jdk8-mips64-public/hotspot: src/share/vm/opto/loopnode.cpp@f95d63e2154a (annotated)

src/share/vm/opto/loopnode.cpp@f95d63e2154a (annotated)

src/share/vm/opto/loopnode.cpp

Tue, 23 Nov 2010 13:22:55 -0800

author: stefank
date: Tue, 23 Nov 2010 13:22:55 -0800
changeset 2314: f95d63e2154a
parent 2118: d6f45b55c972
child 2555: 194c9fdee631
permissions: -rw-r--r--

6989984: Use standard include model for Hospot
Summary: Replaced MakeDeps and the includeDB files with more standardized solutions.
Reviewed-by: coleenp, kvn, kamg

 /*
  * Copyright (c) 1998, 2010, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  *
  */
 #include "precompiled.hpp"
 #include "ci/ciMethodData.hpp"
 #include "compiler/compileLog.hpp"
 #include "libadt/vectset.hpp"
 #include "memory/allocation.inline.hpp"
 #include "opto/addnode.hpp"
 #include "opto/callnode.hpp"
 #include "opto/connode.hpp"
 #include "opto/divnode.hpp"
 #include "opto/idealGraphPrinter.hpp"
 #include "opto/loopnode.hpp"
 #include "opto/mulnode.hpp"
 #include "opto/rootnode.hpp"
 #include "opto/superword.hpp"
 //=============================================================================
 //------------------------------is_loop_iv-------------------------------------
 // Determine if a node is Counted loop induction variable.
 // The method is declared in node.hpp.
 const Node* Node::is_loop_iv() const {
   if (this->is_Phi() && !this->as_Phi()->is_copy() &&
       this->as_Phi()->region()->is_CountedLoop() &&
       this->as_Phi()->region()->as_CountedLoop()->phi() == this) {
     return this;
   } else {
     return NULL;
   }
 }
 //=============================================================================
 //------------------------------dump_spec--------------------------------------
 // Dump special per-node info
 #ifndef PRODUCT
 void LoopNode::dump_spec(outputStream *st) const {
   if( is_inner_loop () ) st->print( "inner " );
   if( is_partial_peel_loop () ) st->print( "partial_peel " );
   if( partial_peel_has_failed () ) st->print( "partial_peel_failed " );
 }
 #endif
 //------------------------------get_early_ctrl---------------------------------
 // Compute earliest legal control
 Node *PhaseIdealLoop::get_early_ctrl( Node *n ) {
   assert( !n->is_Phi() && !n->is_CFG(), "this code only handles data nodes" );
   uint i;
   Node *early;
   if( n->in(0) ) {
     early = n->in(0);
     if( !early->is_CFG() ) // Might be a non-CFG multi-def
       early = get_ctrl(early);        // So treat input as a straight data input
     i = 1;
   } else {
     early = get_ctrl(n->in(1));
     i = 2;
   }
   uint e_d = dom_depth(early);
   assert( early, "" );
   for( ; i < n->req(); i++ ) {
     Node *cin = get_ctrl(n->in(i));
     assert( cin, "" );
     // Keep deepest dominator depth
     uint c_d = dom_depth(cin);
     if( c_d > e_d ) {           // Deeper guy?
       early = cin;              // Keep deepest found so far
       e_d = c_d;
     } else if( c_d == e_d &&    // Same depth?
                early != cin ) { // If not equal, must use slower algorithm
       // If same depth but not equal, one _must_ dominate the other
       // and we want the deeper (i.e., dominated) guy.
       Node *n1 = early;
       Node *n2 = cin;
       while( 1 ) {
         n1 = idom(n1);          // Walk up until break cycle
         n2 = idom(n2);
         if( n1 == cin ||        // Walked early up to cin
             dom_depth(n2) < c_d )
           break;                // early is deeper; keep him
         if( n2 == early ||      // Walked cin up to early
             dom_depth(n1) < c_d ) {
           early = cin;          // cin is deeper; keep him
           break;
         }
       }
       e_d = dom_depth(early);   // Reset depth register cache
     }
   }
   // Return earliest legal location
   assert(early == find_non_split_ctrl(early), "unexpected early control");
   return early;
 }
 //------------------------------set_early_ctrl---------------------------------
 // Set earliest legal control
 void PhaseIdealLoop::set_early_ctrl( Node *n ) {
   Node *early = get_early_ctrl(n);
   // Record earliest legal location
   set_ctrl(n, early);
 }
 //------------------------------set_subtree_ctrl-------------------------------
 // set missing _ctrl entries on new nodes
 void PhaseIdealLoop::set_subtree_ctrl( Node *n ) {
   // Already set?  Get out.
   if( _nodes[n->_idx] ) return;
   // Recursively set _nodes array to indicate where the Node goes
   uint i;
   for( i = 0; i < n->req(); ++i ) {
     Node *m = n->in(i);
     if( m && m != C->root() )
       set_subtree_ctrl( m );
   }
   // Fixup self
   set_early_ctrl( n );
 }
 //------------------------------is_counted_loop--------------------------------
 Node *PhaseIdealLoop::is_counted_loop( Node *x, IdealLoopTree *loop ) {
   PhaseGVN *gvn = &_igvn;
   // Counted loop head must be a good RegionNode with only 3 not NULL
   // control input edges: Self, Entry, LoopBack.
   if ( x->in(LoopNode::Self) == NULL || x->req() != 3 )
     return NULL;
   Node *init_control = x->in(LoopNode::EntryControl);
   Node *back_control = x->in(LoopNode::LoopBackControl);
   if( init_control == NULL || back_control == NULL )    // Partially dead
     return NULL;
   // Must also check for TOP when looking for a dead loop
   if( init_control->is_top() || back_control->is_top() )
     return NULL;
   // Allow funny placement of Safepoint
   if( back_control->Opcode() == Op_SafePoint )
     back_control = back_control->in(TypeFunc::Control);
   // Controlling test for loop
   Node *iftrue = back_control;
   uint iftrue_op = iftrue->Opcode();
   if( iftrue_op != Op_IfTrue &&
       iftrue_op != Op_IfFalse )
     // I have a weird back-control.  Probably the loop-exit test is in
     // the middle of the loop and I am looking at some trailing control-flow
     // merge point.  To fix this I would have to partially peel the loop.
     return NULL; // Obscure back-control
   // Get boolean guarding loop-back test
   Node *iff = iftrue->in(0);
   if( get_loop(iff) != loop || !iff->in(1)->is_Bool() ) return NULL;
   BoolNode *test = iff->in(1)->as_Bool();
   BoolTest::mask bt = test->_test._test;
   float cl_prob = iff->as_If()->_prob;
   if( iftrue_op == Op_IfFalse ) {
     bt = BoolTest(bt).negate();
     cl_prob = 1.0 - cl_prob;
   }
   // Get backedge compare
   Node *cmp = test->in(1);
   int cmp_op = cmp->Opcode();
   if( cmp_op != Op_CmpI )
     return NULL;                // Avoid pointer & float compares
   // Find the trip-counter increment & limit.  Limit must be loop invariant.
   Node *incr  = cmp->in(1);
   Node *limit = cmp->in(2);
   // ---------
   // need 'loop()' test to tell if limit is loop invariant
   // ---------
   if( !is_member( loop, get_ctrl(incr) ) ) { // Swapped trip counter and limit?
     Node *tmp = incr;           // Then reverse order into the CmpI
     incr = limit;
     limit = tmp;
     bt = BoolTest(bt).commute(); // And commute the exit test
   }
   if( is_member( loop, get_ctrl(limit) ) ) // Limit must loop-invariant
     return NULL;
   // Trip-counter increment must be commutative & associative.
   uint incr_op = incr->Opcode();
   if( incr_op == Op_Phi && incr->req() == 3 ) {
     incr = incr->in(2);         // Assume incr is on backedge of Phi
     incr_op = incr->Opcode();
   }
   Node* trunc1 = NULL;
   Node* trunc2 = NULL;
   const TypeInt* iv_trunc_t = NULL;
   if (!(incr = CountedLoopNode::match_incr_with_optional_truncation(incr, &trunc1, &trunc2, &iv_trunc_t))) {
     return NULL; // Funny increment opcode
   }
   // Get merge point
   Node *xphi = incr->in(1);
   Node *stride = incr->in(2);
   if( !stride->is_Con() ) {     // Oops, swap these
     if( !xphi->is_Con() )       // Is the other guy a constant?
       return NULL;              // Nope, unknown stride, bail out
     Node *tmp = xphi;           // 'incr' is commutative, so ok to swap
     xphi = stride;
     stride = tmp;
   }
   //if( loop(xphi) != l) return NULL;// Merge point is in inner loop??
   if( !xphi->is_Phi() ) return NULL; // Too much math on the trip counter
   PhiNode *phi = xphi->as_Phi();
   // Stride must be constant
   const Type *stride_t = stride->bottom_type();
   int stride_con = stride_t->is_int()->get_con();
   assert( stride_con, "missed some peephole opt" );
   // Phi must be of loop header; backedge must wrap to increment
   if( phi->region() != x ) return NULL;
   if( trunc1 == NULL && phi->in(LoopNode::LoopBackControl) != incr ||
       trunc1 != NULL && phi->in(LoopNode::LoopBackControl) != trunc1 ) {
     return NULL;
   }
   Node *init_trip = phi->in(LoopNode::EntryControl);
   //if (!init_trip->is_Con()) return NULL; // avoid rolling over MAXINT/MININT
   // If iv trunc type is smaller than int, check for possible wrap.
   if (!TypeInt::INT->higher_equal(iv_trunc_t)) {
     assert(trunc1 != NULL, "must have found some truncation");
     // Get a better type for the phi (filtered thru if's)
     const TypeInt* phi_ft = filtered_type(phi);
     // Can iv take on a value that will wrap?
     //
     // Ensure iv's limit is not within "stride" of the wrap value.
     //
     // Example for "short" type
     //    Truncation ensures value is in the range -32768..32767 (iv_trunc_t)
     //    If the stride is +10, then the last value of the induction
     //    variable before the increment (phi_ft->_hi) must be
     //    <= 32767 - 10 and (phi_ft->_lo) must be >= -32768 to
     //    ensure no truncation occurs after the increment.
     if (stride_con > 0) {
       if (iv_trunc_t->_hi - phi_ft->_hi < stride_con ||
           iv_trunc_t->_lo > phi_ft->_lo) {
         return NULL;  // truncation may occur
       }
     } else if (stride_con < 0) {
       if (iv_trunc_t->_lo - phi_ft->_lo > stride_con ||
           iv_trunc_t->_hi < phi_ft->_hi) {
         return NULL;  // truncation may occur
       }
     }
     // No possibility of wrap so truncation can be discarded
     // Promote iv type to Int
   } else {
     assert(trunc1 == NULL && trunc2 == NULL, "no truncation for int");
   }
   // =================================================
   // ---- SUCCESS!   Found A Trip-Counted Loop!  -----
   //
   // Canonicalize the condition on the test.  If we can exactly determine
   // the trip-counter exit value, then set limit to that value and use
   // a '!=' test.  Otherwise use condition '<' for count-up loops and
   // '>' for count-down loops.  If the condition is inverted and we will
   // be rolling through MININT to MAXINT, then bail out.
   C->print_method("Before CountedLoop", 3);
   // Check for SafePoint on backedge and remove
   Node *sfpt = x->in(LoopNode::LoopBackControl);
   if( sfpt->Opcode() == Op_SafePoint && is_deleteable_safept(sfpt)) {
     lazy_replace( sfpt, iftrue );
     loop->_tail = iftrue;
   }
   // 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 (C, 3) 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.
   const Type *limit_t = limit->bottom_type();
   const Type *init_t = init_trip->bottom_type();
   Node *one_p = gvn->intcon( 1);
   Node *one_m = gvn->intcon(-1);
   Node *trip_count = NULL;
   Node *hook = new (C, 6) Node(6);
   switch( bt ) {
   case BoolTest::eq:
     return NULL;                // Bail out, but this loop trips at most twice!
   case BoolTest::ne:            // Ahh, the case we desire
     if( stride_con == 1 )
       trip_count = gvn->transform(new (C, 3) SubINode(limit,init_trip));
     else if( stride_con == -1 )
       trip_count = gvn->transform(new (C, 3) SubINode(init_trip,limit));
     else
       return NULL;              // Odd stride; must prove we hit limit exactly
     set_subtree_ctrl( trip_count );
     //_loop.map(trip_count->_idx,loop(limit));
     break;
   case BoolTest::le:            // Maybe convert to '<' case
     limit = gvn->transform(new (C, 3) 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 ) return NULL; // Count down loop rolls through MAXINT
     Node *range = gvn->transform(new (C, 3) SubINode(limit,init_trip));
     set_subtree_ctrl( range );
     hook->init_req(0, range);
     Node *bias  = gvn->transform(new (C, 3) AddINode(range,stride));
     set_subtree_ctrl( bias );
     hook->init_req(1, bias);
     Node *bias1 = gvn->transform(new (C, 3) AddINode(bias,one_m));
     set_subtree_ctrl( bias1 );
     hook->init_req(2, bias1);
     trip_count  = gvn->transform(new (C, 3) 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 (C, 3) 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 ) return NULL; // count up loop rolls through MININT
     Node *range = gvn->transform(new (C, 3) SubINode(limit,init_trip));
     set_subtree_ctrl( range );
     hook->init_req(0, range);
     Node *bias  = gvn->transform(new (C, 3) AddINode(range,stride));
     set_subtree_ctrl( bias );
     hook->init_req(1, bias);
     Node *bias1 = gvn->transform(new (C, 3) AddINode(bias,one_p));
     set_subtree_ctrl( bias1 );
     hook->init_req(2, bias1);
     trip_count  = gvn->transform(new (C, 3) DivINode(0,bias1,stride));
     set_subtree_ctrl( trip_count );
     hook->init_req(3, trip_count);
     break;
   }
   }
   Node *span = gvn->transform(new (C, 3) MulINode(trip_count,stride));
   set_subtree_ctrl( span );
   hook->init_req(5, span);
   limit = gvn->transform(new (C, 3) AddINode(span,init_trip));
   set_subtree_ctrl( limit );
   // Build a canonical trip test.
