8314468: Improve Compiler loops

Co-authored-by: Dean Long <dlong@openjdk.org>
Reviewed-by: rhalade, mschoene, iveresov, kvn

src/hotspot/share/c1/c1_RangeCheckElimination.cpp

@@ -421,8 +421,11 @@ void RangeCheckEliminator::add_access_indexed_info(InstructionList &indices, int
     aii->_max = idx;
     aii->_list = new AccessIndexedList();
   } else if (idx >= aii->_min && idx <= aii->_max) {
-    remove_range_check(ai);
-    return;
+    // Guard against underflow/overflow (see 'range_cond' check in RangeCheckEliminator::in_block_motion)
+    if (aii->_max < 0 || (aii->_max + min_jint) <= aii->_min) {
+      remove_range_check(ai);
+      return;
+    }
   }
   aii->_min = MIN2(aii->_min, idx);
   aii->_max = MAX2(aii->_max, idx);
@@ -484,7 +487,7 @@ void RangeCheckEliminator::in_block_motion(BlockBegin *block, AccessIndexedList
               if (ao->op() == Bytecodes::_isub) {
                 value = -value;
               }
-              base += value;
+              base = java_add(base, value);
               last_integer = base;
               last_instruction = other;
             }
@@ -506,12 +509,12 @@ void RangeCheckEliminator::in_block_motion(BlockBegin *block, AccessIndexedList
         assert(info != nullptr, "Info must not be null");
 
         // if idx < 0, max > 0, max + idx may fall between 0 and
-        // length-1 and if min < 0, min + idx may overflow and be >=
+        // length-1 and if min < 0, min + idx may underflow/overflow and be >=
         // 0. The predicate wouldn't trigger but some accesses could
         // be with a negative index. This test guarantees that for the
         // min and max value that are kept the predicate can't let
         // some incorrect accesses happen.
-        bool range_cond = (info->_max < 0 || info->_max + min_jint <= info->_min);
+        bool range_cond = (info->_max < 0 || (info->_max + min_jint) <= info->_min);
 
         // Generate code only if more than 2 range checks can be eliminated because of that.
         // 2 because at least 2 comparisons are done
@@ -859,7 +862,7 @@ void RangeCheckEliminator::process_access_indexed(BlockBegin *loop_header, Block
         );
 
         remove_range_check(ai);
-    } else if (_optimistic && loop_header) {
+    } else if (false && _optimistic && loop_header) {
       assert(ai->array(), "Array must not be null!");
       assert(ai->index(), "Index must not be null!");