8260370: C2: LoopLimit node is not eliminated

Reviewed-by: kvn, thartmann

src/hotspot/share/opto/compile.cpp

@@ -1840,6 +1840,8 @@ void Compile::process_for_post_loop_opts_igvn(PhaseIterGVN& igvn) {
 
   C->set_post_loop_opts_phase(); // no more loop opts allowed
 
+  assert(!C->major_progress(), "not cleared");
+
   if (_for_post_loop_igvn.length() > 0) {
     while (_for_post_loop_igvn.length() > 0) {
       Node* n = _for_post_loop_igvn.pop();
@@ -1848,6 +1850,11 @@ void Compile::process_for_post_loop_opts_igvn(PhaseIterGVN& igvn) {
     }
     igvn.optimize();
     assert(_for_post_loop_igvn.length() == 0, "no more delayed nodes allowed");
+
+    // Sometimes IGVN sets major progress (e.g., when processing loop nodes).
+    if (C->major_progress()) {
+      C->clear_major_progress(); // ensure that major progress is now clear
+    }
   }
 }
 

src/hotspot/share/opto/loopnode.cpp

@@ -1921,8 +1921,9 @@ Node *LoopLimitNode::Ideal(PhaseGVN *phase, bool can_reshape) {
 
   // Delay following optimizations until all loop optimizations
   // done to keep Ideal graph simple.
-  if (!can_reshape || phase->C->major_progress())
+  if (!can_reshape || !phase->C->post_loop_opts_phase()) {
     return NULL;
+  }
 
   const TypeInt* init_t  = phase->type(in(Init) )->is_int();
   const TypeInt* limit_t = phase->type(in(Limit))->is_int();