src/share/vm/opto/node.cpp

*** 1047,1123 ****
    int iterations_without_region_limit = DominatorSearchLimit;
  
    Node* orig_sub = sub;
    nlist.clear();
    bool this_dominates = false;
!   uint region_input = 0;
    while (sub != NULL) {        // walk 'sub' up the chain to 'this'
      if (sub == this) {
        if (nlist.size() == 0) {
          // No Region nodes except loops were visited before and the EntryControl
          // path was taken for loops: it did not walk in a cycle.
!         return true;
!       } else if (!this_dominates) {
          // Region nodes were visited. Continue walk up to Start or Root
          // to make sure that it did not walk in a cycle.
          this_dominates = true; // first time meet
          iterations_without_region_limit = DominatorSearchLimit; // Reset
-       } else {
-         return false;          // already met before: walk in a cycle
        }
      }
!     if (sub->is_Start() || sub->is_Root())
!       return this_dominates;
! 
      Node* up = sub->find_exact_control(sub->in(0));
!     if (up == NULL || up->is_top())
!       return false; // Conservative answer for dead code
! 
!     if (sub == up && sub->is_Loop()) {
        up = sub->in(1); // in(LoopNode::EntryControl);
!     } else if (sub == up && sub->is_Region() && sub->req() == 3) {
        iterations_without_region_limit = DominatorSearchLimit; // Reset
        uint i = 1;
        uint size = nlist.size();
        if (size == 0) {
!         // No Region nodes (except Loops) were visited before.
          // Take first valid path on the way up to 'this'.
-       } else if (nlist.at(size - 1) == sub) {
-         // This Region node was just visited. Take other path.
-         i = region_input + 1;
-         nlist.pop();
        } else {
          // Was this Region node visited before?
!         for (uint j = 0; j < size; j++) {
!           if (nlist.at(j) == sub) {
!             return false; // The Region node was visited before. Give up.
            }
          }
          // The Region node was not visited before.
-         // Take first valid path on the way up to 'this'.
        }
        for (; i < sub->req(); i++) {
          Node* in = sub->in(i);
          if (in != NULL && !in->is_top() && in != sub) {
            break;
          }
        }
        if (i < sub->req()) {
-         nlist.push(sub);
          up = sub->in(i);
!         region_input = i;
        }
      }
!     if (sub == up)
!       return false;    // some kind of tight cycle
! 
!     if (--iterations_without_region_limit < 0)
!       return false;    // dead cycle
! 
      sub = up;
    }
!   return false;
  }
  
  //------------------------------remove_dead_region-----------------------------
  // This control node is dead.  Follow the subgraph below it making everything
  // using it dead as well.  This will happen normally via the usual IterGVN
--- 1047,1158 ----
    int iterations_without_region_limit = DominatorSearchLimit;
  
    Node* orig_sub = sub;
    nlist.clear();
    bool this_dominates = false;
!   bool result = false; // Conservative answer
! 
    while (sub != NULL) {        // walk 'sub' up the chain to 'this'
      if (sub == this) {
        if (nlist.size() == 0) {
          // No Region nodes except loops were visited before and the EntryControl
          // path was taken for loops: it did not walk in a cycle.
!         result = true;
!         break;
!       } else if (this_dominates) {
!         result = false;          // already met before: walk in a cycle
!         break;
!       } else {
          // Region nodes were visited. Continue walk up to Start or Root
          // to make sure that it did not walk in a cycle.
          this_dominates = true; // first time meet
          iterations_without_region_limit = DominatorSearchLimit; // Reset
       }
      }
!     if (sub->is_Start() || sub->is_Root()) {
!       result = this_dominates;
!       break;
!     }
      Node* up = sub->find_exact_control(sub->in(0));
!     if (up == NULL || up->is_top()) {
!       result = false; // Conservative answer for dead code
!       break;
!     }
!     if (sub == up && (sub->is_Loop() || sub->is_Region() && sub->req() != 3)) {
!       // Take first valid path on the way up to 'this'.
        up = sub->in(1); // in(LoopNode::EntryControl);
!     } else if (sub == up && sub->is_Region()) {
!       assert(sub->req() == 3, "sanity");
        iterations_without_region_limit = DominatorSearchLimit; // Reset
+ 
+       // Try both paths for such Regions.
+       // It is not accurate without regions dominating information.
+       // With such information the other path should be checked for
+       // the most dominating Region which was visited before.
+       bool region_was_visited_before = false;
        uint i = 1;
        uint size = nlist.size();
        if (size == 0) {
!         // No such Region nodes were visited before.
          // Take first valid path on the way up to 'this'.
        } else {
          // Was this Region node visited before?
!         intptr_t ni;
!         int j = size - 1;
!         for (; j >= 0; j--) {
!           ni = (intptr_t)nlist.at(j);
!           if ((Node*)(ni & ~1) == sub) {
!             if ((ni & 1) != 0) {
!               break; // Visited 2 paths. Give up.
!             } else {
!               // The Region node was visited before only once.
!               nlist.remove(j);
!               region_was_visited_before = true;
!               for (; i < sub->req(); i++) {
!                 Node* in = sub->in(i);
!                 if (in != NULL && !in->is_top() && in != sub) {
!                   break;
                  }
                }
+               i++; // Take other path.
+               break;
+             }
+           }
+         }
+         if (j >= 0 && (ni & 1) != 0) {
+           result = false; // Visited 2 paths. Give up.
+           break;
+         }
          // The Region node was not visited before.
        }
        for (; i < sub->req(); i++) {
          Node* in = sub->in(i);
          if (in != NULL && !in->is_top() && in != sub) {
            break;
          }
        }
        if (i < sub->req()) {
          up = sub->in(i);
!         if (region_was_visited_before && sub != up) {
!           // Set 0 bit to indicate that both paths were taken.
!           nlist.push((Node*)((intptr_t)sub + 1));
!         } else {
!           nlist.push(sub);
          }
        }
!     }
!     if (sub == up) {
!       result = false;    // some kind of tight cycle
!       break;
!     }
!     if (--iterations_without_region_limit < 0) {
!       result = false;    // dead cycle
!       break;
!     }
      sub = up;
    }
!   return result;
  }
  
  //------------------------------remove_dead_region-----------------------------
  // This control node is dead.  Follow the subgraph below it making everything
  // using it dead as well.  This will happen normally via the usual IterGVN