[GHC] #8472: Primitive string literals prevent optimization

[GHC]

#8472: Primitive string literals prevent optimization
-------------------------------------+-------------------------------------
        Reporter:  akio              |                Owner:  gridaphobe
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.6.3
      Resolution:                    |             Keywords:  newcomer
Operating System:  Linux             |         Architecture:  x86_64
 Type of failure:  Runtime           |  (amd64)
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2554,
       Wiki Page:                    |  Phab:D2605
-------------------------------------+-------------------------------------

Comment (by akio):

 My patch (Phab:D2605) causes some compiler perf regressions. This happens
 because

 {{{
 f x = ... "foo"# ...
 }}}

 now gets transformed into

 {{{
 foo = "foo"#
 f x = ... foo ...
 }}}

 and this means a larger code size.

 For example, on `perf/compiler/T1969`, the `peak_megabytes_allocated` goes
 from 63 to 68 (a 8% increase), the code size (in terms of the `Term`
 component of `CoreStats`) goes from 12603 to 13271 (a 10% increase), and
 this is fully explained by the above effect, which increases the code size
 by 2 for each top-level string literal.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8472#comment:16>
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