[GHC] #13527: ghc has a stack space leak when prints warnings

[GHC]

#13527: ghc has a stack space leak when prints warnings
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        Reporter:  slyfox            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
      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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Comment (by slyfox):

 I've built ghc-prof and found out GHC is most stressed in
 'ErrUtils.getCaretDiagnostic' where
 source file is read from disk and then chunked by newlines. lexemeToString
 generates a lot of
 heap traffic as it decodes whole file into String.

 This example is enough to take more that 100M of stack:

 {{{#!hs
 {-# LANGUAGE PackageImports #-}
 module Main (main) where

 import qualified StringBuffer as SB

 main = do
     b <- SB.hGetStringBuffer "a.c"
     let s = SB.lexemeToString b (SB.len b)
     print (length $ lines s)
 }}}

 {{{
 $ ghc --make a.hs -o a -package=ghc -debug -rtsopts
 $ ./a +RTS -K100M
 a: Stack space overflow: current size 33624 bytes.
 a: Use `+RTS -Ksize -RTS' to increase it.
 }}}

 Looks like there is 2 bugs here:
 - '''lexemeToString''' takes a lot of stack to decode StringBuffer into
 String
 - '''getCaretDiagnostic ''' could use more efficient mechanism to split
 file into lines before converting everything to String.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13527#comment:1>
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