[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
              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:              |
-------------------------------------+-------------------------------------
 When compiling a set of 3 modules (in a certain order), linking of the
 final executable fails because there conflicting symbols in some of the
 `.o`.

 When doing the compilation in the same order, but with optimizations, it
 succeeds.

 The simple test case:

 A.hs:

 {{{#!hs
 module A where
 main :: IO ()
 main = putStrLn "A"
 }}}

 B.hs:

 {{{#!hs
 module B where
 import A()
 main :: IO ()
 main = putStrLn "B"
 }}}

 C.hs:

 {{{#!hs
 import B()
 main :: IO ()
 main = putStrLn "hi"
 }}}

 When I compile it with in the order specified by the attached `./bug-
 reproduce.sh` and `Makefile`, the following happens:

 {{{
 ./bug-reproduce.sh
 rm -fv a A.o A.hi
 removed 'a'
 removed 'A.o'
 removed 'A.hi'
 rm -fv b B.o B.hi
 removed 'b'
 removed 'B.o'
 removed 'B.hi'
 rm -fv c C.o C.hi
 removed 'c'
 removed 'C.o'
 removed 'C.hi'
 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
 [1 of 2] Compiling A                ( A.hs, A.o ) [flags changed]
 [2 of 2] Compiling B                ( B.hs, B.o )
 Linking b ...
 ghc -Wall  C.hs -o c
 [2 of 3] Compiling B                ( B.hs, B.o ) [flags changed]
 [3 of 3] Compiling Main             ( C.hs, C.o )
 Linking c ...
 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'
 B.o:(.data+0x0): first defined here
 ./A.o: In function `ZCMain_main_srt':
 (.data+0x70): multiple definition of `ZCMain_main_closure'
 B.o:(.data+0x70): first defined here
 ./A.o:(.text+0xb8): multiple definition of `ZCMain_main_info'
 B.o:(.text+0xb8): first defined here
 collect2: error: ld returned 1 exit status
 make: *** [B.o] Error 1
 }}}

 But it succeeds if done as `./bug-reproduce.sh GHC_OPTS=-O1` (probably,
 the optimizations remove the conflicting symbols):

 {{{
 ./bug-reproduce.sh GHC_OPTS=-O1
 rm -fv a A.o A.hi
 removed 'a'
 removed 'A.o'
 removed 'A.hi'
 rm -fv b B.o B.hi
 removed 'b'
 removed 'B.o'
 removed 'B.hi'
 rm -fv c C.o C.hi
 removed 'c'
 removed 'C.o'
 removed 'C.hi'
 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 )
 Linking b ...
 ghc -Wall -O1 C.hs -o c
 [2 of 3] Compiling B                ( B.hs, B.o ) [flags changed]
 [3 of 3] Compiling Main             ( C.hs, C.o )
 Linking c ...
 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 ...
 ghc -Wall -O1 C.hs -o c
 [2 of 3] Compiling B                ( B.hs, B.o ) [flags changed]
 Linking c ...
 }}}

 Couldn't the compiler detect and handle such cases?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10531>
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