Bad interaction between Pattern Synonyms and Text

Compiling this file causes the impossible to happen. It is necessary to enable optimizations. The bug did not occur if the Text parameter was replaced with ByteString or String.

{-# LANGUAGE PatternSynonyms #-}
{-# LANGUAGE OverloadedStrings #-}
module Bug where

{-
 -  Must compile with optimizations
 -
 -  text-1.1.1.3
 -  ghc-7.8.2
 -  Both Darwin and Linux platforms
 -
 -}

import Data.Text(Text)

data T = C Text Bool

f :: a -> b
f _ = undefined
{-# NOINLINE f #-} -- important

pattern P1 a = C "sh" a -- at least two characters
pattern P2    = C "x" True -- this pattern has to come last

g :: Text -> T
g x = case x of
       "" -> f (P1 undefined) -- this has to be a pattern synonym

[1 of 1] Compiling Bug              ( Bug.hs, Bug.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 7.8.2 for x86_64-apple-darwin):
	StgCmmEnv: variable not found
    lvl_s2Jr{v} [lid]
    local binds for:
    main:Bug.f{v rBS} [gid]
    main:Bug.rewriteRule{v rBV} [gid]
    main:Bug.$mP2{v r17q} [gid]
    main:Bug.$WP2{v r17A} [gid]
    main:Bug.$mP1{v r17E} [gid]
    main:Bug.$WP1{v r17R} [gid]
    main:Bug.$WP3{v r3bq} [gid]
    main:Bug.$WP4{v r3ua} [gid]
    main:Bug.$WP5{v r3ub} [gid]
    main:Bug.$WP2_dt{v r3uc} [gid]
    main:Bug.$WP6{v r3ud} [gid]
    main:Bug.$WP7{v r3ue} [gid]
    main:Bug.$WP8{v r3uf} [gid]
    main:Bug.$w$mP1{v r3ug} [gid]
    main:Bug.$w$mP2{v r3uh} [gid]
    main:Bug.$mP3{v r3ui} [gid]
    main:Bug.$mP4{v r3uj} [gid]
    main:Bug.$mP5{v r3uk} [gid]
    main:Bug.$wrewriteRule{v r3ul} [gid]
    main:Bug.rewriteRule1{v r3um} [gid]
    main:Bug.rewriteRule2{v r3un} [gid]
    main:Bug.rewriteRule3{v r3uo} [gid]
    main:Bug.rewriteRule4{v r3up} [gid]
    main:Bug.rewriteRule5{v r3uq} [gid]
    lvl{v r3ur} [gid]


Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

Trac metadata

Trac field	Value
Version	7.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	bos@serpentine.com, diatchki@gmail.com
Operating system
Architecture