8072422: Cleanup: Remove some unused flags/code in loop optimizations

Remove unused flags, change test using them.

Reviewed-by: kvn, twisti

hotspot/src/share/vm/opto/c2_globals.hpp

@@ -229,21 +229,12 @@
   develop(bool, TraceLoopOpts, false,                                       \
           "Trace executed loop optimizations")                              \
                                                                             \
-  diagnostic(bool, LoopLimitCheck, true,                                    \
-          "Generate a loop limits check for overflow")                      \
-                                                                            \
   develop(bool, TraceLoopLimitCheck, false,                                 \
           "Trace generation of loop limits checks")                         \
                                                                             \
-  diagnostic(bool, RangeLimitCheck, true,                                   \
-          "Additional overflow checks during range check elimination")      \
-                                                                            \
   develop(bool, TraceRangeLimitCheck, false,                                \
           "Trace additional overflow checks in RCE")                        \
                                                                             \
-  diagnostic(bool, UnrollLimitCheck, true,                                  \
-          "Additional overflow checks during loop unroll")                  \
-                                                                            \
   /* OptimizeFill not yet supported on PowerPC. */                          \
   product(bool, OptimizeFill, true PPC64_ONLY(&& false),                    \
           "convert fill/copy loops into intrinsic")                         \

hotspot/src/share/vm/opto/graphKit.cpp

@@ -3773,9 +3773,7 @@ void GraphKit::add_predicate(int nargs) {
     add_predicate_impl(Deoptimization::Reason_predicate, nargs);
   }
   // loop's limit check predicate should be near the loop.
-  if (LoopLimitCheck) {
   add_predicate_impl(Deoptimization::Reason_loop_limit_check, nargs);
-  }
 }
 
 //----------------------------- store barriers ----------------------------

hotspot/src/share/vm/opto/loopPredicate.cpp

@@ -313,12 +313,10 @@ Node* PhaseIdealLoop::clone_loop_predicates(Node* old_entry, Node* new_entry,
   // Search original predicates
   Node* entry = old_entry;
   ProjNode* limit_check_proj = NULL;
-  if (LoopLimitCheck) {
   limit_check_proj = find_predicate_insertion_point(entry, Deoptimization::Reason_loop_limit_check);
   if (limit_check_proj != NULL) {
     entry = entry->in(0)->in(0);
   }
-  }
   if (UseLoopPredicate) {
     ProjNode* predicate_proj = find_predicate_insertion_point(entry, Deoptimization::Reason_predicate);
     if (predicate_proj != NULL) { // right pattern that can be used by loop predication
@@ -353,12 +351,10 @@ Node* PhaseIdealLoop::clone_loop_predicates(Node* old_entry, Node* new_entry,
 // Skip related predicates.
 Node* PhaseIdealLoop::skip_loop_predicates(Node* entry) {
   Node* predicate = NULL;
-  if (LoopLimitCheck) {
   predicate = find_predicate_insertion_point(entry, Deoptimization::Reason_loop_limit_check);
   if (predicate != NULL) {
     entry = entry->in(0)->in(0);
   }
-  }
   if (UseLoopPredicate) {
     predicate = find_predicate_insertion_point(entry, Deoptimization::Reason_predicate);
     if (predicate != NULL) { // right pattern that can be used by loop predication
@@ -393,12 +389,10 @@ ProjNode* PhaseIdealLoop::find_predicate_insertion_point(Node* start_c, Deoptimi
 // Find a predicate
 Node* PhaseIdealLoop::find_predicate(Node* entry) {
   Node* predicate = NULL;
-  if (LoopLimitCheck) {
   predicate = find_predicate_insertion_point(entry, Deoptimization::Reason_loop_limit_check);
   if (predicate != NULL) { // right pattern that can be used by loop predication
     return entry;
   }
-  }
   if (UseLoopPredicate) {
     predicate = find_predicate_insertion_point(entry, Deoptimization::Reason_predicate);
     if (predicate != NULL) { // right pattern that can be used by loop predication
@@ -646,19 +640,13 @@ BoolNode* PhaseIdealLoop::rc_predicate(IdealLoopTree *loop, Node* ctrl,
   Node* max_idx_expr  = init;
   int stride_con = stride->get_int();
   if ((stride_con > 0) == (scale > 0) == upper) {
-    if (LoopLimitCheck) {
+    // Limit is not exact.
-      // With LoopLimitCheck limit is not exact.
     // Calculate exact limit here.
     // Note, counted loop's test is '<' or '>'.
     limit = exact_limit(loop);
     max_idx_expr = new SubINode(limit, stride);
     register_new_node(max_idx_expr, ctrl);
     if (TraceLoopPredicate) predString->print("(limit - stride) ");
-    } else {
-      max_idx_expr = new SubINode(limit, stride);
-      register_new_node(max_idx_expr, ctrl);
-      if (TraceLoopPredicate) predString->print("(limit - stride) ");
-    }
   } else {
     if (TraceLoopPredicate) predString->print("init ");
   }
@@ -721,12 +709,9 @@ bool PhaseIdealLoop::loop_predication_impl(IdealLoopTree *loop) {
   Node* entry = head->in(LoopNode::EntryControl);
   ProjNode *predicate_proj = NULL;
   // Loop limit check predicate should be near the loop.
-  if (LoopLimitCheck) {
   predicate_proj = find_predicate_insertion_point(entry, Deoptimization::Reason_loop_limit_check);
   if (predicate_proj != NULL)
     entry = predicate_proj->in(0)->in(0);
-  }
-
   predicate_proj = find_predicate_insertion_point(entry, Deoptimization::Reason_predicate);
   if (!predicate_proj) {
 #ifndef PRODUCT

