[GHC] #5814: LLVM 3.0 doesn't support llvm.memory.barrier

[GHC]

#5814: LLVM 3.0 doesn't support llvm.memory.barrier
------------------------------+---------------------------------------------
 Reporter:  bgamari           |          Owner:  dterei          
     Type:  bug               |         Status:  new             
 Priority:  normal            |      Component:  Compiler (LLVM) 
  Version:  7.5               |       Keywords:                  
       Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
  Failure:  None/Unknown      |       Testcase:                  
Blockedby:                    |       Blocking:                  
  Related:                    |  
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Changes (by bgamari):

  * version:  7.2.2 => 7.5


Comment:

 In the name of release early, release often I'm attaching my hacked patch
 to use the "fence" instruction. The code compiles and seems to run, but
 this is not to say that it is correct. In fact, there are at least two
 outstanding issues,

   1) Logic needs to be wired up to emit llvm.memory.barrier when dealing
 with old LLVMs
   2) Someone with greater knowledge of the synchronization requirements of
 cmm's write barrier primative should take a look at the LLVM atomics
 documentation (http://llvm.org/releases/3.0/docs/Atomics.html) and ensure
 that my use of "fence" is correct

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5814#comment:1>
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