src/share/vm/opto/loopTransform.cpp

*** 1451,1474 ****
    Node *stride = loop_head->stride();
  
    Node *opaq = NULL;
    if (adjust_min_trip) {       // If not maximally unrolling, need adjustment
      // Search for zero-trip guard.
!     assert( loop_head->is_main_loop(), "" );
!     assert( ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "" );
!     Node *iff = ctrl->in(0);
!     assert( iff->Opcode() == Op_If, "" );
!     Node *bol = iff->in(1);
!     assert( bol->Opcode() == Op_Bool, "" );
!     Node *cmp = bol->in(1);
!     assert( cmp->Opcode() == Op_CmpI, "" );
!     opaq = cmp->in(2);
!     // Occasionally it's possible for a zero-trip guard Opaque1 node to be
!     // optimized away and then another round of loop opts attempted.
!     // We can not optimize this particular loop in that case.
!     if (opaq->Opcode() != Op_Opaque1)
!       return; // Cannot find zero-trip guard!  Bail out!
      // Zero-trip test uses an 'opaque' node which is not shared.
      assert(opaq->outcnt() == 1 && opaq->in(1) == limit, "");
    }
  
    C->set_major_progress();
--- 1451,1468 ----
    Node *stride = loop_head->stride();
  
    Node *opaq = NULL;
    if (adjust_min_trip) {       // If not maximally unrolling, need adjustment
      // Search for zero-trip guard.
! 
!     // Check the shape of the graph at the loop entry. If an inappropriate
!     // graph shape is encountered, the compiler bails out loop unrolling;
!     // compilation of the method will still succeed.
!     if (!is_canonical_main_loop_entry(loop_head)) {
!       return;
!     }
!     opaq = ctrl->in(0)->in(1)->in(1)->in(2);
      // Zero-trip test uses an 'opaque' node which is not shared.
      assert(opaq->outcnt() == 1 && opaq->in(1) == limit, "");
    }
  
    C->set_major_progress();
*** 2107,2117 ****
      loop->dump_head();
    }
  #endif
    assert(RangeCheckElimination, "");
    CountedLoopNode *cl = loop->_head->as_CountedLoop();
-   assert(cl->is_main_loop(), "");
  
    // protect against stride not being a constant
    if (!cl->stride_is_con())
      return;
  
--- 2101,2110 ----
*** 2119,2142 ****
    Node *trip_counter = cl->phi();
    // Find the main loop limit; we will trim it's iterations
    // to not ever trip end tests
    Node *main_limit = cl->limit();
  
    // Need to find the main-loop zero-trip guard
    Node *ctrl  = cl->in(LoopNode::EntryControl);
-   assert(ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "");
    Node *iffm = ctrl->in(0);
!   assert(iffm->Opcode() == Op_If, "");
!   Node *bolzm = iffm->in(1);
!   assert(bolzm->Opcode() == Op_Bool, "");
!   Node *cmpzm = bolzm->in(1);
!   assert(cmpzm->is_Cmp(), "");
!   Node *opqzm = cmpzm->in(2);
!   // Can not optimize a loop if zero-trip Opaque1 node is optimized
!   // away and then another round of loop opts attempted.
!   if (opqzm->Opcode() != Op_Opaque1)
!     return;
    assert(opqzm->in(1) == main_limit, "do not understand situation");
  
    // Find the pre-loop limit; we will expand its iterations to
    // not ever trip low tests.
    Node *p_f = iffm->in(0);
--- 2112,2132 ----
    Node *trip_counter = cl->phi();
    // Find the main loop limit; we will trim it's iterations
    // to not ever trip end tests
    Node *main_limit = cl->limit();
  
+   // Check graph shape. Cannot optimize a loop if zero-trip
+   // Opaque1 node is optimized away and then another round
+   // of loop opts attempted.
+   if (!is_canonical_main_loop_entry(cl)) {
+     return;
+   }
+ 
    // Need to find the main-loop zero-trip guard
    Node *ctrl  = cl->in(LoopNode::EntryControl);
    Node *iffm = ctrl->in(0);
!   Node *opqzm = iffm->in(1)->in(1)->in(2);
    assert(opqzm->in(1) == main_limit, "do not understand situation");
  
    // Find the pre-loop limit; we will expand its iterations to
    // not ever trip low tests.
    Node *p_f = iffm->in(0);