hotspot/src/share/vm/opto/loopTransform.cpp

@@ -1468,7 +1468,6 @@ void PhaseIdealLoop::do_unroll( IdealLoopTree *loop, Node_List &old_new, bool ad
   C->set_major_progress();
 
   Node* new_limit = NULL;
-  if (UnrollLimitCheck) {
   int stride_con = stride->get_int();
   int stride_p = (stride_con > 0) ? stride_con : -stride_con;
   uint old_trip_count = loop_head->trip_count();
@@ -1620,58 +1619,6 @@ void PhaseIdealLoop::do_unroll( IdealLoopTree *loop, Node_List &old_new, bool ad
   // Double the count of original iterations in the unrolled loop body.
   loop_head->double_unrolled_count();
 
-  } else { // LoopLimitCheck
-
-    // Adjust max trip count. The trip count is intentionally rounded
-    // down here (e.g. 15-> 7-> 3-> 1) because if we unwittingly over-unroll,
-    // the main, unrolled, part of the loop will never execute as it is protected
-    // by the min-trip test.  See bug 4834191 for a case where we over-unrolled
-    // and later determined that part of the unrolled loop was dead.
-    loop_head->set_trip_count(loop_head->trip_count() / 2);
-
-    // Double the count of original iterations in the unrolled loop body.
-    loop_head->double_unrolled_count();
-
-    // -----------
-    // Step 2: Cut back the trip counter for an unroll amount of 2.
-    // Loop will normally trip (limit - init)/stride_con.  Since it's a
-    // CountedLoop this is exact (stride divides limit-init exactly).
-    // We are going to double the loop body, so we want to knock off any
-    // odd iteration: (trip_cnt & ~1).  Then back compute a new limit.
-    Node *span = new SubINode( limit, init );
-    register_new_node( span, ctrl );
-    Node *trip = new DivINode( 0, span, stride );
-    register_new_node( trip, ctrl );
-    Node *mtwo = _igvn.intcon(-2);
-    set_ctrl(mtwo, C->root());
-    Node *rond = new AndINode( trip, mtwo );
-    register_new_node( rond, ctrl );
-    Node *spn2 = new MulINode( rond, stride );
-    register_new_node( spn2, ctrl );
-    new_limit = new AddINode( spn2, init );
-    register_new_node( new_limit, ctrl );
-
-    // Hammer in the new limit
-    Node *ctrl2 = loop_end->in(0);
-    Node *cmp2 = new CmpINode( loop_head->incr(), new_limit );
-    register_new_node( cmp2, ctrl2 );
-    Node *bol2 = new BoolNode( cmp2, loop_end->test_trip() );
-    register_new_node( bol2, ctrl2 );
-    _igvn.replace_input_of(loop_end, CountedLoopEndNode::TestValue, bol2);
-
-    // Step 3: Find the min-trip test guaranteed before a 'main' loop.
-    // Make it a 1-trip test (means at least 2 trips).
-    if( adjust_min_trip ) {
-      assert( new_limit != NULL, "" );
-      // Guard test uses an 'opaque' node which is not shared.  Hence I
-      // can edit it's inputs directly.  Hammer in the new limit for the
-      // minimum-trip guard.
-      assert( opaq->outcnt() == 1, "" );
-      _igvn.hash_delete(opaq);
-      opaq->set_req(1, new_limit);
-    }
-  } // LoopLimitCheck
-
   // ---------
   // Step 4: Clone the loop body.  Move it inside the loop.  This loop body
   // represents the odd iterations; since the loop trips an even number of
@@ -1904,7 +1851,6 @@ void PhaseIdealLoop::add_constraint( int stride_con, int scale_con, Node *offset
     //   )
 
