCs that hadrian produces end up producing bad code for
| the `iToBase62` function after a few optimisation passes.
|
| In the case where `quotRem` returns (overflowError, 0),
| GHC isn't careful enough to realise q is _|_ and happily inlines,
| distributes and floats code around until we end up trying to access
| index `minBound :: Int` of an array of 62 chars, as a result of
| inlining
| the definition of `quotRem` for Ints, in particular the minBound
| branch [2].
|
| I will separately look into reproducing the bad transformation on a
| small
| self-contained example and filling a ticket.
|
| [1]:
| https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.c
| om%2Fsnowleopard%2Fhadrian%2Fissues%2F641&data=02%7C01%7Csimonpj%40mi
| crosoft.com%7Cea714d654b04488aada908d6111955e2%7C72f988bf86f141af91ab2d7c
| d011db47%7C1%7C0%7C636715197856324232&sdata=a7dM0YbraOY69xKhJcwVuQqBn
| 3n3nTdVuMFNjie6iHA%3D&reserved=0
| [2]:
| https://git.haskell.org/ghc.git/blob/HEAD:/libraries/base/GHC/Real.hs#l36
| 6
|
| Test Plan: fixes hadrian#641
|
| Reviewers: bgamari, tdammers
|
| Reviewed By: tdammers
|
| Subscribers: tdammers, rwbarton, carter
|
| Differential Revision: https://phabricator.haskell.org/D5106
|
|
| >---------------------------------------------------------------
|
| ed789516e201e4fad771e5588da47a62e53b42b8
| compiler/basicTypes/Unique.hs | 2 +-
| 1 file changed, 1 insertion(+), 1 deletion(-)
|
| diff --git a/compiler/basicTypes/Unique.hs
| b/compiler/basicTypes/Unique.hs index 4a709d2..b5c0fce 100644
| --- a/compiler/basicTypes/Unique.hs
| +++ b/compiler/basicTypes/Unique.hs
| @@ -325,7 +325,7 @@ iToBase62 n_
| go n cs | n < 62
| = let !c = chooseChar62 n in c : cs
| | otherwise
| - = go q (c : cs) where (q, r) = quotRem n 62
| + = go q (c : cs) where (!q, r) = quotRem n 62
| !c = chooseChar62 r
|
| chooseChar62 :: Int -> Char
|
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