jdk8-mips64-public/hotspot: src/share/vm/opto/loopTransform.cpp@98cb887364d3 (annotated)

src/share/vm/opto/loopTransform.cpp@98cb887364d3 (annotated)

src/share/vm/opto/loopTransform.cpp

Fri, 27 Feb 2009 13:27:09 -0800

author: twisti
date: Fri, 27 Feb 2009 13:27:09 -0800
changeset 1040: 98cb887364d3
parent 855: a1980da045cc
child 1224: 273b2358ef1a
permissions: -rw-r--r--

6810672: Comment typos
Summary: I have collected some typos I have found while looking at the code.
Reviewed-by: kvn, never

 /*
  * Copyright 2000-2008 Sun Microsystems, Inc.  All Rights Reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.
  *
  * This code is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  * version 2 for more details (a copy is included in the LICENSE file that
  * accompanied this code).
  *
  * You should have received a copy of the GNU General Public License version
  * 2 along with this work; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  *
  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
  * CA 95054 USA or visit www.sun.com if you need additional information or
  * have any questions.
  *
  */
 #include "incls/_precompiled.incl"
 #include "incls/_loopTransform.cpp.incl"
 //------------------------------is_loop_exit-----------------------------------
 // Given an IfNode, return the loop-exiting projection or NULL if both
 // arms remain in the loop.
 Node *IdealLoopTree::is_loop_exit(Node *iff) const {
   if( iff->outcnt() != 2 ) return NULL; // Ignore partially dead tests
   PhaseIdealLoop *phase = _phase;
   // Test is an IfNode, has 2 projections.  If BOTH are in the loop
   // we need loop unswitching instead of peeling.
   if( !is_member(phase->get_loop( iff->raw_out(0) )) )
     return iff->raw_out(0);
   if( !is_member(phase->get_loop( iff->raw_out(1) )) )
     return iff->raw_out(1);
   return NULL;
 }
 //=============================================================================
 //------------------------------record_for_igvn----------------------------
 // Put loop body on igvn work list
 void IdealLoopTree::record_for_igvn() {
   for( uint i = 0; i < _body.size(); i++ ) {
     Node *n = _body.at(i);
     _phase->_igvn._worklist.push(n);
   }
 }
 //------------------------------compute_profile_trip_cnt----------------------------
 // Compute loop trip count from profile data as
 //    (backedge_count + loop_exit_count) / loop_exit_count
 void IdealLoopTree::compute_profile_trip_cnt( PhaseIdealLoop *phase ) {
   if (!_head->is_CountedLoop()) {
     return;
   }
   CountedLoopNode* head = _head->as_CountedLoop();
   if (head->profile_trip_cnt() != COUNT_UNKNOWN) {
     return; // Already computed
   }
   float trip_cnt = (float)max_jint; // default is big
   Node* back = head->in(LoopNode::LoopBackControl);
   while (back != head) {
     if ((back->Opcode() == Op_IfTrue || back->Opcode() == Op_IfFalse) &&
         back->in(0) &&
         back->in(0)->is_If() &&
         back->in(0)->as_If()->_fcnt != COUNT_UNKNOWN &&
         back->in(0)->as_If()->_prob != PROB_UNKNOWN) {
       break;
     }
     back = phase->idom(back);
   }
   if (back != head) {
     assert((back->Opcode() == Op_IfTrue || back->Opcode() == Op_IfFalse) &&
            back->in(0), "if-projection exists");
     IfNode* back_if = back->in(0)->as_If();
     float loop_back_cnt = back_if->_fcnt * back_if->_prob;
     // Now compute a loop exit count
     float loop_exit_cnt = 0.0f;
     for( uint i = 0; i < _body.size(); i++ ) {
       Node *n = _body[i];
       if( n->is_If() ) {
         IfNode *iff = n->as_If();
         if( iff->_fcnt != COUNT_UNKNOWN && iff->_prob != PROB_UNKNOWN ) {
           Node *exit = is_loop_exit(iff);
           if( exit ) {
             float exit_prob = iff->_prob;
             if (exit->Opcode() == Op_IfFalse) exit_prob = 1.0 - exit_prob;
             if (exit_prob > PROB_MIN) {
               float exit_cnt = iff->_fcnt * exit_prob;
               loop_exit_cnt += exit_cnt;
             }
           }
         }
       }
     }
     if (loop_exit_cnt > 0.0f) {
       trip_cnt = (loop_back_cnt + loop_exit_cnt) / loop_exit_cnt;
     } else {
       // No exit count so use
       trip_cnt = loop_back_cnt;
     }
   }
 #ifndef PRODUCT
   if (TraceProfileTripCount) {
     tty->print_cr("compute_profile_trip_cnt  lp: %d cnt: %f\n", head->_idx, trip_cnt);
   }
 #endif
   head->set_profile_trip_cnt(trip_cnt);
 }
 //---------------------is_invariant_addition-----------------------------
 // Return nonzero index of invariant operand for an Add or Sub
 // of (nonconstant) invariant and variant values. Helper for reassociate_invariants.
 int IdealLoopTree::is_invariant_addition(Node* n, PhaseIdealLoop *phase) {
   int op = n->Opcode();
   if (op == Op_AddI || op == Op_SubI) {
     bool in1_invar = this->is_invariant(n->in(1));
     bool in2_invar = this->is_invariant(n->in(2));
     if (in1_invar && !in2_invar) return 1;
     if (!in1_invar && in2_invar) return 2;
   }
   return 0;
 }
 //---------------------reassociate_add_sub-----------------------------
 // Reassociate invariant add and subtract expressions:
 //
 // inv1 + (x + inv2)  =>  ( inv1 + inv2) + x
 // (x + inv2) + inv1  =>  ( inv1 + inv2) + x
 // inv1 + (x - inv2)  =>  ( inv1 - inv2) + x
 // inv1 - (inv2 - x)  =>  ( inv1 - inv2) + x
 // (x + inv2) - inv1  =>  (-inv1 + inv2) + x
 // (x - inv2) + inv1  =>  ( inv1 - inv2) + x
 // (x - inv2) - inv1  =>  (-inv1 - inv2) + x
 // inv1 + (inv2 - x)  =>  ( inv1 + inv2) - x
 // inv1 - (x - inv2)  =>  ( inv1 + inv2) - x
 // (inv2 - x) + inv1  =>  ( inv1 + inv2) - x
 // (inv2 - x) - inv1  =>  (-inv1 + inv2) - x
 // inv1 - (x + inv2)  =>  ( inv1 - inv2) - x
 //
 Node* IdealLoopTree::reassociate_add_sub(Node* n1, PhaseIdealLoop *phase) {
   if (!n1->is_Add() && !n1->is_Sub() || n1->outcnt() == 0) return NULL;
   if (is_invariant(n1)) return NULL;
   int inv1_idx = is_invariant_addition(n1, phase);
   if (!inv1_idx) return NULL;
   // Don't mess with add of constant (igvn moves them to expression tree root.)
   if (n1->is_Add() && n1->in(2)->is_Con()) return NULL;
   Node* inv1 = n1->in(inv1_idx);
   Node* n2 = n1->in(3 - inv1_idx);
   int inv2_idx = is_invariant_addition(n2, phase);
   if (!inv2_idx) return NULL;
   Node* x    = n2->in(3 - inv2_idx);
   Node* inv2 = n2->in(inv2_idx);
   bool neg_x    = n2->is_Sub() && inv2_idx == 1;
   bool neg_inv2 = n2->is_Sub() && inv2_idx == 2;
   bool neg_inv1 = n1->is_Sub() && inv1_idx == 2;
   if (n1->is_Sub() && inv1_idx == 1) {
     neg_x    = !neg_x;
     neg_inv2 = !neg_inv2;
   }
   Node* inv1_c = phase->get_ctrl(inv1);
   Node* inv2_c = phase->get_ctrl(inv2);
   Node* n_inv1;
   if (neg_inv1) {
     Node *zero = phase->_igvn.intcon(0);
     phase->set_ctrl(zero, phase->C->root());
     n_inv1 = new (phase->C, 3) SubINode(zero, inv1);
     phase->register_new_node(n_inv1, inv1_c);
   } else {
     n_inv1 = inv1;
   }
   Node* inv;
   if (neg_inv2) {
     inv = new (phase->C, 3) SubINode(n_inv1, inv2);
   } else {
     inv = new (phase->C, 3) AddINode(n_inv1, inv2);
   }
   phase->register_new_node(inv, phase->get_early_ctrl(inv));
   Node* addx;
   if (neg_x) {
     addx = new (phase->C, 3) SubINode(inv, x);
   } else {
     addx = new (phase->C, 3) AddINode(x, inv);
   }
   phase->register_new_node(addx, phase->get_ctrl(x));
   phase->_igvn.hash_delete(n1);
   phase->_igvn.subsume_node(n1, addx);
   return addx;
 }
 //---------------------reassociate_invariants-----------------------------
 // Reassociate invariant expressions:
 void IdealLoopTree::reassociate_invariants(PhaseIdealLoop *phase) {
   for (int i = _body.size() - 1; i >= 0; i--) {
     Node *n = _body.at(i);
     for (int j = 0; j < 5; j++) {
       Node* nn = reassociate_add_sub(n, phase);
       if (nn == NULL) break;
       n = nn; // again
     };
   }
 }
 //------------------------------policy_peeling---------------------------------
 // Return TRUE or FALSE if the loop should be peeled or not.  Peel if we can
 // make some loop-invariant test (usually a null-check) happen before the loop.
 bool IdealLoopTree::policy_peeling( PhaseIdealLoop *phase ) const {
   Node *test = ((IdealLoopTree*)this)->tail();
   int  body_size = ((IdealLoopTree*)this)->_body.size();
   int  uniq      = phase->C->unique();
   // Peeling does loop cloning which can result in O(N^2) node construction
   if( body_size > 255 /* Prevent overflow for large body_size */
       || (body_size * body_size + uniq > MaxNodeLimit) ) {
     return false;           // too large to safely clone
   }
   while( test != _head ) {      // Scan till run off top of loop
     if( test->is_If() ) {       // Test?