     if (low_limit->get_int() == -max_jint) {
-      if (!RangeLimitCheck) return;
       // We need this guard when scale*pre_limit+offset >= limit
       // due to underflow. So we need execute pre-loop until
       // scale*I+offset >= min_int. But (min_int-offset) will
@@ -1956,7 +1902,6 @@ void PhaseIdealLoop::add_constraint( int stride_con, int scale_con, Node *offset
     *pre_limit = adjust_limit((-stride_con), scale, plus_one, upper_limit, *pre_limit, pre_ctrl);
 
     if (low_limit->get_int() == -max_jint) {
-      if (!RangeLimitCheck) return;
       // We need this guard when scale*main_limit+offset >= limit
       // due to underflow. So we need execute main-loop while
       // scale*I+offset+1 > min_int. But (min_int-offset-1) will
@@ -2258,7 +2203,7 @@ void PhaseIdealLoop::do_range_check( IdealLoopTree *loop, Node_List &old_new ) {
           add_constraint( stride_con, scale_con, offset, zero, limit, pre_ctrl, &pre_limit, &main_limit );
           if (!conditional_rc) {
             // (0-offset)/scale could be outside of loop iterations range.
-            conditional_rc = !loop->dominates_backedge(iff) || RangeLimitCheck;
+            conditional_rc = !loop->dominates_backedge(iff);
           }
         } else {
           if (PrintOpto) {
@@ -2294,7 +2239,7 @@ void PhaseIdealLoop::do_range_check( IdealLoopTree *loop, Node_List &old_new ) {
             // ((MIN_INT+1)-offset)/scale could be outside of loop iterations range.
             // Note: negative offset is replaced with 0 but (MIN_INT+1)/scale could
             // still be outside of loop range.
-            conditional_rc = !loop->dominates_backedge(iff) || RangeLimitCheck;
+            conditional_rc = !loop->dominates_backedge(iff);
           }
           break;
         default:
@@ -2340,26 +2285,6 @@ void PhaseIdealLoop::do_range_check( IdealLoopTree *loop, Node_List &old_new ) {
   // Note:: we are making the main loop limit no longer precise;
   // need to round up based on stride.
   cl->set_nonexact_trip_count();
-  if (!LoopLimitCheck && stride_con != 1 && stride_con != -1) { // Cutout for common case
-    // "Standard" round-up logic:  ([main_limit-init+(y-1)]/y)*y+init
-    // Hopefully, compiler will optimize for powers of 2.
-    Node *ctrl = get_ctrl(main_limit);
-    Node *stride = cl->stride();
-    Node *init = cl->init_trip()->uncast();
-    Node *span = new SubINode(main_limit,init);
-    register_new_node(span,ctrl);
-    Node *rndup = _igvn.intcon(stride_con + ((stride_con>0)?-1:1));
-    Node *add = new AddINode(span,rndup);
-    register_new_node(add,ctrl);
-    Node *div = new DivINode(0,add,stride);
-    register_new_node(div,ctrl);
-    Node *mul = new MulINode(div,stride);
-    register_new_node(mul,ctrl);
-    Node *newlim = new AddINode(mul,init);
-    register_new_node(newlim,ctrl);
-    main_limit = newlim;
-  }
-
   Node *main_cle = cl->loopexit();
   Node *main_bol = main_cle->in(1);
   // Hacking loop bounds; need private copies of exit test

hotspot/src/share/vm/opto/loopUnswitch.cpp

@@ -138,7 +138,7 @@ void PhaseIdealLoop::do_unswitching (IdealLoopTree *loop, Node_List &old_new) {
   Node* uniqc = proj_true->unique_ctrl_out();
   Node* entry = head->in(LoopNode::EntryControl);
   Node* predicate = find_predicate(entry);
-  if (predicate != NULL && LoopLimitCheck && UseLoopPredicate) {
+  if (predicate != NULL && UseLoopPredicate) {
     // We may have two predicates, find first.
     entry = find_predicate(entry->in(0)->in(0));
     if (entry != NULL) predicate = entry;

hotspot/src/share/vm/opto/loopnode.cpp

@@ -463,8 +463,6 @@ bool PhaseIdealLoop::is_counted_loop( Node *x, IdealLoopTree *loop ) {
 