   // Clone code, as old values may be in use.
   incr = incr->clone();
   incr->set_req(1,phi);
   incr->set_req(2,stride);
   incr = _igvn.register_new_node_with_optimizer(incr);
   set_early_ctrl( incr );
   _igvn.hash_delete(phi);
   phi->set_req_X( LoopNode::LoopBackControl, incr, &_igvn );
   // If phi type is more restrictive than Int, raise to
   // Int to prevent (almost) infinite recursion in igvn
   // which can only handle integer types for constants or minint..maxint.
   if (!TypeInt::INT->higher_equal(phi->bottom_type())) {
     Node* nphi = PhiNode::make(phi->in(0), phi->in(LoopNode::EntryControl), TypeInt::INT);
     nphi->set_req(LoopNode::LoopBackControl, phi->in(LoopNode::LoopBackControl));
     nphi = _igvn.register_new_node_with_optimizer(nphi);
     set_ctrl(nphi, get_ctrl(phi));
     _igvn.replace_node(phi, nphi);
     phi = nphi->as_Phi();
   }
   cmp = cmp->clone();
   cmp->set_req(1,incr);
   cmp->set_req(2,limit);
   cmp = _igvn.register_new_node_with_optimizer(cmp);
   set_ctrl(cmp, iff->in(0));
   Node *tmp = test->clone();
   assert( tmp->is_Bool(), "" );
   test = (BoolNode*)tmp;
   (*(BoolTest*)&test->_test)._test = bt; //BoolTest::ne;
   test->set_req(1,cmp);
   _igvn.register_new_node_with_optimizer(test);
   set_ctrl(test, iff->in(0));
   // If the exit test is dead, STOP!
   if( test == NULL ) return NULL;
   _igvn.hash_delete(iff);
   iff->set_req_X( 1, test, &_igvn );
   // Replace the old IfNode with a new LoopEndNode
   Node *lex = _igvn.register_new_node_with_optimizer(new (C, 2) CountedLoopEndNode( iff->in(0), iff->in(1), cl_prob, iff->as_If()->_fcnt ));
   IfNode *le = lex->as_If();
   uint dd = dom_depth(iff);
   set_idom(le, le->in(0), dd); // Update dominance for loop exit
   set_loop(le, loop);
   // Get the loop-exit control
   Node *if_f = iff->as_If()->proj_out(!(iftrue_op == Op_IfTrue));
   // Need to swap loop-exit and loop-back control?
   if( iftrue_op == Op_IfFalse ) {
     Node *ift2=_igvn.register_new_node_with_optimizer(new (C, 1) IfTrueNode (le));
     Node *iff2=_igvn.register_new_node_with_optimizer(new (C, 1) IfFalseNode(le));
     loop->_tail = back_control = ift2;
     set_loop(ift2, loop);
     set_loop(iff2, get_loop(if_f));
     // Lazy update of 'get_ctrl' mechanism.
     lazy_replace_proj( if_f  , iff2 );
     lazy_replace_proj( iftrue, ift2 );
     // Swap names
     if_f   = iff2;
     iftrue = ift2;
   } else {
     _igvn.hash_delete(if_f  );
     _igvn.hash_delete(iftrue);
     if_f  ->set_req_X( 0, le, &_igvn );
     iftrue->set_req_X( 0, le, &_igvn );
   }
   set_idom(iftrue, le, dd+1);
   set_idom(if_f,   le, dd+1);
   // Now setup a new CountedLoopNode to replace the existing LoopNode
   CountedLoopNode *l = new (C, 3) CountedLoopNode(init_control, back_control);
   // The following assert is approximately true, and defines the intention
   // of can_be_counted_loop.  It fails, however, because phase->type
   // is not yet initialized for this loop and its parts.
   //assert(l->can_be_counted_loop(this), "sanity");
   _igvn.register_new_node_with_optimizer(l);
   set_loop(l, loop);
   loop->_head = l;
   // Fix all data nodes placed at the old loop head.
   // Uses the lazy-update mechanism of 'get_ctrl'.
   lazy_replace( x, l );
   set_idom(l, init_control, dom_depth(x));
   // Check for immediately preceding SafePoint and remove
   Node *sfpt2 = le->in(0);
   if( sfpt2->Opcode() == Op_SafePoint && is_deleteable_safept(sfpt2))
     lazy_replace( sfpt2, sfpt2->in(TypeFunc::Control));
   // Free up intermediate goo
   _igvn.remove_dead_node(hook);
   C->print_method("After CountedLoop", 3);
   // Return trip counter
   return trip_count;
 }
 //------------------------------Ideal------------------------------------------
 // Return a node which is more "ideal" than the current node.
 // Attempt to convert into a counted-loop.
 Node *LoopNode::Ideal(PhaseGVN *phase, bool can_reshape) {
   if (!can_be_counted_loop(phase)) {
     phase->C->set_major_progress();
   }
   return RegionNode::Ideal(phase, can_reshape);
 }
 //=============================================================================
 //------------------------------Ideal------------------------------------------
 // Return a node which is more "ideal" than the current node.
 // Attempt to convert into a counted-loop.
 Node *CountedLoopNode::Ideal(PhaseGVN *phase, bool can_reshape) {
   return RegionNode::Ideal(phase, can_reshape);
 }
 //------------------------------dump_spec--------------------------------------
 // Dump special per-node info
 #ifndef PRODUCT
 void CountedLoopNode::dump_spec(outputStream *st) const {
   LoopNode::dump_spec(st);
   if( stride_is_con() ) {
     st->print("stride: %d ",stride_con());
   } else {
     st->print("stride: not constant ");
   }
   if( is_pre_loop () ) st->print("pre of N%d" , _main_idx );
   if( is_main_loop() ) st->print("main of N%d", _idx );
   if( is_post_loop() ) st->print("post of N%d", _main_idx );
 }
 #endif
 //=============================================================================
 int CountedLoopEndNode::stride_con() const {
   return stride()->bottom_type()->is_int()->get_con();
 }
 //----------------------match_incr_with_optional_truncation--------------------
 // Match increment with optional truncation:
 // CHAR: (i+1)&0x7fff, BYTE: ((i+1)<<8)>>8, or SHORT: ((i+1)<<16)>>16
 // Return NULL for failure. Success returns the increment node.
 Node* CountedLoopNode::match_incr_with_optional_truncation(
                       Node* expr, Node** trunc1, Node** trunc2, const TypeInt** trunc_type) {
   // Quick cutouts:
   if (expr == NULL || expr->req() != 3)  return false;
   Node *t1 = NULL;
   Node *t2 = NULL;
   const TypeInt* trunc_t = TypeInt::INT;
   Node* n1 = expr;
   int   n1op = n1->Opcode();
   // Try to strip (n1 & M) or (n1 << N >> N) from n1.
   if (n1op == Op_AndI &&
       n1->in(2)->is_Con() &&
       n1->in(2)->bottom_type()->is_int()->get_con() == 0x7fff) {
     // %%% This check should match any mask of 2**K-1.
     t1 = n1;
     n1 = t1->in(1);
     n1op = n1->Opcode();
     trunc_t = TypeInt::CHAR;
   } else if (n1op == Op_RShiftI &&
              n1->in(1) != NULL &&
              n1->in(1)->Opcode() == Op_LShiftI &&
              n1->in(2) == n1->in(1)->in(2) &&
              n1->in(2)->is_Con()) {
     jint shift = n1->in(2)->bottom_type()->is_int()->get_con();
     // %%% This check should match any shift in [1..31].
     if (shift == 16 || shift == 8) {
       t1 = n1;
       t2 = t1->in(1);
       n1 = t2->in(1);
       n1op = n1->Opcode();
       if (shift == 16) {
         trunc_t = TypeInt::SHORT;
       } else if (shift == 8) {
         trunc_t = TypeInt::BYTE;
       }
     }
   }
   // If (maybe after stripping) it is an AddI, we won:
   if (n1op == Op_AddI) {
     *trunc1 = t1;
     *trunc2 = t2;
     *trunc_type = trunc_t;
     return n1;
   }
   // failed
   return NULL;
 }
 //------------------------------filtered_type--------------------------------
 // Return a type based on condition control flow
 // A successful return will be a type that is restricted due
 // to a series of dominating if-tests, such as:
 //    if (i < 10) {
 //       if (i > 0) {
 //          here: "i" type is [1..10)
 //       }
 //    }
 // or a control flow merge
 //    if (i < 10) {
 //       do {
 //          phi( , ) -- at top of loop type is [min_int..10)
 //         i = ?
 //       } while ( i < 10)
 //
 const TypeInt* PhaseIdealLoop::filtered_type( Node *n, Node* n_ctrl) {
   assert(n && n->bottom_type()->is_int(), "must be int");
   const TypeInt* filtered_t = NULL;
   if (!n->is_Phi()) {
     assert(n_ctrl != NULL || n_ctrl == C->top(), "valid control");
     filtered_t = filtered_type_from_dominators(n, n_ctrl);
   } else {
     Node* phi    = n->as_Phi();
     Node* region = phi->in(0);
     assert(n_ctrl == NULL || n_ctrl == region, "ctrl parameter must be region");
     if (region && region != C->top()) {
       for (uint i = 1; i < phi->req(); i++) {
         Node* val   = phi->in(i);
         Node* use_c = region->in(i);
         const TypeInt* val_t = filtered_type_from_dominators(val, use_c);
         if (val_t != NULL) {
           if (filtered_t == NULL) {
             filtered_t = val_t;
           } else {
             filtered_t = filtered_t->meet(val_t)->is_int();
           }
         }
       }
     }
   }
   const TypeInt* n_t = _igvn.type(n)->is_int();
   if (filtered_t != NULL) {
     n_t = n_t->join(filtered_t)->is_int();
   }
   return n_t;
 }
 //------------------------------filtered_type_from_dominators--------------------------------
 // Return a possibly more restrictive type for val based on condition control flow of dominators
 const TypeInt* PhaseIdealLoop::filtered_type_from_dominators( Node* val, Node *use_ctrl) {
   if (val->is_Con()) {
      return val->bottom_type()->is_int();
   }
   uint if_limit = 10; // Max number of dominating if's visited
   const TypeInt* rtn_t = NULL;
   if (use_ctrl && use_ctrl != C->top()) {
     Node* val_ctrl = get_ctrl(val);
     uint val_dom_depth = dom_depth(val_ctrl);
     Node* pred = use_ctrl;
     uint if_cnt = 0;
     while (if_cnt < if_limit) {
       if ((pred->Opcode() == Op_IfTrue || pred->Opcode() == Op_IfFalse)) {
         if_cnt++;
         const TypeInt* if_t = IfNode::filtered_int_type(&_igvn, val, pred);
         if (if_t != NULL) {
           if (rtn_t == NULL) {
             rtn_t = if_t;
           } else {
             rtn_t = rtn_t->join(if_t)->is_int();
           }
         }
       }
       pred = idom(pred);
       if (pred == NULL || pred == C->top()) {
         break;
       }
       // Stop if going beyond definition block of val
       if (dom_depth(pred) < val_dom_depth) {
         break;
       }
     }
   }
   return rtn_t;
 }
 //------------------------------dump_spec--------------------------------------
 // Dump special per-node info
 #ifndef PRODUCT
 void CountedLoopEndNode::dump_spec(outputStream *st) const {
   if( in(TestValue)->is_Bool() ) {
     BoolTest bt( test_trip()); // Added this for g++.
     st->print("[");
     bt.dump_on(st);
     st->print("]");
   }
   st->print(" ");
   IfNode::dump_spec(st);
 }
 #endif
 //=============================================================================
 //------------------------------is_member--------------------------------------
 // Is 'l' a member of 'this'?
 int IdealLoopTree::is_member( const IdealLoopTree *l ) const {
   while( l->_nest > _nest ) l = l->_parent;
   return l == this;
 }
 //------------------------------set_nest---------------------------------------
 // Set loop tree nesting depth.  Accumulate _has_call bits.
 int IdealLoopTree::set_nest( uint depth ) {
   _nest = depth;
   int bits = _has_call;
   if( _child ) bits |= _child->set_nest(depth+1);
   if( bits ) _has_call = 1;
   if( _next  ) bits |= _next ->set_nest(depth  );
   return bits;
 }
 //------------------------------split_fall_in----------------------------------
 // Split out multiple fall-in edges from the loop header.  Move them to a
 // private RegionNode before the loop.  This becomes the loop landing pad.
 void IdealLoopTree::split_fall_in( PhaseIdealLoop *phase, int fall_in_cnt ) {
   PhaseIterGVN &igvn = phase->_igvn;
   uint i;
   // Make a new RegionNode to be the landing pad.
   Node *landing_pad = new (phase->C, fall_in_cnt+1) RegionNode( fall_in_cnt+1 );
   phase->set_loop(landing_pad,_parent);
   // Gather all the fall-in control paths into the landing pad
   uint icnt = fall_in_cnt;
   uint oreq = _head->req();
   for( i = oreq-1; i>0; i-- )
     if( !phase->is_member( this, _head->in(i) ) )
       landing_pad->set_req(icnt--,_head->in(i));
   // Peel off PhiNode edges as well
   for (DUIterator_Fast jmax, j = _head->fast_outs(jmax); j < jmax; j++) {
     Node *oj = _head->fast_out(j);
     if( oj->is_Phi() ) {
       PhiNode* old_phi = oj->as_Phi();
       assert( old_phi->region() == _head, "" );
       igvn.hash_delete(old_phi);   // Yank from hash before hacking edges
       Node *p = PhiNode::make_blank(landing_pad, old_phi);
       uint icnt = fall_in_cnt;
       for( i = oreq-1; i>0; i-- ) {
         if( !phase->is_member( this, _head->in(i) ) ) {
           p->init_req(icnt--, old_phi->in(i));
           // Go ahead and clean out old edges from old phi
           old_phi->del_req(i);
         }
       }
       // Search for CSE's here, because ZKM.jar does a lot of
       // loop hackery and we need to be a little incremental
       // with the CSE to avoid O(N^2) node blow-up.
       Node *p2 = igvn.hash_find_insert(p); // Look for a CSE
       if( p2 ) {                // Found CSE
         p->destruct();          // Recover useless new node
         p = p2;                 // Use old node
       } else {
         igvn.register_new_node_with_optimizer(p, old_phi);
       }
       // Make old Phi refer to new Phi.
       old_phi->add_req(p);
       // Check for the special case of making the old phi useless and
       // disappear it.  In JavaGrande I have a case where this useless
       // Phi is the loop limit and prevents recognizing a CountedLoop
       // which in turn prevents removing an empty loop.
       Node *id_old_phi = old_phi->Identity( &igvn );
       if( id_old_phi != old_phi ) { // Found a simple identity?
         // Note that I cannot call 'replace_node' here, because
         // that will yank the edge from old_phi to the Region and
         // I'm mid-iteration over the Region's uses.
         for (DUIterator_Last imin, i = old_phi->last_outs(imin); i >= imin; ) {
           Node* use = old_phi->last_out(i);
           igvn.hash_delete(use);
           igvn._worklist.push(use);
           uint uses_found = 0;
           for (uint j = 0; j < use->len(); j++) {
             if (use->in(j) == old_phi) {
               if (j < use->req()) use->set_req (j, id_old_phi);
               else                use->set_prec(j, id_old_phi);
               uses_found++;
             }
           }
           i -= uses_found;    // we deleted 1 or more copies of this edge
         }
       }
       igvn._worklist.push(old_phi);
     }
   }
   // Finally clean out the fall-in edges from the RegionNode
   for( i = oreq-1; i>0; i-- ) {
     if( !phase->is_member( this, _head->in(i) ) ) {
       _head->del_req(i);
     }
   }
   // Transform landing pad
   igvn.register_new_node_with_optimizer(landing_pad, _head);
   // Insert landing pad into the header
   _head->add_req(landing_pad);
 }
 //------------------------------split_outer_loop-------------------------------
 // Split out the outermost loop from this shared header.
 void IdealLoopTree::split_outer_loop( PhaseIdealLoop *phase ) {
   PhaseIterGVN &igvn = phase->_igvn;
   // Find index of outermost loop; it should also be my tail.
   uint outer_idx = 1;
   while( _head->in(outer_idx) != _tail ) outer_idx++;
   // Make a LoopNode for the outermost loop.
   Node *ctl = _head->in(LoopNode::EntryControl);
   Node *outer = new (phase->C, 3) LoopNode( ctl, _head->in(outer_idx) );
   outer = igvn.register_new_node_with_optimizer(outer, _head);
   phase->set_created_loop_node();
   // Outermost loop falls into '_head' loop
   _head->set_req(LoopNode::EntryControl, outer);
   _head->del_req(outer_idx);
   // Split all the Phis up between '_head' loop and 'outer' loop.
   for (DUIterator_Fast jmax, j = _head->fast_outs(jmax); j < jmax; j++) {
     Node *out = _head->fast_out(j);
     if( out->is_Phi() ) {
       PhiNode *old_phi = out->as_Phi();
       assert( old_phi->region() == _head, "" );
       Node *phi = PhiNode::make_blank(outer, old_phi);
       phi->init_req(LoopNode::EntryControl,    old_phi->in(LoopNode::EntryControl));
       phi->init_req(LoopNode::LoopBackControl, old_phi->in(outer_idx));
       phi = igvn.register_new_node_with_optimizer(phi, old_phi);
       // Make old Phi point to new Phi on the fall-in path
       igvn.hash_delete(old_phi);
       old_phi->set_req(LoopNode::EntryControl, phi);
       old_phi->del_req(outer_idx);
       igvn._worklist.push(old_phi);
     }
   }
   // Use the new loop head instead of the old shared one
   _head = outer;
   phase->set_loop(_head, this);
 }
 //------------------------------fix_parent-------------------------------------
 static void fix_parent( IdealLoopTree *loop, IdealLoopTree *parent ) {
   loop->_parent = parent;
   if( loop->_child ) fix_parent( loop->_child, loop   );
   if( loop->_next  ) fix_parent( loop->_next , parent );
 }
 //------------------------------estimate_path_freq-----------------------------
 static float estimate_path_freq( Node *n ) {
   // Try to extract some path frequency info
   IfNode *iff;
   for( int i = 0; i < 50; i++ ) { // Skip through a bunch of uncommon tests
     uint nop = n->Opcode();
     if( nop == Op_SafePoint ) {   // Skip any safepoint
       n = n->in(0);
       continue;
     }
     if( nop == Op_CatchProj ) {   // Get count from a prior call
       // Assume call does not always throw exceptions: means the call-site
       // count is also the frequency of the fall-through path.
       assert( n->is_CatchProj(), "" );
       if( ((CatchProjNode*)n)->_con != CatchProjNode::fall_through_index )
         return 0.0f;            // Assume call exception path is rare
       Node *call = n->in(0)->in(0)->in(0);
       assert( call->is_Call(), "expect a call here" );
       const JVMState *jvms = ((CallNode*)call)->jvms();
       ciMethodData* methodData = jvms->method()->method_data();
       if (!methodData->is_mature())  return 0.0f; // No call-site data
       ciProfileData* data = methodData->bci_to_data(jvms->bci());
       if ((data == NULL) || !data->is_CounterData()) {
         // no call profile available, try call's control input
         n = n->in(0);
         continue;
       }
       return data->as_CounterData()->count()/FreqCountInvocations;
     }
     // See if there's a gating IF test
     Node *n_c = n->in(0);
     if( !n_c->is_If() ) break;       // No estimate available
     iff = n_c->as_If();
     if( iff->_fcnt != COUNT_UNKNOWN )   // Have a valid count?
       // Compute how much count comes on this path
       return ((nop == Op_IfTrue) ? iff->_prob : 1.0f - iff->_prob) * iff->_fcnt;
     // Have no count info.  Skip dull uncommon-trap like branches.
     if( (nop == Op_IfTrue  && iff->_prob < PROB_LIKELY_MAG(5)) ||
         (nop == Op_IfFalse && iff->_prob > PROB_UNLIKELY_MAG(5)) )
       break;
     // Skip through never-taken branch; look for a real loop exit.
     n = iff->in(0);
   }
   return 0.0f;                  // No estimate available
 }
 //------------------------------merge_many_backedges---------------------------
 // Merge all the backedges from the shared header into a private Region.
 // Feed that region as the one backedge to this loop.
 void IdealLoopTree::merge_many_backedges( PhaseIdealLoop *phase ) {
   uint i;
   // Scan for the top 2 hottest backedges
   float hotcnt = 0.0f;
   float warmcnt = 0.0f;
   uint hot_idx = 0;
   // Loop starts at 2 because slot 1 is the fall-in path
   for( i = 2; i < _head->req(); i++ ) {
     float cnt = estimate_path_freq(_head->in(i));
     if( cnt > hotcnt ) {       // Grab hottest path
       warmcnt = hotcnt;
       hotcnt = cnt;
       hot_idx = i;
     } else if( cnt > warmcnt ) { // And 2nd hottest path
       warmcnt = cnt;
     }
   }
   // See if the hottest backedge is worthy of being an inner loop
   // by being much hotter than the next hottest backedge.
   if( hotcnt <= 0.0001 ||
       hotcnt < 2.0*warmcnt ) hot_idx = 0;// No hot backedge
   // Peel out the backedges into a private merge point; peel
   // them all except optionally hot_idx.
   PhaseIterGVN &igvn = phase->_igvn;
   Node *hot_tail = NULL;
   // Make a Region for the merge point
   Node *r = new (phase->C, 1) RegionNode(1);
   for( i = 2; i < _head->req(); i++ ) {
     if( i != hot_idx )
       r->add_req( _head->in(i) );
     else hot_tail = _head->in(i);
   }
   igvn.register_new_node_with_optimizer(r, _head);
   // Plug region into end of loop _head, followed by hot_tail
   while( _head->req() > 3 ) _head->del_req( _head->req()-1 );
   _head->set_req(2, r);
   if( hot_idx ) _head->add_req(hot_tail);
   // Split all the Phis up between '_head' loop and the Region 'r'
   for (DUIterator_Fast jmax, j = _head->fast_outs(jmax); j < jmax; j++) {
     Node *out = _head->fast_out(j);
     if( out->is_Phi() ) {
       PhiNode* n = out->as_Phi();
       igvn.hash_delete(n);      // Delete from hash before hacking edges
       Node *hot_phi = NULL;
       Node *phi = new (phase->C, r->req()) PhiNode(r, n->type(), n->adr_type());
       // Check all inputs for the ones to peel out
       uint j = 1;
       for( uint i = 2; i < n->req(); i++ ) {
         if( i != hot_idx )
           phi->set_req( j++, n->in(i) );
         else hot_phi = n->in(i);
       }
       // Register the phi but do not transform until whole place transforms
       igvn.register_new_node_with_optimizer(phi, n);
       // Add the merge phi to the old Phi
       while( n->req() > 3 ) n->del_req( n->req()-1 );
       n->set_req(2, phi);
       if( hot_idx ) n->add_req(hot_phi);
     }
   }
   // Insert a new IdealLoopTree inserted below me.  Turn it into a clone
   // of self loop tree.  Turn self into a loop headed by _head and with
   // tail being the new merge point.
   IdealLoopTree *ilt = new IdealLoopTree( phase, _head, _tail );
   phase->set_loop(_tail,ilt);   // Adjust tail
   _tail = r;                    // Self's tail is new merge point
   phase->set_loop(r,this);
   ilt->_child = _child;         // New guy has my children
   _child = ilt;                 // Self has new guy as only child
   ilt->_parent = this;          // new guy has self for parent
   ilt->_nest = _nest;           // Same nesting depth (for now)
   // Starting with 'ilt', look for child loop trees using the same shared
   // header.  Flatten these out; they will no longer be loops in the end.
   IdealLoopTree **pilt = &_child;
   while( ilt ) {
     if( ilt->_head == _head ) {
       uint i;
       for( i = 2; i < _head->req(); i++ )
         if( _head->in(i) == ilt->_tail )
           break;                // Still a loop
       if( i == _head->req() ) { // No longer a loop
         // Flatten ilt.  Hang ilt's "_next" list from the end of
         // ilt's '_child' list.  Move the ilt's _child up to replace ilt.
         IdealLoopTree **cp = &ilt->_child;
         while( *cp ) cp = &(*cp)->_next;   // Find end of child list
         *cp = ilt->_next;       // Hang next list at end of child list
         *pilt = ilt->_child;    // Move child up to replace ilt
         ilt->_head = NULL;      // Flag as a loop UNIONED into parent
         ilt = ilt->_child;      // Repeat using new ilt
         continue;               // do not advance over ilt->_child
       }
       assert( ilt->_tail == hot_tail, "expected to only find the hot inner loop here" );
       phase->set_loop(_head,ilt);
     }
     pilt = &ilt->_child;        // Advance to next
     ilt = *pilt;
   }
   if( _child ) fix_parent( _child, this );
 }
 //------------------------------beautify_loops---------------------------------
 // Split shared headers and insert loop landing pads.
 // Insert a LoopNode to replace the RegionNode.
 // Return TRUE if loop tree is structurally changed.
 bool IdealLoopTree::beautify_loops( PhaseIdealLoop *phase ) {
   bool result = false;
   // Cache parts in locals for easy
   PhaseIterGVN &igvn = phase->_igvn;
   phase->C->print_method("Before beautify loops", 3);
   igvn.hash_delete(_head);      // Yank from hash before hacking edges
   // Check for multiple fall-in paths.  Peel off a landing pad if need be.
   int fall_in_cnt = 0;
   for( uint i = 1; i < _head->req(); i++ )
     if( !phase->is_member( this, _head->in(i) ) )
       fall_in_cnt++;
   assert( fall_in_cnt, "at least 1 fall-in path" );
   if( fall_in_cnt > 1 )         // Need a loop landing pad to merge fall-ins
     split_fall_in( phase, fall_in_cnt );
   // Swap inputs to the _head and all Phis to move the fall-in edge to
   // the left.
   fall_in_cnt = 1;
   while( phase->is_member( this, _head->in(fall_in_cnt) ) )
     fall_in_cnt++;
   if( fall_in_cnt > 1 ) {
     // Since I am just swapping inputs I do not need to update def-use info
     Node *tmp = _head->in(1);
     _head->set_req( 1, _head->in(fall_in_cnt) );
     _head->set_req( fall_in_cnt, tmp );
     // Swap also all Phis
     for (DUIterator_Fast imax, i = _head->fast_outs(imax); i < imax; i++) {
       Node* phi = _head->fast_out(i);
       if( phi->is_Phi() ) {
         igvn.hash_delete(phi); // Yank from hash before hacking edges
         tmp = phi->in(1);
         phi->set_req( 1, phi->in(fall_in_cnt) );
         phi->set_req( fall_in_cnt, tmp );
       }
     }
   }
   assert( !phase->is_member( this, _head->in(1) ), "left edge is fall-in" );
   assert(  phase->is_member( this, _head->in(2) ), "right edge is loop" );
   // If I am a shared header (multiple backedges), peel off the many
   // backedges into a private merge point and use the merge point as
   // the one true backedge.
   if( _head->req() > 3 ) {
     // Merge the many backedges into a single backedge.
     merge_many_backedges( phase );
     result = true;
   }
   // If I am a shared header (multiple backedges), peel off myself loop.
   // I better be the outermost loop.
   if( _head->req() > 3 ) {
     split_outer_loop( phase );
     result = true;
   } else if( !_head->is_Loop() && !_irreducible ) {
     // Make a new LoopNode to replace the old loop head
     Node *l = new (phase->C, 3) LoopNode( _head->in(1), _head->in(2) );
     l = igvn.register_new_node_with_optimizer(l, _head);
     phase->set_created_loop_node();
     // Go ahead and replace _head
     phase->_igvn.replace_node( _head, l );
     _head = l;
     phase->set_loop(_head, this);
   }
   // Now recursively beautify nested loops
   if( _child ) result |= _child->beautify_loops( phase );
   if( _next  ) result |= _next ->beautify_loops( phase );
   return result;
 }
 //------------------------------allpaths_check_safepts----------------------------
 // Allpaths backwards scan from loop tail, terminating each path at first safepoint
 // encountered.  Helper for check_safepts.
 void IdealLoopTree::allpaths_check_safepts(VectorSet &visited, Node_List &stack) {
   assert(stack.size() == 0, "empty stack");
   stack.push(_tail);
   visited.Clear();
   visited.set(_tail->_idx);
   while (stack.size() > 0) {
     Node* n = stack.pop();
     if (n->is_Call() && n->as_Call()->guaranteed_safepoint()) {
       // Terminate this path
     } else if (n->Opcode() == Op_SafePoint) {
       if (_phase->get_loop(n) != this) {
         if (_required_safept == NULL) _required_safept = new Node_List();
         _required_safept->push(n);  // save the one closest to the tail
       }
       // Terminate this path
     } else {
       uint start = n->is_Region() ? 1 : 0;
       uint end   = n->is_Region() && !n->is_Loop() ? n->req() : start + 1;
       for (uint i = start; i < end; i++) {
         Node* in = n->in(i);
         assert(in->is_CFG(), "must be");
         if (!visited.test_set(in->_idx) && is_member(_phase->get_loop(in))) {
           stack.push(in);
         }
       }
     }
   }
 }
 //------------------------------check_safepts----------------------------
 // Given dominators, try to find loops with calls that must always be
 // executed (call dominates loop tail).  These loops do not need non-call
 // safepoints (ncsfpt).
 //
 // A complication is that a safepoint in a inner loop may be needed
 // by an outer loop. In the following, the inner loop sees it has a
 // call (block 3) on every path from the head (block 2) to the
 // backedge (arc 3->2).  So it deletes the ncsfpt (non-call safepoint)
 // in block 2, _but_ this leaves the outer loop without a safepoint.
 //
 //          entry  0
 //                 |
 //                 v
 // outer 1,2    +->1
 //              |  |
 //              |  v
 //              |  2<---+  ncsfpt in 2
 //              |_/|\   |
 //                 | v  |
 // inner 2,3      /  3  |  call in 3
 //               /   |  |
 //              v    +--+
 //        exit  4
 //
 //
 // This method creates a list (_required_safept) of ncsfpt nodes that must
 // be protected is created for each loop. When a ncsfpt maybe deleted, it
 // is first looked for in the lists for the outer loops of the current loop.
 //
 // The insights into the problem:
 //  A) counted loops are okay
 //  B) innermost loops are okay (only an inner loop can delete
 //     a ncsfpt needed by an outer loop)
 //  C) a loop is immune from an inner loop deleting a safepoint
 //     if the loop has a call on the idom-path
 //  D) a loop is also immune if it has a ncsfpt (non-call safepoint) on the
 //     idom-path that is not in a nested loop
 //  E) otherwise, an ncsfpt on the idom-path that is nested in an inner
 //     loop needs to be prevented from deletion by an inner loop
 //
 // There are two analyses:
 //  1) The first, and cheaper one, scans the loop body from
 //     tail to head following the idom (immediate dominator)
 //     chain, looking for the cases (C,D,E) above.
 //     Since inner loops are scanned before outer loops, there is summary
 //     information about inner loops.  Inner loops can be skipped over
 //     when the tail of an inner loop is encountered.
 //
 //  2) The second, invoked if the first fails to find a call or ncsfpt on
 //     the idom path (which is rare), scans all predecessor control paths
 //     from the tail to the head, terminating a path when a call or sfpt
 //     is encountered, to find the ncsfpt's that are closest to the tail.
 //
 void IdealLoopTree::check_safepts(VectorSet &visited, Node_List &stack) {
   // Bottom up traversal
   IdealLoopTree* ch = _child;
   while (ch != NULL) {
     ch->check_safepts(visited, stack);
     ch = ch->_next;
   }
   if (!_head->is_CountedLoop() && !_has_sfpt && _parent != NULL && !_irreducible) {
     bool  has_call         = false; // call on dom-path
     bool  has_local_ncsfpt = false; // ncsfpt on dom-path at this loop depth
     Node* nonlocal_ncsfpt  = NULL;  // ncsfpt on dom-path at a deeper depth
     // Scan the dom-path nodes from tail to head
     for (Node* n = tail(); n != _head; n = _phase->idom(n)) {
       if (n->is_Call() && n->as_Call()->guaranteed_safepoint()) {
         has_call = true;
         _has_sfpt = 1;          // Then no need for a safept!
         break;
       } else if (n->Opcode() == Op_SafePoint) {
         if (_phase->get_loop(n) == this) {
           has_local_ncsfpt = true;
           break;
         }
         if (nonlocal_ncsfpt == NULL) {
           nonlocal_ncsfpt = n; // save the one closest to the tail
         }
       } else {
         IdealLoopTree* nlpt = _phase->get_loop(n);
         if (this != nlpt) {
           // If at an inner loop tail, see if the inner loop has already
           // recorded seeing a call on the dom-path (and stop.)  If not,
           // jump to the head of the inner loop.
           assert(is_member(nlpt), "nested loop");
           Node* tail = nlpt->_tail;
           if (tail->in(0)->is_If()) tail = tail->in(0);
           if (n == tail) {
             // If inner loop has call on dom-path, so does outer loop
             if (nlpt->_has_sfpt) {
               has_call = true;
               _has_sfpt = 1;
               break;
             }
             // Skip to head of inner loop
             assert(_phase->is_dominator(_head, nlpt->_head), "inner head dominated by outer head");
             n = nlpt->_head;
           }
         }
       }
     }
     // Record safept's that this loop needs preserved when an
     // inner loop attempts to delete it's safepoints.
     if (_child != NULL && !has_call && !has_local_ncsfpt) {
       if (nonlocal_ncsfpt != NULL) {
         if (_required_safept == NULL) _required_safept = new Node_List();
         _required_safept->push(nonlocal_ncsfpt);
       } else {
         // Failed to find a suitable safept on the dom-path.  Now use
         // an all paths walk from tail to head, looking for safepoints to preserve.
         allpaths_check_safepts(visited, stack);
       }
     }
   }
 }
 //---------------------------is_deleteable_safept----------------------------
 // Is safept not required by an outer loop?
 bool PhaseIdealLoop::is_deleteable_safept(Node* sfpt) {
   assert(sfpt->Opcode() == Op_SafePoint, "");
   IdealLoopTree* lp = get_loop(sfpt)->_parent;
   while (lp != NULL) {
     Node_List* sfpts = lp->_required_safept;
     if (sfpts != NULL) {
       for (uint i = 0; i < sfpts->size(); i++) {
         if (sfpt == sfpts->at(i))
           return false;
       }
     }
     lp = lp->_parent;
   }
   return true;
 }
 //------------------------------counted_loop-----------------------------------
 // Convert to counted loops where possible
 void IdealLoopTree::counted_loop( PhaseIdealLoop *phase ) {
   // For grins, set the inner-loop flag here
   if( !_child ) {
     if( _head->is_Loop() ) _head->as_Loop()->set_inner_loop();
   }
   if( _head->is_CountedLoop() ||
       phase->is_counted_loop( _head, this ) ) {
     _has_sfpt = 1;              // Indicate we do not need a safepoint here
     // Look for a safepoint to remove
     for (Node* n = tail(); n != _head; n = phase->idom(n))
       if (n->Opcode() == Op_SafePoint && phase->get_loop(n) == this &&
           phase->is_deleteable_safept(n))
         phase->lazy_replace(n,n->in(TypeFunc::Control));
     CountedLoopNode *cl = _head->as_CountedLoop();
     Node *incr = cl->incr();
     if( !incr ) return;         // Dead loop?
     Node *init = cl->init_trip();
     Node *phi  = cl->phi();
     // protect against stride not being a constant
     if( !cl->stride_is_con() ) return;
     int stride_con = cl->stride_con();
     // Look for induction variables
     // Visit all children, looking for Phis
     for (DUIterator i = cl->outs(); cl->has_out(i); i++) {
       Node *out = cl->out(i);
       // Look for other phis (secondary IVs). Skip dead ones
       if (!out->is_Phi() || out == phi || !phase->has_node(out)) continue;
       PhiNode* phi2 = out->as_Phi();
       Node *incr2 = phi2->in( LoopNode::LoopBackControl );
       // Look for induction variables of the form:  X += constant
       if( phi2->region() != _head ||
           incr2->req() != 3 ||
           incr2->in(1) != phi2 ||
           incr2 == incr ||
           incr2->Opcode() != Op_AddI ||
           !incr2->in(2)->is_Con() )
         continue;
       // Check for parallel induction variable (parallel to trip counter)
       // via an affine function.  In particular, count-down loops with
       // count-up array indices are common. We only RCE references off
       // the trip-counter, so we need to convert all these to trip-counter
       // expressions.
       Node *init2 = phi2->in( LoopNode::EntryControl );
       int stride_con2 = incr2->in(2)->get_int();
       // The general case here gets a little tricky.  We want to find the
       // GCD of all possible parallel IV's and make a new IV using this
       // GCD for the loop.  Then all possible IVs are simple multiples of
       // the GCD.  In practice, this will cover very few extra loops.
       // Instead we require 'stride_con2' to be a multiple of 'stride_con',
       // where +/-1 is the common case, but other integer multiples are
       // also easy to handle.
       int ratio_con = stride_con2/stride_con;
       if( ratio_con * stride_con == stride_con2 ) { // Check for exact
         // Convert to using the trip counter.  The parallel induction
         // variable differs from the trip counter by a loop-invariant
         // amount, the difference between their respective initial values.
         // It is scaled by the 'ratio_con'.
         Compile* C = phase->C;
         Node* ratio = phase->_igvn.intcon(ratio_con);
         phase->set_ctrl(ratio, C->root());
         Node* ratio_init = new (C, 3) MulINode(init, ratio);
         phase->_igvn.register_new_node_with_optimizer(ratio_init, init);
         phase->set_early_ctrl(ratio_init);
         Node* diff = new (C, 3) SubINode(init2, ratio_init);
         phase->_igvn.register_new_node_with_optimizer(diff, init2);
         phase->set_early_ctrl(diff);
         Node* ratio_idx = new (C, 3) MulINode(phi, ratio);
         phase->_igvn.register_new_node_with_optimizer(ratio_idx, phi);
         phase->set_ctrl(ratio_idx, cl);
         Node* add  = new (C, 3) AddINode(ratio_idx, diff);
         phase->_igvn.register_new_node_with_optimizer(add);
         phase->set_ctrl(add, cl);
         phase->_igvn.replace_node( phi2, add );
         // Sometimes an induction variable is unused
         if (add->outcnt() == 0) {
           phase->_igvn.remove_dead_node(add);
         }
         --i; // deleted this phi; rescan starting with next position
         continue;
       }
     }
   } else if (_parent != NULL && !_irreducible) {
     // Not a counted loop.
     // Look for a safepoint on the idom-path to remove, preserving the first one
     bool found = false;
     Node* n = tail();
     for (; n != _head && !found; n = phase->idom(n)) {
       if (n->Opcode() == Op_SafePoint && phase->get_loop(n) == this)
         found = true; // Found one
     }
     // Skip past it and delete the others
     for (; n != _head; n = phase->idom(n)) {
       if (n->Opcode() == Op_SafePoint && phase->get_loop(n) == this &&
           phase->is_deleteable_safept(n))
         phase->lazy_replace(n,n->in(TypeFunc::Control));
     }
   }
   // Recursively
   if( _child ) _child->counted_loop( phase );
   if( _next  ) _next ->counted_loop( phase );
 }
 #ifndef PRODUCT
 //------------------------------dump_head--------------------------------------
 // Dump 1 liner for loop header info
 void IdealLoopTree::dump_head( ) const {
   for( uint i=0; i<_nest; i++ )
     tty->print("  ");
   tty->print("Loop: N%d/N%d ",_head->_idx,_tail->_idx);
   if( _irreducible ) tty->print(" IRREDUCIBLE");
   if( _head->is_CountedLoop() ) {
     CountedLoopNode *cl = _head->as_CountedLoop();
     tty->print(" counted");
     if( cl->is_pre_loop () ) tty->print(" pre" );
     if( cl->is_main_loop() ) tty->print(" main");
     if( cl->is_post_loop() ) tty->print(" post");
   }
   tty->cr();
 }
 //------------------------------dump-------------------------------------------
 // Dump loops by loop tree
 void IdealLoopTree::dump( ) const {
   dump_head();
   if( _child ) _child->dump();
   if( _next  ) _next ->dump();
 }
 #endif
 static void log_loop_tree(IdealLoopTree* root, IdealLoopTree* loop, CompileLog* log) {
   if (loop == root) {
     if (loop->_child != NULL) {
       log->begin_head("loop_tree");
       log->end_head();
       if( loop->_child ) log_loop_tree(root, loop->_child, log);
       log->tail("loop_tree");
       assert(loop->_next == NULL, "what?");
     }
   } else {
     Node* head = loop->_head;
     log->begin_head("loop");
     log->print(" idx='%d' ", head->_idx);
     if (loop->_irreducible) log->print("irreducible='1' ");
     if (head->is_Loop()) {
       if (head->as_Loop()->is_inner_loop()) log->print("inner_loop='1' ");
       if (head->as_Loop()->is_partial_peel_loop()) log->print("partial_peel_loop='1' ");
     }
     if (head->is_CountedLoop()) {
       CountedLoopNode* cl = head->as_CountedLoop();
       if (cl->is_pre_loop())  log->print("pre_loop='%d' ",  cl->main_idx());
       if (cl->is_main_loop()) log->print("main_loop='%d' ", cl->_idx);
       if (cl->is_post_loop()) log->print("post_loop='%d' ",  cl->main_idx());
     }
     log->end_head();
     if( loop->_child ) log_loop_tree(root, loop->_child, log);
     log->tail("loop");
     if( loop->_next  ) log_loop_tree(root, loop->_next, log);
   }
 }
 //---------------------collect_potentially_useful_predicates-----------------------
 // Helper function to collect potentially useful predicates to prevent them from
 // being eliminated by PhaseIdealLoop::eliminate_useless_predicates
 void PhaseIdealLoop::collect_potentially_useful_predicates(
                          IdealLoopTree * loop, Unique_Node_List &useful_predicates) {
   if (loop->_child) { // child
     collect_potentially_useful_predicates(loop->_child, useful_predicates);
   }
   // self (only loops that we can apply loop predication may use their predicates)
   if (loop->_head->is_Loop()     &&
       !loop->_irreducible        &&
       !loop->tail()->is_top()) {
     LoopNode *lpn  = loop->_head->as_Loop();
     Node* entry = lpn->in(LoopNode::EntryControl);
     ProjNode *predicate_proj = find_predicate_insertion_point(entry);
     if (predicate_proj != NULL ) { // right pattern that can be used by loop predication
       assert(entry->in(0)->in(1)->in(1)->Opcode()==Op_Opaque1, "must be");
       useful_predicates.push(entry->in(0)->in(1)->in(1)); // good one
     }
   }
   if ( loop->_next ) { // sibling
     collect_potentially_useful_predicates(loop->_next, useful_predicates);
   }
 }
 //------------------------eliminate_useless_predicates-----------------------------
 // Eliminate all inserted predicates if they could not be used by loop predication.
 void PhaseIdealLoop::eliminate_useless_predicates() {
   if (C->predicate_count() == 0) return; // no predicate left
   Unique_Node_List useful_predicates; // to store useful predicates
   if (C->has_loops()) {
     collect_potentially_useful_predicates(_ltree_root->_child, useful_predicates);
   }
   for (int i = C->predicate_count(); i > 0; i--) {
      Node * n = C->predicate_opaque1_node(i-1);
      assert(n->Opcode() == Op_Opaque1, "must be");
      if (!useful_predicates.member(n)) { // not in the useful list
        _igvn.replace_node(n, n->in(1));
      }
   }
 }
 //=============================================================================
 //----------------------------build_and_optimize-------------------------------
 // Create a PhaseLoop.  Build the ideal Loop tree.  Map each Ideal Node to
 // its corresponding LoopNode.  If 'optimize' is true, do some loop cleanups.
 void PhaseIdealLoop::build_and_optimize(bool do_split_ifs, bool do_loop_pred) {
   int old_progress = C->major_progress();
   // Reset major-progress flag for the driver's heuristics
   C->clear_major_progress();
 #ifndef PRODUCT
   // Capture for later assert
   uint unique = C->unique();
   _loop_invokes++;
   _loop_work += unique;
 #endif
   // True if the method has at least 1 irreducible loop
   _has_irreducible_loops = false;
   _created_loop_node = false;
   Arena *a = Thread::current()->resource_area();
   VectorSet visited(a);
   // Pre-grow the mapping from Nodes to IdealLoopTrees.
   _nodes.map(C->unique(), NULL);
   memset(_nodes.adr(), 0, wordSize * C->unique());
   // Pre-build the top-level outermost loop tree entry
   _ltree_root = new IdealLoopTree( this, C->root(), C->root() );
   // Do not need a safepoint at the top level
   _ltree_root->_has_sfpt = 1;
   // Empty pre-order array
   allocate_preorders();
   // Build a loop tree on the fly.  Build a mapping from CFG nodes to
   // IdealLoopTree entries.  Data nodes are NOT walked.
   build_loop_tree();
   // Check for bailout, and return
   if (C->failing()) {
     return;
   }
   // No loops after all
   if( !_ltree_root->_child && !_verify_only ) C->set_has_loops(false);
   // There should always be an outer loop containing the Root and Return nodes.
   // If not, we have a degenerate empty program.  Bail out in this case.
   if (!has_node(C->root())) {
     if (!_verify_only) {
       C->clear_major_progress();
       C->record_method_not_compilable("empty program detected during loop optimization");
     }
     return;
   }
   // Nothing to do, so get out
   if( !C->has_loops() && !do_split_ifs && !_verify_me && !_verify_only ) {
     _igvn.optimize();           // Cleanup NeverBranches
     return;
   }
   // Set loop nesting depth
   _ltree_root->set_nest( 0 );
   // Split shared headers and insert loop landing pads.
   // Do not bother doing this on the Root loop of course.
   if( !_verify_me && !_verify_only && _ltree_root->_child ) {
     if( _ltree_root->_child->beautify_loops( this ) ) {
       // Re-build loop tree!
       _ltree_root->_child = NULL;
       _nodes.clear();
       reallocate_preorders();
       build_loop_tree();
       // Check for bailout, and return
       if (C->failing()) {
         return;
       }
       // Reset loop nesting depth
       _ltree_root->set_nest( 0 );
       C->print_method("After beautify loops", 3);
     }
   }
   // Build Dominators for elision of NULL checks & loop finding.
   // Since nodes do not have a slot for immediate dominator, make
   // a persistent side array for that info indexed on node->_idx.
   _idom_size = C->unique();
   _idom      = NEW_RESOURCE_ARRAY( Node*, _idom_size );
   _dom_depth = NEW_RESOURCE_ARRAY( uint,  _idom_size );
   _dom_stk   = NULL; // Allocated on demand in recompute_dom_depth
   memset( _dom_depth, 0, _idom_size * sizeof(uint) );
   Dominators();
   if (!_verify_only) {
     // As a side effect, Dominators removed any unreachable CFG paths
     // into RegionNodes.  It doesn't do this test against Root, so
     // we do it here.
     for( uint i = 1; i < C->root()->req(); i++ ) {
       if( !_nodes[C->root()->in(i)->_idx] ) {    // Dead path into Root?
         _igvn.hash_delete(C->root());
         C->root()->del_req(i);
         _igvn._worklist.push(C->root());
         i--;                      // Rerun same iteration on compressed edges
       }
     }
     // Given dominators, try to find inner loops with calls that must
     // always be executed (call dominates loop tail).  These loops do
     // not need a separate safepoint.
     Node_List cisstack(a);
     _ltree_root->check_safepts(visited, cisstack);
   }
   // Walk the DATA nodes and place into loops.  Find earliest control
   // node.  For CFG nodes, the _nodes array starts out and remains
   // holding the associated IdealLoopTree pointer.  For DATA nodes, the
   // _nodes array holds the earliest legal controlling CFG node.
   // Allocate stack with enough space to avoid frequent realloc
   int stack_size = (C->unique() >> 1) + 16; // (unique>>1)+16 from Java2D stats
   Node_Stack nstack( a, stack_size );
   visited.Clear();
   Node_List worklist(a);
   // Don't need C->root() on worklist since
   // it will be processed among C->top() inputs
   worklist.push( C->top() );
   visited.set( C->top()->_idx ); // Set C->top() as visited now
   build_loop_early( visited, worklist, nstack );
   // Given early legal placement, try finding counted loops.  This placement
   // is good enough to discover most loop invariants.
   if( !_verify_me && !_verify_only )
     _ltree_root->counted_loop( this );
   // Find latest loop placement.  Find ideal loop placement.
   visited.Clear();
   init_dom_lca_tags();
   // Need C->root() on worklist when processing outs
   worklist.push( C->root() );
   NOT_PRODUCT( C->verify_graph_edges(); )
   worklist.push( C->top() );
   build_loop_late( visited, worklist, nstack );
   if (_verify_only) {
     // restore major progress flag
     for (int i = 0; i < old_progress; i++)
       C->set_major_progress();
     assert(C->unique() == unique, "verification mode made Nodes? ? ?");
     assert(_igvn._worklist.size() == 0, "shouldn't push anything");
     return;
   }
   // some parser-inserted loop predicates could never be used by loop
   // predication. Eliminate them before loop optimization
   if (UseLoopPredicate) {
     eliminate_useless_predicates();
   }
   // clear out the dead code
   while(_deadlist.size()) {
     _igvn.remove_globally_dead_node(_deadlist.pop());
   }
 #ifndef PRODUCT
   C->verify_graph_edges();
   if( _verify_me ) {             // Nested verify pass?
     // Check to see if the verify mode is broken
     assert(C->unique() == unique, "non-optimize mode made Nodes? ? ?");
     return;
   }
   if( VerifyLoopOptimizations ) verify();
 #endif
   if (ReassociateInvariants) {
     // Reassociate invariants and prep for split_thru_phi
     for (LoopTreeIterator iter(_ltree_root); !iter.done(); iter.next()) {
       IdealLoopTree* lpt = iter.current();
       if (!lpt->is_counted() || !lpt->is_inner()) continue;
       lpt->reassociate_invariants(this);
       // Because RCE opportunities can be masked by split_thru_phi,
       // look for RCE candidates and inhibit split_thru_phi
       // on just their loop-phi's for this pass of loop opts
       if (SplitIfBlocks && do_split_ifs) {
         if (lpt->policy_range_check(this)) {
           lpt->_rce_candidate = 1; // = true
         }
       }
     }
   }
   // Check for aggressive application of split-if and other transforms
   // that require basic-block info (like cloning through Phi's)
   if( SplitIfBlocks && do_split_ifs ) {
     visited.Clear();
     split_if_with_blocks( visited, nstack );
     NOT_PRODUCT( if( VerifyLoopOptimizations ) verify(); );
   }
   // Perform loop predication before iteration splitting
   if (do_loop_pred && C->has_loops() && !C->major_progress()) {
     _ltree_root->_child->loop_predication(this);
   }
   if (OptimizeFill && UseLoopPredicate && C->has_loops() && !C->major_progress()) {
     if (do_intrinsify_fill()) {
       C->set_major_progress();
     }
   }
   // Perform iteration-splitting on inner loops.  Split iterations to avoid
   // range checks or one-shot null checks.
   // If split-if's didn't hack the graph too bad (no CFG changes)
   // then do loop opts.
   if (C->has_loops() && !C->major_progress()) {
     memset( worklist.adr(), 0, worklist.Size()*sizeof(Node*) );
     _ltree_root->_child->iteration_split( this, worklist );
     // No verify after peeling!  GCM has hoisted code out of the loop.
     // After peeling, the hoisted code could sink inside the peeled area.
     // The peeling code does not try to recompute the best location for
     // all the code before the peeled area, so the verify pass will always
     // complain about it.
   }
   // Do verify graph edges in any case
   NOT_PRODUCT( C->verify_graph_edges(); );
   if (!do_split_ifs) {
     // We saw major progress in Split-If to get here.  We forced a
     // pass with unrolling and not split-if, however more split-if's
     // might make progress.  If the unrolling didn't make progress
     // then the major-progress flag got cleared and we won't try
     // another round of Split-If.  In particular the ever-common
     // instance-of/check-cast pattern requires at least 2 rounds of
     // Split-If to clear out.
     C->set_major_progress();
   }
   // Repeat loop optimizations if new loops were seen
   if (created_loop_node()) {
     C->set_major_progress();
   }
   // Convert scalar to superword operations
   if (UseSuperWord && C->has_loops() && !C->major_progress()) {
     // SuperWord transform
     SuperWord sw(this);
     for (LoopTreeIterator iter(_ltree_root); !iter.done(); iter.next()) {
       IdealLoopTree* lpt = iter.current();
       if (lpt->is_counted()) {
         sw.transform_loop(lpt);
       }
     }
   }
   // Cleanup any modified bits
   _igvn.optimize();
   // disable assert until issue with split_flow_path is resolved (6742111)
   // assert(!_has_irreducible_loops || C->parsed_irreducible_loop() || C->is_osr_compilation(),
   //        "shouldn't introduce irreducible loops");
   if (C->log() != NULL) {
     log_loop_tree(_ltree_root, _ltree_root, C->log());
   }
 }
 #ifndef PRODUCT
 //------------------------------print_statistics-------------------------------
 int PhaseIdealLoop::_loop_invokes=0;// Count of PhaseIdealLoop invokes
 int PhaseIdealLoop::_loop_work=0; // Sum of PhaseIdealLoop x unique
 void PhaseIdealLoop::print_statistics() {
   tty->print_cr("PhaseIdealLoop=%d, sum _unique=%d", _loop_invokes, _loop_work);
 }
 //------------------------------verify-----------------------------------------
 // Build a verify-only PhaseIdealLoop, and see that it agrees with me.
 static int fail;                // debug only, so its multi-thread dont care
 void PhaseIdealLoop::verify() const {
   int old_progress = C->major_progress();
   ResourceMark rm;
   PhaseIdealLoop loop_verify( _igvn, this );
   VectorSet visited(Thread::current()->resource_area());
   fail = 0;
   verify_compare( C->root(), &loop_verify, visited );
   assert( fail == 0, "verify loops failed" );
   // Verify loop structure is the same
   _ltree_root->verify_tree(loop_verify._ltree_root, NULL);
   // Reset major-progress.  It was cleared by creating a verify version of
   // PhaseIdealLoop.
   for( int i=0; i<old_progress; i++ )
     C->set_major_progress();
 }
 //------------------------------verify_compare---------------------------------
 // Make sure me and the given PhaseIdealLoop agree on key data structures
 void PhaseIdealLoop::verify_compare( Node *n, const PhaseIdealLoop *loop_verify, VectorSet &visited ) const {
   if( !n ) return;
   if( visited.test_set( n->_idx ) ) return;
   if( !_nodes[n->_idx] ) {      // Unreachable
     assert( !loop_verify->_nodes[n->_idx], "both should be unreachable" );
     return;
   }
   uint i;
   for( i = 0; i < n->req(); i++ )
     verify_compare( n->in(i), loop_verify, visited );
   // Check the '_nodes' block/loop structure
   i = n->_idx;
   if( has_ctrl(n) ) {           // We have control; verify has loop or ctrl
     if( _nodes[i] != loop_verify->_nodes[i] &&
         get_ctrl_no_update(n) != loop_verify->get_ctrl_no_update(n) ) {
       tty->print("Mismatched control setting for: ");
       n->dump();
       if( fail++ > 10 ) return;
       Node *c = get_ctrl_no_update(n);
       tty->print("We have it as: ");
       if( c->in(0) ) c->dump();
         else tty->print_cr("N%d",c->_idx);
       tty->print("Verify thinks: ");
       if( loop_verify->has_ctrl(n) )
         loop_verify->get_ctrl_no_update(n)->dump();
       else
         loop_verify->get_loop_idx(n)->dump();
       tty->cr();
     }
   } else {                    // We have a loop
     IdealLoopTree *us = get_loop_idx(n);
     if( loop_verify->has_ctrl(n) ) {
       tty->print("Mismatched loop setting for: ");
       n->dump();
       if( fail++ > 10 ) return;
       tty->print("We have it as: ");
       us->dump();
       tty->print("Verify thinks: ");
       loop_verify->get_ctrl_no_update(n)->dump();
       tty->cr();
     } else if (!C->major_progress()) {
       // Loop selection can be messed up if we did a major progress
       // operation, like split-if.  Do not verify in that case.
       IdealLoopTree *them = loop_verify->get_loop_idx(n);
       if( us->_head != them->_head ||  us->_tail != them->_tail ) {
         tty->print("Unequals loops for: ");
         n->dump();
         if( fail++ > 10 ) return;
         tty->print("We have it as: ");
         us->dump();
         tty->print("Verify thinks: ");
         them->dump();
         tty->cr();
       }
     }
   }
   // Check for immediate dominators being equal
   if( i >= _idom_size ) {
     if( !n->is_CFG() ) return;
     tty->print("CFG Node with no idom: ");
     n->dump();
     return;
   }
   if( !n->is_CFG() ) return;
   if( n == C->root() ) return; // No IDOM here
   assert(n->_idx == i, "sanity");
   Node *id = idom_no_update(n);
   if( id != loop_verify->idom_no_update(n) ) {
     tty->print("Unequals idoms for: ");
     n->dump();
     if( fail++ > 10 ) return;
     tty->print("We have it as: ");
     id->dump();
     tty->print("Verify thinks: ");
     loop_verify->idom_no_update(n)->dump();
     tty->cr();
   }
 }
 //------------------------------verify_tree------------------------------------
 // Verify that tree structures match.  Because the CFG can change, siblings
 // within the loop tree can be reordered.  We attempt to deal with that by
 // reordering the verify's loop tree if possible.
 void IdealLoopTree::verify_tree(IdealLoopTree *loop, const IdealLoopTree *parent) const {
   assert( _parent == parent, "Badly formed loop tree" );
   // Siblings not in same order?  Attempt to re-order.
   if( _head != loop->_head ) {
     // Find _next pointer to update
     IdealLoopTree **pp = &loop->_parent->_child;
     while( *pp != loop )
       pp = &((*pp)->_next);
     // Find proper sibling to be next
     IdealLoopTree **nn = &loop->_next;
     while( (*nn) && (*nn)->_head != _head )
       nn = &((*nn)->_next);
     // Check for no match.
     if( !(*nn) ) {
       // Annoyingly, irreducible loops can pick different headers
       // after a major_progress operation, so the rest of the loop
       // tree cannot be matched.
       if (_irreducible && Compile::current()->major_progress())  return;
       assert( 0, "failed to match loop tree" );
     }
     // Move (*nn) to (*pp)
     IdealLoopTree *hit = *nn;
     *nn = hit->_next;
     hit->_next = loop;
     *pp = loop;
     loop = hit;
     // Now try again to verify
   }
   assert( _head  == loop->_head , "mismatched loop head" );
   Node *tail = _tail;           // Inline a non-updating version of
   while( !tail->in(0) )         // the 'tail()' call.
     tail = tail->in(1);
   assert( tail == loop->_tail, "mismatched loop tail" );
   // Counted loops that are guarded should be able to find their guards
   if( _head->is_CountedLoop() && _head->as_CountedLoop()->is_main_loop() ) {
     CountedLoopNode *cl = _head->as_CountedLoop();
     Node *init = cl->init_trip();
     Node *ctrl = cl->in(LoopNode::EntryControl);
     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, "" );
     Node *add  = cmp->in(1);
     Node *opaq;
     if( add->Opcode() == Op_Opaque1 ) {
       opaq = add;
     } else {
       assert( add->Opcode() == Op_AddI || add->Opcode() == Op_ConI , "" );
       assert( add == init, "" );
       opaq = cmp->in(2);
     }
     assert( opaq->Opcode() == Op_Opaque1, "" );
   }
   if (_child != NULL)  _child->verify_tree(loop->_child, this);
   if (_next  != NULL)  _next ->verify_tree(loop->_next,  parent);
   // Innermost loops need to verify loop bodies,
   // but only if no 'major_progress'
   int fail = 0;
   if (!Compile::current()->major_progress() && _child == NULL) {
     for( uint i = 0; i < _body.size(); i++ ) {
       Node *n = _body.at(i);
       if (n->outcnt() == 0)  continue; // Ignore dead
       uint j;
       for( j = 0; j < loop->_body.size(); j++ )
         if( loop->_body.at(j) == n )
           break;
       if( j == loop->_body.size() ) { // Not found in loop body
         // Last ditch effort to avoid assertion: Its possible that we
         // have some users (so outcnt not zero) but are still dead.
         // Try to find from root.
         if (Compile::current()->root()->find(n->_idx)) {
           fail++;
           tty->print("We have that verify does not: ");
           n->dump();
         }
       }
     }
     for( uint i2 = 0; i2 < loop->_body.size(); i2++ ) {
       Node *n = loop->_body.at(i2);
       if (n->outcnt() == 0)  continue; // Ignore dead
       uint j;
       for( j = 0; j < _body.size(); j++ )
         if( _body.at(j) == n )
           break;
       if( j == _body.size() ) { // Not found in loop body
         // Last ditch effort to avoid assertion: Its possible that we
         // have some users (so outcnt not zero) but are still dead.
         // Try to find from root.
         if (Compile::current()->root()->find(n->_idx)) {
           fail++;
           tty->print("Verify has that we do not: ");
           n->dump();
         }
       }
     }
     assert( !fail, "loop body mismatch" );
   }
 }
 #endif
 //------------------------------set_idom---------------------------------------
 void PhaseIdealLoop::set_idom(Node* d, Node* n, uint dom_depth) {
   uint idx = d->_idx;
   if (idx >= _idom_size) {
     uint newsize = _idom_size<<1;
     while( idx >= newsize ) {
       newsize <<= 1;
     }
     _idom      = REALLOC_RESOURCE_ARRAY( Node*,     _idom,_idom_size,newsize);
     _dom_depth = REALLOC_RESOURCE_ARRAY( uint, _dom_depth,_idom_size,newsize);
     memset( _dom_depth + _idom_size, 0, (newsize - _idom_size) * sizeof(uint) );
     _idom_size = newsize;
   }
   _idom[idx] = n;
   _dom_depth[idx] = dom_depth;
 }
 //------------------------------recompute_dom_depth---------------------------------------
 // The dominator tree is constructed with only parent pointers.
 // This recomputes the depth in the tree by first tagging all
 // nodes as "no depth yet" marker.  The next pass then runs up
 // the dom tree from each node marked "no depth yet", and computes
 // the depth on the way back down.
 void PhaseIdealLoop::recompute_dom_depth() {
   uint no_depth_marker = C->unique();
   uint i;
   // Initialize depth to "no depth yet"
   for (i = 0; i < _idom_size; i++) {
     if (_dom_depth[i] > 0 && _idom[i] != NULL) {
      _dom_depth[i] = no_depth_marker;
     }
   }
   if (_dom_stk == NULL) {
     uint init_size = C->unique() / 100; // Guess that 1/100 is a reasonable initial size.
     if (init_size < 10) init_size = 10;
     _dom_stk = new (C->node_arena()) GrowableArray<uint>(C->node_arena(), init_size, 0, 0);
   }
   // Compute new depth for each node.
   for (i = 0; i < _idom_size; i++) {
     uint j = i;
     // Run up the dom tree to find a node with a depth
     while (_dom_depth[j] == no_depth_marker) {
       _dom_stk->push(j);
       j = _idom[j]->_idx;
     }
     // Compute the depth on the way back down this tree branch
     uint dd = _dom_depth[j] + 1;
     while (_dom_stk->length() > 0) {
       uint j = _dom_stk->pop();
       _dom_depth[j] = dd;
       dd++;
     }
   }
 }
 //------------------------------sort-------------------------------------------
 // Insert 'loop' into the existing loop tree.  'innermost' is a leaf of the
 // loop tree, not the root.
 IdealLoopTree *PhaseIdealLoop::sort( IdealLoopTree *loop, IdealLoopTree *innermost ) {
   if( !innermost ) return loop; // New innermost loop
   int loop_preorder = get_preorder(loop->_head); // Cache pre-order number
   assert( loop_preorder, "not yet post-walked loop" );
   IdealLoopTree **pp = &innermost;      // Pointer to previous next-pointer
   IdealLoopTree *l = *pp;               // Do I go before or after 'l'?
   // Insert at start of list
   while( l ) {                  // Insertion sort based on pre-order
     if( l == loop ) return innermost; // Already on list!
     int l_preorder = get_preorder(l->_head); // Cache pre-order number
     assert( l_preorder, "not yet post-walked l" );
     // Check header pre-order number to figure proper nesting
     if( loop_preorder > l_preorder )
       break;                    // End of insertion
     // If headers tie (e.g., shared headers) check tail pre-order numbers.
     // Since I split shared headers, you'd think this could not happen.
     // BUT: I must first do the preorder numbering before I can discover I
     // have shared headers, so the split headers all get the same preorder
     // number as the RegionNode they split from.
     if( loop_preorder == l_preorder &&
         get_preorder(loop->_tail) < get_preorder(l->_tail) )
       break;                    // Also check for shared headers (same pre#)
     pp = &l->_parent;           // Chain up list
     l = *pp;
   }
   // Link into list
   // Point predecessor to me
   *pp = loop;
   // Point me to successor
   IdealLoopTree *p = loop->_parent;
   loop->_parent = l;            // Point me to successor
   if( p ) sort( p, innermost ); // Insert my parents into list as well
   return innermost;
 }
 //------------------------------build_loop_tree--------------------------------
 // I use a modified Vick/Tarjan algorithm.  I need pre- and a post- visit
 // bits.  The _nodes[] array is mapped by Node index and holds a NULL for
 // not-yet-pre-walked, pre-order # for pre-but-not-post-walked and holds the
 // tightest enclosing IdealLoopTree for post-walked.
 //
 // During my forward walk I do a short 1-layer lookahead to see if I can find
 // a loop backedge with that doesn't have any work on the backedge.  This
 // helps me construct nested loops with shared headers better.
 //
 // Once I've done the forward recursion, I do the post-work.  For each child
 // I check to see if there is a backedge.  Backedges define a loop!  I
 // insert an IdealLoopTree at the target of the backedge.
 //
 // During the post-work I also check to see if I have several children
 // belonging to different loops.  If so, then this Node is a decision point
 // where control flow can choose to change loop nests.  It is at this
 // decision point where I can figure out how loops are nested.  At this
 // time I can properly order the different loop nests from my children.
 // Note that there may not be any backedges at the decision point!
 //
 // Since the decision point can be far removed from the backedges, I can't
 // order my loops at the time I discover them.  Thus at the decision point
 // I need to inspect loop header pre-order numbers to properly nest my
 // loops.  This means I need to sort my childrens' loops by pre-order.
 // The sort is of size number-of-control-children, which generally limits
 // it to size 2 (i.e., I just choose between my 2 target loops).
 void PhaseIdealLoop::build_loop_tree() {
   // Allocate stack of size C->unique()/2 to avoid frequent realloc
   GrowableArray <Node *> bltstack(C->unique() >> 1);
   Node *n = C->root();
   bltstack.push(n);
   int pre_order = 1;
   int stack_size;
   while ( ( stack_size = bltstack.length() ) != 0 ) {
     n = bltstack.top(); // Leave node on stack
     if ( !is_visited(n) ) {
       // ---- Pre-pass Work ----
       // Pre-walked but not post-walked nodes need a pre_order number.
       set_preorder_visited( n, pre_order ); // set as visited
       // ---- Scan over children ----
       // Scan first over control projections that lead to loop headers.
       // This helps us find inner-to-outer loops with shared headers better.
       // Scan children's children for loop headers.
       for ( int i = n->outcnt() - 1; i >= 0; --i ) {
         Node* m = n->raw_out(i);       // Child
         if( m->is_CFG() && !is_visited(m) ) { // Only for CFG children
           // Scan over children's children to find loop
           for (DUIterator_Fast jmax, j = m->fast_outs(jmax); j < jmax; j++) {
             Node* l = m->fast_out(j);
             if( is_visited(l) &&       // Been visited?
                 !is_postvisited(l) &&  // But not post-visited
                 get_preorder(l) < pre_order ) { // And smaller pre-order
               // Found!  Scan the DFS down this path before doing other paths
               bltstack.push(m);
               break;
             }
           }
         }
       }
       pre_order++;
     }
     else if ( !is_postvisited(n) ) {
       // Note: build_loop_tree_impl() adds out edges on rare occasions,
       // such as com.sun.rsasign.am::a.
       // For non-recursive version, first, process current children.
       // On next iteration, check if additional children were added.
       for ( int k = n->outcnt() - 1; k >= 0; --k ) {
         Node* u = n->raw_out(k);
         if ( u->is_CFG() && !is_visited(u) ) {
           bltstack.push(u);
         }
       }
       if ( bltstack.length() == stack_size ) {
         // There were no additional children, post visit node now
         (void)bltstack.pop(); // Remove node from stack
         pre_order = build_loop_tree_impl( n, pre_order );
         // Check for bailout
         if (C->failing()) {
           return;
         }
         // Check to grow _preorders[] array for the case when
         // build_loop_tree_impl() adds new nodes.
         check_grow_preorders();
       }
     }
     else {
       (void)bltstack.pop(); // Remove post-visited node from stack
     }
   }
 }
 //------------------------------build_loop_tree_impl---------------------------
 int PhaseIdealLoop::build_loop_tree_impl( Node *n, int pre_order ) {
   // ---- Post-pass Work ----
   // Pre-walked but not post-walked nodes need a pre_order number.
   // Tightest enclosing loop for this Node
   IdealLoopTree *innermost = NULL;
   // For all children, see if any edge is a backedge.  If so, make a loop
   // for it.  Then find the tightest enclosing loop for the self Node.
   for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax; i++) {
     Node* m = n->fast_out(i);   // Child
     if( n == m ) continue;      // Ignore control self-cycles
     if( !m->is_CFG() ) continue;// Ignore non-CFG edges
     IdealLoopTree *l;           // Child's loop
     if( !is_postvisited(m) ) {  // Child visited but not post-visited?
       // Found a backedge
       assert( get_preorder(m) < pre_order, "should be backedge" );
       // Check for the RootNode, which is already a LoopNode and is allowed
       // to have multiple "backedges".
       if( m == C->root()) {     // Found the root?
         l = _ltree_root;        // Root is the outermost LoopNode
       } else {                  // Else found a nested loop
         // Insert a LoopNode to mark this loop.
         l = new IdealLoopTree(this, m, n);
       } // End of Else found a nested loop
       if( !has_loop(m) )        // If 'm' does not already have a loop set
         set_loop(m, l);         // Set loop header to loop now
     } else {                    // Else not a nested loop
       if( !_nodes[m->_idx] ) continue; // Dead code has no loop
       l = get_loop(m);          // Get previously determined loop
       // If successor is header of a loop (nest), move up-loop till it
       // is a member of some outer enclosing loop.  Since there are no
       // shared headers (I've split them already) I only need to go up
       // at most 1 level.
       while( l && l->_head == m ) // Successor heads loop?
         l = l->_parent;         // Move up 1 for me
       // If this loop is not properly parented, then this loop
       // has no exit path out, i.e. its an infinite loop.
       if( !l ) {
         // Make loop "reachable" from root so the CFG is reachable.  Basically
         // insert a bogus loop exit that is never taken.  'm', the loop head,
         // points to 'n', one (of possibly many) fall-in paths.  There may be
         // many backedges as well.
         // Here I set the loop to be the root loop.  I could have, after
         // inserting a bogus loop exit, restarted the recursion and found my
         // new loop exit.  This would make the infinite loop a first-class
         // loop and it would then get properly optimized.  What's the use of
         // optimizing an infinite loop?
         l = _ltree_root;        // Oops, found infinite loop
         if (!_verify_only) {
           // Insert the NeverBranch between 'm' and it's control user.
           NeverBranchNode *iff = new (C, 1) NeverBranchNode( m );
           _igvn.register_new_node_with_optimizer(iff);
           set_loop(iff, l);
           Node *if_t = new (C, 1) CProjNode( iff, 0 );
           _igvn.register_new_node_with_optimizer(if_t);
           set_loop(if_t, l);
           Node* cfg = NULL;       // Find the One True Control User of m
           for (DUIterator_Fast jmax, j = m->fast_outs(jmax); j < jmax; j++) {
             Node* x = m->fast_out(j);
             if (x->is_CFG() && x != m && x != iff)
               { cfg = x; break; }
           }
           assert(cfg != NULL, "must find the control user of m");
           uint k = 0;             // Probably cfg->in(0)
           while( cfg->in(k) != m ) k++; // But check incase cfg is a Region
           cfg->set_req( k, if_t ); // Now point to NeverBranch
           // Now create the never-taken loop exit
           Node *if_f = new (C, 1) CProjNode( iff, 1 );
           _igvn.register_new_node_with_optimizer(if_f);
           set_loop(if_f, l);
           // Find frame ptr for Halt.  Relies on the optimizer
           // V-N'ing.  Easier and quicker than searching through
           // the program structure.