       Node *ctrl = phase->get_ctrl(test->in(1));
       if (ctrl->is_top())
         return false;           // Found dead test on live IF?  No peeling!
       // Standard IF only has one input value to check for loop invariance
       assert( test->Opcode() == Op_If || test->Opcode() == Op_CountedLoopEnd, "Check this code when new subtype is added");
       // Condition is not a member of this loop?
       if( !is_member(phase->get_loop(ctrl)) &&
           is_loop_exit(test) )
         return true;            // Found reason to peel!
     }
     // Walk up dominators to loop _head looking for test which is
     // executed on every path thru loop.
     test = phase->idom(test);
   }
   return false;
 }
 //------------------------------peeled_dom_test_elim---------------------------
 // If we got the effect of peeling, either by actually peeling or by making
 // a pre-loop which must execute at least once, we can remove all
 // loop-invariant dominated tests in the main body.
 void PhaseIdealLoop::peeled_dom_test_elim( IdealLoopTree *loop, Node_List &old_new ) {
   bool progress = true;
   while( progress ) {
     progress = false;           // Reset for next iteration
     Node *prev = loop->_head->in(LoopNode::LoopBackControl);//loop->tail();
     Node *test = prev->in(0);
     while( test != loop->_head ) { // Scan till run off top of loop
       int p_op = prev->Opcode();
       if( (p_op == Op_IfFalse || p_op == Op_IfTrue) &&
           test->is_If() &&      // Test?
           !test->in(1)->is_Con() && // And not already obvious?
           // Condition is not a member of this loop?
           !loop->is_member(get_loop(get_ctrl(test->in(1))))){
         // Walk loop body looking for instances of this test
         for( uint i = 0; i < loop->_body.size(); i++ ) {
           Node *n = loop->_body.at(i);
           if( n->is_If() && n->in(1) == test->in(1) /*&& n != loop->tail()->in(0)*/ ) {
             // IfNode was dominated by version in peeled loop body
             progress = true;
             dominated_by( old_new[prev->_idx], n );
           }
         }
       }
       prev = test;
       test = idom(test);
     } // End of scan tests in loop
   } // End of while( progress )
 }
 //------------------------------do_peeling-------------------------------------
 // Peel the first iteration of the given loop.
 // Step 1: Clone the loop body.  The clone becomes the peeled iteration.
 //         The pre-loop illegally has 2 control users (old & new loops).
 // Step 2: Make the old-loop fall-in edges point to the peeled iteration.
 //         Do this by making the old-loop fall-in edges act as if they came
 //         around the loopback from the prior iteration (follow the old-loop
 //         backedges) and then map to the new peeled iteration.  This leaves
 //         the pre-loop with only 1 user (the new peeled iteration), but the
 //         peeled-loop backedge has 2 users.
 // Step 3: Cut the backedge on the clone (so its not a loop) and remove the
 //         extra backedge user.
 void PhaseIdealLoop::do_peeling( IdealLoopTree *loop, Node_List &old_new ) {
   C->set_major_progress();
   // Peeling a 'main' loop in a pre/main/post situation obfuscates the
   // 'pre' loop from the main and the 'pre' can no longer have it's
   // iterations adjusted.  Therefore, we need to declare this loop as
   // no longer a 'main' loop; it will need new pre and post loops before
   // we can do further RCE.
   Node *h = loop->_head;
   if( h->is_CountedLoop() ) {
     CountedLoopNode *cl = h->as_CountedLoop();
     assert(cl->trip_count() > 0, "peeling a fully unrolled loop");
     cl->set_trip_count(cl->trip_count() - 1);
     if( cl->is_main_loop() ) {
       cl->set_normal_loop();
 #ifndef PRODUCT
       if( PrintOpto && VerifyLoopOptimizations ) {
         tty->print("Peeling a 'main' loop; resetting to 'normal' ");
         loop->dump_head();
       }
 #endif
     }
   }
   // Step 1: Clone the loop body.  The clone becomes the peeled iteration.
   //         The pre-loop illegally has 2 control users (old & new loops).
   clone_loop( loop, old_new, dom_depth(loop->_head) );
   // Step 2: Make the old-loop fall-in edges point to the peeled iteration.
   //         Do this by making the old-loop fall-in edges act as if they came
   //         around the loopback from the prior iteration (follow the old-loop
   //         backedges) and then map to the new peeled iteration.  This leaves
   //         the pre-loop with only 1 user (the new peeled iteration), but the
   //         peeled-loop backedge has 2 users.
   for (DUIterator_Fast jmax, j = loop->_head->fast_outs(jmax); j < jmax; j++) {
     Node* old = loop->_head->fast_out(j);
     if( old->in(0) == loop->_head && old->req() == 3 &&
         (old->is_Loop() || old->is_Phi()) ) {
       Node *new_exit_value = old_new[old->in(LoopNode::LoopBackControl)->_idx];
       if( !new_exit_value )     // Backedge value is ALSO loop invariant?
         // Then loop body backedge value remains the same.
         new_exit_value = old->in(LoopNode::LoopBackControl);
       _igvn.hash_delete(old);
       old->set_req(LoopNode::EntryControl, new_exit_value);
     }
   }
   // Step 3: Cut the backedge on the clone (so its not a loop) and remove the
   //         extra backedge user.
   Node *nnn = old_new[loop->_head->_idx];
   _igvn.hash_delete(nnn);
   nnn->set_req(LoopNode::LoopBackControl, C->top());
   for (DUIterator_Fast j2max, j2 = nnn->fast_outs(j2max); j2 < j2max; j2++) {
     Node* use = nnn->fast_out(j2);
     if( use->in(0) == nnn && use->req() == 3 && use->is_Phi() ) {
       _igvn.hash_delete(use);
       use->set_req(LoopNode::LoopBackControl, C->top());
     }
   }
   // Step 4: Correct dom-depth info.  Set to loop-head depth.
   int dd = dom_depth(loop->_head);
   set_idom(loop->_head, loop->_head->in(1), dd);
   for (uint j3 = 0; j3 < loop->_body.size(); j3++) {
     Node *old = loop->_body.at(j3);
     Node *nnn = old_new[old->_idx];
     if (!has_ctrl(nnn))
       set_idom(nnn, idom(nnn), dd-1);
     // While we're at it, remove any SafePoints from the peeled code
     if( old->Opcode() == Op_SafePoint ) {
       Node *nnn = old_new[old->_idx];
       lazy_replace(nnn,nnn->in(TypeFunc::Control));
     }
   }
   // Now force out all loop-invariant dominating tests.  The optimizer
   // finds some, but we _know_ they are all useless.
   peeled_dom_test_elim(loop,old_new);
   loop->record_for_igvn();
 }
 //------------------------------policy_maximally_unroll------------------------
 // Return exact loop trip count, or 0 if not maximally unrolling
 bool IdealLoopTree::policy_maximally_unroll( PhaseIdealLoop *phase ) const {
   CountedLoopNode *cl = _head->as_CountedLoop();
   assert( cl->is_normal_loop(), "" );
   Node *init_n = cl->init_trip();
   Node *limit_n = cl->limit();
   // Non-constant bounds
   if( init_n   == NULL || !init_n->is_Con()  ||
       limit_n  == NULL || !limit_n->is_Con() ||
       // protect against stride not being a constant
       !cl->stride_is_con() ) {
     return false;
   }
   int init   = init_n->get_int();
   int limit  = limit_n->get_int();
   int span   = limit - init;
   int stride = cl->stride_con();
   if (init >= limit || stride > span) {
     // return a false (no maximally unroll) and the regular unroll/peel
     // route will make a small mess which CCP will fold away.
     return false;
   }
   uint trip_count = span/stride;   // trip_count can be greater than 2 Gig.
   assert( (int)trip_count*stride == span, "must divide evenly" );
   // Real policy: if we maximally unroll, does it get too big?
   // Allow the unrolled mess to get larger than standard loop
   // size.  After all, it will no longer be a loop.
   uint body_size    = _body.size();
   uint unroll_limit = (uint)LoopUnrollLimit * 4;
   assert( (intx)unroll_limit == LoopUnrollLimit * 4, "LoopUnrollLimit must fit in 32bits");
   cl->set_trip_count(trip_count);
   if( trip_count <= unroll_limit && body_size <= unroll_limit ) {
     uint new_body_size = body_size * trip_count;
     if (new_body_size <= unroll_limit &&
         body_size == new_body_size / trip_count &&
         // Unrolling can result in a large amount of node construction
         new_body_size < MaxNodeLimit - phase->C->unique()) {
       return true;    // maximally unroll
     }
   }
   return false;               // Do not maximally unroll
 }
 //------------------------------policy_unroll----------------------------------
 // Return TRUE or FALSE if the loop should be unrolled or not.  Unroll if
 // the loop is a CountedLoop and the body is small enough.
 bool IdealLoopTree::policy_unroll( PhaseIdealLoop *phase ) const {
   CountedLoopNode *cl = _head->as_CountedLoop();
   assert( cl->is_normal_loop() || cl->is_main_loop(), "" );
   // protect against stride not being a constant
   if( !cl->stride_is_con() ) return false;
   // protect against over-unrolling
   if( cl->trip_count() <= 1 ) return false;
   int future_unroll_ct = cl->unrolled_count() * 2;
   // Don't unroll if the next round of unrolling would push us
   // over the expected trip count of the loop.  One is subtracted
   // from the expected trip count because the pre-loop normally
   // executes 1 iteration.
   if (UnrollLimitForProfileCheck > 0 &&
       cl->profile_trip_cnt() != COUNT_UNKNOWN &&
       future_unroll_ct        > UnrollLimitForProfileCheck &&
       (float)future_unroll_ct > cl->profile_trip_cnt() - 1.0) {
     return false;
   }
   // When unroll count is greater than LoopUnrollMin, don't unroll if:
   //   the residual iterations are more than 10% of the trip count
   //   and rounds of "unroll,optimize" are not making significant progress
   //   Progress defined as current size less than 20% larger than previous size.
   if (UseSuperWord && cl->node_count_before_unroll() > 0 &&
       future_unroll_ct > LoopUnrollMin &&
       (future_unroll_ct - 1) * 10.0 > cl->profile_trip_cnt() &&
 .2 * cl->node_count_before_unroll() < (double)_body.size()) {
     return false;
   }
   Node *init_n = cl->init_trip();
   Node *limit_n = cl->limit();
   // Non-constant bounds.
   // Protect against over-unrolling when init or/and limit are not constant
   // (so that trip_count's init value is maxint) but iv range is known.
   if( init_n   == NULL || !init_n->is_Con()  ||
       limit_n  == NULL || !limit_n->is_Con() ) {
     Node* phi = cl->phi();
     if( phi != NULL ) {
       assert(phi->is_Phi() && phi->in(0) == _head, "Counted loop should have iv phi.");
       const TypeInt* iv_type = phase->_igvn.type(phi)->is_int();
       int next_stride = cl->stride_con() * 2; // stride after this unroll
       if( next_stride > 0 ) {
         if( iv_type->_lo + next_stride <= iv_type->_lo || // overflow
             iv_type->_lo + next_stride >  iv_type->_hi ) {
           return false;  // over-unrolling
         }
       } else if( next_stride < 0 ) {
         if( iv_type->_hi + next_stride >= iv_type->_hi || // overflow
             iv_type->_hi + next_stride <  iv_type->_lo ) {
           return false;  // over-unrolling
         }
       }
     }
   }
   // Adjust body_size to determine if we unroll or not
   uint body_size = _body.size();
   // Key test to unroll CaffeineMark's Logic test
   int xors_in_loop = 0;
   // Also count ModL, DivL and MulL which expand mightly
   for( uint k = 0; k < _body.size(); k++ ) {
     switch( _body.at(k)->Opcode() ) {
     case Op_XorI: xors_in_loop++; break; // CaffeineMark's Logic test
     case Op_ModL: body_size += 30; break;
     case Op_DivL: body_size += 30; break;
     case Op_MulL: body_size += 10; break;
     }
   }
   // Check for being too big
   if( body_size > (uint)LoopUnrollLimit ) {
     if( xors_in_loop >= 4 && body_size < (uint)LoopUnrollLimit*4) return true;
     // Normal case: loop too big
     return false;
   }
   // Check for stride being a small enough constant
   if( abs(cl->stride_con()) > (1<<3) ) return false;
   // Unroll once!  (Each trip will soon do double iterations)
   return true;
 }
 //------------------------------policy_align-----------------------------------
 // Return TRUE or FALSE if the loop should be cache-line aligned.  Gather the
 // expression that does the alignment.  Note that only one array base can be
 // aligned in a loop (unless the VM guarantees mutual alignment).  Note that
 // if we vectorize short memory ops into longer memory ops, we may want to
 // increase alignment.
 bool IdealLoopTree::policy_align( PhaseIdealLoop *phase ) const {
   return false;
 }
 //------------------------------policy_range_check-----------------------------
 // Return TRUE or FALSE if the loop should be range-check-eliminated.
 // Actually we do iteration-splitting, a more powerful form of RCE.
 bool IdealLoopTree::policy_range_check( PhaseIdealLoop *phase ) const {
   if( !RangeCheckElimination ) return false;
   CountedLoopNode *cl = _head->as_CountedLoop();
   // If we unrolled with no intention of doing RCE and we later
   // changed our minds, we got no pre-loop.  Either we need to
   // make a new pre-loop, or we gotta disallow RCE.
   if( cl->is_main_no_pre_loop() ) return false; // Disallowed for now.
   Node *trip_counter = cl->phi();
   // Check loop body for tests of trip-counter plus loop-invariant vs
   // loop-invariant.
   for( uint i = 0; i < _body.size(); i++ ) {
     Node *iff = _body[i];
     if( iff->Opcode() == Op_If ) { // Test?
       // Comparing trip+off vs limit
       Node *bol = iff->in(1);
       if( bol->req() != 2 ) continue; // dead constant test
       Node *cmp = bol->in(1);
       Node *rc_exp = cmp->in(1);
       Node *limit = cmp->in(2);
       Node *limit_c = phase->get_ctrl(limit);
       if( limit_c == phase->C->top() )
         return false;           // Found dead test on live IF?  No RCE!
       if( is_member(phase->get_loop(limit_c) ) ) {
         // Compare might have operands swapped; commute them
         rc_exp = cmp->in(2);
         limit  = cmp->in(1);
         limit_c = phase->get_ctrl(limit);
         if( is_member(phase->get_loop(limit_c) ) )
           continue;             // Both inputs are loop varying; cannot RCE
       }
       if (!phase->is_scaled_iv_plus_offset(rc_exp, trip_counter, NULL, NULL)) {
         continue;
       }
       // Yeah!  Found a test like 'trip+off vs limit'
       // Test is an IfNode, has 2 projections.  If BOTH are in the loop
       // we need loop unswitching instead of iteration splitting.
       if( is_loop_exit(iff) )
         return true;            // Found reason to split iterations
     } // End of is IF
   }
   return false;
 }
 //------------------------------policy_peel_only-------------------------------
 // Return TRUE or FALSE if the loop should NEVER be RCE'd or aligned.  Useful
 // for unrolling loops with NO array accesses.
 bool IdealLoopTree::policy_peel_only( PhaseIdealLoop *phase ) const {
   for( uint i = 0; i < _body.size(); i++ )
     if( _body[i]->is_Mem() )
       return false;
   // No memory accesses at all!
   return true;
 }
 //------------------------------clone_up_backedge_goo--------------------------
 // If Node n lives in the back_ctrl block and cannot float, we clone a private
 // version of n in preheader_ctrl block and return that, otherwise return n.
 Node *PhaseIdealLoop::clone_up_backedge_goo( Node *back_ctrl, Node *preheader_ctrl, Node *n ) {
   if( get_ctrl(n) != back_ctrl ) return n;
   Node *x = NULL;               // If required, a clone of 'n'
   // Check for 'n' being pinned in the backedge.
   if( n->in(0) && n->in(0) == back_ctrl ) {
     x = n->clone();             // Clone a copy of 'n' to preheader
     x->set_req( 0, preheader_ctrl ); // Fix x's control input to preheader
   }
   // Recursive fixup any other input edges into x.
   // If there are no changes we can just return 'n', otherwise
   // we need to clone a private copy and change it.
   for( uint i = 1; i < n->req(); i++ ) {
     Node *g = clone_up_backedge_goo( back_ctrl, preheader_ctrl, n->in(i) );
     if( g != n->in(i) ) {
       if( !x )
         x = n->clone();
       x->set_req(i, g);
     }
   }
   if( x ) {                     // x can legally float to pre-header location
     register_new_node( x, preheader_ctrl );
     return x;
   } else {                      // raise n to cover LCA of uses
     set_ctrl( n, find_non_split_ctrl(back_ctrl->in(0)) );
   }
   return n;
 }
 //------------------------------insert_pre_post_loops--------------------------
 // Insert pre and post loops.  If peel_only is set, the pre-loop can not have
 // more iterations added.  It acts as a 'peel' only, no lower-bound RCE, no
 // alignment.  Useful to unroll loops that do no array accesses.
 void PhaseIdealLoop::insert_pre_post_loops( IdealLoopTree *loop, Node_List &old_new, bool peel_only ) {
   C->set_major_progress();
   // Find common pieces of the loop being guarded with pre & post loops
   CountedLoopNode *main_head = loop->_head->as_CountedLoop();
   assert( main_head->is_normal_loop(), "" );
   CountedLoopEndNode *main_end = main_head->loopexit();
   assert( main_end->outcnt() == 2, "1 true, 1 false path only" );
   uint dd_main_head = dom_depth(main_head);
   uint max = main_head->outcnt();
   Node *pre_header= main_head->in(LoopNode::EntryControl);
   Node *init      = main_head->init_trip();
   Node *incr      = main_end ->incr();
   Node *limit     = main_end ->limit();
   Node *stride    = main_end ->stride();
   Node *cmp       = main_end ->cmp_node();
   BoolTest::mask b_test = main_end->test_trip();
   // Need only 1 user of 'bol' because I will be hacking the loop bounds.
   Node *bol = main_end->in(CountedLoopEndNode::TestValue);
   if( bol->outcnt() != 1 ) {
     bol = bol->clone();
     register_new_node(bol,main_end->in(CountedLoopEndNode::TestControl));
     _igvn.hash_delete(main_end);
     main_end->set_req(CountedLoopEndNode::TestValue, bol);
   }
   // Need only 1 user of 'cmp' because I will be hacking the loop bounds.
   if( cmp->outcnt() != 1 ) {
     cmp = cmp->clone();
     register_new_node(cmp,main_end->in(CountedLoopEndNode::TestControl));
     _igvn.hash_delete(bol);
     bol->set_req(1, cmp);
   }
   //------------------------------
   // Step A: Create Post-Loop.
   Node* main_exit = main_end->proj_out(false);
   assert( main_exit->Opcode() == Op_IfFalse, "" );
   int dd_main_exit = dom_depth(main_exit);
   // Step A1: Clone the loop body.  The clone becomes the post-loop.  The main
   // loop pre-header illegally has 2 control users (old & new loops).
   clone_loop( loop, old_new, dd_main_exit );
   assert( old_new[main_end ->_idx]->Opcode() == Op_CountedLoopEnd, "" );
   CountedLoopNode *post_head = old_new[main_head->_idx]->as_CountedLoop();
   post_head->set_post_loop(main_head);
   // Reduce the post-loop trip count.
   CountedLoopEndNode* post_end = old_new[main_end ->_idx]->as_CountedLoopEnd();
   post_end->_prob = PROB_FAIR;
   // Build the main-loop normal exit.
   IfFalseNode *new_main_exit = new (C, 1) IfFalseNode(main_end);
   _igvn.register_new_node_with_optimizer( new_main_exit );
   set_idom(new_main_exit, main_end, dd_main_exit );
   set_loop(new_main_exit, loop->_parent);
   // Step A2: Build a zero-trip guard for the post-loop.  After leaving the
   // main-loop, the post-loop may not execute at all.  We 'opaque' the incr
   // (the main-loop trip-counter exit value) because we will be changing
   // the exit value (via unrolling) so we cannot constant-fold away the zero
   // trip guard until all unrolling is done.
   Node *zer_opaq = new (C, 2) Opaque1Node(C, incr);
   Node *zer_cmp  = new (C, 3) CmpINode( zer_opaq, limit );
   Node *zer_bol  = new (C, 2) BoolNode( zer_cmp, b_test );
   register_new_node( zer_opaq, new_main_exit );
   register_new_node( zer_cmp , new_main_exit );
   register_new_node( zer_bol , new_main_exit );
   // Build the IfNode
   IfNode *zer_iff = new (C, 2) IfNode( new_main_exit, zer_bol, PROB_FAIR, COUNT_UNKNOWN );
   _igvn.register_new_node_with_optimizer( zer_iff );
   set_idom(zer_iff, new_main_exit, dd_main_exit);
   set_loop(zer_iff, loop->_parent);
   // Plug in the false-path, taken if we need to skip post-loop
   _igvn.hash_delete( main_exit );
   main_exit->set_req(0, zer_iff);
   _igvn._worklist.push(main_exit);
   set_idom(main_exit, zer_iff, dd_main_exit);
   set_idom(main_exit->unique_out(), zer_iff, dd_main_exit);
   // Make the true-path, must enter the post loop
   Node *zer_taken = new (C, 1) IfTrueNode( zer_iff );
   _igvn.register_new_node_with_optimizer( zer_taken );
   set_idom(zer_taken, zer_iff, dd_main_exit);
   set_loop(zer_taken, loop->_parent);
   // Plug in the true path
   _igvn.hash_delete( post_head );
   post_head->set_req(LoopNode::EntryControl, zer_taken);
   set_idom(post_head, zer_taken, dd_main_exit);
   // Step A3: Make the fall-in values to the post-loop come from the
   // fall-out values of the main-loop.
   for (DUIterator_Fast imax, i = main_head->fast_outs(imax); i < imax; i++) {
     Node* main_phi = main_head->fast_out(i);
     if( main_phi->is_Phi() && main_phi->in(0) == main_head && main_phi->outcnt() >0 ) {
       Node *post_phi = old_new[main_phi->_idx];
       Node *fallmain  = clone_up_backedge_goo(main_head->back_control(),
                                               post_head->init_control(),
                                               main_phi->in(LoopNode::LoopBackControl));
       _igvn.hash_delete(post_phi);
       post_phi->set_req( LoopNode::EntryControl, fallmain );
     }
   }
   // Update local caches for next stanza
   main_exit = new_main_exit;
   //------------------------------
   // Step B: Create Pre-Loop.
   // Step B1: Clone the loop body.  The clone becomes the pre-loop.  The main
   // loop pre-header illegally has 2 control users (old & new loops).
   clone_loop( loop, old_new, dd_main_head );
   CountedLoopNode*    pre_head = old_new[main_head->_idx]->as_CountedLoop();
   CountedLoopEndNode* pre_end  = old_new[main_end ->_idx]->as_CountedLoopEnd();
   pre_head->set_pre_loop(main_head);
   Node *pre_incr = old_new[incr->_idx];
   // Reduce the pre-loop trip count.
   pre_end->_prob = PROB_FAIR;
   // Find the pre-loop normal exit.
   Node* pre_exit = pre_end->proj_out(false);
   assert( pre_exit->Opcode() == Op_IfFalse, "" );
   IfFalseNode *new_pre_exit = new (C, 1) IfFalseNode(pre_end);
   _igvn.register_new_node_with_optimizer( new_pre_exit );
   set_idom(new_pre_exit, pre_end, dd_main_head);
   set_loop(new_pre_exit, loop->_parent);
   // Step B2: Build a zero-trip guard for the main-loop.  After leaving the
   // pre-loop, the main-loop may not execute at all.  Later in life this
   // zero-trip guard will become the minimum-trip guard when we unroll
   // the main-loop.
   Node *min_opaq = new (C, 2) Opaque1Node(C, limit);
   Node *min_cmp  = new (C, 3) CmpINode( pre_incr, min_opaq );
   Node *min_bol  = new (C, 2) BoolNode( min_cmp, b_test );
   register_new_node( min_opaq, new_pre_exit );
   register_new_node( min_cmp , new_pre_exit );
   register_new_node( min_bol , new_pre_exit );
   // Build the IfNode (assume the main-loop is executed always).
   IfNode *min_iff = new (C, 2) IfNode( new_pre_exit, min_bol, PROB_ALWAYS, COUNT_UNKNOWN );
   _igvn.register_new_node_with_optimizer( min_iff );
   set_idom(min_iff, new_pre_exit, dd_main_head);
   set_loop(min_iff, loop->_parent);
   // Plug in the false-path, taken if we need to skip main-loop
   _igvn.hash_delete( pre_exit );
   pre_exit->set_req(0, min_iff);
   set_idom(pre_exit, min_iff, dd_main_head);
   set_idom(pre_exit->unique_out(), min_iff, dd_main_head);
   // Make the true-path, must enter the main loop
   Node *min_taken = new (C, 1) IfTrueNode( min_iff );
   _igvn.register_new_node_with_optimizer( min_taken );
   set_idom(min_taken, min_iff, dd_main_head);
   set_loop(min_taken, loop->_parent);
   // Plug in the true path
   _igvn.hash_delete( main_head );
   main_head->set_req(LoopNode::EntryControl, min_taken);
   set_idom(main_head, min_taken, dd_main_head);
   // Step B3: Make the fall-in values to the main-loop come from the
   // fall-out values of the pre-loop.
   for (DUIterator_Fast i2max, i2 = main_head->fast_outs(i2max); i2 < i2max; i2++) {
     Node* main_phi = main_head->fast_out(i2);
     if( main_phi->is_Phi() && main_phi->in(0) == main_head && main_phi->outcnt() > 0 ) {
       Node *pre_phi = old_new[main_phi->_idx];
       Node *fallpre  = clone_up_backedge_goo(pre_head->back_control(),
                                              main_head->init_control(),
                                              pre_phi->in(LoopNode::LoopBackControl));
       _igvn.hash_delete(main_phi);
       main_phi->set_req( LoopNode::EntryControl, fallpre );
     }
   }
   // Step B4: Shorten the pre-loop to run only 1 iteration (for now).
   // RCE and alignment may change this later.
   Node *cmp_end = pre_end->cmp_node();
   assert( cmp_end->in(2) == limit, "" );
   Node *pre_limit = new (C, 3) AddINode( init, stride );
   // Save the original loop limit in this Opaque1 node for
   // use by range check elimination.
   Node *pre_opaq  = new (C, 3) Opaque1Node(C, pre_limit, limit);
   register_new_node( pre_limit, pre_head->in(0) );
   register_new_node( pre_opaq , pre_head->in(0) );
   // Since no other users of pre-loop compare, I can hack limit directly
   assert( cmp_end->outcnt() == 1, "no other users" );
   _igvn.hash_delete(cmp_end);
   cmp_end->set_req(2, peel_only ? pre_limit : pre_opaq);
   // Special case for not-equal loop bounds:
   // Change pre loop test, main loop test, and the
   // main loop guard test to use lt or gt depending on stride
   // direction:
   // positive stride use <
   // negative stride use >
   if (pre_end->in(CountedLoopEndNode::TestValue)->as_Bool()->_test._test == BoolTest::ne) {
     BoolTest::mask new_test = (main_end->stride_con() > 0) ? BoolTest::lt : BoolTest::gt;
     // Modify pre loop end condition
     Node* pre_bol = pre_end->in(CountedLoopEndNode::TestValue)->as_Bool();
     BoolNode* new_bol0 = new (C, 2) BoolNode(pre_bol->in(1), new_test);
     register_new_node( new_bol0, pre_head->in(0) );
     _igvn.hash_delete(pre_end);
     pre_end->set_req(CountedLoopEndNode::TestValue, new_bol0);
     // Modify main loop guard condition
     assert(min_iff->in(CountedLoopEndNode::TestValue) == min_bol, "guard okay");
     BoolNode* new_bol1 = new (C, 2) BoolNode(min_bol->in(1), new_test);
     register_new_node( new_bol1, new_pre_exit );
     _igvn.hash_delete(min_iff);
     min_iff->set_req(CountedLoopEndNode::TestValue, new_bol1);
     // Modify main loop end condition
     BoolNode* main_bol = main_end->in(CountedLoopEndNode::TestValue)->as_Bool();
     BoolNode* new_bol2 = new (C, 2) BoolNode(main_bol->in(1), new_test);
     register_new_node( new_bol2, main_end->in(CountedLoopEndNode::TestControl) );
     _igvn.hash_delete(main_end);
     main_end->set_req(CountedLoopEndNode::TestValue, new_bol2);
   }
   // Flag main loop
   main_head->set_main_loop();
   if( peel_only ) main_head->set_main_no_pre_loop();
   // It's difficult to be precise about the trip-counts
   // for the pre/post loops.  They are usually very short,
   // so guess that 4 trips is a reasonable value.
   post_head->set_profile_trip_cnt(4.0);
   pre_head->set_profile_trip_cnt(4.0);
   // Now force out all loop-invariant dominating tests.  The optimizer
   // finds some, but we _know_ they are all useless.
   peeled_dom_test_elim(loop,old_new);
 }
 //------------------------------is_invariant-----------------------------
 // Return true if n is invariant
 bool IdealLoopTree::is_invariant(Node* n) const {
   Node *n_c = _phase->get_ctrl(n);
   if (n_c->is_top()) return false;
   return !is_member(_phase->get_loop(n_c));
 }
 //------------------------------do_unroll--------------------------------------
 // Unroll the loop body one step - make each trip do 2 iterations.
 void PhaseIdealLoop::do_unroll( IdealLoopTree *loop, Node_List &old_new, bool adjust_min_trip ) {
   assert( LoopUnrollLimit, "" );
 #ifndef PRODUCT
   if( PrintOpto && VerifyLoopOptimizations ) {
     tty->print("Unrolling ");
     loop->dump_head();
   }
 #endif
   CountedLoopNode *loop_head = loop->_head->as_CountedLoop();
   CountedLoopEndNode *loop_end = loop_head->loopexit();
   assert( loop_end, "" );
   // Remember loop node count before unrolling to detect
   // if rounds of unroll,optimize are making progress
   loop_head->set_node_count_before_unroll(loop->_body.size());
   Node *ctrl  = loop_head->in(LoopNode::EntryControl);
   Node *limit = loop_head->limit();
   Node *init  = loop_head->init_trip();
   Node *strid = loop_head->stride();
   Node *opaq = NULL;
   if( adjust_min_trip ) {       // If not maximally unrolling, need adjustment
     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 pre-loop 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 pre-loop!  Bail out!
   }
   C->set_major_progress();
   // 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 (C, 3) SubINode( limit, init );
   register_new_node( span, ctrl );
   Node *trip = new (C, 3) DivINode( 0, span, strid );
   register_new_node( trip, ctrl );
   Node *mtwo = _igvn.intcon(-2);
   set_ctrl(mtwo, C->root());
   Node *rond = new (C, 3) AndINode( trip, mtwo );
   register_new_node( rond, ctrl );
   Node *spn2 = new (C, 3) MulINode( rond, strid );
   register_new_node( spn2, ctrl );
   Node *lim2 = new (C, 3) AddINode( spn2, init );
   register_new_node( lim2, ctrl );
   // Hammer in the new limit
   Node *ctrl2 = loop_end->in(0);
   Node *cmp2 = new (C, 3) CmpINode( loop_head->incr(), lim2 );
   register_new_node( cmp2, ctrl2 );
   Node *bol2 = new (C, 2) BoolNode( cmp2, loop_end->test_trip() );
   register_new_node( bol2, ctrl2 );
   _igvn.hash_delete(loop_end);
   loop_end->set_req(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 ) {
     // 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, lim2);
   }
   // ---------
   // 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
   // times its backedge is never taken.  Kill the backedge.
   uint dd = dom_depth(loop_head);
   clone_loop( loop, old_new, dd );
   // Make backedges of the clone equal to backedges of the original.
   // Make the fall-in from the original come from the fall-out of the clone.
   for (DUIterator_Fast jmax, j = loop_head->fast_outs(jmax); j < jmax; j++) {
     Node* phi = loop_head->fast_out(j);
     if( phi->is_Phi() && phi->in(0) == loop_head && phi->outcnt() > 0 ) {
       Node *newphi = old_new[phi->_idx];
       _igvn.hash_delete( phi );
       _igvn.hash_delete( newphi );
       phi   ->set_req(LoopNode::   EntryControl, newphi->in(LoopNode::LoopBackControl));
       newphi->set_req(LoopNode::LoopBackControl, phi   ->in(LoopNode::LoopBackControl));
       phi   ->set_req(LoopNode::LoopBackControl, C->top());
     }
   }
   Node *clone_head = old_new[loop_head->_idx];
   _igvn.hash_delete( clone_head );
   loop_head ->set_req(LoopNode::   EntryControl, clone_head->in(LoopNode::LoopBackControl));
   clone_head->set_req(LoopNode::LoopBackControl, loop_head ->in(LoopNode::LoopBackControl));
   loop_head ->set_req(LoopNode::LoopBackControl, C->top());
   loop->_head = clone_head;     // New loop header
   set_idom(loop_head,  loop_head ->in(LoopNode::EntryControl), dd);
   set_idom(clone_head, clone_head->in(LoopNode::EntryControl), dd);
   // Kill the clone's backedge
   Node *newcle = old_new[loop_end->_idx];
   _igvn.hash_delete( newcle );
   Node *one = _igvn.intcon(1);
   set_ctrl(one, C->root());
   newcle->set_req(1, one);
   // Force clone into same loop body
   uint max = loop->_body.size();
   for( uint k = 0; k < max; k++ ) {
     Node *old = loop->_body.at(k);
     Node *nnn = old_new[old->_idx];
     loop->_body.push(nnn);
     if (!has_ctrl(old))
       set_loop(nnn, loop);
   }
   loop->record_for_igvn();
 }
 //------------------------------do_maximally_unroll----------------------------
 void PhaseIdealLoop::do_maximally_unroll( IdealLoopTree *loop, Node_List &old_new ) {
   CountedLoopNode *cl = loop->_head->as_CountedLoop();
   assert( cl->trip_count() > 0, "");
   // If loop is tripping an odd number of times, peel odd iteration
   if( (cl->trip_count() & 1) == 1 ) {
     do_peeling( loop, old_new );
   }
   // Now its tripping an even number of times remaining.  Double loop body.
   // Do not adjust pre-guards; they are not needed and do not exist.
   if( cl->trip_count() > 0 ) {
     do_unroll( loop, old_new, false );
   }
 }
 //------------------------------dominates_backedge---------------------------------
 // Returns true if ctrl is executed on every complete iteration
 bool IdealLoopTree::dominates_backedge(Node* ctrl) {
   assert(ctrl->is_CFG(), "must be control");
   Node* backedge = _head->as_Loop()->in(LoopNode::LoopBackControl);
   return _phase->dom_lca_internal(ctrl, backedge) == ctrl;
 }
 //------------------------------add_constraint---------------------------------
 // Constrain the main loop iterations so the condition:
 //    scale_con * I + offset  <  limit
 // always holds true.  That is, either increase the number of iterations in
 // the pre-loop or the post-loop until the condition holds true in the main
 // loop.  Stride, scale, offset and limit are all loop invariant.  Further,
 // stride and scale are constants (offset and limit often are).
 void PhaseIdealLoop::add_constraint( int stride_con, int scale_con, Node *offset, Node *limit, Node *pre_ctrl, Node **pre_limit, Node **main_limit ) {
   // Compute "I :: (limit-offset)/scale_con"
   Node *con = new (C, 3) SubINode( limit, offset );
   register_new_node( con, pre_ctrl );
   Node *scale = _igvn.intcon(scale_con);
   set_ctrl(scale, C->root());
   Node *X = new (C, 3) DivINode( 0, con, scale );
   register_new_node( X, pre_ctrl );
   // For positive stride, the pre-loop limit always uses a MAX function
   // and the main loop a MIN function.  For negative stride these are
   // reversed.
   // Also for positive stride*scale the affine function is increasing, so the
   // pre-loop must check for underflow and the post-loop for overflow.
   // Negative stride*scale reverses this; pre-loop checks for overflow and
   // post-loop for underflow.
   if( stride_con*scale_con > 0 ) {
     // Compute I < (limit-offset)/scale_con
     // Adjust main-loop last iteration to be MIN/MAX(main_loop,X)
     *main_limit = (stride_con > 0)
       ? (Node*)(new (C, 3) MinINode( *main_limit, X ))
       : (Node*)(new (C, 3) MaxINode( *main_limit, X ));
     register_new_node( *main_limit, pre_ctrl );
   } else {
     // Compute (limit-offset)/scale_con + SGN(-scale_con) <= I
     // Add the negation of the main-loop constraint to the pre-loop.
     // See footnote [++] below for a derivation of the limit expression.
     Node *incr = _igvn.intcon(scale_con > 0 ? -1 : 1);
     set_ctrl(incr, C->root());
     Node *adj = new (C, 3) AddINode( X, incr );
     register_new_node( adj, pre_ctrl );
     *pre_limit = (scale_con > 0)
       ? (Node*)new (C, 3) MinINode( *pre_limit, adj )
       : (Node*)new (C, 3) MaxINode( *pre_limit, adj );
     register_new_node( *pre_limit, pre_ctrl );
 //   [++] Here's the algebra that justifies the pre-loop limit expression:
 //
 //   NOT( scale_con * I + offset  <  limit )
 //      ==
 //   scale_con * I + offset  >=  limit
 //      ==
 //   SGN(scale_con) * I  >=  (limit-offset)/|scale_con|
 //      ==
 //   (limit-offset)/|scale_con|   <=  I * SGN(scale_con)
 //      ==
 //   (limit-offset)/|scale_con|-1  <  I * SGN(scale_con)
 //      ==
 //   ( if (scale_con > 0) /*common case*/
 //       (limit-offset)/scale_con - 1  <  I
 //     else
 //       (limit-offset)/scale_con + 1  >  I
 //    )
 //   ( if (scale_con > 0) /*common case*/
 //       (limit-offset)/scale_con + SGN(-scale_con)  <  I
 //     else
 //       (limit-offset)/scale_con + SGN(-scale_con)  >  I
   }
 }
 //------------------------------is_scaled_iv---------------------------------
 // Return true if exp is a constant times an induction var
 bool PhaseIdealLoop::is_scaled_iv(Node* exp, Node* iv, int* p_scale) {
   if (exp == iv) {
     if (p_scale != NULL) {
       *p_scale = 1;
     }
     return true;
   }
   int opc = exp->Opcode();
   if (opc == Op_MulI) {
     if (exp->in(1) == iv && exp->in(2)->is_Con()) {
       if (p_scale != NULL) {
         *p_scale = exp->in(2)->get_int();
       }
       return true;
     }
     if (exp->in(2) == iv && exp->in(1)->is_Con()) {
       if (p_scale != NULL) {
         *p_scale = exp->in(1)->get_int();
       }
       return true;
     }
   } else if (opc == Op_LShiftI) {
     if (exp->in(1) == iv && exp->in(2)->is_Con()) {
       if (p_scale != NULL) {
         *p_scale = 1 << exp->in(2)->get_int();
       }
       return true;
     }
   }
   return false;
 }
 //-----------------------------is_scaled_iv_plus_offset------------------------------
 // Return true if exp is a simple induction variable expression: k1*iv + (invar + k2)
 bool PhaseIdealLoop::is_scaled_iv_plus_offset(Node* exp, Node* iv, int* p_scale, Node** p_offset, int depth) {
   if (is_scaled_iv(exp, iv, p_scale)) {
     if (p_offset != NULL) {
       Node *zero = _igvn.intcon(0);
       set_ctrl(zero, C->root());
       *p_offset = zero;
     }
     return true;
   }
   int opc = exp->Opcode();
   if (opc == Op_AddI) {
     if (is_scaled_iv(exp->in(1), iv, p_scale)) {
       if (p_offset != NULL) {
         *p_offset = exp->in(2);
       }
       return true;
     }
     if (exp->in(2)->is_Con()) {
       Node* offset2 = NULL;
       if (depth < 2 &&
           is_scaled_iv_plus_offset(exp->in(1), iv, p_scale,
                                    p_offset != NULL ? &offset2 : NULL, depth+1)) {
         if (p_offset != NULL) {
           Node *ctrl_off2 = get_ctrl(offset2);
           Node* offset = new (C, 3) AddINode(offset2, exp->in(2));
           register_new_node(offset, ctrl_off2);
           *p_offset = offset;
         }
         return true;
       }
     }
   } else if (opc == Op_SubI) {
     if (is_scaled_iv(exp->in(1), iv, p_scale)) {
       if (p_offset != NULL) {
         Node *zero = _igvn.intcon(0);
         set_ctrl(zero, C->root());
         Node *ctrl_off = get_ctrl(exp->in(2));
         Node* offset = new (C, 3) SubINode(zero, exp->in(2));
         register_new_node(offset, ctrl_off);
         *p_offset = offset;
       }
       return true;
     }
     if (is_scaled_iv(exp->in(2), iv, p_scale)) {
       if (p_offset != NULL) {
         *p_scale *= -1;
         *p_offset = exp->in(1);
       }
       return true;
     }
   }
   return false;
 }
 //------------------------------do_range_check---------------------------------
 // Eliminate range-checks and other trip-counter vs loop-invariant tests.
 void PhaseIdealLoop::do_range_check( IdealLoopTree *loop, Node_List &old_new ) {
 #ifndef PRODUCT
   if( PrintOpto && VerifyLoopOptimizations ) {
     tty->print("Range Check Elimination ");
     loop->dump_head();
   }
 #endif
   assert( RangeCheckElimination, "" );
   CountedLoopNode *cl = loop->_head->as_CountedLoop();
   assert( cl->is_main_loop(), "" );
   // Find the trip counter; we are iteration splitting based on it
   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();
   // Find the pre-loop limit; we will expand it's iterations to
   // not ever trip low tests.
   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 *p_f = iffm->in(0);
   assert( p_f->Opcode() == Op_IfFalse, "" );
   CountedLoopEndNode *pre_end = p_f->in(0)->as_CountedLoopEnd();
   assert( pre_end->loopnode()->is_pre_loop(), "" );
   Node *pre_opaq1 = pre_end->limit();
   // Occasionally it's possible for a pre-loop 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( pre_opaq1->Opcode() != Op_Opaque1 )
     return;
   Opaque1Node *pre_opaq = (Opaque1Node*)pre_opaq1;
   Node *pre_limit = pre_opaq->in(1);
   // Where do we put new limit calculations
   Node *pre_ctrl = pre_end->loopnode()->in(LoopNode::EntryControl);
   // Ensure the original loop limit is available from the
   // pre-loop Opaque1 node.
   Node *orig_limit = pre_opaq->original_loop_limit();
   if( orig_limit == NULL || _igvn.type(orig_limit) == Type::TOP )
     return;
   // Need to find the main-loop zero-trip guard
   Node *bolzm = iffm->in(1);
   assert( bolzm->Opcode() == Op_Bool, "" );
   Node *cmpzm = bolzm->in(1);
   assert( cmpzm->is_Cmp(), "" );
   Node *opqzm = cmpzm->in(2);
   if( opqzm->Opcode() != Op_Opaque1 )
     return;
   assert( opqzm->in(1) == main_limit, "do not understand situation" );
   // Must know if its a count-up or count-down loop
   // protect against stride not being a constant
   if ( !cl->stride_is_con() ) {
     return;
   }
   int stride_con = cl->stride_con();
   Node *zero = _igvn.intcon(0);
   Node *one  = _igvn.intcon(1);
   set_ctrl(zero, C->root());
   set_ctrl(one,  C->root());
   // Range checks that do not dominate the loop backedge (ie.
   // conditionally executed) can lengthen the pre loop limit beyond
   // the original loop limit. To prevent this, the pre limit is
   // (for stride > 0) MINed with the original loop limit (MAXed
   // stride < 0) when some range_check (rc) is conditionally
   // executed.
   bool conditional_rc = false;
   // Check loop body for tests of trip-counter plus loop-invariant vs
   // loop-invariant.
   for( uint i = 0; i < loop->_body.size(); i++ ) {
     Node *iff = loop->_body[i];
     if( iff->Opcode() == Op_If ) { // Test?