   Node *hook = new Node(6);
 
-  if (LoopLimitCheck) {
-
   // ===================================================
   // Generate loop limit check to avoid integer overflow
   // in cases like next (cyclic loops):
@@ -593,103 +591,6 @@ bool PhaseIdealLoop::is_counted_loop( Node *x, IdealLoopTree *loop ) {
   }
   set_subtree_ctrl( limit );
 
-  } else { // LoopLimitCheck
-
-  // If compare points to incr, we are ok.  Otherwise the compare
-  // can directly point to the phi; in this case adjust the compare so that
-  // it points to the incr by adjusting the limit.
-  if (cmp->in(1) == phi || cmp->in(2) == phi)
-    limit = gvn->transform(new AddINode(limit,stride));
-
-  // trip-count for +-tive stride should be: (limit - init_trip + stride - 1)/stride.
-  // Final value for iterator should be: trip_count * stride + init_trip.
-  Node *one_p = gvn->intcon( 1);
-  Node *one_m = gvn->intcon(-1);
-
-  Node *trip_count = NULL;
-  switch( bt ) {
-  case BoolTest::eq:
-    ShouldNotReachHere();
-  case BoolTest::ne:            // Ahh, the case we desire
-    if (stride_con == 1)
-      trip_count = gvn->transform(new SubINode(limit,init_trip));
-    else if (stride_con == -1)
-      trip_count = gvn->transform(new SubINode(init_trip,limit));
-    else
-      ShouldNotReachHere();
-    set_subtree_ctrl(trip_count);
-    //_loop.map(trip_count->_idx,loop(limit));
-    break;
-  case BoolTest::le:            // Maybe convert to '<' case
-    limit = gvn->transform(new AddINode(limit,one_p));
-    set_subtree_ctrl( limit );
-    hook->init_req(4, limit);
-
-    bt = BoolTest::lt;
-    // Make the new limit be in the same loop nest as the old limit
-    //_loop.map(limit->_idx,limit_loop);
-    // Fall into next case
-  case BoolTest::lt: {          // Maybe convert to '!=' case
-    if (stride_con < 0) // Count down loop rolls through MAXINT
-      ShouldNotReachHere();
-    Node *range = gvn->transform(new SubINode(limit,init_trip));
-    set_subtree_ctrl( range );
-    hook->init_req(0, range);
-
-    Node *bias  = gvn->transform(new AddINode(range,stride));
-    set_subtree_ctrl( bias );
-    hook->init_req(1, bias);
-
-    Node *bias1 = gvn->transform(new AddINode(bias,one_m));
-    set_subtree_ctrl( bias1 );
-    hook->init_req(2, bias1);
-
-    trip_count  = gvn->transform(new DivINode(0,bias1,stride));
-    set_subtree_ctrl( trip_count );
-    hook->init_req(3, trip_count);
-    break;
-  }
-
-  case BoolTest::ge:            // Maybe convert to '>' case
-    limit = gvn->transform(new AddINode(limit,one_m));
-    set_subtree_ctrl( limit );
-    hook->init_req(4 ,limit);
-
-    bt = BoolTest::gt;
-    // Make the new limit be in the same loop nest as the old limit
-    //_loop.map(limit->_idx,limit_loop);
-    // Fall into next case
-  case BoolTest::gt: {          // Maybe convert to '!=' case
-    if (stride_con > 0) // count up loop rolls through MININT
-      ShouldNotReachHere();
-    Node *range = gvn->transform(new SubINode(limit,init_trip));
-    set_subtree_ctrl( range );
-    hook->init_req(0, range);
-
-    Node *bias  = gvn->transform(new AddINode(range,stride));
-    set_subtree_ctrl( bias );
-    hook->init_req(1, bias);
-
-    Node *bias1 = gvn->transform(new AddINode(bias,one_p));
-    set_subtree_ctrl( bias1 );
-    hook->init_req(2, bias1);
-
-    trip_count  = gvn->transform(new DivINode(0,bias1,stride));
-    set_subtree_ctrl( trip_count );
-    hook->init_req(3, trip_count);
-    break;
-  }
-  } // switch( bt )
-
-  Node *span = gvn->transform(new MulINode(trip_count,stride));
-  set_subtree_ctrl( span );
-  hook->init_req(5, span);
-
-  limit = gvn->transform(new AddINode(span,init_trip));
-  set_subtree_ctrl( limit );
-
-  } // LoopLimitCheck
-
   if (!UseCountedLoopSafepoints) {
     // Check for SafePoint on backedge and remove
     Node *sfpt = x->in(LoopNode::LoopBackControl);
@@ -829,7 +730,7 @@ Node* PhaseIdealLoop::exact_limit( IdealLoopTree *loop ) {
   CountedLoopNode *cl = loop->_head->as_CountedLoop();
   assert(cl->is_valid_counted_loop(), "");
 
