[GHC] #9577: String literals are wasting space

[GHC]

#9577: String literals are wasting space
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              Reporter:  xnyhps      |            Owner:  xnyhps
                  Type:  bug         |           Status:  new
              Priority:  low         |        Milestone:
             Component:  Compiler    |          Version:  7.8.2
  (NCG)                              |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:  Runtime     |  Related Tickets:
  performance bug                    |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by tibbe):

 Replying to [comment:6 xnyhps]:
 > For the record, this is the rewrite rule used by ByteString:
 >
 > *
 https://github.com/haskell/bytestring/blob/master/Data/ByteString/Internal.hs#L250,
 calling
 https://github.com/haskell/bytestring/blob/master/Data/ByteString/Internal.hs#L271.
 >
 >   This just wraps the `Addr#` directly, no copying here. However,
 [https://github.com/haskell/bytestring/blob/master/Data/ByteString/Internal.hs#L522
 append] does call `memcpy` twice. I don't think GHC has the kind of
 optimizations that can turn a `memcpy` call into SIMD instructions
 directly, but maybe `memcpy` is more efficient when called with aligned
 buffers. I'll try to test this.

 The memcpy implementation (used by e.g. `copyByteArray#`) does unroll
 memcpys of statically known size and alignment, if aligned to a word, so I
 definitely think we should try to align our data that way. In 7.10 (if
 Phab:D166 goes in) we'll do even better and use a `REP-MOVSB` instruction
 on Ivy bridge and newer. `REP-MOVSB` is almost as fast as an unrolled AVX
 loop.

 The memcpy unrolling is implemented in
 source:compiler/nativeGen/X86/CodeGen.hs.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9577#comment:7>
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