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| author | Alp Mestanogullari <alp@well-typed.com> | 2018-09-02 22:06:55 +0200 |
|---|---|---|
| committer | Krzysztof Gogolewski <krz.gogolewski@gmail.com> | 2018-09-02 22:06:56 +0200 |
| commit | ed789516e201e4fad771e5588da47a62e53b42b8 (patch) | |
| tree | bb174287a018fc05d1aa6be0d1760246a53279c4 | |
| parent | 6dea7c161e458ddb3ea4afd366887c8d963c6585 (diff) | |
| download | haskell-ed789516e201e4fad771e5588da47a62e53b42b8.tar.gz | |
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://github.com/snowleopard/hadrian/issues/641
[2]: https://git.haskell.org/ghc.git/blob/HEAD:/libraries/base/GHC/Real.hs#l366
Test Plan: fixes hadrian#641
Reviewers: bgamari, tdammers
Reviewed By: tdammers
Subscribers: tdammers, rwbarton, carter
Differential Revision: https://phabricator.haskell.org/D5106
| -rw-r--r-- | compiler/basicTypes/Unique.hs | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/compiler/basicTypes/Unique.hs b/compiler/basicTypes/Unique.hs index 4a709d238e..b5c0fcec58 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 |