[GHC] #13996: Non-cheap primop is duplicated

[GHC]

#13996: Non-cheap primop is duplicated
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        Reporter:  simonpj           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      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 mboes):

 > better to push it inside the inner lambda, so the two lambdas come
 together (generally a big win).

 Note in particular that `-fno-lambda-eta-expansion` can be a huge
 pessimization in the following way. Consider this program:

 {{{#!hs
 module Main where

 f :: Double -> Double -> Double
 f t = let s = sin t in \x -> x + s

 main = do
   print $ sum [ f t x | t <- [1..10000], x <- [1..10000]]
 }}}

 `ghc --make -O2` yields a program that runs in constant space. Whereas
 adding `-fno-do-lambda-eta-expansion` to the command-line yields a program
 that segfaults, because its memory consumption blew up and it ultimately
 ran out of space.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13996#comment:2>
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