Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * Copyright 1998-2007 Sun Microsystems, Inc.  All Rights Reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

  * CA 95054 USA or visit www.sun.com if you need additional information or

  * have any questions.

  *

  */

 class CmpNode;

 class CountedLoopEndNode;

 class CountedLoopNode;

 class IdealLoopTree;

 class LoopNode;

 class Node;

 class PhaseIdealLoop;

 class VectorSet;

 struct small_cache;

 //

 //                  I D E A L I Z E D   L O O P S

 //

 // Idealized loops are the set of loops I perform more interesting

 // transformations on, beyond simple hoisting.

 //------------------------------LoopNode---------------------------------------

 // Simple loop header.  Fall in path on left, loop-back path on right.

 class LoopNode : public RegionNode {

   // Size is bigger to hold the flags.  However, the flags do not change

   // the semantics so it does not appear in the hash & cmp functions.

   virtual uint size_of() const { return sizeof(*this); }

 protected:

   short _loop_flags;

   // Names for flag bitfields

   enum { pre_post_main=0, inner_loop=8, partial_peel_loop=16, partial_peel_failed=32  };

   char _unswitch_count;

   enum { _unswitch_max=3 };

 public:

   // Names for edge indices

   enum { Self=0, EntryControl, LoopBackControl };

   int is_inner_loop() const { return _loop_flags & inner_loop; }

   void set_inner_loop() { _loop_flags |= inner_loop; }

   int is_partial_peel_loop() const { return _loop_flags & partial_peel_loop; }

   void set_partial_peel_loop() { _loop_flags |= partial_peel_loop; }

   int partial_peel_has_failed() const { return _loop_flags & partial_peel_failed; }

   void mark_partial_peel_failed() { _loop_flags |= partial_peel_failed; }

   int unswitch_max() { return _unswitch_max; }

   int unswitch_count() { return _unswitch_count; }

   void set_unswitch_count(int val) {

     assert (val <= unswitch_max(), "too many unswitches");

     _unswitch_count = val;

   }

   LoopNode( Node *entry, Node *backedge ) : RegionNode(3), _loop_flags(0), _unswitch_count(0) {

     init_class_id(Class_Loop);

     init_req(EntryControl, entry);

     init_req(LoopBackControl, backedge);

   }

   virtual Node *Ideal(PhaseGVN *phase, bool can_reshape);

   virtual int Opcode() const;

   bool can_be_counted_loop(PhaseTransform* phase) const {

     return req() == 3 && in(0) != NULL &&

       in(1) != NULL && phase->type(in(1)) != Type::TOP &&

       in(2) != NULL && phase->type(in(2)) != Type::TOP;

   }

 #ifndef PRODUCT

   virtual void dump_spec(outputStream *st) const;

 #endif

 };

 //------------------------------Counted Loops----------------------------------

 // Counted loops are all trip-counted loops, with exactly 1 trip-counter exit

 // path (and maybe some other exit paths).  The trip-counter exit is always

 // last in the loop.  The trip-counter does not have to stride by a constant,

 // but it does have to stride by a loop-invariant amount; the exit value is

 // also loop invariant.

 // CountedLoopNodes and CountedLoopEndNodes come in matched pairs.  The

 // CountedLoopNode has the incoming loop control and the loop-back-control

 // which is always the IfTrue before the matching CountedLoopEndNode.  The

 // CountedLoopEndNode has an incoming control (possibly not the

 // CountedLoopNode if there is control flow in the loop), the post-increment

 // trip-counter value, and the limit.  The trip-counter value is always of

 // the form (Op old-trip-counter stride).  The old-trip-counter is produced

 // by a Phi connected to the CountedLoopNode.  The stride is loop invariant.

 // The Op is any commutable opcode, including Add, Mul, Xor.  The

 // CountedLoopEndNode also takes in the loop-invariant limit value.

 // From a CountedLoopNode I can reach the matching CountedLoopEndNode via the

 // loop-back control.  From CountedLoopEndNodes I can reach CountedLoopNodes

 // via the old-trip-counter from the Op node.

 //------------------------------CountedLoopNode--------------------------------

 // CountedLoopNodes head simple counted loops.  CountedLoopNodes have as

 // inputs the incoming loop-start control and the loop-back control, so they

 // act like RegionNodes.  They also take in the initial trip counter, the

 // loop-invariant stride and the loop-invariant limit value.  CountedLoopNodes

 // produce a loop-body control and the trip counter value.  Since

 // CountedLoopNodes behave like RegionNodes I still have a standard CFG model.

 class CountedLoopNode : public LoopNode {

   // Size is bigger to hold _main_idx.  However, _main_idx does not change

   // the semantics so it does not appear in the hash & cmp functions.

   virtual uint size_of() const { return sizeof(*this); }

   // For Pre- and Post-loops during debugging ONLY, this holds the index of

   // the Main CountedLoop.  Used to assert that we understand the graph shape.

   node_idx_t _main_idx;

   // Known trip count calculated by policy_maximally_unroll

   int   _trip_count;

   // Expected trip count from profile data

   float _profile_trip_cnt;

   // Log2 of original loop bodies in unrolled loop

   int _unrolled_count_log2;

   // Node count prior to last unrolling - used to decide if

   // unroll,optimize,unroll,optimize,... is making progress

   int _node_count_before_unroll;

 public:

   CountedLoopNode( Node *entry, Node *backedge )

     : LoopNode(entry, backedge), _trip_count(max_jint),

       _profile_trip_cnt(COUNT_UNKNOWN), _unrolled_count_log2(0),

       _node_count_before_unroll(0) {

     init_class_id(Class_CountedLoop);

     // Initialize _trip_count to the largest possible value.

     // Will be reset (lower) if the loop's trip count is known.

   }

   virtual int Opcode() const;

   virtual Node *Ideal(PhaseGVN *phase, bool can_reshape);

   Node *init_control() const { return in(EntryControl); }

   Node *back_control() const { return in(LoopBackControl); }

   CountedLoopEndNode *loopexit() const;

   Node *init_trip() const;

   Node *stride() const;

   int   stride_con() const;

   bool  stride_is_con() const;

   Node *limit() const;

   Node *incr() const;

   Node *phi() const;

   // Match increment with optional truncation

   static Node* match_incr_with_optional_truncation(Node* expr, Node** trunc1, Node** trunc2, const TypeInt** trunc_type);

   // A 'main' loop has a pre-loop and a post-loop.  The 'main' loop

   // can run short a few iterations and may start a few iterations in.

   // It will be RCE'd and unrolled and aligned.

   // A following 'post' loop will run any remaining iterations.  Used

   // during Range Check Elimination, the 'post' loop will do any final

   // iterations with full checks.  Also used by Loop Unrolling, where

   // the 'post' loop will do any epilog iterations needed.  Basically,

   // a 'post' loop can not profitably be further unrolled or RCE'd.

   // A preceding 'pre' loop will run at least 1 iteration (to do peeling),

   // it may do under-flow checks for RCE and may do alignment iterations

   // so the following main loop 'knows' that it is striding down cache

   // lines.

   // A 'main' loop that is ONLY unrolled or peeled, never RCE'd or

   // Aligned, may be missing it's pre-loop.

   enum { Normal=0, Pre=1, Main=2, Post=3, PrePostFlagsMask=3, Main_Has_No_Pre_Loop=4 };

   int is_normal_loop() const { return (_loop_flags&PrePostFlagsMask) == Normal; }

   int is_pre_loop   () const { return (_loop_flags&PrePostFlagsMask) == Pre;    }

   int is_main_loop  () const { return (_loop_flags&PrePostFlagsMask) == Main;   }

   int is_post_loop  () const { return (_loop_flags&PrePostFlagsMask) == Post;   }

   int is_main_no_pre_loop() const { return _loop_flags & Main_Has_No_Pre_Loop; }

   void set_main_no_pre_loop() { _loop_flags |= Main_Has_No_Pre_Loop; }

   void set_pre_loop  (CountedLoopNode *main) { assert(is_normal_loop(),""); _loop_flags |= Pre ; _main_idx = main->_idx; }

   void set_main_loop (                     ) { assert(is_normal_loop(),""); _loop_flags |= Main;                         }

   void set_post_loop (CountedLoopNode *main) { assert(is_normal_loop(),""); _loop_flags |= Post; _main_idx = main->_idx; }

   void set_normal_loop(                    ) { _loop_flags &= ~PrePostFlagsMask; }

   void set_trip_count(int tc) { _trip_count = tc; }

   int trip_count()            { return _trip_count; }

   void set_profile_trip_cnt(float ptc) { _profile_trip_cnt = ptc; }

   float profile_trip_cnt()             { return _profile_trip_cnt; }

   void double_unrolled_count() { _unrolled_count_log2++; }

   int  unrolled_count()        { return 1 << MIN2(_unrolled_count_log2, BitsPerInt-3); }

   void set_node_count_before_unroll(int ct) { _node_count_before_unroll = ct; }

   int  node_count_before_unroll()           { return _node_count_before_unroll; }

 #ifndef PRODUCT

   virtual void dump_spec(outputStream *st) const;

 #endif

 };

 //------------------------------CountedLoopEndNode-----------------------------

 // CountedLoopEndNodes end simple trip counted loops.  They act much like

 // IfNodes.

 class CountedLoopEndNode : public IfNode {

 public:

   enum { TestControl, TestValue };

   CountedLoopEndNode( Node *control, Node *test, float prob, float cnt )

     : IfNode( control, test, prob, cnt) {

     init_class_id(Class_CountedLoopEnd);

   }

   virtual int Opcode() const;

   Node *cmp_node() const            { return (in(TestValue)->req() >=2) ? in(TestValue)->in(1) : NULL; }

   Node *incr() const                { Node *tmp = cmp_node(); return (tmp && tmp->req()==3) ? tmp->in(1) : NULL; }

   Node *limit() const               { Node *tmp = cmp_node(); return (tmp && tmp->req()==3) ? tmp->in(2) : NULL; }

   Node *stride() const              { Node *tmp = incr    (); return (tmp && tmp->req()==3) ? tmp->in(2) : NULL; }

   Node *phi() const                 { Node *tmp = incr    (); return (tmp && tmp->req()==3) ? tmp->in(1) : NULL; }

   Node *init_trip() const           { Node *tmp = phi     (); return (tmp && tmp->req()==3) ? tmp->in(1) : NULL; }

   int stride_con() const;

   bool stride_is_con() const        { Node *tmp = stride  (); return (tmp != NULL && tmp->is_Con()); }

   BoolTest::mask test_trip() const  { return in(TestValue)->as_Bool()->_test._test; }

   CountedLoopNode *loopnode() const {

     Node *ln = phi()->in(0);

     assert( ln->Opcode() == Op_CountedLoop, "malformed loop" );

     return (CountedLoopNode*)ln; }

 #ifndef PRODUCT

   virtual void dump_spec(outputStream *st) const;

 #endif

 };

 inline CountedLoopEndNode *CountedLoopNode::loopexit() const {

   Node *bc = back_control();

   if( bc == NULL ) return NULL;

   Node *le = bc->in(0);

   if( le->Opcode() != Op_CountedLoopEnd )

     return NULL;

   return (CountedLoopEndNode*)le;

 }

 inline Node *CountedLoopNode::init_trip() const { return loopexit() ? loopexit()->init_trip() : NULL; }

 inline Node *CountedLoopNode::stride() const { return loopexit() ? loopexit()->stride() : NULL; }

 inline int CountedLoopNode::stride_con() const { return loopexit() ? loopexit()->stride_con() : 0; }

 inline bool CountedLoopNode::stride_is_con() const { return loopexit() && loopexit()->stride_is_con(); }

 inline Node *CountedLoopNode::limit() const { return loopexit() ? loopexit()->limit() : NULL; }

 inline Node *CountedLoopNode::incr() const { return loopexit() ? loopexit()->incr() : NULL; }

 inline Node *CountedLoopNode::phi() const { return loopexit() ? loopexit()->phi() : NULL; }

 // -----------------------------IdealLoopTree----------------------------------

 class IdealLoopTree : public ResourceObj {

 public:

   IdealLoopTree *_parent;       // Parent in loop tree

   IdealLoopTree *_next;         // Next sibling in loop tree

   IdealLoopTree *_child;        // First child in loop tree

   // The head-tail backedge defines the loop.

   // If tail is NULL then this loop has multiple backedges as part of the

   // same loop.  During cleanup I'll peel off the multiple backedges; merge

   // them at the loop bottom and flow 1 real backedge into the loop.

   Node *_head;                  // Head of loop

   Node *_tail;                  // Tail of loop

   inline Node *tail();          // Handle lazy update of _tail field

   PhaseIdealLoop* _phase;

   Node_List _body;              // Loop body for inner loops

   uint8 _nest;                  // Nesting depth

   uint8 _irreducible:1,         // True if irreducible

         _has_call:1,            // True if has call safepoint

         _has_sfpt:1,            // True if has non-call safepoint

         _rce_candidate:1;       // True if candidate for range check elimination

   Node_List* _required_safept;  // A inner loop cannot delete these safepts;

   bool  _allow_optimizations;   // Allow loop optimizations

   IdealLoopTree( PhaseIdealLoop* phase, Node *head, Node *tail )

     : _parent(0), _next(0), _child(0),

       _head(head), _tail(tail),

       _phase(phase),

       _required_safept(NULL),

       _allow_optimizations(true),

       _nest(0), _irreducible(0), _has_call(0), _has_sfpt(0), _rce_candidate(0)

   { }

   // Is 'l' a member of 'this'?

   int is_member( const IdealLoopTree *l ) const; // Test for nested membership

   // Set loop nesting depth.  Accumulate has_call bits.

   int set_nest( uint depth );

   // 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 split_fall_in( PhaseIdealLoop *phase, int fall_in_cnt );

   // Split out the outermost loop from this shared header.

   void split_outer_loop( PhaseIdealLoop *phase );

   // Merge all the backedges from the shared header into a private Region.

   // Feed that region as the one backedge to this loop.

   void merge_many_backedges( PhaseIdealLoop *phase );

   // Split shared headers and insert loop landing pads.

   // Insert a LoopNode to replace the RegionNode.

   // Returns TRUE if loop tree is structurally changed.

   bool beautify_loops( PhaseIdealLoop *phase );

   // Perform iteration-splitting on inner loops.  Split iterations to avoid

   // range checks or one-shot null checks.

   void iteration_split( PhaseIdealLoop *phase, Node_List &old_new );

   // Driver for various flavors of iteration splitting

   void iteration_split_impl( PhaseIdealLoop *phase, Node_List &old_new );

   // 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).

   void check_safepts(VectorSet &visited, Node_List &stack);

   // Allpaths backwards scan from loop tail, terminating each path at first safepoint

   // encountered.

   void allpaths_check_safepts(VectorSet &visited, Node_List &stack);

   // Convert to counted loops where possible

   void counted_loop( PhaseIdealLoop *phase );

   // Check for Node being a loop-breaking test

   Node *is_loop_exit(Node *iff) const;

   // Returns true if ctrl is executed on every complete iteration

   bool dominates_backedge(Node* ctrl);

   // Remove simplistic dead code from loop body

   void DCE_loop_body();

   // Look for loop-exit tests with my 50/50 guesses from the Parsing stage.

   // Replace with a 1-in-10 exit guess.

   void adjust_loop_exit_prob( PhaseIdealLoop *phase );

   // Return TRUE or FALSE if the loop should never be RCE'd or aligned.

   // Useful for unrolling loops with NO array accesses.

   bool policy_peel_only( PhaseIdealLoop *phase ) const;

   // Return TRUE or FALSE if the loop should be unswitched -- clone

   // loop with an invariant test

   bool policy_unswitching( PhaseIdealLoop *phase ) const;

   // Micro-benchmark spamming.  Remove empty loops.

   bool policy_do_remove_empty_loop( PhaseIdealLoop *phase );

   // Return TRUE or FALSE if the loop should be peeled or not.  Peel if we can

   // make some loop-invariant test (usually a null-check) happen before the

   // loop.

   bool policy_peeling( PhaseIdealLoop *phase ) const;

   // Return TRUE or FALSE if the loop should be maximally unrolled. Stash any

   // known trip count in the counted loop node.

   bool policy_maximally_unroll( PhaseIdealLoop *phase ) const;

   // Return TRUE or FALSE if the loop should be unrolled or not.  Unroll if

   // the loop is a CountedLoop and the body is small enough.

   bool policy_unroll( PhaseIdealLoop *phase ) const;

   // Return TRUE or FALSE if the loop should be range-check-eliminated.

   // Gather a list of IF tests that are dominated by iteration splitting;

   // also gather the end of the first split and the start of the 2nd split.

   bool policy_range_check( PhaseIdealLoop *phase ) const;

   // Return TRUE or FALSE if the loop should be cache-line aligned.

   // Gather the expression that does the alignment.  Note that only

   // one array base can be aligned in a loop (unless the VM guarentees

   // mutual alignment).  Note that if we vectorize short memory ops

   // into longer memory ops, we may want to increase alignment.

   bool policy_align( PhaseIdealLoop *phase ) const;

   // Compute loop trip count from profile data

   void compute_profile_trip_cnt( PhaseIdealLoop *phase );

   // Reassociate invariant expressions.

   void reassociate_invariants(PhaseIdealLoop *phase);

   // Reassociate invariant add and subtract expressions.

   Node* reassociate_add_sub(Node* n1, PhaseIdealLoop *phase);

   // Return nonzero index of invariant operand if invariant and variant

   // are combined with an Add or Sub. Helper for reassoicate_invariants.

   int is_invariant_addition(Node* n, PhaseIdealLoop *phase);

   // Return true if n is invariant

   bool is_invariant(Node* n) const;

   // Put loop body on igvn work list

   void record_for_igvn();

   bool is_loop()    { return !_irreducible && _tail && !_tail->is_top(); }

   bool is_inner()   { return is_loop() && _child == NULL; }

   bool is_counted() { return is_loop() && _head != NULL && _head->is_CountedLoop(); }

 #ifndef PRODUCT

   void dump_head( ) const;      // Dump loop head only

   void dump() const;            // Dump this loop recursively

   void verify_tree(IdealLoopTree *loop, const IdealLoopTree *parent) const;

 #endif

 };

 // -----------------------------PhaseIdealLoop---------------------------------

 // Computes the mapping from Nodes to IdealLoopTrees.  Organizes IdealLoopTrees into a

 // loop tree.  Drives the loop-based transformations on the ideal graph.

 class PhaseIdealLoop : public PhaseTransform {

   friend class IdealLoopTree;

   friend class SuperWord;

   // Pre-computed def-use info

   PhaseIterGVN &_igvn;

   // Head of loop tree

   IdealLoopTree *_ltree_root;

   // Array of pre-order numbers, plus post-visited bit.

   // ZERO for not pre-visited.  EVEN for pre-visited but not post-visited.

   // ODD for post-visited.  Other bits are the pre-order number.

   uint *_preorders;

   uint _max_preorder;

   // Allocate _preorders[] array

   void allocate_preorders() {

     _max_preorder = C->unique()+8;

     _preorders = NEW_RESOURCE_ARRAY(uint, _max_preorder);

     memset(_preorders, 0, sizeof(uint) * _max_preorder);

   }

   // Allocate _preorders[] array

   void reallocate_preorders() {

     if ( _max_preorder < C->unique() ) {

       _preorders = REALLOC_RESOURCE_ARRAY(uint, _preorders, _max_preorder, C->unique());

       _max_preorder = C->unique();

     }

     memset(_preorders, 0, sizeof(uint) * _max_preorder);

   }

   // Check to grow _preorders[] array for the case when build_loop_tree_impl()

   // adds new nodes.

   void check_grow_preorders( ) {

     if ( _max_preorder < C->unique() ) {

       uint newsize = _max_preorder<<1;  // double size of array

       _preorders = REALLOC_RESOURCE_ARRAY(uint, _preorders, _max_preorder, newsize);

       memset(&_preorders[_max_preorder],0,sizeof(uint)*(newsize-_max_preorder));

       _max_preorder = newsize;

     }

   }

   // Check for pre-visited.  Zero for NOT visited; non-zero for visited.

   int is_visited( Node *n ) const { return _preorders[n->_idx]; }

   // Pre-order numbers are written to the Nodes array as low-bit-set values.

   void set_preorder_visited( Node *n, int pre_order ) {

     assert( !is_visited( n ), "already set" );

     _preorders[n->_idx] = (pre_order<<1);

   };

   // Return pre-order number.

   int get_preorder( Node *n ) const { assert( is_visited(n), "" ); return _preorders[n->_idx]>>1; }

   // Check for being post-visited.

   // Should be previsited already (checked with assert(is_visited(n))).

   int is_postvisited( Node *n ) const { assert( is_visited(n), "" ); return _preorders[n->_idx]&1; }

   // Mark as post visited

   void set_postvisited( Node *n ) { assert( !is_postvisited( n ), "" ); _preorders[n->_idx] |= 1; }

   // Set/get control node out.  Set lower bit to distinguish from IdealLoopTree

   // Returns true if "n" is a data node, false if it's a control node.

   bool has_ctrl( Node *n ) const { return ((intptr_t)_nodes[n->_idx]) & 1; }

   // clear out dead code after build_loop_late

   Node_List _deadlist;

   // Support for faster execution of get_late_ctrl()/dom_lca()

   // when a node has many uses and dominator depth is deep.

   Node_Array _dom_lca_tags;

   void   init_dom_lca_tags();

   void   clear_dom_lca_tags();

   // Inline wrapper for frequent cases:

   // 1) only one use

   // 2) a use is the same as the current LCA passed as 'n1'

   Node *dom_lca_for_get_late_ctrl( Node *lca, Node *n, Node *tag ) {

     assert( n->is_CFG(), "" );

     // Fast-path NULL lca

     if( lca != NULL && lca != n ) {

       assert( lca->is_CFG(), "" );

       // find LCA of all uses

       n = dom_lca_for_get_late_ctrl_internal( lca, n, tag );

     }

     return find_non_split_ctrl(n);

   }

   Node *dom_lca_for_get_late_ctrl_internal( Node *lca, Node *n, Node *tag );

   // true if CFG node d dominates CFG node n

   bool is_dominator(Node *d, Node *n);

   // Helper function for directing control inputs away from CFG split

   // points.

   Node *find_non_split_ctrl( Node *ctrl ) const {

     if (ctrl != NULL) {

       if (ctrl->is_MultiBranch()) {

         ctrl = ctrl->in(0);

       }

       assert(ctrl->is_CFG(), "CFG");

     }

     return ctrl;

   }

 public:

   bool has_node( Node* n ) const { return _nodes[n->_idx] != NULL; }

   // check if transform created new nodes that need _ctrl recorded

   Node *get_late_ctrl( Node *n, Node *early );

   Node *get_early_ctrl( Node *n );

   void set_early_ctrl( Node *n );

   void set_subtree_ctrl( Node *root );

   void set_ctrl( Node *n, Node *ctrl ) {

     assert( !has_node(n) || has_ctrl(n), "" );

     assert( ctrl->in(0), "cannot set dead control node" );

     assert( ctrl == find_non_split_ctrl(ctrl), "must set legal crtl" );

     _nodes.map( n->_idx, (Node*)((intptr_t)ctrl + 1) );

   }

   // Set control and update loop membership

   void set_ctrl_and_loop(Node* n, Node* ctrl) {

     IdealLoopTree* old_loop = get_loop(get_ctrl(n));

     IdealLoopTree* new_loop = get_loop(ctrl);

     if (old_loop != new_loop) {

       if (old_loop->_child == NULL) old_loop->_body.yank(n);

       if (new_loop->_child == NULL) new_loop->_body.push(n);

     }

     set_ctrl(n, ctrl);

   }

   // Control nodes can be replaced or subsumed.  During this pass they

   // get their replacement Node in slot 1.  Instead of updating the block

   // location of all Nodes in the subsumed block, we lazily do it.  As we

   // pull such a subsumed block out of the array, we write back the final

   // correct block.

   Node *get_ctrl( Node *i ) {

     assert(has_node(i), "");

     Node *n = get_ctrl_no_update(i);

     _nodes.map( i->_idx, (Node*)((intptr_t)n + 1) );

     assert(has_node(i) && has_ctrl(i), "");

     assert(n == find_non_split_ctrl(n), "must return legal ctrl" );

     return n;

   }

 private:

   Node *get_ctrl_no_update( Node *i ) const {

     assert( has_ctrl(i), "" );

     Node *n = (Node*)(((intptr_t)_nodes[i->_idx]) & ~1);

     if (!n->in(0)) {

       // Skip dead CFG nodes

       do {

         n = (Node*)(((intptr_t)_nodes[n->_idx]) & ~1);

       } while (!n->in(0));

       n = find_non_split_ctrl(n);

     }

     return n;

   }

   // Check for loop being set

   // "n" must be a control node. Returns true if "n" is known to be in a loop.

   bool has_loop( Node *n ) const {

     assert(!has_node(n) || !has_ctrl(n), "");

     return has_node(n);

   }

   // Set loop

   void set_loop( Node *n, IdealLoopTree *loop ) {

     _nodes.map(n->_idx, (Node*)loop);

   }

   // Lazy-dazy update of 'get_ctrl' and 'idom_at' mechanisms.  Replace

   // the 'old_node' with 'new_node'.  Kill old-node.  Add a reference

   // from old_node to new_node to support the lazy update.  Reference

   // replaces loop reference, since that is not neede for dead node.

 public:

   void lazy_update( Node *old_node, Node *new_node ) {

     assert( old_node != new_node, "no cycles please" );

     //old_node->set_req( 1, new_node /*NO DU INFO*/ );

     // Nodes always have DU info now, so re-use the side array slot

     // for this node to provide the forwarding pointer.

     _nodes.map( old_node->_idx, (Node*)((intptr_t)new_node + 1) );

   }

   void lazy_replace( Node *old_node, Node *new_node ) {

     _igvn.hash_delete(old_node);

     _igvn.subsume_node( old_node, new_node );

     lazy_update( old_node, new_node );

   }

   void lazy_replace_proj( Node *old_node, Node *new_node ) {

     assert( old_node->req() == 1, "use this for Projs" );

     _igvn.hash_delete(old_node); // Must hash-delete before hacking edges

     old_node->add_req( NULL );

     lazy_replace( old_node, new_node );

   }

 private:

   // Place 'n' in some loop nest, where 'n' is a CFG node

   void build_loop_tree();

   int build_loop_tree_impl( Node *n, int pre_order );

   // Insert loop into the existing loop tree.  'innermost' is a leaf of the

   // loop tree, not the root.

   IdealLoopTree *sort( IdealLoopTree *loop, IdealLoopTree *innermost );

   // Place Data nodes in some loop nest

   void build_loop_early( VectorSet &visited, Node_List &worklist, Node_Stack &nstack, const PhaseIdealLoop *verify_me );

   void build_loop_late ( VectorSet &visited, Node_List &worklist, Node_Stack &nstack, const PhaseIdealLoop *verify_me );

   void build_loop_late_post ( Node* n, const PhaseIdealLoop *verify_me );

   // Array of immediate dominance info for each CFG node indexed by node idx

 private:

   uint _idom_size;

   Node **_idom;                 // Array of immediate dominators

   uint *_dom_depth;           // Used for fast LCA test

   GrowableArray<uint>* _dom_stk; // For recomputation of dom depth

   Node* idom_no_update(Node* d) const {

     assert(d->_idx < _idom_size, "oob");

     Node* n = _idom[d->_idx];

     assert(n != NULL,"Bad immediate dominator info.");

     while (n->in(0) == NULL) {  // Skip dead CFG nodes

       //n = n->in(1);

       n = (Node*)(((intptr_t)_nodes[n->_idx]) & ~1);

       assert(n != NULL,"Bad immediate dominator info.");

     }

     return n;

   }

   Node *idom(Node* d) const {

     uint didx = d->_idx;

     Node *n = idom_no_update(d);

     _idom[didx] = n;            // Lazily remove dead CFG nodes from table.

     return n;

   }

   uint dom_depth(Node* d) const {

     assert(d->_idx < _idom_size, "");

     return _dom_depth[d->_idx];

   }

   void set_idom(Node* d, Node* n, uint dom_depth);

   // Locally compute IDOM using dom_lca call

   Node *compute_idom( Node *region ) const;

   // Recompute dom_depth

   void recompute_dom_depth();

   // Is safept not required by an outer loop?

   bool is_deleteable_safept(Node* sfpt);

 public:

   // Dominators for the sea of nodes

   void Dominators();

   Node *dom_lca( Node *n1, Node *n2 ) const {

     return find_non_split_ctrl(dom_lca_internal(n1, n2));

   }

   Node *dom_lca_internal( Node *n1, Node *n2 ) const;

   // Compute the Ideal Node to Loop mapping

   PhaseIdealLoop( PhaseIterGVN &igvn, const PhaseIdealLoop *verify_me, bool do_split_ifs );

   // True if the method has at least 1 irreducible loop

   bool _has_irreducible_loops;

   // Per-Node transform

   virtual Node *transform( Node *a_node ) { return 0; }

   Node *is_counted_loop( Node *x, IdealLoopTree *loop );

   // Return a post-walked LoopNode

   IdealLoopTree *get_loop( Node *n ) const {

     // Dead nodes have no loop, so return the top level loop instead

     if (!has_node(n))  return _ltree_root;

     assert(!has_ctrl(n), "");

     return (IdealLoopTree*)_nodes[n->_idx];

   }

   // Is 'n' a (nested) member of 'loop'?

   int is_member( const IdealLoopTree *loop, Node *n ) const {

     return loop->is_member(get_loop(n)); }

   // This is the basic building block of the loop optimizations.  It clones an

   // entire loop body.  It makes an old_new loop body mapping; with this

   // mapping you can find the new-loop equivalent to an old-loop node.  All

   // new-loop nodes are exactly equal to their old-loop counterparts, all

   // edges are the same.  All exits from the old-loop now have a RegionNode

   // that merges the equivalent new-loop path.  This is true even for the

   // normal "loop-exit" condition.  All uses of loop-invariant old-loop values

   // now come from (one or more) Phis that merge their new-loop equivalents.

   // Parameter side_by_side_idom:

   //   When side_by_size_idom is NULL, the dominator tree is constructed for

   //      the clone loop to dominate the original.  Used in construction of

   //      pre-main-post loop sequence.

   //   When nonnull, the clone and original are side-by-side, both are

   //      dominated by the passed in side_by_side_idom node.  Used in

   //      construction of unswitched loops.

   void clone_loop( IdealLoopTree *loop, Node_List &old_new, int dom_depth,

                    Node* side_by_side_idom = NULL);

   // If we got the effect of peeling, either by actually peeling or by

   // making a pre-loop which must execute at least once, we can remove

   // all loop-invariant dominated tests in the main body.

   void peeled_dom_test_elim( IdealLoopTree *loop, Node_List &old_new );

   // Generate code to do a loop peel for the given loop (and body).

   // old_new is a temp array.

   void do_peeling( IdealLoopTree *loop, Node_List &old_new );

   // Add pre and post loops around the given loop.  These loops are used

   // during RCE, unrolling and aligning loops.

   void insert_pre_post_loops( IdealLoopTree *loop, Node_List &old_new, bool peel_only );

   // If Node n lives in the back_ctrl block, we clone a private version of n

   // in preheader_ctrl block and return that, otherwise return n.

