#15909: prepareAlts does not take into account equalities which are in scope
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Reporter: mpickering | Owner: (none)
Type: bug | Status: new
Priority: normal | Milestone: 8.6.3
Component: Compiler | Version: 8.6.2
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
Wiki Page: |
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Comment (by RyanGlScott):
Here is a much simpler example which demonstrates the issue:
{{{#!hs
{-# LANGUAGE GADTs #-}
module Bug where
data T a where
TInt :: T Int
TBool :: T Bool
f1 :: T Int -> ()
f1 TInt = ()
f2 :: a ~ Int => T a -> ()
f2 TInt = ()
}}}
{{{
$ /opt/ghc/8.6.2/bin/ghc Bug.hs -O2 -ddump-simpl
[1 of 1] Compiling Bug ( Bug.hs, Bug.o )
==================== Tidy Core ====================
...
f1
= \ (ds_d1tE :: T Int) ->
case ds_d1tE of { TInt co_a1s1 [Dmd=