8253353: Crash in C2: guarantee(n != NULL) failed: No Node

Co-authored-by: Fei Yang <fyang@openjdk.org>
Reviewed-by: vlivanov, neliasso

src/hotspot/share/opto/loopnode.cpp

@@ -291,6 +291,7 @@ IdealLoopTree* PhaseIdealLoop::insert_outer_loop(IdealLoopTree* loop, LoopNode*
   loop->_parent = outer_ilt;
   loop->_next = NULL;
   loop->_nest++;
+  assert(loop->_nest <= SHRT_MAX, "sanity");
   return outer_ilt;
 }
 
@@ -2614,6 +2615,7 @@ bool IdealLoopTree::is_member(const IdealLoopTree *l) const {
 //------------------------------set_nest---------------------------------------
 // Set loop tree nesting depth.  Accumulate _has_call bits.
 int IdealLoopTree::set_nest( uint depth ) {
+  assert(depth <= SHRT_MAX, "sanity");
   _nest = depth;
   int bits = _has_call;
   if( _child ) bits |= _child->set_nest(depth+1);

src/hotspot/share/opto/loopnode.hpp

@@ -611,7 +611,7 @@ class IdealLoopTree : public ResourceObj {
 
   Node_List _body;              // Loop body for inner loops
 
-  uint8_t _nest;                // Nesting depth
+  uint16_t _nest;               // Nesting depth
   uint8_t _irreducible:1,       // True if irreducible
           _has_call:1,          // True if has call safepoint
           _has_sfpt:1,          // True if has non-call safepoint