-  if (!LoopLimitCheck || ABS(cl->stride_con()) == 1 ||
+  if (ABS(cl->stride_con()) == 1 ||
       cl->limit()->Opcode() == Op_LoopLimit) {
     // Old code has exact limit (it could be incorrect in case of int overflow).
     // Loop limit is exact with stride == 1. And loop may already have exact limit.
@@ -1897,13 +1798,11 @@ void IdealLoopTree::dump_head( ) const {
   tty->print("Loop: N%d/N%d ",_head->_idx,_tail->_idx);
   if (_irreducible) tty->print(" IRREDUCIBLE");
   Node* entry = _head->in(LoopNode::EntryControl);
-  if (LoopLimitCheck) {
   Node* predicate = PhaseIdealLoop::find_predicate_insertion_point(entry, Deoptimization::Reason_loop_limit_check);
   if (predicate != NULL ) {
     tty->print(" limit_check");
     entry = entry->in(0)->in(0);
   }
-  }
   if (UseLoopPredicate) {
     entry = PhaseIdealLoop::find_predicate_insertion_point(entry, Deoptimization::Reason_predicate);
     if (entry != NULL) {
@@ -2322,7 +2221,7 @@ void PhaseIdealLoop::build_and_optimize(bool do_split_ifs, bool skip_loop_opts)
   // Some parser-inserted loop predicates could never be used by loop
   // predication or they were moved away from loop during some optimizations.
   // For example, peeling. Eliminate them before next loop optimizations.
-  if (UseLoopPredicate || LoopLimitCheck) {
+  if (UseLoopPredicate) {
     eliminate_useless_predicates();
   }
 

hotspot/src/share/vm/opto/parse1.cpp

@@ -661,8 +661,7 @@ void Parse::do_all_blocks() {
         // (Note that dead locals do not get phis built, ever.)
         ensure_phis_everywhere();
 
-        if (block->is_SEL_head() &&
+        if (block->is_SEL_head() && UseLoopPredicate) {
-            (UseLoopPredicate || LoopLimitCheck)) {
           // Add predicate to single entry (not irreducible) loop head.
           assert(!block->has_merged_backedge(), "only entry paths should be merged for now");
           // Need correct bci for predicate.

hotspot/test/compiler/loopopts/TestCastIINoLoopLimitCheck.java

@@ -26,10 +26,19 @@
  * @test
  * @bug 8073184
  * @summary CastII that guards counted loops confuses range check elimination with LoopLimitCheck off
- * @run main/othervm -XX:+IgnoreUnrecognizedVMOptions -XX:+UnlockDiagnosticVMOptions -XX:-LoopLimitCheck -XX:CompileOnly=TestCastIINoLoopLimitCheck.m -Xcomp  TestCastIINoLoopLimitCheck
+ * @run main/othervm -XX:+IgnoreUnrecognizedVMOptions -XX:CompileOnly=TestCastIINoLoopLimitCheck.m -Xcomp  TestCastIINoLoopLimitCheck
  *
  */
 
+/*
+ * The test was originally run with
+ *
+ * -XX:+UnlockDiagnosticVMOptions -XX:-LoopLimitCheck
+ *
+ * to trigger a problem with code guarded with !LoopLimitCheck.
+ * JDK-8072422 has removed that code but kept the test because the
+ * test generates an interesting graph shape.
+ */
 public class TestCastIINoLoopLimitCheck {
 
     static void m(int i, int index, char[] buf) {