           Node *frame = new (C, 1) ParmNode( C->start(), TypeFunc::FramePtr );
           _igvn.register_new_node_with_optimizer(frame);
           // Halt & Catch Fire
           Node *halt = new (C, TypeFunc::Parms) HaltNode( if_f, frame );
           _igvn.register_new_node_with_optimizer(halt);
           set_loop(halt, l);
           C->root()->add_req(halt);
         }
         set_loop(C->root(), _ltree_root);
       }
     }
     // Weeny check for irreducible.  This child was already visited (this
     // IS the post-work phase).  Is this child's loop header post-visited
     // as well?  If so, then I found another entry into the loop.
     if (!_verify_only) {
       while( is_postvisited(l->_head) ) {
         // found irreducible
         l->_irreducible = 1; // = true
         l = l->_parent;
         _has_irreducible_loops = true;
         // Check for bad CFG here to prevent crash, and bailout of compile
         if (l == NULL) {
           C->record_method_not_compilable("unhandled CFG detected during loop optimization");
           return pre_order;
         }
       }
     }
     // This Node might be a decision point for loops.  It is only if
     // it's children belong to several different loops.  The sort call
     // does a trivial amount of work if there is only 1 child or all
     // children belong to the same loop.  If however, the children
     // belong to different loops, the sort call will properly set the
     // _parent pointers to show how the loops nest.
     //
     // In any case, it returns the tightest enclosing loop.
     innermost = sort( l, innermost );
   }
   // Def-use info will have some dead stuff; dead stuff will have no
   // loop decided on.
   // Am I a loop header?  If so fix up my parent's child and next ptrs.
   if( innermost && innermost->_head == n ) {
     assert( get_loop(n) == innermost, "" );
     IdealLoopTree *p = innermost->_parent;
     IdealLoopTree *l = innermost;
     while( p && l->_head == n ) {
       l->_next = p->_child;     // Put self on parents 'next child'
       p->_child = l;            // Make self as first child of parent
       l = p;                    // Now walk up the parent chain
       p = l->_parent;
     }
   } else {
     // Note that it is possible for a LoopNode to reach here, if the
     // backedge has been made unreachable (hence the LoopNode no longer
     // denotes a Loop, and will eventually be removed).
     // Record tightest enclosing loop for self.  Mark as post-visited.
     set_loop(n, innermost);
     // Also record has_call flag early on
     if( innermost ) {
       if( n->is_Call() && !n->is_CallLeaf() && !n->is_macro() ) {
         // Do not count uncommon calls
         if( !n->is_CallStaticJava() || !n->as_CallStaticJava()->_name ) {
           Node *iff = n->in(0)->in(0);
           if( !iff->is_If() ||
               (n->in(0)->Opcode() == Op_IfFalse &&
                (1.0 - iff->as_If()->_prob) >= 0.01) ||
               (iff->as_If()->_prob >= 0.01) )
             innermost->_has_call = 1;
         }
       } else if( n->is_Allocate() && n->as_Allocate()->_is_scalar_replaceable ) {
         // Disable loop optimizations if the loop has a scalar replaceable
         // allocation. This disabling may cause a potential performance lost
         // if the allocation is not eliminated for some reason.
         innermost->_allow_optimizations = false;
         innermost->_has_call = 1; // = true
       }
     }
   }
   // Flag as post-visited now
   set_postvisited(n);
   return pre_order;
 }
 //------------------------------build_loop_early-------------------------------
 // Put Data nodes into some loop nest, by setting the _nodes[]->loop mapping.
 // First pass computes the earliest controlling node possible.  This is the
 // controlling input with the deepest dominating depth.
 void PhaseIdealLoop::build_loop_early( VectorSet &visited, Node_List &worklist, Node_Stack &nstack ) {
   while (worklist.size() != 0) {
     // Use local variables nstack_top_n & nstack_top_i to cache values
     // on nstack's top.
     Node *nstack_top_n = worklist.pop();
     uint  nstack_top_i = 0;
 //while_nstack_nonempty:
     while (true) {
       // Get parent node and next input's index from stack's top.
       Node  *n = nstack_top_n;
       uint   i = nstack_top_i;
       uint cnt = n->req(); // Count of inputs
       if (i == 0) {        // Pre-process the node.
         if( has_node(n) &&            // Have either loop or control already?
             !has_ctrl(n) ) {          // Have loop picked out already?
           // During "merge_many_backedges" we fold up several nested loops
           // into a single loop.  This makes the members of the original
           // loop bodies pointing to dead loops; they need to move up
           // to the new UNION'd larger loop.  I set the _head field of these
           // dead loops to NULL and the _parent field points to the owning
           // loop.  Shades of UNION-FIND algorithm.
           IdealLoopTree *ilt;
           while( !(ilt = get_loop(n))->_head ) {
             // Normally I would use a set_loop here.  But in this one special
             // case, it is legal (and expected) to change what loop a Node
             // belongs to.
             _nodes.map(n->_idx, (Node*)(ilt->_parent) );
           }
           // Remove safepoints ONLY if I've already seen I don't need one.
           // (the old code here would yank a 2nd safepoint after seeing a
           // first one, even though the 1st did not dominate in the loop body
           // and thus could be avoided indefinitely)
           if( !_verify_only && !_verify_me && ilt->_has_sfpt && n->Opcode() == Op_SafePoint &&
               is_deleteable_safept(n)) {
             Node *in = n->in(TypeFunc::Control);
             lazy_replace(n,in);       // Pull safepoint now
             // Carry on with the recursion "as if" we are walking
             // only the control input
             if( !visited.test_set( in->_idx ) ) {
               worklist.push(in);      // Visit this guy later, using worklist
             }
             // Get next node from nstack:
             // - skip n's inputs processing by setting i > cnt;
             // - we also will not call set_early_ctrl(n) since
             //   has_node(n) == true (see the condition above).
             i = cnt + 1;
           }
         }
       } // if (i == 0)
       // Visit all inputs
       bool done = true;       // Assume all n's inputs will be processed
       while (i < cnt) {
         Node *in = n->in(i);
         ++i;
         if (in == NULL) continue;
         if (in->pinned() && !in->is_CFG())
           set_ctrl(in, in->in(0));
         int is_visited = visited.test_set( in->_idx );
         if (!has_node(in)) {  // No controlling input yet?
           assert( !in->is_CFG(), "CFG Node with no controlling input?" );
           assert( !is_visited, "visit only once" );
           nstack.push(n, i);  // Save parent node and next input's index.
           nstack_top_n = in;  // Process current input now.
           nstack_top_i = 0;
           done = false;       // Not all n's inputs processed.
           break; // continue while_nstack_nonempty;
         } else if (!is_visited) {
           // This guy has a location picked out for him, but has not yet
           // been visited.  Happens to all CFG nodes, for instance.
           // Visit him using the worklist instead of recursion, to break
           // cycles.  Since he has a location already we do not need to
           // find his location before proceeding with the current Node.
           worklist.push(in);  // Visit this guy later, using worklist
         }
       }
       if (done) {
         // All of n's inputs have been processed, complete post-processing.
         // Compute earliest point this Node can go.
         // CFG, Phi, pinned nodes already know their controlling input.
         if (!has_node(n)) {
           // Record earliest legal location
           set_early_ctrl( n );
         }
         if (nstack.is_empty()) {
           // Finished all nodes on stack.
           // Process next node on the worklist.
           break;
         }
         // Get saved parent node and next input's index.
         nstack_top_n = nstack.node();
         nstack_top_i = nstack.index();
         nstack.pop();
       }
     } // while (true)
   }
 }
 //------------------------------dom_lca_internal--------------------------------
 // Pair-wise LCA
 Node *PhaseIdealLoop::dom_lca_internal( Node *n1, Node *n2 ) const {
   if( !n1 ) return n2;          // Handle NULL original LCA
   assert( n1->is_CFG(), "" );
   assert( n2->is_CFG(), "" );
   // find LCA of all uses
   uint d1 = dom_depth(n1);
   uint d2 = dom_depth(n2);
   while (n1 != n2) {
     if (d1 > d2) {
       n1 =      idom(n1);
       d1 = dom_depth(n1);
     } else if (d1 < d2) {
       n2 =      idom(n2);
       d2 = dom_depth(n2);
     } else {
       // Here d1 == d2.  Due to edits of the dominator-tree, sections
       // of the tree might have the same depth.  These sections have
       // to be searched more carefully.
       // Scan up all the n1's with equal depth, looking for n2.
       Node *t1 = idom(n1);
       while (dom_depth(t1) == d1) {
         if (t1 == n2)  return n2;
         t1 = idom(t1);
       }
       // Scan up all the n2's with equal depth, looking for n1.
       Node *t2 = idom(n2);
       while (dom_depth(t2) == d2) {
         if (t2 == n1)  return n1;
         t2 = idom(t2);
       }
       // Move up to a new dominator-depth value as well as up the dom-tree.
       n1 = t1;
       n2 = t2;
       d1 = dom_depth(n1);
       d2 = dom_depth(n2);
     }
   }
   return n1;
 }
 //------------------------------compute_idom-----------------------------------
 // Locally compute IDOM using dom_lca call.  Correct only if the incoming
 // IDOMs are correct.
 Node *PhaseIdealLoop::compute_idom( Node *region ) const {
   assert( region->is_Region(), "" );
   Node *LCA = NULL;
   for( uint i = 1; i < region->req(); i++ ) {
     if( region->in(i) != C->top() )
       LCA = dom_lca( LCA, region->in(i) );
   }
   return LCA;
 }
 bool PhaseIdealLoop::verify_dominance(Node* n, Node* use, Node* LCA, Node* early) {
   bool had_error = false;
 #ifdef ASSERT
   if (early != C->root()) {
     // Make sure that there's a dominance path from use to LCA
     Node* d = use;
     while (d != LCA) {
       d = idom(d);
       if (d == C->root()) {
         tty->print_cr("*** Use %d isn't dominated by def %s", use->_idx, n->_idx);
         n->dump();
         use->dump();
         had_error = true;
         break;
       }
     }
   }
 #endif
   return had_error;
 }
 Node* PhaseIdealLoop::compute_lca_of_uses(Node* n, Node* early, bool verify) {
   // Compute LCA over list of uses
   bool had_error = false;
   Node *LCA = NULL;
   for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax && LCA != early; i++) {
     Node* c = n->fast_out(i);
     if (_nodes[c->_idx] == NULL)
       continue;                 // Skip the occasional dead node
     if( c->is_Phi() ) {         // For Phis, we must land above on the path
       for( uint j=1; j<c->req(); j++ ) {// For all inputs
         if( c->in(j) == n ) {   // Found matching input?
           Node *use = c->in(0)->in(j);
           if (_verify_only && use->is_top()) continue;
           LCA = dom_lca_for_get_late_ctrl( LCA, use, n );
           if (verify) had_error = verify_dominance(n, use, LCA, early) || had_error;
         }
       }
     } else {
       // For CFG data-users, use is in the block just prior
       Node *use = has_ctrl(c) ? get_ctrl(c) : c->in(0);
       LCA = dom_lca_for_get_late_ctrl( LCA, use, n );
       if (verify) had_error = verify_dominance(n, use, LCA, early) || had_error;
     }
   }
   assert(!had_error, "bad dominance");
   return LCA;
 }
 //------------------------------get_late_ctrl----------------------------------
 // Compute latest legal control.
 Node *PhaseIdealLoop::get_late_ctrl( Node *n, Node *early ) {
   assert(early != NULL, "early control should not be NULL");
   Node* LCA = compute_lca_of_uses(n, early);
 #ifdef ASSERT
   if (LCA == C->root() && LCA != early) {
     // def doesn't dominate uses so print some useful debugging output
     compute_lca_of_uses(n, early, true);
   }
 #endif
   // if this is a load, check for anti-dependent stores
   // We use a conservative algorithm to identify potential interfering
   // instructions and for rescheduling the load.  The users of the memory
   // input of this load are examined.  Any use which is not a load and is
   // dominated by early is considered a potentially interfering store.
   // This can produce false positives.
   if (n->is_Load() && LCA != early) {
     Node_List worklist;
     Node *mem = n->in(MemNode::Memory);
     for (DUIterator_Fast imax, i = mem->fast_outs(imax); i < imax; i++) {
       Node* s = mem->fast_out(i);
       worklist.push(s);
     }
     while(worklist.size() != 0 && LCA != early) {
       Node* s = worklist.pop();
       if (s->is_Load()) {
         continue;
       } else if (s->is_MergeMem()) {
         for (DUIterator_Fast imax, i = s->fast_outs(imax); i < imax; i++) {
           Node* s1 = s->fast_out(i);
           worklist.push(s1);
         }
       } else {
         Node *sctrl = has_ctrl(s) ? get_ctrl(s) : s->in(0);
         assert(sctrl != NULL || s->outcnt() == 0, "must have control");
         if (sctrl != NULL && !sctrl->is_top() && is_dominator(early, sctrl)) {
           LCA = dom_lca_for_get_late_ctrl(LCA, sctrl, n);
         }
       }
     }
   }
   assert(LCA == find_non_split_ctrl(LCA), "unexpected late control");
   return LCA;
 }
 // true if CFG node d dominates CFG node n
 bool PhaseIdealLoop::is_dominator(Node *d, Node *n) {
   if (d == n)
     return true;
   assert(d->is_CFG() && n->is_CFG(), "must have CFG nodes");
   uint dd = dom_depth(d);
   while (dom_depth(n) >= dd) {
     if (n == d)
       return true;
     n = idom(n);
   }
   return false;
 }
 //------------------------------dom_lca_for_get_late_ctrl_internal-------------
 // Pair-wise LCA with tags.
 // Tag each index with the node 'tag' currently being processed
 // before advancing up the dominator chain using idom().
 // Later calls that find a match to 'tag' know that this path has already
 // been considered in the current LCA (which is input 'n1' by convention).
 // Since get_late_ctrl() is only called once for each node, the tag array
 // does not need to be cleared between calls to get_late_ctrl().
