[GHC] #10531: modules that can be linked successfully when compiled with optimizations, fail to link with: multiple definition of `__stginit_ZCMain'

[GHC]

#10531: modules that can be linked successfully when compiled with optimizations,
fail to link with: multiple definition of `__stginit_ZCMain'
-------------------------------------+-------------------------------------
        Reporter:  imz               |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.6.1
      Resolution:                    |                Keywords:
Operating System:  Linux             |            Architecture:  x86_64
 Type of failure:  GHC rejects       |  (amd64)
  valid program                      |               Test Case:  attached
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
-------------------------------------+-------------------------------------

Comment (by imz):

 One difference is that without `-O1` it doesn't recompile `A.hs` when
 compiling `B.hs`, whereas with `-O1` it does (although superficially there
 is no extra reason to do so in the second case, i.e., no change in flags
 which might cause this: `A.hs` has been compiled with `-O1` already in the
 second case; it could be understood if `-O1` always caused recompilation,
 no matter what the previous flags were):

 {{{
 removed 'A.o'
 ghc -Wall  A.hs -main-is A.main -o a
 [1 of 1] Compiling A                ( A.hs, A.o )
 Linking a ...
 ghc -Wall  B.hs -main-is B.main -o b
 [2 of 2] Compiling B                ( B.hs, B.o ) [flags changed]
 Linking b ...
 ./A.o: In function `siv_closure':
 (.data+0x0): multiple definition of `__stginit_ZCMain'
 }}}

 vs

 {{{
 removed 'A.o'
 ghc -Wall -O1 A.hs -main-is A.main -o a
 [1 of 1] Compiling A                ( A.hs, A.o )
 Linking a ...
 ghc -Wall -O1 B.hs -main-is B.main -o b
 [1 of 2] Compiling A                ( A.hs, A.o ) [flags changed]
 [2 of 2] Compiling B                ( B.hs, B.o ) [flags changed]
 Linking b ...
 }}}
 (success)

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10531#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler