[GHC] #14545: -prof causes -N to default to 1

29 Nov 2017

      #14545: -prof causes -N to default to 1
-------------------------------------+-------------------------------------
           Reporter:  gelisam        |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.2
           Keywords:                 |  Operating System:  MacOS X
       Architecture:  x86_64         |   Type of failure:  Incorrect result
  (amd64)                            |  at runtime
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Given a simple test program which prints `getNumCapabilities`:

 {{{#!hs
 import Control.Concurrent

 main :: IO ()
 main = print =<< getNumCapabilities
 }}}

 Compiling this with `-threaded` and running the program with `+RTS -N` is
 supposed to set the number of capabilities to the number of cores on the
 machine. This normally prints 8 on my machine:

 {{{#!bash
 $ rm -rf Main Main.hi Main.o && ghc -threaded Main.hs && ./Main +RTS -N
 [1 of 1] Compiling Main             ( Main.hs, Main.o )
 Linking Main ...
 8
 }}}

 But when I compile with `-prof`, it prints 1 instead! Expected output:
 still 8.

 {{{#!bash
 $ rm -rf Main Main.hi Main.o && ghc -prof -threaded Main.hs && ./Main +RTS
 -N
 [1 of 1] Compiling Main             ( Main.hs, Main.o )
 Linking Main ...
 1
 }}}

 If I use `+RTS -N8` instead, it prints 8 as expected.

 Reproduced with GHC 8.0.2 and GHC 8.8.2.

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14545
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