RFR: 8254734: "dead loop detected" assert failure with patch from 8223051

[Roland Westrelin]

compiler/c2/TestDeadDataLoopIGVN.java ran with -server -Xcomp
-XX:+CreateCoredumpOnCrash -ea -esa -XX:CompileThreshold=100
-XX:+UnlockExperimentalVMOptions -server -XX:-TieredCompilation and
the patch from 8223051 (long counted loops, not integrated yet) fails
with:

assert(no_dead_loop) failed: dead loop detected

I can reproduce the failure with only this change from 8223051:
diff --git a/src/hotspot/share/opto/callnode.cpp b/src/hotspot/share/opto/callnode.cpp
index 268cec7732c..295cb4ecaf9 100644
--- a/src/hotspot/share/opto/callnode.cpp
+++ b/src/hotspot/share/opto/callnode.cpp
@@ -1159,7 +1159,7 @@ Node* SafePointNode::Identity(PhaseGVN* phase) {
   if( in(TypeFunc::Control)->is_SafePoint() )
     return in(TypeFunc::Control);
 
-  if( in(0)->is_Proj() ) {
+  if (in(0)->is_Proj() && !phase->C->major_progress()) {
     Node *n0 = in(0)->in(0);
     // Check if he is a call projection (except Leaf Call)
     if( n0->is_Catch() ) {
diff --git a/src/hotspot/share/opto/parse1.cpp b/src/hotspot/share/opto/parse1.cpp
index 4b88c379dea..baf2bf9bacc 100644
--- a/src/hotspot/share/opto/parse1.cpp
+++ b/src/hotspot/share/opto/parse1.cpp
@@ -2254,23 +2254,7 @@ void Parse::return_current(Node* value) {
 
 //------------------------------add_safepoint----------------------------------
 void Parse::add_safepoint() {
-  // See if we can avoid this safepoint.  No need for a SafePoint immediately
-  // after a Call (except Leaf Call) or another SafePoint.
-  Node *proj = control();
   uint parms = TypeFunc::Parms+1;
-  if( proj->is_Proj() ) {
-    Node *n0 = proj->in(0);
-    if( n0->is_Catch() ) {
-      n0 = n0->in(0)->in(0);
-      assert( n0->is_Call(), "expect a call here" );
-    }
-    if( n0->is_Call() ) {
-      if( n0->as_Call()->guaranteed_safepoint() )
-        return;
-    } else if( n0->is_SafePoint() && n0->req() >= parms ) {
-      return;
-    }
-  }
 
   // Clear out dead values from the debug info.
   kill_dead_locals();
so it's unrelated to the long counted loops transformation itself.

At IGVN time, a dead loop is optimized. The loop contains the
following subgraph:

(LoadI .. (AddP (CastPP .. (Phi (Proj (CallStaticJava .. (AddI

The projection is on the backedge of the phi. The AddI points back to
the LoadI. The CallStaticJava is a boxing method call. The LoadI is a
boxed value load.

The phi is optimized out as the loop is unreachable:

(LoadI .. (AddP (Proj (CallStaticJava .. (AddI

The LoadI is then optimized by code MemNode::can_see_stored_value():
    // Load boxed value from result of valueOf() call is input parameter.
    if (this->is_Load() && ld_adr->is_AddP() &&
        (tp != NULL) && tp->is_ptr_to_boxed_value()) {
      intptr_t ignore = 0;
      Node* base = AddPNode::Ideal_base_and_offset(ld_adr, phase, ignore);
      BarrierSetC2* bs = BarrierSet::barrier_set()->barrier_set_c2();
      base = bs->step_over_gc_barrier(base);
      if (base != NULL && base->is_Proj() &&
          base->as_Proj()->_con == TypeFunc::Parms &&
          base->in(0)->is_CallStaticJava() &&
          base->in(0)->as_CallStaticJava()->is_boxing_method()) {
        return base->in(0)->in(TypeFunc::Parms);
      }
    }
to the AddI. Because the AddI has the LoadI as input we end up with a
dead loop. I propose extending the dead loop safe logic to take the
pattern with a boxing method load into account.

-------------

Commit messages:
 - fix

Changes: https://git.openjdk.java.net/jdk/pull/649/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=649&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254734
  Stats: 28 lines in 2 files changed: 23 ins; 4 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/649.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/649/head:pull/649

PR: https://git.openjdk.java.net/jdk/pull/649