------- Comment #12 from bonzini at gnu dot org 2009-03-13 07:28 ------- I think you need a matching memory constraint instead of just "m" or the bug might resurface.
(define_memory_constraint "H" "@internal" (match_test "cmpxchg8b_memory_operand (op, GET_MODE (op))") -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39431
