--- a/hotspot/src/share/vm/opto/cfgnode.cpp	Wed Jan 25 07:03:26 2017 +0100
+++ b/hotspot/src/share/vm/opto/cfgnode.cpp	Wed Jan 25 07:05:38 2017 +0100
@@ -2097,6 +2097,7 @@
   uint ideal_reg = _type->ideal_reg();
   assert( ideal_reg != Node::NotAMachineReg, "invalid type at Phi" );
   if( ideal_reg == 0 ) return RegMask::Empty;
+  assert(ideal_reg != Op_RegFlags, "flags register is not spillable");
   return *(Compile::current()->matcher()->idealreg2spillmask[ideal_reg]);
 }