| I doubt there's a bug in uniqAway; it's more likely the in scope set
| is not correct.
I think Edward is probably right here.
| -----Original Message-----
| From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of
| Edward Z. Yang
| Sent: 06 January 2016 00:50
| To: Bartosz Nitka
| Cc: ghc-devs Devs
| Subject: Re: uniqAway and collisions
|
| Hello Bartosz,
|
| The principle between uniqAway is described in the "Secrets of the GHC
| Inliner" paper
|
| https://na01.safelinks.protection.outlook.com/?url=http%3a%2f%2fresear
| ch.microsoft.com%2fen-
| us%2fum%2fpeople%2fsimonpj%2fPapers%2finlining%2f&data=01%7c01%7csimon
| pj%40064d.mgd.microsoft.com%7c9562a48ea0714da096be08d316334bef%7c72f98
| 8bf86f141af91ab2d7cd011db47%7c1&sdata=D0h2%2btGYDNVaqU8wiKWvq3QA%2bLbz
| 6q2BY%2f0IZA9nq%2bk%3d
|
| I doubt there's a bug in uniqAway; it's more likely the in scope set
| is not correct.
|
| Edward
|
| Excerpts from Bartosz Nitka's message of 2016-01-05 09:39:54 -0800:
| > Hi,
| >
| > I'm running into core lint issues [1] with my determinism patch [2]
| > and they appear to come down to uniqAway coming up with a Unique
| > that's already used in the expression. That creates a collision,
| > making next substitution substitute more than it needs.
| >
| > I have 2 questions:
| >
| > 1. When is it safe to use uniqAway?
| >
| > 2. Is my conclusion reasonable given this trace: (full trace here
| [3])?
| >
| > I. We start out with (line 123):
| >
| > CallStack (from ImplicitParams):
| > pprSTrace, called at compiler/coreSyn/CoreLint.hs:659:12 in
| ghc:CoreLint
| > e: EqConstr
| > @ (s_Xpw a_Xpz)
| > @ (s_Xpw b_Xpy)
| > @ s_Xpw
| > @ b_Xpy
| > @ a_Xpz
| > @~ (_N :: s_Xpw a_Xpz ~# s_Xpw a_Xpz)
| > @~ (_N :: s_Xpw b_Xpy ~# s_Xpw b_Xpy)
| > dt_aq3
| > fun: EqConstr
| > args: [TYPE: s_Xpw a_Xpz, TYPE: s_Xpw b_Xpy, TYPE: s_Xpw,
| > TYPE: b_Xpy, TYPE: a_Xpz, CO: _N, CO: _N,
| > dt_aq3]
| > fun_ty: forall a_apr b_aps (s_Xpw :: * -> *) b_Xpy a_Xpz.
| > (a_apr ~# s_Xpw a_Xpz, b_aps ~# s_Xpw b_Xpy) =>
| > EqTypes a_Xpz b_Xpy -> EqTypes a_apr b_aps
| >
| > II. Then we create s_Xpz with uniqAway (line 499) which has the same
| > unique as a_Xpz above
| >
| > CallStack (from ImplicitParams):
| > pprSTrace, called at compiler/types/TyCoRep.hs:1947:5 in
| ghc:TyCoRep
| > old_var: s_Xpy
| > new_var: s_Xpz
| >
| > III. Which causes trouble when we want to substitute s_Xpw for s_Xpz
| > and we substitute a_Xpz as well (line 733):
| >
| > CallStack (from ImplicitParams):
| > pprSTrace, called at compiler/coreSyn/CoreLint.hs:813:11 in
| ghc:CoreLint
| > substTyWith [tv] [arg_ty] body_ty forall b_XpB a_XpD.
| > (s_Xpw s_Xpw ~# s_Xpw a_XpD,
| s_Xpw
| > b_Xpy ~# s_Xpw b_XpB) =>
| > EqTypes a_XpD b_XpB -> EqTypes
| > (s_Xpw
| > s_Xpw) (s_Xpw b_Xpy)
| >
| > The uniqAway comes from substTyVarBndrCallback which blames to
| nokinds
| > patch.
| >
| > Thanks,
| > Bartosz
| > [1] https://phabricator.haskell.org/P77
| > [2] https://phabricator.haskell.org/P76
| > [3] https://phabricator.haskell.org/P78
| _______________________________________________
| ghc-devs mailing list
| ghc-devs@haskell.org
| https://na01.safelinks.protection.outlook.com/?url=http%3a%2f%2fmail.h
| askell.org%2fcgi-bin%2fmailman%2flistinfo%2fghc-
| devs&data=01%7c01%7csimonpj%40064d.mgd.microsoft.com%7c9562a48ea0714da
| 096be08d316334bef%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=GEAnP46
| gF85287E%2bovF9vH6KmZqqeWGKNjeKvfMXcjA%3d
