[GHC] #12893: Profiling defeats stream fusion when using vector library

[GHC]

#12893: Profiling defeats stream fusion when using vector library
-------------------------------------+-------------------------------------
        Reporter:  newhoggy          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:  stream-fusion
                                     |  profiling
Operating System:  MacOS X           |         Architecture:  x86_64
 Type of failure:  Runtime           |  (amd64)
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by guaraqe):

 I think the problem that the OP is reporting is that there are no cost
 centers in the program, yet no optimization is done. There are no manual
 `SCC`s and compilation is done with `-fno-prof-count-entries  -fno-prof-
 cafs -fno-prof-auto -O2`, so we would expect that there would be no
 barriers for optimization.

 This can be wrong if for some reason the GHC flags are not passed to the
 `vector` library, and it is still being compiled with automatic cost
 centers, which would indeed block fusion. If that is the case, it would be
 nice to have a way to pass these flags all the way down.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12893#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler