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 /*

  * Copyright (c) 2000, 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

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  */

 #include "precompiled.hpp"

 #include "memory/allocation.inline.hpp"

 #include "opto/addnode.hpp"

 #include "opto/cfgnode.hpp"

 #include "opto/connode.hpp"

 #include "opto/phaseX.hpp"

 #include "opto/runtime.hpp"

 #include "opto/subnode.hpp"

 // Portions of code courtesy of Clifford Click

 // Optimization - Graph Style

 extern int explicit_null_checks_elided;

 //=============================================================================

 //------------------------------Value------------------------------------------

 // Return a tuple for whichever arm of the IF is reachable

 const Type *IfNode::Value( PhaseTransform *phase ) const {

   if( !in(0) ) return Type::TOP;

   if( phase->type(in(0)) == Type::TOP )

     return Type::TOP;

   const Type *t = phase->type(in(1));

   if( t == Type::TOP )          // data is undefined

     return TypeTuple::IFNEITHER; // unreachable altogether

   if( t == TypeInt::ZERO )      // zero, or false

     return TypeTuple::IFFALSE;  // only false branch is reachable

   if( t == TypeInt::ONE )       // 1, or true

     return TypeTuple::IFTRUE;   // only true branch is reachable

   assert( t == TypeInt::BOOL, "expected boolean type" );

   return TypeTuple::IFBOTH;     // No progress

 }

 const RegMask &IfNode::out_RegMask() const {

   return RegMask::Empty;

 }

 //------------------------------split_if---------------------------------------

 // Look for places where we merge constants, then test on the merged value.

 // If the IF test will be constant folded on the path with the constant, we

 // win by splitting the IF to before the merge point.

 static Node* split_if(IfNode *iff, PhaseIterGVN *igvn) {

   // I could be a lot more general here, but I'm trying to squeeze this

   // in before the Christmas '98 break so I'm gonna be kinda restrictive

   // on the patterns I accept.  CNC

   // Look for a compare of a constant and a merged value

   Node *i1 = iff->in(1);

   if( !i1->is_Bool() ) return NULL;

   BoolNode *b = i1->as_Bool();

   Node *cmp = b->in(1);

   if( !cmp->is_Cmp() ) return NULL;

   i1 = cmp->in(1);

   if( i1 == NULL || !i1->is_Phi() ) return NULL;

   PhiNode *phi = i1->as_Phi();

   if( phi->is_copy() ) return NULL;

   Node *con2 = cmp->in(2);

   if( !con2->is_Con() ) return NULL;

   // See that the merge point contains some constants

   Node *con1=NULL;

   uint i4;

   for( i4 = 1; i4 < phi->req(); i4++ ) {

     con1 = phi->in(i4);

     if( !con1 ) return NULL;    // Do not optimize partially collapsed merges

     if( con1->is_Con() ) break; // Found a constant

     // Also allow null-vs-not-null checks

     const TypePtr *tp = igvn->type(con1)->isa_ptr();

     if( tp && tp->_ptr == TypePtr::NotNull )

       break;

   }

   if( i4 >= phi->req() ) return NULL; // Found no constants

   igvn->C->set_has_split_ifs(true); // Has chance for split-if

   // Make sure that the compare can be constant folded away

   Node *cmp2 = cmp->clone();

   cmp2->set_req(1,con1);

   cmp2->set_req(2,con2);

   const Type *t = cmp2->Value(igvn);

   // This compare is dead, so whack it!

   igvn->remove_dead_node(cmp2);

   if( !t->singleton() ) return NULL;

   // No intervening control, like a simple Call

   Node *r = iff->in(0);

   if( !r->is_Region() ) return NULL;

   if( phi->region() != r ) return NULL;

   // No other users of the cmp/bool

   if (b->outcnt() != 1 || cmp->outcnt() != 1) {

     //tty->print_cr("many users of cmp/bool");

     return NULL;

   }

   // Make sure we can determine where all the uses of merged values go

   for (DUIterator_Fast jmax, j = r->fast_outs(jmax); j < jmax; j++) {

     Node* u = r->fast_out(j);

     if( u == r ) continue;

     if( u == iff ) continue;

     if( u->outcnt() == 0 ) continue; // use is dead & ignorable

     if( !u->is_Phi() ) {

       /*

       if( u->is_Start() ) {

         tty->print_cr("Region has inlined start use");

       } else {

         tty->print_cr("Region has odd use");

         u->dump(2);

       }*/

       return NULL;

     }

     if( u != phi ) {

       // CNC - do not allow any other merged value

       //tty->print_cr("Merging another value");

       //u->dump(2);

       return NULL;

     }

     // Make sure we can account for all Phi uses

     for (DUIterator_Fast kmax, k = u->fast_outs(kmax); k < kmax; k++) {

       Node* v = u->fast_out(k); // User of the phi

       // CNC - Allow only really simple patterns.

       // In particular I disallow AddP of the Phi, a fairly common pattern

       if( v == cmp ) continue;  // The compare is OK

       if( (v->is_ConstraintCast()) &&

           v->in(0)->in(0) == iff )

         continue;               // CastPP/II of the IfNode is OK

       // Disabled following code because I cannot tell if exactly one

       // path dominates without a real dominator check. CNC 9/9/1999

       //uint vop = v->Opcode();

       //if( vop == Op_Phi ) {     // Phi from another merge point might be OK

       //  Node *r = v->in(0);     // Get controlling point

       //  if( !r ) return NULL;   // Degraded to a copy

       //  // Find exactly one path in (either True or False doms, but not IFF)

       //  int cnt = 0;

       //  for( uint i = 1; i < r->req(); i++ )

       //    if( r->in(i) && r->in(i)->in(0) == iff )

       //      cnt++;

       //  if( cnt == 1 ) continue; // Exactly one of True or False guards Phi

       //}

       if( !v->is_Call() ) {

         /*

         if( v->Opcode() == Op_AddP ) {

           tty->print_cr("Phi has AddP use");

         } else if( v->Opcode() == Op_CastPP ) {

           tty->print_cr("Phi has CastPP use");

         } else if( v->Opcode() == Op_CastII ) {

           tty->print_cr("Phi has CastII use");

         } else {

           tty->print_cr("Phi has use I cant be bothered with");

         }

         */

       }

       return NULL;

       /* CNC - Cut out all the fancy acceptance tests

       // Can we clone this use when doing the transformation?

       // If all uses are from Phis at this merge or constants, then YES.

       if( !v->in(0) && v != cmp ) {

         tty->print_cr("Phi has free-floating use");

         v->dump(2);

         return NULL;

       }

       for( uint l = 1; l < v->req(); l++ ) {

         if( (!v->in(l)->is_Phi() || v->in(l)->in(0) != r) &&

             !v->in(l)->is_Con() ) {

           tty->print_cr("Phi has use");

           v->dump(2);

           return NULL;

         } // End of if Phi-use input is neither Phi nor Constant

       } // End of for all inputs to Phi-use

       */

     } // End of for all uses of Phi

   } // End of for all uses of Region

   // Only do this if the IF node is in a sane state

   if (iff->outcnt() != 2)

     return NULL;

   // Got a hit!  Do the Mondo Hack!

   //

   //ABC  a1c   def   ghi            B     1     e     h   A C   a c   d f   g i

   // R - Phi - Phi - Phi            Rc - Phi - Phi - Phi   Rx - Phi - Phi - Phi

   //     cmp - 2                         cmp - 2               cmp - 2

   //       bool                            bool_c                bool_x

   //       if                               if_c                  if_x

   //      T  F                              T  F                  T  F

   // ..s..    ..t ..                   ..s..    ..t..        ..s..    ..t..

   //

   // Split the paths coming into the merge point into 2 separate groups of

   // merges.  On the left will be all the paths feeding constants into the

   // Cmp's Phi.  On the right will be the remaining paths.  The Cmp's Phi

   // will fold up into a constant; this will let the Cmp fold up as well as

   // all the control flow.  Below the original IF we have 2 control

   // dependent regions, 's' and 't'.  Now we will merge the two paths

   // just prior to 's' and 't' from the two IFs.  At least 1 path (and quite

   // likely 2 or more) will promptly constant fold away.

   PhaseGVN *phase = igvn;

   // Make a region merging constants and a region merging the rest

   uint req_c = 0;

   for (uint ii = 1; ii < r->req(); ii++) {

     if( phi->in(ii) == con1 ) {

       req_c++;

     }

   }

   Node *region_c = new (igvn->C, req_c + 1) RegionNode(req_c + 1);

   Node *phi_c    = con1;

   uint  len      = r->req();

   Node *region_x = new (igvn->C, len - req_c + 1) RegionNode(len - req_c + 1);

   Node *phi_x    = PhiNode::make_blank(region_x, phi);

   for (uint i = 1, i_c = 1, i_x = 1; i < len; i++) {

     if( phi->in(i) == con1 ) {

       region_c->init_req( i_c++, r  ->in(i) );

     } else {

       region_x->init_req( i_x,   r  ->in(i) );

       phi_x   ->init_req( i_x++, phi->in(i) );

     }

   }

   // Register the new RegionNodes but do not transform them.  Cannot

   // transform until the entire Region/Phi conglomerate has been hacked

   // as a single huge transform.

   igvn->register_new_node_with_optimizer( region_c );

   igvn->register_new_node_with_optimizer( region_x );

   // Prevent the untimely death of phi_x.  Currently he has no uses.  He is

   // about to get one.  If this only use goes away, then phi_x will look dead.

   // However, he will be picking up some more uses down below.

   Node *hook = new (igvn->C, 4) Node(4);

   hook->init_req(0, phi_x);

   hook->init_req(1, phi_c);

   phi_x = phase->transform( phi_x );

   // Make the compare

   Node *cmp_c = phase->makecon(t);

   Node *cmp_x = cmp->clone();

   cmp_x->set_req(1,phi_x);

   cmp_x->set_req(2,con2);

   cmp_x = phase->transform(cmp_x);

   // Make the bool

   Node *b_c = phase->transform(new (igvn->C, 2) BoolNode(cmp_c,b->_test._test));

   Node *b_x = phase->transform(new (igvn->C, 2) BoolNode(cmp_x,b->_test._test));

   // Make the IfNode

   IfNode *iff_c = new (igvn->C, 2) IfNode(region_c,b_c,iff->_prob,iff->_fcnt);

   igvn->set_type_bottom(iff_c);

   igvn->_worklist.push(iff_c);

   hook->init_req(2, iff_c);

   IfNode *iff_x = new (igvn->C, 2) IfNode(region_x,b_x,iff->_prob, iff->_fcnt);

   igvn->set_type_bottom(iff_x);

   igvn->_worklist.push(iff_x);

   hook->init_req(3, iff_x);

   // Make the true/false arms

   Node *iff_c_t = phase->transform(new (igvn->C, 1) IfTrueNode (iff_c));

   Node *iff_c_f = phase->transform(new (igvn->C, 1) IfFalseNode(iff_c));

   Node *iff_x_t = phase->transform(new (igvn->C, 1) IfTrueNode (iff_x));

   Node *iff_x_f = phase->transform(new (igvn->C, 1) IfFalseNode(iff_x));

   // Merge the TRUE paths

   Node *region_s = new (igvn->C, 3) RegionNode(3);

   igvn->_worklist.push(region_s);

   region_s->init_req(1, iff_c_t);

   region_s->init_req(2, iff_x_t);

   igvn->register_new_node_with_optimizer( region_s );

   // Merge the FALSE paths

   Node *region_f = new (igvn->C, 3) RegionNode(3);

   igvn->_worklist.push(region_f);

   region_f->init_req(1, iff_c_f);

   region_f->init_req(2, iff_x_f);

   igvn->register_new_node_with_optimizer( region_f );

   igvn->hash_delete(cmp);// Remove soon-to-be-dead node from hash table.

   cmp->set_req(1,NULL);  // Whack the inputs to cmp because it will be dead

   cmp->set_req(2,NULL);

   // Check for all uses of the Phi and give them a new home.

   // The 'cmp' got cloned, but CastPP/IIs need to be moved.

   Node *phi_s = NULL;     // do not construct unless needed

   Node *phi_f = NULL;     // do not construct unless needed

   for (DUIterator_Last i2min, i2 = phi->last_outs(i2min); i2 >= i2min; --i2) {

     Node* v = phi->last_out(i2);// User of the phi

     igvn->hash_delete(v);       // Have to fixup other Phi users

     igvn->_worklist.push(v);

     uint vop = v->Opcode();

     Node *proj = NULL;

     if( vop == Op_Phi ) {       // Remote merge point

       Node *r = v->in(0);

       for (uint i3 = 1; i3 < r->req(); i3++)

         if (r->in(i3) && r->in(i3)->in(0) == iff) {

           proj = r->in(i3);

           break;

         }

     } else if( v->is_ConstraintCast() ) {

       proj = v->in(0);          // Controlling projection

     } else {

       assert( 0, "do not know how to handle this guy" );

     }

     Node *proj_path_data, *proj_path_ctrl;

     if( proj->Opcode() == Op_IfTrue ) {

       if( phi_s == NULL ) {

         // Only construct phi_s if needed, otherwise provides

         // interfering use.

         phi_s = PhiNode::make_blank(region_s,phi);

         phi_s->init_req( 1, phi_c );

         phi_s->init_req( 2, phi_x );

         hook->add_req(phi_s);

         phi_s = phase->transform(phi_s);

       }

       proj_path_data = phi_s;

       proj_path_ctrl = region_s;

     } else {

       if( phi_f == NULL ) {

         // Only construct phi_f if needed, otherwise provides

         // interfering use.

         phi_f = PhiNode::make_blank(region_f,phi);

         phi_f->init_req( 1, phi_c );

         phi_f->init_req( 2, phi_x );

         hook->add_req(phi_f);

         phi_f = phase->transform(phi_f);

       }

       proj_path_data = phi_f;

       proj_path_ctrl = region_f;

     }

     // Fixup 'v' for for the split

     if( vop == Op_Phi ) {       // Remote merge point

       uint i;

       for( i = 1; i < v->req(); i++ )

         if( v->in(i) == phi )

           break;

       v->set_req(i, proj_path_data );

     } else if( v->is_ConstraintCast() ) {

       v->set_req(0, proj_path_ctrl );

       v->set_req(1, proj_path_data );

     } else

       ShouldNotReachHere();

   }

   // Now replace the original iff's True/False with region_s/region_t.

   // This makes the original iff go dead.

   for (DUIterator_Last i3min, i3 = iff->last_outs(i3min); i3 >= i3min; --i3) {

     Node* p = iff->last_out(i3);

     assert( p->Opcode() == Op_IfTrue || p->Opcode() == Op_IfFalse, "" );

     Node *u = (p->Opcode() == Op_IfTrue) ? region_s : region_f;

     // Replace p with u

     igvn->add_users_to_worklist(p);

     for (DUIterator_Last lmin, l = p->last_outs(lmin); l >= lmin;) {

       Node* x = p->last_out(l);

       igvn->hash_delete(x);

       uint uses_found = 0;

       for( uint j = 0; j < x->req(); j++ ) {

         if( x->in(j) == p ) {

           x->set_req(j, u);

           uses_found++;

         }

       }

       l -= uses_found;    // we deleted 1 or more copies of this edge

     }

     igvn->remove_dead_node(p);

   }

   // Force the original merge dead

   igvn->hash_delete(r);

   // First, remove region's dead users.

   for (DUIterator_Last lmin, l = r->last_outs(lmin); l >= lmin;) {

     Node* u = r->last_out(l);

     if( u == r ) {

       r->set_req(0, NULL);

     } else {

       assert(u->outcnt() == 0, "only dead users");

       igvn->remove_dead_node(u);

     }

     l -= 1;

   }

   igvn->remove_dead_node(r);

   // Now remove the bogus extra edges used to keep things alive

   igvn->remove_dead_node( hook );

   // Must return either the original node (now dead) or a new node

   // (Do not return a top here, since that would break the uniqueness of top.)

   return new (igvn->C, 1) ConINode(TypeInt::ZERO);

 }

 //------------------------------is_range_check---------------------------------

 // Return 0 if not a range check.  Return 1 if a range check and set index and

 // offset.  Return 2 if we had to negate the test.  Index is NULL if the check

 // is versus a constant.

 int IfNode::is_range_check(Node* &range, Node* &index, jint &offset) {

   Node* b = in(1);

   if (b == NULL || !b->is_Bool())  return 0;

   BoolNode* bn = b->as_Bool();

   Node* cmp = bn->in(1);

   if (cmp == NULL)  return 0;

   if (cmp->Opcode() != Op_CmpU)  return 0;

   Node* l = cmp->in(1);

   Node* r = cmp->in(2);

   int flip_test = 1;

   if (bn->_test._test == BoolTest::le) {

     l = cmp->in(2);

     r = cmp->in(1);

     flip_test = 2;

   } else if (bn->_test._test != BoolTest::lt) {

     return 0;

   }

   if (l->is_top())  return 0;   // Top input means dead test

   if (r->Opcode() != Op_LoadRange)  return 0;

   // We have recognized one of these forms:

   //  Flip 1:  If (Bool[<] CmpU(l, LoadRange)) ...

   //  Flip 2:  If (Bool[<=] CmpU(LoadRange, l)) ...

   // Make sure it's a real range check by requiring an uncommon trap

   // along the OOB path.  Otherwise, it's possible that the user wrote

   // something which optimized to look like a range check but behaves

   // in some other way.

   Node* iftrap = proj_out(flip_test == 2 ? true : false);

   bool found_trap = false;

   if (iftrap != NULL) {

     Node* u = iftrap->unique_ctrl_out();

     if (u != NULL) {

       // It could be a merge point (Region) for uncommon trap.

       if (u->is_Region()) {

         Node* c = u->unique_ctrl_out();

         if (c != NULL) {

           iftrap = u;

           u = c;

         }

       }

       if (u->in(0) == iftrap && u->is_CallStaticJava()) {

         int req = u->as_CallStaticJava()->uncommon_trap_request();

         if (Deoptimization::trap_request_reason(req) ==

             Deoptimization::Reason_range_check) {

           found_trap = true;

         }

       }

     }

   }

   if (!found_trap)  return 0;   // sorry, no cigar

   // Look for index+offset form

   Node* ind = l;

   jint  off = 0;

   if (l->is_top()) {

     return 0;

   } else if (l->is_Add()) {

     if ((off = l->in(1)->find_int_con(0)) != 0) {

       ind = l->in(2);

     } else if ((off = l->in(2)->find_int_con(0)) != 0) {

       ind = l->in(1);

     }

   } else if ((off = l->find_int_con(-1)) >= 0) {

     // constant offset with no variable index

     ind = NULL;

   } else {

     // variable index with no constant offset (or dead negative index)

     off = 0;

   }

   // Return all the values:

   index  = ind;

   offset = off;

   range  = r;

   return flip_test;

 }

 //------------------------------adjust_check-----------------------------------

 // Adjust (widen) a prior range check

 static void adjust_check(Node* proj, Node* range, Node* index,

                          int flip, jint off_lo, PhaseIterGVN* igvn) {

   PhaseGVN *gvn = igvn;

   // Break apart the old check

   Node *iff = proj->in(0);

   Node *bol = iff->in(1);

   if( bol->is_top() ) return;   // In case a partially dead range check appears

   // bail (or bomb[ASSERT/DEBUG]) if NOT projection-->IfNode-->BoolNode

   DEBUG_ONLY( if( !bol->is_Bool() ) { proj->dump(3); fatal("Expect projection-->IfNode-->BoolNode"); } )

   if( !bol->is_Bool() ) return;

   Node *cmp = bol->in(1);

   // Compute a new check

   Node *new_add = gvn->intcon(off_lo);

   if( index ) {

     new_add = off_lo ? gvn->transform(new (gvn->C, 3) AddINode( index, new_add )) : index;

   }

   Node *new_cmp = (flip == 1)

     ? new (gvn->C, 3) CmpUNode( new_add, range )

     : new (gvn->C, 3) CmpUNode( range, new_add );

   new_cmp = gvn->transform(new_cmp);

   // See if no need to adjust the existing check

   if( new_cmp == cmp ) return;

   // Else, adjust existing check

   Node *new_bol = gvn->transform( new (gvn->C, 2) BoolNode( new_cmp, bol->as_Bool()->_test._test ) );

   igvn->hash_delete( iff );

   iff->set_req_X( 1, new_bol, igvn );

 }

 //------------------------------up_one_dom-------------------------------------

 // Walk up the dominator tree one step.  Return NULL at root or true

 // complex merges.  Skips through small diamonds.

 Node* IfNode::up_one_dom(Node *curr, bool linear_only) {

   Node *dom = curr->in(0);

   if( !dom )                    // Found a Region degraded to a copy?

     return curr->nonnull_req(); // Skip thru it

   if( curr != dom )             // Normal walk up one step?

     return dom;

   // Use linear_only if we are still parsing, since we cannot

   // trust the regions to be fully filled in.

   if (linear_only)

     return NULL;

   if( dom->is_Root() )

     return NULL;

   // Else hit a Region.  Check for a loop header

   if( dom->is_Loop() )

     return dom->in(1);          // Skip up thru loops

   // Check for small diamonds

   Node *din1, *din2, *din3, *din4;

   if( dom->req() == 3 &&        // 2-path merge point

       (din1 = dom ->in(1)) &&   // Left  path exists

       (din2 = dom ->in(2)) &&   // Right path exists

       (din3 = din1->in(0)) &&   // Left  path up one

       (din4 = din2->in(0)) ) {  // Right path up one

     if( din3->is_Call() &&      // Handle a slow-path call on either arm

         (din3 = din3->in(0)) )

       din3 = din3->in(0);

     if( din4->is_Call() &&      // Handle a slow-path call on either arm

         (din4 = din4->in(0)) )

       din4 = din4->in(0);

     if( din3 == din4 && din3->is_If() )

       return din3;              // Skip around diamonds

   }

   // Give up the search at true merges

   return NULL;                  // Dead loop?  Or hit root?

 }

 //------------------------------filtered_int_type--------------------------------

 // Return a possibly more restrictive type for val based on condition control flow for an if

 const TypeInt* IfNode::filtered_int_type(PhaseGVN* gvn, Node *val, Node* if_proj) {

   assert(if_proj &&

          (if_proj->Opcode() == Op_IfTrue || if_proj->Opcode() == Op_IfFalse), "expecting an if projection");

   if (if_proj->in(0) && if_proj->in(0)->is_If()) {

     IfNode* iff = if_proj->in(0)->as_If();

     if (iff->in(1) && iff->in(1)->is_Bool()) {

       BoolNode* bol = iff->in(1)->as_Bool();

       if (bol->in(1) && bol->in(1)->is_Cmp()) {

         const CmpNode* cmp  = bol->in(1)->as_Cmp();

         if (cmp->in(1) == val) {

           const TypeInt* cmp2_t = gvn->type(cmp->in(2))->isa_int();

           if (cmp2_t != NULL) {

             jint lo = cmp2_t->_lo;

             jint hi = cmp2_t->_hi;

             BoolTest::mask msk = if_proj->Opcode() == Op_IfTrue ? bol->_test._test : bol->_test.negate();

             switch (msk) {

             case BoolTest::ne:

               // Can't refine type

               return NULL;

             case BoolTest::eq:

               return cmp2_t;

             case BoolTest::lt:

               lo = TypeInt::INT->_lo;

               if (hi - 1 < hi) {

                 hi = hi - 1;

               }

               break;

             case BoolTest::le:

               lo = TypeInt::INT->_lo;

               break;

             case BoolTest::gt:

               if (lo + 1 > lo) {

                 lo = lo + 1;

               }

               hi = TypeInt::INT->_hi;

               break;

             case BoolTest::ge:

               // lo unchanged

               hi = TypeInt::INT->_hi;

               break;

             }

             const TypeInt* rtn_t = TypeInt::make(lo, hi, cmp2_t->_widen);

             return rtn_t;

           }

         }

       }

     }

   }

   return NULL;

 }

 //------------------------------fold_compares----------------------------

 // See if a pair of CmpIs can be converted into a CmpU.  In some cases

 // the direction of this if is determined by the preceding if so it

 // can be eliminate entirely.  Given an if testing (CmpI n c) check

 // for an immediately control dependent if that is testing (CmpI n c2)

 // and has one projection leading to this if and the other projection

 // leading to a region that merges one of this ifs control

 // projections.

 //

 //                   If

 //                  / |

 //                 /  |

 //                /   |

 //              If    |

 //              /\    |

 //             /  \   |

 //            /    \  |

 //           /    Region

 //

 Node* IfNode::fold_compares(PhaseGVN* phase) {

   if (!EliminateAutoBox || Opcode() != Op_If) return NULL;

   Node* this_cmp = in(1)->in(1);

   if (this_cmp != NULL && this_cmp->Opcode() == Op_CmpI &&

       this_cmp->in(2)->is_Con() && this_cmp->in(2) != phase->C->top()) {

     Node* ctrl = in(0);

     BoolNode* this_bool = in(1)->as_Bool();

     Node* n = this_cmp->in(1);

     int hi = this_cmp->in(2)->get_int();

     if (ctrl != NULL && ctrl->is_Proj() && ctrl->outcnt() == 1 &&

         ctrl->in(0)->is_If() &&

         ctrl->in(0)->outcnt() == 2 &&

         ctrl->in(0)->in(1)->is_Bool() &&

         ctrl->in(0)->in(1)->in(1)->Opcode() == Op_CmpI &&

         ctrl->in(0)->in(1)->in(1)->in(2)->is_Con() &&

         ctrl->in(0)->in(1)->in(1)->in(1) == n) {

       IfNode* dom_iff = ctrl->in(0)->as_If();

       Node* otherproj = dom_iff->proj_out(!ctrl->as_Proj()->_con);

       if (otherproj->outcnt() == 1 && otherproj->unique_out()->is_Region() &&

           this_bool->_test._test != BoolTest::ne && this_bool->_test._test != BoolTest::eq) {

         // Identify which proj goes to the region and which continues on

         RegionNode* region = otherproj->unique_out()->as_Region();

         Node* success = NULL;

         Node* fail = NULL;

         for (int i = 0; i < 2; i++) {

           Node* proj = proj_out(i);

           if (success == NULL && proj->outcnt() == 1 && proj->unique_out() == region) {

             success = proj;

           } else if (fail == NULL) {

             fail = proj;

           } else {

             success = fail = NULL;

           }

         }

         if (success != NULL && fail != NULL && !region->has_phi()) {

           int lo = dom_iff->in(1)->in(1)->in(2)->get_int();

           BoolNode* dom_bool = dom_iff->in(1)->as_Bool();

           Node* dom_cmp =  dom_bool->in(1);

           const TypeInt* failtype  = filtered_int_type(phase, n, ctrl);

           if (failtype != NULL) {

             const TypeInt* type2 = filtered_int_type(phase, n, fail);

             if (type2 != NULL) {

               failtype = failtype->join(type2)->is_int();

             } else {

               failtype = NULL;

             }

           }

           if (failtype != NULL &&

               dom_bool->_test._test != BoolTest::ne && dom_bool->_test._test != BoolTest::eq) {

             int bound = failtype->_hi - failtype->_lo + 1;

             if (failtype->_hi != max_jint && failtype->_lo != min_jint && bound > 1) {

               // Merge the two compares into a single unsigned compare by building  (CmpU (n - lo) hi)

               BoolTest::mask cond = fail->as_Proj()->_con ? BoolTest::lt : BoolTest::ge;

               Node* adjusted = phase->transform(new (phase->C, 3) SubINode(n, phase->intcon(failtype->_lo)));

               Node* newcmp = phase->transform(new (phase->C, 3) CmpUNode(adjusted, phase->intcon(bound)));

               Node* newbool = phase->transform(new (phase->C, 2) BoolNode(newcmp, cond));

               phase->hash_delete(dom_iff);

               dom_iff->set_req(1, phase->intcon(ctrl->as_Proj()->_con));

               phase->is_IterGVN()->_worklist.push(dom_iff);

               phase->hash_delete(this);

               set_req(1, newbool);

               return this;

             }

             if (failtype->_lo > failtype->_hi) {

               // previous if determines the result of this if so

               // replace Bool with constant

               phase->hash_delete(this);

               set_req(1, phase->intcon(success->as_Proj()->_con));

               return this;

             }

           }

         }

       }

     }

   }

   return NULL;

 }

 //------------------------------remove_useless_bool----------------------------

 // Check for people making a useless boolean: things like

 // if( (x < y ? true : false) ) { ... }

 // Replace with if( x < y ) { ... }

 static Node *remove_useless_bool(IfNode *iff, PhaseGVN *phase) {

   Node *i1 = iff->in(1);

   if( !i1->is_Bool() ) return NULL;

   BoolNode *bol = i1->as_Bool();

   Node *cmp = bol->in(1);

   if( cmp->Opcode() != Op_CmpI ) return NULL;

   // Must be comparing against a bool

   const Type *cmp2_t = phase->type( cmp->in(2) );

   if( cmp2_t != TypeInt::ZERO &&

       cmp2_t != TypeInt::ONE )

     return NULL;

   // Find a prior merge point merging the boolean

   i1 = cmp->in(1);

   if( !i1->is_Phi() ) return NULL;

   PhiNode *phi = i1->as_Phi();

   if( phase->type( phi ) != TypeInt::BOOL )

     return NULL;

   // Check for diamond pattern

   int true_path = phi->is_diamond_phi();

   if( true_path == 0 ) return NULL;

   // Make sure that iff and the control of the phi are different. This

   // should really only happen for dead control flow since it requires

   // an illegal cycle.

   if (phi->in(0)->in(1)->in(0) == iff) return NULL;

   // phi->region->if_proj->ifnode->bool->cmp

   BoolNode *bol2 = phi->in(0)->in(1)->in(0)->in(1)->as_Bool();

   // Now get the 'sense' of the test correct so we can plug in

   // either iff2->in(1) or its complement.

   int flip = 0;

   if( bol->_test._test == BoolTest::ne ) flip = 1-flip;

   else if( bol->_test._test != BoolTest::eq ) return NULL;

   if( cmp2_t == TypeInt::ZERO ) flip = 1-flip;

   const Type *phi1_t = phase->type( phi->in(1) );

   const Type *phi2_t = phase->type( phi->in(2) );

   // Check for Phi(0,1) and flip

   if( phi1_t == TypeInt::ZERO ) {

     if( phi2_t != TypeInt::ONE ) return NULL;

     flip = 1-flip;

   } else {

     // Check for Phi(1,0)

     if( phi1_t != TypeInt::ONE  ) return NULL;

     if( phi2_t != TypeInt::ZERO ) return NULL;

   }

   if( true_path == 2 ) {

     flip = 1-flip;

   }

   Node* new_bol = (flip ? phase->transform( bol2->negate(phase) ) : bol2);

   assert(new_bol != iff->in(1), "must make progress");

   iff->set_req(1, new_bol);

   // Intervening diamond probably goes dead

   phase->C->set_major_progress();

   return iff;

 }

 static IfNode* idealize_test(PhaseGVN* phase, IfNode* iff);

 //------------------------------Ideal------------------------------------------

 // Return a node which is more "ideal" than the current node.  Strip out

 // control copies

 Node *IfNode::Ideal(PhaseGVN *phase, bool can_reshape) {

   if (remove_dead_region(phase, can_reshape))  return this;

   // No Def-Use info?

   if (!can_reshape)  return NULL;

   PhaseIterGVN *igvn = phase->is_IterGVN();

   // Don't bother trying to transform a dead if

   if (in(0)->is_top())  return NULL;

   // Don't bother trying to transform an if with a dead test

   if (in(1)->is_top())  return NULL;

   // Another variation of a dead test

   if (in(1)->is_Con())  return NULL;

   // Another variation of a dead if

   if (outcnt() < 2)  return NULL;

   // Canonicalize the test.

   Node* idt_if = idealize_test(phase, this);

   if (idt_if != NULL)  return idt_if;

   // Try to split the IF

   Node *s = split_if(this, igvn);

   if (s != NULL)  return s;

   // Check for people making a useless boolean: things like

   // if( (x < y ? true : false) ) { ... }

   // Replace with if( x < y ) { ... }

   Node *bol2 = remove_useless_bool(this, phase);

   if( bol2 ) return bol2;

   // Setup to scan up the CFG looking for a dominating test

   Node *dom = in(0);

   Node *prev_dom = this;

   // Check for range-check vs other kinds of tests

   Node *index1, *range1;

   jint offset1;

   int flip1 = is_range_check(range1, index1, offset1);

   if( flip1 ) {

     Node *first_prev_dom = NULL;

     // Try to remove extra range checks.  All 'up_one_dom' gives up at merges

     // so all checks we inspect post-dominate the top-most check we find.

     // If we are going to fail the current check and we reach the top check

     // then we are guaranteed to fail, so just start interpreting there.

     // We 'expand' the top 2 range checks to include all post-dominating

     // checks.

     // The top 2 range checks seen

     Node *prev_chk1 = NULL;

     Node *prev_chk2 = NULL;

     // Low and high offsets seen so far

     jint off_lo = offset1;

     jint off_hi = offset1;

     // Scan for the top 2 checks and collect range of offsets

     for( int dist = 0; dist < 999; dist++ ) { // Range-Check scan limit

       if( dom->Opcode() == Op_If &&  // Not same opcode?

           prev_dom->in(0) == dom ) { // One path of test does dominate?

         if( dom == this ) return NULL; // dead loop

         // See if this is a range check

         Node *index2, *range2;

         jint offset2;

         int flip2 = dom->as_If()->is_range_check(range2, index2, offset2);

         // See if this is a _matching_ range check, checking against

         // the same array bounds.

         if( flip2 == flip1 && range2 == range1 && index2 == index1 &&

             dom->outcnt() == 2 ) {

           // Gather expanded bounds

           off_lo = MIN2(off_lo,offset2);

           off_hi = MAX2(off_hi,offset2);

           // Record top 2 range checks

           prev_chk2 = prev_chk1;

           prev_chk1 = prev_dom;

           // If we match the test exactly, then the top test covers

           // both our lower and upper bounds.

           if( dom->in(1) == in(1) )

             prev_chk2 = prev_chk1;

         }

       }

       prev_dom = dom;

       dom = up_one_dom( dom );

       if( !dom ) break;

     }

     // Attempt to widen the dominating range check to cover some later

     // ones.  Since range checks "fail" by uncommon-trapping to the

     // interpreter, widening a check can make us speculative enter the

     // interpreter.  If we see range-check deopt's, do not widen!

     if (!phase->C->allow_range_check_smearing())  return NULL;

     // Constant indices only need to check the upper bound.

     // Non-constance indices must check both low and high.

     if( index1 ) {

       // Didn't find 2 prior covering checks, so cannot remove anything.

       if( !prev_chk2 ) return NULL;

       // 'Widen' the offsets of the 1st and 2nd covering check

       adjust_check( prev_chk1, range1, index1, flip1, off_lo, igvn );

       // Do not call adjust_check twice on the same projection

       // as the first call may have transformed the BoolNode to a ConI

       if( prev_chk1 != prev_chk2 ) {

         adjust_check( prev_chk2, range1, index1, flip1, off_hi, igvn );

       }

       // Test is now covered by prior checks, dominate it out

       prev_dom = prev_chk2;

     } else {

       // Didn't find prior covering check, so cannot remove anything.

       if( !prev_chk1 ) return NULL;

       // 'Widen' the offset of the 1st and only covering check

       adjust_check( prev_chk1, range1, index1, flip1, off_hi, igvn );

       // Test is now covered by prior checks, dominate it out

       prev_dom = prev_chk1;

     }

   } else {                      // Scan for an equivalent test

     Node *cmp;

     int dist = 0;               // Cutoff limit for search

     int op = Opcode();

     if( op == Op_If &&

         (cmp=in(1)->in(1))->Opcode() == Op_CmpP ) {

       if( cmp->in(2) != NULL && // make sure cmp is not already dead

           cmp->in(2)->bottom_type() == TypePtr::NULL_PTR ) {

         dist = 64;              // Limit for null-pointer scans

       } else {

         dist = 4;               // Do not bother for random pointer tests

       }

     } else {

       dist = 4;                 // Limit for random junky scans

     }

     // Normal equivalent-test check.

     if( !dom ) return NULL;     // Dead loop?

     Node* result = fold_compares(phase);

     if (result != NULL) {

       return result;

     }

     // Search up the dominator tree for an If with an identical test

     while( dom->Opcode() != op    ||  // Not same opcode?

            dom->in(1)    != in(1) ||  // Not same input 1?

            (req() == 3 && dom->in(2) != in(2)) || // Not same input 2?

            prev_dom->in(0) != dom ) { // One path of test does not dominate?

       if( dist < 0 ) return NULL;

       dist--;

       prev_dom = dom;

       dom = up_one_dom( dom );

       if( !dom ) return NULL;

     }

     // Check that we did not follow a loop back to ourselves

     if( this == dom )

       return NULL;

     if( dist > 2 )              // Add to count of NULL checks elided

       explicit_null_checks_elided++;

   } // End of Else scan for an equivalent test

   // Hit!  Remove this IF

 #ifndef PRODUCT

   if( TraceIterativeGVN ) {

     tty->print("   Removing IfNode: "); this->dump();

   }

   if( VerifyOpto && !phase->allow_progress() ) {

     // Found an equivalent dominating test,

     // we can not guarantee reaching a fix-point for these during iterativeGVN

     // since intervening nodes may not change.

     return NULL;

   }

 #endif

   // Replace dominated IfNode

   dominated_by( prev_dom, igvn );

   // Must return either the original node (now dead) or a new node

   // (Do not return a top here, since that would break the uniqueness of top.)

   return new (phase->C, 1) ConINode(TypeInt::ZERO);

 }

 //------------------------------dominated_by-----------------------------------

 void IfNode::dominated_by( Node *prev_dom, PhaseIterGVN *igvn ) {

   igvn->hash_delete(this);      // Remove self to prevent spurious V-N

   Node *idom = in(0);

   // Need opcode to decide which way 'this' test goes

   int prev_op = prev_dom->Opcode();

   Node *top = igvn->C->top(); // Shortcut to top

   // Now walk the current IfNode's projections.

   // Loop ends when 'this' has no more uses.

   for (DUIterator_Last imin, i = last_outs(imin); i >= imin; --i) {

     Node *ifp = last_out(i);     // Get IfTrue/IfFalse

     igvn->add_users_to_worklist(ifp);

     // Check which projection it is and set target.

     // Data-target is either the dominating projection of the same type

     // or TOP if the dominating projection is of opposite type.

     // Data-target will be used as the new control edge for the non-CFG

     // nodes like Casts and Loads.

     Node *data_target = (ifp->Opcode() == prev_op ) ? prev_dom : top;

     // Control-target is just the If's immediate dominator or TOP.

     Node *ctrl_target = (ifp->Opcode() == prev_op ) ?     idom : top;

     // For each child of an IfTrue/IfFalse projection, reroute.

     // Loop ends when projection has no more uses.

     for (DUIterator_Last jmin, j = ifp->last_outs(jmin); j >= jmin; --j) {

       Node* s = ifp->last_out(j);   // Get child of IfTrue/IfFalse

       igvn->hash_delete(s);         // Yank from hash table before edge hacking

       if( !s->depends_only_on_test() ) {

         // Find the control input matching this def-use edge.

         // For Regions it may not be in slot 0.

         uint l;

         for( l = 0; s->in(l) != ifp; l++ ) { }

         s->set_req(l, ctrl_target);

       } else {                      // Else, for control producers,

         s->set_req(0, data_target); // Move child to data-target

       }

       igvn->_worklist.push(s);  // Revisit collapsed Phis

     } // End for each child of a projection

     igvn->remove_dead_node(ifp);

   } // End for each IfTrue/IfFalse child of If

   // Kill the IfNode

   igvn->remove_dead_node(this);

 }

 //------------------------------Identity---------------------------------------

 // If the test is constant & we match, then we are the input Control

 Node *IfTrueNode::Identity( PhaseTransform *phase ) {

   // Can only optimize if cannot go the other way

   const TypeTuple *t = phase->type(in(0))->is_tuple();

   return ( t == TypeTuple::IFNEITHER || t == TypeTuple::IFTRUE )

     ? in(0)->in(0)              // IfNode control

     : this;                     // no progress

 }

 //------------------------------dump_spec--------------------------------------

 #ifndef PRODUCT

 void IfNode::dump_spec(outputStream *st) const {

   st->print("P=%f, C=%f",_prob,_fcnt);

 }

 #endif

 //------------------------------idealize_test----------------------------------

 // Try to canonicalize tests better.  Peek at the Cmp/Bool/If sequence and

 // come up with a canonical sequence.  Bools getting 'eq', 'gt' and 'ge' forms

 // converted to 'ne', 'le' and 'lt' forms.  IfTrue/IfFalse get swapped as

 // needed.

 static IfNode* idealize_test(PhaseGVN* phase, IfNode* iff) {

   assert(iff->in(0) != NULL, "If must be live");

   if (iff->outcnt() != 2)  return NULL; // Malformed projections.

   Node* old_if_f = iff->proj_out(false);

   Node* old_if_t = iff->proj_out(true);

   // CountedLoopEnds want the back-control test to be TRUE, irregardless of

   // whether they are testing a 'gt' or 'lt' condition.  The 'gt' condition

   // happens in count-down loops

   if (iff->is_CountedLoopEnd())  return NULL;

   if (!iff->in(1)->is_Bool())  return NULL; // Happens for partially optimized IF tests

   BoolNode *b = iff->in(1)->as_Bool();

   BoolTest bt = b->_test;

   // Test already in good order?

   if( bt.is_canonical() )

     return NULL;

   // Flip test to be canonical.  Requires flipping the IfFalse/IfTrue and

   // cloning the IfNode.

   Node* new_b = phase->transform( new (phase->C, 2) BoolNode(b->in(1), bt.negate()) );

   if( !new_b->is_Bool() ) return NULL;

   b = new_b->as_Bool();

   PhaseIterGVN *igvn = phase->is_IterGVN();

   assert( igvn, "Test is not canonical in parser?" );

   // The IF node never really changes, but it needs to be cloned

   iff = new (phase->C, 2) IfNode( iff->in(0), b, 1.0-iff->_prob, iff->_fcnt);

   Node *prior = igvn->hash_find_insert(iff);

   if( prior ) {

     igvn->remove_dead_node(iff);

     iff = (IfNode*)prior;

   } else {

     // Cannot call transform on it just yet

     igvn->set_type_bottom(iff);

   }

   igvn->_worklist.push(iff);

   // Now handle projections.  Cloning not required.

   Node* new_if_f = (Node*)(new (phase->C, 1) IfFalseNode( iff ));

   Node* new_if_t = (Node*)(new (phase->C, 1) IfTrueNode ( iff ));

   igvn->register_new_node_with_optimizer(new_if_f);

   igvn->register_new_node_with_optimizer(new_if_t);

   // Flip test, so flip trailing control

   igvn->replace_node(old_if_f, new_if_t);

   igvn->replace_node(old_if_t, new_if_f);

   // Progress

   return iff;

 }

 //------------------------------Identity---------------------------------------

 // If the test is constant & we match, then we are the input Control

 Node *IfFalseNode::Identity( PhaseTransform *phase ) {

   // Can only optimize if cannot go the other way

   const TypeTuple *t = phase->type(in(0))->is_tuple();

   return ( t == TypeTuple::IFNEITHER || t == TypeTuple::IFFALSE )

     ? in(0)->in(0)              // IfNode control

     : this;                     // no progress

 }