[commit: ghc] master: StgCmmPrim: Add missing write barrier. (2cb8cc2)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/2cb8cc26df6af431d30b6964710ea2d859ca2bcd/ghc

>---------------------------------------------------------------

commit 2cb8cc26df6af431d30b6964710ea2d859ca2bcd
Author: Peter Trommler <ptrommler at acm.org>
Date:   Wed Oct 19 09:02:54 2016 -0400

    StgCmmPrim: Add missing write barrier.
    
    On architectures with weak memory consistency a write barrier
    is needed before the write to the pointer array.
    
    Fixes #12469
    
    Test Plan: rebuilt Stackage nightly twice on powerpc64le
    
    Reviewers: hvr, rrnewton, erikd, austin, simonmar, bgamari
    
    Reviewed By: erikd, bgamari
    
    Subscribers: thomie
    
    Differential Revision: https://phabricator.haskell.org/D2525
    
    GHC Trac Issues: #12469


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2cb8cc26df6af431d30b6964710ea2d859ca2bcd
 compiler/codeGen/StgCmmPrim.hs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/compiler/codeGen/StgCmmPrim.hs b/compiler/codeGen/StgCmmPrim.hs
index 2169465..34c2d06 100644
--- a/compiler/codeGen/StgCmmPrim.hs
+++ b/compiler/codeGen/StgCmmPrim.hs
@@ -1350,6 +1350,10 @@ doWritePtrArrayOp :: CmmExpr
 doWritePtrArrayOp addr idx val
   = do dflags <- getDynFlags
        let ty = cmmExprType dflags val
+       -- This write barrier is to ensure that the heap writes to the object
+       -- referred to by val have happened before we write val into the array.
+       -- See #12469 for details.
+       emitPrimCall [] MO_WriteBarrier []
        mkBasicIndexedWrite (arrPtrsHdrSize dflags) Nothing addr ty idx val
        emit (setInfo addr (CmmLit (CmmLabel mkMAP_DIRTY_infoLabel)))
   -- the write barrier.  We must write a byte into the mark table: