Cherry-picking r14877 from trunk:
    
    Liveness & Deadcode: fix i386-specific issue with move instructions accessing
      the x87 FP stack, which must not be eliminated.
    CSEgen: harden against the same x87-specific issue + against reuse of
      values in fixed hardware registers that were destroyed by a prior
      operation.
    
    
    git-svn-id: http://caml.inria.fr/svn/ocaml/version/4.02@14878 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02