       // Test is an IfNode, has 2 projections.  If BOTH are in the loop
       // we need loop unswitching instead of iteration splitting.
       Node *exit = loop->is_loop_exit(iff);
       if( !exit ) continue;
       int flip = (exit->Opcode() == Op_IfTrue) ? 1 : 0;
       // Get boolean condition to test
       Node *i1 = iff->in(1);
       if( !i1->is_Bool() ) continue;
       BoolNode *bol = i1->as_Bool();
       BoolTest b_test = bol->_test;
       // Flip sense of test if exit condition is flipped
       if( flip )
         b_test = b_test.negate();
       // Get compare
       Node *cmp = bol->in(1);
       // Look for trip_counter + offset vs limit
       Node *rc_exp = cmp->in(1);
       Node *limit  = cmp->in(2);
       jint scale_con= 1;        // Assume trip counter not scaled
       Node *limit_c = get_ctrl(limit);
       if( loop->is_member(get_loop(limit_c) ) ) {
         // Compare might have operands swapped; commute them
         b_test = b_test.commute();
         rc_exp = cmp->in(2);
         limit  = cmp->in(1);
         limit_c = get_ctrl(limit);
         if( loop->is_member(get_loop(limit_c) ) )
           continue;             // Both inputs are loop varying; cannot RCE
       }
       // Here we know 'limit' is loop invariant
       // 'limit' maybe pinned below the zero trip test (probably from a
       // previous round of rce), in which case, it can't be used in the
       // zero trip test expression which must occur before the zero test's if.
       if( limit_c == ctrl ) {
         continue;  // Don't rce this check but continue looking for other candidates.
       }
       // Check for scaled induction variable plus an offset
       Node *offset = NULL;
       if (!is_scaled_iv_plus_offset(rc_exp, trip_counter, &scale_con, &offset)) {
         continue;
       }
       Node *offset_c = get_ctrl(offset);
       if( loop->is_member( get_loop(offset_c) ) )
         continue;               // Offset is not really loop invariant
       // Here we know 'offset' is loop invariant.
       // As above for the 'limit', the 'offset' maybe pinned below the
       // zero trip test.
       if( offset_c == ctrl ) {
         continue; // Don't rce this check but continue looking for other candidates.
       }
       // At this point we have the expression as:
       //   scale_con * trip_counter + offset :: limit
       // where scale_con, offset and limit are loop invariant.  Trip_counter
       // monotonically increases by stride_con, a constant.  Both (or either)
       // stride_con and scale_con can be negative which will flip about the
       // sense of the test.
       // Adjust pre and main loop limits to guard the correct iteration set
       if( cmp->Opcode() == Op_CmpU ) {// Unsigned compare is really 2 tests
         if( b_test._test == BoolTest::lt ) { // Range checks always use lt
           // The overflow limit: scale*I+offset < limit
           add_constraint( stride_con, scale_con, offset, limit, pre_ctrl, &pre_limit, &main_limit );
           // The underflow limit: 0 <= scale*I+offset.
           // Some math yields: -scale*I-(offset+1) < 0
           Node *plus_one = new (C, 3) AddINode( offset, one );
           register_new_node( plus_one, pre_ctrl );
           Node *neg_offset = new (C, 3) SubINode( zero, plus_one );
           register_new_node( neg_offset, pre_ctrl );
           add_constraint( stride_con, -scale_con, neg_offset, zero, pre_ctrl, &pre_limit, &main_limit );
           if (!conditional_rc) {
             conditional_rc = !loop->dominates_backedge(iff);
           }
         } else {
 #ifndef PRODUCT
           if( PrintOpto )
             tty->print_cr("missed RCE opportunity");
 #endif
           continue;             // In release mode, ignore it
         }
       } else {                  // Otherwise work on normal compares
         switch( b_test._test ) {
         case BoolTest::ge:      // Convert X >= Y to -X <= -Y
           scale_con = -scale_con;
           offset = new (C, 3) SubINode( zero, offset );
           register_new_node( offset, pre_ctrl );
           limit  = new (C, 3) SubINode( zero, limit  );
           register_new_node( limit, pre_ctrl );
           // Fall into LE case
         case BoolTest::le:      // Convert X <= Y to X < Y+1
           limit = new (C, 3) AddINode( limit, one );
           register_new_node( limit, pre_ctrl );
           // Fall into LT case
         case BoolTest::lt:
           add_constraint( stride_con, scale_con, offset, limit, pre_ctrl, &pre_limit, &main_limit );
           if (!conditional_rc) {
             conditional_rc = !loop->dominates_backedge(iff);
           }
           break;
         default:
 #ifndef PRODUCT
           if( PrintOpto )
             tty->print_cr("missed RCE opportunity");
 #endif
           continue;             // Unhandled case
         }
       }
       // Kill the eliminated test
       C->set_major_progress();
       Node *kill_con = _igvn.intcon( 1-flip );
       set_ctrl(kill_con, C->root());
       _igvn.hash_delete(iff);
       iff->set_req(1, kill_con);
       _igvn._worklist.push(iff);
       // Find surviving projection
       assert(iff->is_If(), "");
       ProjNode* dp = ((IfNode*)iff)->proj_out(1-flip);
       // Find loads off the surviving projection; remove their control edge
       for (DUIterator_Fast imax, i = dp->fast_outs(imax); i < imax; i++) {
         Node* cd = dp->fast_out(i); // Control-dependent node
         if( cd->is_Load() ) {   // Loads can now float around in the loop
           _igvn.hash_delete(cd);
           // Allow the load to float around in the loop, or before it
           // but NOT before the pre-loop.
           cd->set_req(0, ctrl);   // ctrl, not NULL
           _igvn._worklist.push(cd);
           --i;
           --imax;
         }
       }
     } // End of is IF
   }
   // Update loop limits
   if (conditional_rc) {
     pre_limit = (stride_con > 0) ? (Node*)new (C,3) MinINode(pre_limit, orig_limit)
                                  : (Node*)new (C,3) MaxINode(pre_limit, orig_limit);
     register_new_node(pre_limit, pre_ctrl);
   }
   _igvn.hash_delete(pre_opaq);
   pre_opaq->set_req(1, pre_limit);
   // Note:: we are making the main loop limit no longer precise;
   // need to round up based on stride.
   if( 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();
     Node *span = new (C, 3) SubINode(main_limit,init);
     register_new_node(span,ctrl);
     Node *rndup = _igvn.intcon(stride_con + ((stride_con>0)?-1:1));
     Node *add = new (C, 3) AddINode(span,rndup);
     register_new_node(add,ctrl);
     Node *div = new (C, 3) DivINode(0,add,stride);
     register_new_node(div,ctrl);
     Node *mul = new (C, 3) MulINode(div,stride);
     register_new_node(mul,ctrl);
     Node *newlim = new (C, 3) 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
   if( main_bol->outcnt() > 1 ) {// BoolNode shared?
     _igvn.hash_delete(main_cle);
     main_bol = main_bol->clone();// Clone a private BoolNode
     register_new_node( main_bol, main_cle->in(0) );
     main_cle->set_req(1,main_bol);
   }
   Node *main_cmp = main_bol->in(1);
   if( main_cmp->outcnt() > 1 ) { // CmpNode shared?
     _igvn.hash_delete(main_bol);
     main_cmp = main_cmp->clone();// Clone a private CmpNode
     register_new_node( main_cmp, main_cle->in(0) );
     main_bol->set_req(1,main_cmp);
   }
   // Hack the now-private loop bounds
   _igvn.hash_delete(main_cmp);
   main_cmp->set_req(2, main_limit);
   _igvn._worklist.push(main_cmp);
   // The OpaqueNode is unshared by design
   _igvn.hash_delete(opqzm);
   assert( opqzm->outcnt() == 1, "cannot hack shared node" );
   opqzm->set_req(1,main_limit);
   _igvn._worklist.push(opqzm);
 }
 //------------------------------DCE_loop_body----------------------------------
 // Remove simplistic dead code from loop body
 void IdealLoopTree::DCE_loop_body() {
   for( uint i = 0; i < _body.size(); i++ )
     if( _body.at(i)->outcnt() == 0 )
       _body.map( i--, _body.pop() );
 }
 //------------------------------adjust_loop_exit_prob--------------------------
 // Look for loop-exit tests with the 50/50 (or worse) guesses from the parsing stage.
