Re: [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
      Resolution:                    |             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:                    |
-------------------------------------+-------------------------------------
Description changed by gelisam:

Old description:
...
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.
New description:

 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 8.2.2.

--

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14545#comment:1
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