8273585: String.charAt performance degrades due to JDK-8268698

Reviewed-by: roland, kvn

Author: y1yang0

src/hotspot/share/opto/loopnode.cpp

@@ -3416,7 +3416,7 @@ void PhaseIdealLoop::replace_parallel_iv(IdealLoopTree *loop) {
     // Look for induction variables of the form:  X += constant
     if (phi2->region() != loop->_head ||
         incr2->req() != 3 ||
-        incr2->in(1) != phi2 ||
+        incr2->in(1)->uncast() != phi2 ||
         incr2 == incr ||
         incr2->Opcode() != Op_AddI ||
         !incr2->in(2)->is_Con())