 // Replace with a 1-in-10 exit guess.
 void IdealLoopTree::adjust_loop_exit_prob( PhaseIdealLoop *phase ) {
   Node *test = tail();
   while( test != _head ) {
     uint top = test->Opcode();
     if( top == Op_IfTrue || top == Op_IfFalse ) {
       int test_con = ((ProjNode*)test)->_con;
       assert(top == (uint)(test_con? Op_IfTrue: Op_IfFalse), "sanity");
       IfNode *iff = test->in(0)->as_If();
       if( iff->outcnt() == 2 ) {        // Ignore dead tests
         Node *bol = iff->in(1);
         if( bol && bol->req() > 1 && bol->in(1) &&
             ((bol->in(1)->Opcode() == Op_StorePConditional ) ||
              (bol->in(1)->Opcode() == Op_StoreIConditional ) ||
              (bol->in(1)->Opcode() == Op_StoreLConditional ) ||
              (bol->in(1)->Opcode() == Op_CompareAndSwapI ) ||
              (bol->in(1)->Opcode() == Op_CompareAndSwapL ) ||
              (bol->in(1)->Opcode() == Op_CompareAndSwapP ) ||
              (bol->in(1)->Opcode() == Op_CompareAndSwapN )))
           return;               // Allocation loops RARELY take backedge
         // Find the OTHER exit path from the IF
         Node* ex = iff->proj_out(1-test_con);
         float p = iff->_prob;
         if( !phase->is_member( this, ex ) && iff->_fcnt == COUNT_UNKNOWN ) {
           if( top == Op_IfTrue ) {
             if( p < (PROB_FAIR + PROB_UNLIKELY_MAG(3))) {
               iff->_prob = PROB_STATIC_FREQUENT;
             }
           } else {
             if( p > (PROB_FAIR - PROB_UNLIKELY_MAG(3))) {
               iff->_prob = PROB_STATIC_INFREQUENT;
             }
           }
         }
       }
     }
     test = phase->idom(test);
   }
 }
 //------------------------------policy_do_remove_empty_loop--------------------
 // Micro-benchmark spamming.  Policy is to always remove empty loops.
 // The 'DO' part is to replace the trip counter with the value it will
 // have on the last iteration.  This will break the loop.
 bool IdealLoopTree::policy_do_remove_empty_loop( PhaseIdealLoop *phase ) {
   // Minimum size must be empty loop
   if( _body.size() > 7/*number of nodes in an empty loop*/ ) return false;
   if( !_head->is_CountedLoop() ) return false;     // Dead loop
   CountedLoopNode *cl = _head->as_CountedLoop();
   if( !cl->loopexit() ) return false; // Malformed loop
   if( !phase->is_member(this,phase->get_ctrl(cl->loopexit()->in(CountedLoopEndNode::TestValue)) ) )
     return false;             // Infinite loop
 #ifndef PRODUCT
   if( PrintOpto )
     tty->print_cr("Removing empty loop");
 #endif
 #ifdef ASSERT
   // Ensure only one phi which is the iv.
   Node* iv = NULL;
   for (DUIterator_Fast imax, i = cl->fast_outs(imax); i < imax; i++) {
     Node* n = cl->fast_out(i);
     if (n->Opcode() == Op_Phi) {
       assert(iv == NULL, "Too many phis" );
       iv = n;
     }
   }
   assert(iv == cl->phi(), "Wrong phi" );
 #endif
   // Replace the phi at loop head with the final value of the last
   // iteration.  Then the CountedLoopEnd will collapse (backedge never
   // taken) and all loop-invariant uses of the exit values will be correct.
   Node *phi = cl->phi();
   Node *final = new (phase->C, 3) SubINode( cl->limit(), cl->stride() );
   phase->register_new_node(final,cl->in(LoopNode::EntryControl));
   phase->_igvn.hash_delete(phi);
   phase->_igvn.subsume_node(phi,final);
   phase->C->set_major_progress();
   return true;
 }
 //=============================================================================
 //------------------------------iteration_split_impl---------------------------
 bool IdealLoopTree::iteration_split_impl( PhaseIdealLoop *phase, Node_List &old_new ) {
   // Check and remove empty loops (spam micro-benchmarks)
   if( policy_do_remove_empty_loop(phase) )
     return true;                     // Here we removed an empty loop
   bool should_peel = policy_peeling(phase); // Should we peel?
   bool should_unswitch = policy_unswitching(phase);
   // Non-counted loops may be peeled; exactly 1 iteration is peeled.
   // This removes loop-invariant tests (usually null checks).
   if( !_head->is_CountedLoop() ) { // Non-counted loop
     if (PartialPeelLoop && phase->partial_peel(this, old_new)) {
       // Partial peel succeeded so terminate this round of loop opts
       return false;
     }
     if( should_peel ) {            // Should we peel?
 #ifndef PRODUCT
       if (PrintOpto) tty->print_cr("should_peel");
 #endif
       phase->do_peeling(this,old_new);
     } else if( should_unswitch ) {
       phase->do_unswitching(this, old_new);
     }
     return true;
   }
   CountedLoopNode *cl = _head->as_CountedLoop();
   if( !cl->loopexit() ) return true; // Ignore various kinds of broken loops
   // Do nothing special to pre- and post- loops
   if( cl->is_pre_loop() || cl->is_post_loop() ) return true;
   // Compute loop trip count from profile data
   compute_profile_trip_cnt(phase);
   // Before attempting fancy unrolling, RCE or alignment, see if we want
   // to completely unroll this loop or do loop unswitching.
   if( cl->is_normal_loop() ) {
     bool should_maximally_unroll =  policy_maximally_unroll(phase);
     if( should_maximally_unroll ) {
       // Here we did some unrolling and peeling.  Eventually we will
       // completely unroll this loop and it will no longer be a loop.
       phase->do_maximally_unroll(this,old_new);
       return true;
     }
     if (should_unswitch) {
       phase->do_unswitching(this, old_new);
       return true;
     }
   }
   // Counted loops may be peeled, may need some iterations run up
   // front for RCE, and may want to align loop refs to a cache
   // line.  Thus we clone a full loop up front whose trip count is
   // at least 1 (if peeling), but may be several more.
   // The main loop will start cache-line aligned with at least 1
   // iteration of the unrolled body (zero-trip test required) and
   // will have some range checks removed.
   // A post-loop will finish any odd iterations (leftover after
   // unrolling), plus any needed for RCE purposes.
   bool should_unroll = policy_unroll(phase);
   bool should_rce = policy_range_check(phase);
   bool should_align = policy_align(phase);
   // If not RCE'ing (iteration splitting) or Aligning, then we do not
   // need a pre-loop.  We may still need to peel an initial iteration but
   // we will not be needing an unknown number of pre-iterations.
   //
   // Basically, if may_rce_align reports FALSE first time through,
   // we will not be able to later do RCE or Aligning on this loop.
   bool may_rce_align = !policy_peel_only(phase) || should_rce || should_align;
   // If we have any of these conditions (RCE, alignment, unrolling) met, then
   // we switch to the pre-/main-/post-loop model.  This model also covers
   // peeling.
   if( should_rce || should_align || should_unroll ) {
     if( cl->is_normal_loop() )  // Convert to 'pre/main/post' loops
       phase->insert_pre_post_loops(this,old_new, !may_rce_align);
     // Adjust the pre- and main-loop limits to let the pre and post loops run
     // with full checks, but the main-loop with no checks.  Remove said
     // checks from the main body.
     if( should_rce )
       phase->do_range_check(this,old_new);
     // Double loop body for unrolling.  Adjust the minimum-trip test (will do
     // twice as many iterations as before) and the main body limit (only do
     // an even number of trips).  If we are peeling, we might enable some RCE
     // and we'd rather unroll the post-RCE'd loop SO... do not unroll if
     // peeling.
     if( should_unroll && !should_peel )
       phase->do_unroll(this,old_new, true);
     // Adjust the pre-loop limits to align the main body
     // iterations.
     if( should_align )
       Unimplemented();
   } else {                      // Else we have an unchanged counted loop
     if( should_peel )           // Might want to peel but do nothing else
       phase->do_peeling(this,old_new);
   }
   return true;
 }
 //=============================================================================
 //------------------------------iteration_split--------------------------------
 bool IdealLoopTree::iteration_split( PhaseIdealLoop *phase, Node_List &old_new ) {
   // Recursively iteration split nested loops
   if( _child && !_child->iteration_split( phase, old_new ))
     return false;
   // Clean out prior deadwood
   DCE_loop_body();
   // Look for loop-exit tests with my 50/50 guesses from the Parsing stage.
   // Replace with a 1-in-10 exit guess.
   if( _parent /*not the root loop*/ &&
       !_irreducible &&
       // Also ignore the occasional dead backedge
       !tail()->is_top() ) {
     adjust_loop_exit_prob(phase);
   }
   // Gate unrolling, RCE and peeling efforts.
   if( !_child &&                // If not an inner loop, do not split
       !_irreducible &&
       _allow_optimizations &&
       !tail()->is_top() ) {     // Also ignore the occasional dead backedge
     if (!_has_call) {
       if (!iteration_split_impl( phase, old_new )) {
         return false;
       }
     } else if (policy_unswitching(phase)) {
       phase->do_unswitching(this, old_new);
     }
   }
   // Minor offset re-organization to remove loop-fallout uses of
   // trip counter.
   if( _head->is_CountedLoop() ) phase->reorg_offsets( this );
   if( _next && !_next->iteration_split( phase, old_new ))
     return false;
   return true;
 }

Mercurial > jdk8-mips64-public > hotspot / annotate

src/share/vm/opto/loopTransform.cpp@98cb887364d3 (annotated)

src/share/vm/opto/loopTransform.cpp