8087128: C2: Disallow definition split on MachCopySpill nodes

Reviewed-by: kvn

src/share/vm/opto/reg_split.cpp

@@ -1171,9 +1171,8 @@ uint PhaseChaitin::Split(uint maxlrg, ResourceArea* split_arena) {
               (deflrg._direct_conflict || deflrg._must_spill)) ||
              // Check for LRG being up in a register and we are inside a high
              // pressure area.  Spill it down immediately.
-             (defup && is_high_pressure(b,&deflrg,insidx))) ) {
+             (defup && is_high_pressure(b,&deflrg,insidx) && !n->is_SpillCopy())) ) {
           assert( !n->rematerialize(), "" );
-          assert( !n->is_SpillCopy(), "" );
           // Do a split at the def site.
           maxlrg = split_DEF( n, b, insidx, maxlrg, Reachblock, debug_defs, splits, slidx );
           // If it wasn't split bail