[GHC] #7258: Compiling DynFlags is jolly slow

[GHC]

#7258: Compiling DynFlags is jolly slow
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        Reporter:  simonpj           |                Owner:  simonpj
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.6.1
      Resolution:                    |             Keywords:  deriving-perf
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by alexbiehl):

 Replying to [comment:66 simonpj]:
 > > What about using a different kind of data structure like a map or
 similar
 >
 > Of course that the first thing we should do, once we are convinced
 that's where the time is going! (We only ave suggestive evidence so far.)
 Small maps should be cheap; that's the business of the containers library.

 `LocalReg` is `Uniquable` so something like this should work:

 {{{
 type LocalRegSet = UniqSet LocalReg

 emptyLocalRegSet :: LocalRegSet
 emptyLocalRegSet = emptyUniqSet

 nullLocalRegSet :: LocalRegSet -> Bool
 nullLocalRegSet = isEmptyUniqSet

 elemLocalRegSet :: LocalReg -> LocalRegSet -> Bool
 elemLocalRegSet = elementOfUniqSet

 insertLocalRegSet :: LocalRegSet -> LocalReg -> LocalRegSet
 insertLocalRegSet = addOneToUniqSet

 cannot_inline = skipped `regsUsedIn` rhs -- Note [dependent assignments]
                 || l `elemLocalRegSet` skipped
                 || not (okToInline dflags rhs node)

 regsUsedIn :: LocalRegSet -> CmmExpr -> Bool
 regsUsedIn ls _ | nullLocalRegSet ls = False
 regsUsedIn ls e = wrapRecExpf f e False
   where f (CmmReg (CmmLocal l))      _ | l `elemLocalRegSet` ls = True
         f (CmmRegOff (CmmLocal l) _) _ | l `elemLocalRegSet` ls = True
         f _ z = z

 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7258#comment:67>
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