 // Algorithm trades a larger constant factor for better asymptotic behavior
 //
 Node *PhaseIdealLoop::dom_lca_for_get_late_ctrl_internal( Node *n1, Node *n2, Node *tag ) {
   uint d1 = dom_depth(n1);
   uint d2 = dom_depth(n2);
   do {
     if (d1 > d2) {
       // current lca is deeper than n2
       _dom_lca_tags.map(n1->_idx, tag);
       n1 =      idom(n1);
       d1 = dom_depth(n1);
     } else if (d1 < d2) {
       // n2 is deeper than current lca
       Node *memo = _dom_lca_tags[n2->_idx];
       if( memo == tag ) {
         return n1;    // Return the current LCA
       }
       _dom_lca_tags.map(n2->_idx, tag);
       n2 =      idom(n2);
       d2 = dom_depth(n2);
     } else {
       // Here d1 == d2.  Due to edits of the dominator-tree, sections
       // of the tree might have the same depth.  These sections have
       // to be searched more carefully.
       // Scan up all the n1's with equal depth, looking for n2.
       _dom_lca_tags.map(n1->_idx, tag);
       Node *t1 = idom(n1);
       while (dom_depth(t1) == d1) {
         if (t1 == n2)  return n2;
         _dom_lca_tags.map(t1->_idx, tag);
         t1 = idom(t1);
       }
       // Scan up all the n2's with equal depth, looking for n1.
       _dom_lca_tags.map(n2->_idx, tag);
       Node *t2 = idom(n2);
       while (dom_depth(t2) == d2) {
         if (t2 == n1)  return n1;
         _dom_lca_tags.map(t2->_idx, tag);
         t2 = idom(t2);
       }
       // Move up to a new dominator-depth value as well as up the dom-tree.
       n1 = t1;
       n2 = t2;
       d1 = dom_depth(n1);
       d2 = dom_depth(n2);
     }
   } while (n1 != n2);
   return n1;
 }
 //------------------------------init_dom_lca_tags------------------------------
 // Tag could be a node's integer index, 32bits instead of 64bits in some cases
 // Intended use does not involve any growth for the array, so it could
 // be of fixed size.
 void PhaseIdealLoop::init_dom_lca_tags() {
   uint limit = C->unique() + 1;
   _dom_lca_tags.map( limit, NULL );
 #ifdef ASSERT
   for( uint i = 0; i < limit; ++i ) {
     assert(_dom_lca_tags[i] == NULL, "Must be distinct from each node pointer");
   }
 #endif // ASSERT
 }
 //------------------------------clear_dom_lca_tags------------------------------
 // Tag could be a node's integer index, 32bits instead of 64bits in some cases
 // Intended use does not involve any growth for the array, so it could
 // be of fixed size.
 void PhaseIdealLoop::clear_dom_lca_tags() {
   uint limit = C->unique() + 1;
   _dom_lca_tags.map( limit, NULL );
   _dom_lca_tags.clear();
 #ifdef ASSERT
   for( uint i = 0; i < limit; ++i ) {
     assert(_dom_lca_tags[i] == NULL, "Must be distinct from each node pointer");
   }
 #endif // ASSERT
 }
 //------------------------------build_loop_late--------------------------------
 // Put Data nodes into some loop nest, by setting the _nodes[]->loop mapping.
 // Second pass finds latest legal placement, and ideal loop placement.
 void PhaseIdealLoop::build_loop_late( VectorSet &visited, Node_List &worklist, Node_Stack &nstack ) {
   while (worklist.size() != 0) {
     Node *n = worklist.pop();
     // Only visit once
     if (visited.test_set(n->_idx)) continue;
     uint cnt = n->outcnt();
     uint   i = 0;
     while (true) {
       assert( _nodes[n->_idx], "no dead nodes" );
       // Visit all children
       if (i < cnt) {
         Node* use = n->raw_out(i);
         ++i;
         // Check for dead uses.  Aggressively prune such junk.  It might be
         // dead in the global sense, but still have local uses so I cannot
         // easily call 'remove_dead_node'.
         if( _nodes[use->_idx] != NULL || use->is_top() ) { // Not dead?
           // Due to cycles, we might not hit the same fixed point in the verify
           // pass as we do in the regular pass.  Instead, visit such phis as
           // simple uses of the loop head.
           if( use->in(0) && (use->is_CFG() || use->is_Phi()) ) {
             if( !visited.test(use->_idx) )
               worklist.push(use);
           } else if( !visited.test_set(use->_idx) ) {
             nstack.push(n, i); // Save parent and next use's index.
             n   = use;         // Process all children of current use.
             cnt = use->outcnt();
             i   = 0;
           }
         } else {
           // Do not visit around the backedge of loops via data edges.
           // push dead code onto a worklist
           _deadlist.push(use);
         }
       } else {
         // All of n's children have been processed, complete post-processing.
         build_loop_late_post(n);
         if (nstack.is_empty()) {
           // Finished all nodes on stack.
           // Process next node on the worklist.
           break;
         }
         // Get saved parent node and next use's index. Visit the rest of uses.
         n   = nstack.node();
         cnt = n->outcnt();
         i   = nstack.index();
         nstack.pop();
       }
     }
   }
 }
 //------------------------------build_loop_late_post---------------------------
 // Put Data nodes into some loop nest, by setting the _nodes[]->loop mapping.
 // Second pass finds latest legal placement, and ideal loop placement.
 void PhaseIdealLoop::build_loop_late_post( Node *n ) {
   if (n->req() == 2 && n->Opcode() == Op_ConvI2L && !C->major_progress() && !_verify_only) {
     _igvn._worklist.push(n);  // Maybe we'll normalize it, if no more loops.
   }
   // CFG and pinned nodes already handled
   if( n->in(0) ) {
     if( n->in(0)->is_top() ) return; // Dead?
     // We'd like +VerifyLoopOptimizations to not believe that Mod's/Loads
     // _must_ be pinned (they have to observe their control edge of course).
     // Unlike Stores (which modify an unallocable resource, the memory
     // state), Mods/Loads can float around.  So free them up.
     bool pinned = true;
     switch( n->Opcode() ) {
     case Op_DivI:
     case Op_DivF:
     case Op_DivD:
     case Op_ModI:
     case Op_ModF:
     case Op_ModD:
     case Op_LoadB:              // Same with Loads; they can sink
     case Op_LoadUS:             // during loop optimizations.
     case Op_LoadD:
     case Op_LoadF:
     case Op_LoadI:
     case Op_LoadKlass:
     case Op_LoadNKlass:
     case Op_LoadL:
     case Op_LoadS:
     case Op_LoadP:
     case Op_LoadN:
     case Op_LoadRange:
     case Op_LoadD_unaligned:
     case Op_LoadL_unaligned:
     case Op_StrComp:            // Does a bunch of load-like effects
     case Op_StrEquals:
     case Op_StrIndexOf:
     case Op_AryEq:
       pinned = false;
     }
     if( pinned ) {
       IdealLoopTree *chosen_loop = get_loop(n->is_CFG() ? n : get_ctrl(n));
       if( !chosen_loop->_child )       // Inner loop?
         chosen_loop->_body.push(n); // Collect inner loops
       return;
     }
   } else {                      // No slot zero
     if( n->is_CFG() ) {         // CFG with no slot 0 is dead
       _nodes.map(n->_idx,0);    // No block setting, it's globally dead
       return;
     }
     assert(!n->is_CFG() || n->outcnt() == 0, "");
   }
   // Do I have a "safe range" I can select over?
   Node *early = get_ctrl(n);// Early location already computed
   // Compute latest point this Node can go
   Node *LCA = get_late_ctrl( n, early );
   // LCA is NULL due to uses being dead
   if( LCA == NULL ) {
 #ifdef ASSERT
     for (DUIterator i1 = n->outs(); n->has_out(i1); i1++) {
       assert( _nodes[n->out(i1)->_idx] == NULL, "all uses must also be dead");
     }
 #endif
     _nodes.map(n->_idx, 0);     // This node is useless
     _deadlist.push(n);
     return;
   }
   assert(LCA != NULL && !LCA->is_top(), "no dead nodes");
   Node *legal = LCA;            // Walk 'legal' up the IDOM chain
   Node *least = legal;          // Best legal position so far
   while( early != legal ) {     // While not at earliest legal
 #ifdef ASSERT
     if (legal->is_Start() && !early->is_Root()) {
       // Bad graph. Print idom path and fail.
       tty->print_cr( "Bad graph detected in build_loop_late");
       tty->print("n: ");n->dump(); tty->cr();
       tty->print("early: ");early->dump(); tty->cr();
       int ct = 0;
       Node *dbg_legal = LCA;
       while(!dbg_legal->is_Start() && ct < 100) {
         tty->print("idom[%d] ",ct); dbg_legal->dump(); tty->cr();
         ct++;
         dbg_legal = idom(dbg_legal);
       }
       assert(false, "Bad graph detected in build_loop_late");
     }
 #endif
     // Find least loop nesting depth
     legal = idom(legal);        // Bump up the IDOM tree
     // Check for lower nesting depth
     if( get_loop(legal)->_nest < get_loop(least)->_nest )
       least = legal;
   }
   assert(early == legal || legal != C->root(), "bad dominance of inputs");
   // Try not to place code on a loop entry projection
   // which can inhibit range check elimination.
   if (least != early) {
     Node* ctrl_out = least->unique_ctrl_out();
     if (ctrl_out && ctrl_out->is_CountedLoop() &&
         least == ctrl_out->in(LoopNode::EntryControl)) {
       Node* least_dom = idom(least);
       if (get_loop(least_dom)->is_member(get_loop(least))) {
         least = least_dom;
       }
     }
   }
 #ifdef ASSERT
   // If verifying, verify that 'verify_me' has a legal location
   // and choose it as our location.
   if( _verify_me ) {
     Node *v_ctrl = _verify_me->get_ctrl_no_update(n);
     Node *legal = LCA;
     while( early != legal ) {   // While not at earliest legal
       if( legal == v_ctrl ) break;  // Check for prior good location
       legal = idom(legal)      ;// Bump up the IDOM tree
     }
     // Check for prior good location
     if( legal == v_ctrl ) least = legal; // Keep prior if found
   }
 #endif
   // Assign discovered "here or above" point
   least = find_non_split_ctrl(least);
   set_ctrl(n, least);
   // Collect inner loop bodies
   IdealLoopTree *chosen_loop = get_loop(least);
   if( !chosen_loop->_child )   // Inner loop?
     chosen_loop->_body.push(n);// Collect inner loops
 }
 #ifndef PRODUCT
 //------------------------------dump-------------------------------------------
 void PhaseIdealLoop::dump( ) const {
   ResourceMark rm;
   Arena* arena = Thread::current()->resource_area();
   Node_Stack stack(arena, C->unique() >> 2);
   Node_List rpo_list;
   VectorSet visited(arena);
   visited.set(C->top()->_idx);
   rpo( C->root(), stack, visited, rpo_list );
   // Dump root loop indexed by last element in PO order
   dump( _ltree_root, rpo_list.size(), rpo_list );
 }
 void PhaseIdealLoop::dump( IdealLoopTree *loop, uint idx, Node_List &rpo_list ) const {
   loop->dump_head();
   // Now scan for CFG nodes in the same loop
   for( uint j=idx; j > 0;  j-- ) {
     Node *n = rpo_list[j-1];
     if( !_nodes[n->_idx] )      // Skip dead nodes
       continue;
     if( get_loop(n) != loop ) { // Wrong loop nest
       if( get_loop(n)->_head == n &&    // Found nested loop?
           get_loop(n)->_parent == loop )
         dump(get_loop(n),rpo_list.size(),rpo_list);     // Print it nested-ly
       continue;
     }
     // Dump controlling node
     for( uint x = 0; x < loop->_nest; x++ )
       tty->print("  ");
     tty->print("C");
     if( n == C->root() ) {
       n->dump();
     } else {
       Node* cached_idom   = idom_no_update(n);
       Node *computed_idom = n->in(0);
       if( n->is_Region() ) {
         computed_idom = compute_idom(n);
         // computed_idom() will return n->in(0) when idom(n) is an IfNode (or
         // any MultiBranch ctrl node), so apply a similar transform to
         // the cached idom returned from idom_no_update.
         cached_idom = find_non_split_ctrl(cached_idom);
       }
       tty->print(" ID:%d",computed_idom->_idx);
       n->dump();
       if( cached_idom != computed_idom ) {
         tty->print_cr("*** BROKEN IDOM!  Computed as: %d, cached as: %d",
                       computed_idom->_idx, cached_idom->_idx);
       }
     }
     // Dump nodes it controls
     for( uint k = 0; k < _nodes.Size(); k++ ) {
       // (k < C->unique() && get_ctrl(find(k)) == n)
       if (k < C->unique() && _nodes[k] == (Node*)((intptr_t)n + 1)) {
         Node *m = C->root()->find(k);
         if( m && m->outcnt() > 0 ) {
           if (!(has_ctrl(m) && get_ctrl_no_update(m) == n)) {
             tty->print_cr("*** BROKEN CTRL ACCESSOR!  _nodes[k] is %p, ctrl is %p",
                           _nodes[k], has_ctrl(m) ? get_ctrl_no_update(m) : NULL);
           }
           for( uint j = 0; j < loop->_nest; j++ )
             tty->print("  ");
           tty->print(" ");
           m->dump();
         }
       }
     }
   }
 }
 // Collect a R-P-O for the whole CFG.
 // Result list is in post-order (scan backwards for RPO)
 void PhaseIdealLoop::rpo( Node *start, Node_Stack &stk, VectorSet &visited, Node_List &rpo_list ) const {
   stk.push(start, 0);
   visited.set(start->_idx);
   while (stk.is_nonempty()) {
     Node* m   = stk.node();
     uint  idx = stk.index();
     if (idx < m->outcnt()) {
       stk.set_index(idx + 1);
       Node* n = m->raw_out(idx);
       if (n->is_CFG() && !visited.test_set(n->_idx)) {
         stk.push(n, 0);
       }
     } else {
       rpo_list.push(m);
       stk.pop();
     }
   }
 }
 #endif
 //=============================================================================
 //------------------------------LoopTreeIterator-----------------------------------
 // Advance to next loop tree using a preorder, left-to-right traversal.
 void LoopTreeIterator::next() {
   assert(!done(), "must not be done.");
   if (_curnt->_child != NULL) {
     _curnt = _curnt->_child;
   } else if (_curnt->_next != NULL) {
     _curnt = _curnt->_next;
   } else {
     while (_curnt != _root && _curnt->_next == NULL) {
       _curnt = _curnt->_parent;
     }
     if (_curnt == _root) {
       _curnt = NULL;
       assert(done(), "must be done.");
     } else {
       assert(_curnt->_next != NULL, "must be more to do");
       _curnt = _curnt->_next;
     }
   }
 }

Mercurial > jdk8-mips64-public > hotspot / annotate

src/share/vm/opto/loopnode.cpp@f95d63e2154a (annotated)

src/share/vm/opto/loopnode.cpp