[GHC] #12855: ghc-8.0.2_rc1 inlines string literals too aggressively, breaks tests of http-client-0.4.30

[GHC]

#12855: ghc-8.0.2_rc1 inlines string literals too aggressively, breaks tests of
http-client-0.4.30
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        Reporter:  slyfox            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.0.2
       Component:  Compiler          |              Version:  8.0.1
      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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Description changed by slyfox:

@@ -24,1 +24,1 @@
- breaks pinter-chasing in bytestring package.
+ breaks pointer-chasing in bytestring package.

New description:

 GHC version 8.0.1.20161117

 {{{#!hs
 -- $ cat BodySpec.hs
 -- $ ghc --make -O1 -package={base,bytestring} BodySpec.hs -o a && ./a
 {- # OPTIONS_GHC -Wall -Werror #-}
 module Main (main) where

 import qualified Data.ByteString as S
 import qualified Data.ByteString.Char8 as S8

 main :: IO ()
 main = (S8.concat (map S.singleton (S.unpack (S8.pack "<foo>"))) ==
 S8.empty) `seq` return ()
 }}}

 {{{
 $ ghc --make -O1 -package={base,bytestring} BodySpec.hs -o a && ./a
 Segmentation fault (core dumped)
 }}}

 The cause is similar to #12757: low-level optimisations inline string
 literal (or it's wrapping value? i don't know) in multiple places. That
 breaks pointer-chasing in bytestring package.

 {{{
 $ strings a | fgrep '<foo>'
 <foo>
 <foo>
 <foo>
 <foo>
 }}}

--

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12855#comment:1>
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