[GHC] #7585: Core lint failure when optimizing coercions in branched axioms
GHC
cvs-ghc at haskell.org
Tue Jan 15 16:58:14 CET 2013
#7585: Core lint failure when optimizing coercions in branched axioms
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Reporter: goldfire | Owner: goldfire
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 7.7 | Keywords: TypeFamilies
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: Compile-time crash | Blockedby:
Blocking: | Related:
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The attached code causes the failure.
Core Lint correctly checks branched axioms for internal consistency --
when using branch ''n'' of an axiom, we must ensure that no branch ''m <
n'' can possibly apply, no matter what the instantiation for any type
variables in the branch may be. However, the coercion optimizer does not
respect this property. It will replace coercions used in axioms with
equivalent coercions that do not respect this internal consistency
property. Everything works out OK in the end (without {{{-dcore-lint}}},
the file compiles and runs correctly), but we go through an invalid state
on the way.
In particular, the {{{TrPushAx}}} rules are to blame.
I'm not sure what the best fix for this is, but it seems to be my job to
find it.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7585>
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