[GHC] #8219: x86 definition of cas() is wrong

[GHC]

#8219: x86 definition of cas() is wrong
-------------------------------------+------------------------------------
        Reporter:  parcs             |            Owner:
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Runtime System    |          Version:  7.7
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by parcs):

 Sorry, my original test case is needlessly convoluted. Here's a more
 straightforward one:

 === cas.c
 {{{
 #!c
 #include <assert.h>

 static int
 cas (int *p, int o, int n)
 {
     asm ("lock cmpxchg %3,%1"
             :"=a"(o), "=m"(*(volatile int *)p)
             :"0"(o), "r"(n));
     return o;
 }

 int v;

 int
 main (int argc, char **argv)
 {
     v = 42;
     cas (&v, 42, 1);
     assert(v == 1);

     return 0;
 }
 }}}

 === Command Line
 {{{
 $ gcc -O2 cas.c
 $ ./a.out
 a.out: cas.c:19: main: Assertion `v == 1' failed.
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8219#comment:3>
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