8286197: C2: Optimize MemorySegment shape in int loop

src/hotspot/share/opto/castnode.cpp

@@ -382,13 +382,18 @@ Node *CastLLNode::Ideal(PhaseGVN *phase, bool can_reshape) {
   if (in1 != NULL && in1->Opcode() == Op_ConvI2L) {
     const Type* t = Value(phase);
     const Type* t_in = phase->type(in1);
-    if (t != Type::TOP && t_in != Type::TOP && t != t_in) {
+    if (t != Type::TOP && t_in != Type::TOP) {
       const TypeLong* tl = t->is_long();
-      const TypeInt* ti = TypeInt::make(checked_cast<jint>(tl->_lo), checked_cast<jint>(tl->_hi), tl->_widen);
-      Node* castii = phase->transform(new CastIINode(in(0), in1->in(1), ti));
-      Node* convi2l = in1->clone();
-      convi2l->set_req(1, castii);
-      return convi2l;
+      const TypeLong* t_in_l = t_in->is_long();
+      assert(tl->_lo >= t_in_l->_lo && tl->_hi <= t_in_l->_hi, "CastLL type should be narrower than or equal to the type of its input");
+      assert((tl != t_in_l) == (tl->_lo > t_in_l->_lo || tl->_hi < t_in_l->_hi), "if type differs then this nodes's type must be narrower");
+      if (tl != t_in_l) {
+        const TypeInt* ti = TypeInt::make(checked_cast<jint>(tl->_lo), checked_cast<jint>(tl->_hi), tl->_widen);
+        Node* castii = phase->transform(new CastIINode(in(0), in1->in(1), ti));
+        Node* convi2l = in1->clone();
+        convi2l->set_req(1, castii);
+        return convi2l;
+      }
     }
   }
   return NULL;

src/hotspot/share/opto/loopopts.cpp

@@ -1081,7 +1081,7 @@ Node *PhaseIdealLoop::split_if_with_blocks_pre( Node *n ) {
     return n;
   }
 
-// Check for having no control input; not pinned.  Allow
+  // Check for having no control input; not pinned.  Allow
   // dominating control.
   if (n->in(0)) {
     Node *dom = idom(n_blk);