8176441: assert(false) failed: modified node was not processed by IGVN.transform_old()

The shiftNode needs to be added to the IGVN worklist after being modified.

Reviewed-by: kvn, vlivanov

hotspot/src/share/vm/opto/mulnode.cpp

@@ -648,6 +648,7 @@ static int maskShiftAmount(PhaseGVN *phase, Node *shiftNode, int nBits) {
 
   if (shift != maskedShift) {
     shiftNode->set_req(2, phase->intcon(maskedShift)); // Replace shift count with masked value.
+    phase->igvn_rehash_node_delayed(shiftNode);
   }
 
   return maskedShift;