   Node *clone_up_backedge_goo( Node *back_ctrl, Node *preheader_ctrl, Node *n );

   // Take steps to maximally unroll the loop.  Peel any odd iterations, then

   // unroll to do double iterations.  The next round of major loop transforms

   // will repeat till the doubled loop body does all remaining iterations in 1

   // pass.

   void do_maximally_unroll( IdealLoopTree *loop, Node_List &old_new );

   // Unroll the loop body one step - make each trip do 2 iterations.

   void do_unroll( IdealLoopTree *loop, Node_List &old_new, bool adjust_min_trip );

   // Return true if exp is a constant times an induction var

   bool is_scaled_iv(Node* exp, Node* iv, int* p_scale);

   // Return true if exp is a scaled induction var plus (or minus) constant

   bool is_scaled_iv_plus_offset(Node* exp, Node* iv, int* p_scale, Node** p_offset, int depth = 0);

   // Eliminate range-checks and other trip-counter vs loop-invariant tests.

   void do_range_check( IdealLoopTree *loop, Node_List &old_new );

   // Create a slow version of the loop by cloning the loop

   // and inserting an if to select fast-slow versions.

   ProjNode* create_slow_version_of_loop(IdealLoopTree *loop,

                                         Node_List &old_new);

   // Clone loop with an invariant test (that does not exit) and

   // insert a clone of the test that selects which version to

   // execute.

   void do_unswitching (IdealLoopTree *loop, Node_List &old_new);

   // Find candidate "if" for unswitching

   IfNode* find_unswitching_candidate(const IdealLoopTree *loop) const;

   // Range Check Elimination uses this function!

   // Constrain the main loop iterations so the affine function:

   //    scale_con * I + offset  <  limit

   // always holds true.  That is, either increase the number of iterations in

   // the pre-loop or the post-loop until the condition holds true in the main

   // loop.  Scale_con, offset and limit are all loop invariant.

   void add_constraint( int stride_con, int scale_con, Node *offset, Node *limit, Node *pre_ctrl, Node **pre_limit, Node **main_limit );

   // Partially peel loop up through last_peel node.

   bool partial_peel( IdealLoopTree *loop, Node_List &old_new );

   // Create a scheduled list of nodes control dependent on ctrl set.

   void scheduled_nodelist( IdealLoopTree *loop, VectorSet& ctrl, Node_List &sched );

   // Has a use in the vector set

   bool has_use_in_set( Node* n, VectorSet& vset );

   // Has use internal to the vector set (ie. not in a phi at the loop head)

   bool has_use_internal_to_set( Node* n, VectorSet& vset, IdealLoopTree *loop );

   // clone "n" for uses that are outside of loop

   void clone_for_use_outside_loop( IdealLoopTree *loop, Node* n, Node_List& worklist );

   // clone "n" for special uses that are in the not_peeled region

   void clone_for_special_use_inside_loop( IdealLoopTree *loop, Node* n,

                                           VectorSet& not_peel, Node_List& sink_list, Node_List& worklist );

   // Insert phi(lp_entry_val, back_edge_val) at use->in(idx) for loop lp if phi does not already exist

   void insert_phi_for_loop( Node* use, uint idx, Node* lp_entry_val, Node* back_edge_val, LoopNode* lp );

 #ifdef ASSERT

   // Validate the loop partition sets: peel and not_peel

   bool is_valid_loop_partition( IdealLoopTree *loop, VectorSet& peel, Node_List& peel_list, VectorSet& not_peel );

   // Ensure that uses outside of loop are of the right form

   bool is_valid_clone_loop_form( IdealLoopTree *loop, Node_List& peel_list,

                                  uint orig_exit_idx, uint clone_exit_idx);

   bool is_valid_clone_loop_exit_use( IdealLoopTree *loop, Node* use, uint exit_idx);

 #endif

   // Returns nonzero constant stride if-node is a possible iv test (otherwise returns zero.)

   int stride_of_possible_iv( Node* iff );

   bool is_possible_iv_test( Node* iff ) { return stride_of_possible_iv(iff) != 0; }

   // Return the (unique) control output node that's in the loop (if it exists.)

   Node* stay_in_loop( Node* n, IdealLoopTree *loop);

   // Insert a signed compare loop exit cloned from an unsigned compare.

   IfNode* insert_cmpi_loop_exit(IfNode* if_cmpu, IdealLoopTree *loop);

   void remove_cmpi_loop_exit(IfNode* if_cmp, IdealLoopTree *loop);

   // Utility to register node "n" with PhaseIdealLoop

   void register_node(Node* n, IdealLoopTree *loop, Node* pred, int ddepth);

   // Utility to create an if-projection

   ProjNode* proj_clone(ProjNode* p, IfNode* iff);

   // Force the iff control output to be the live_proj

   Node* short_circuit_if(IfNode* iff, ProjNode* live_proj);

   // Insert a region before an if projection

   RegionNode* insert_region_before_proj(ProjNode* proj);

   // Insert a new if before an if projection

   ProjNode* insert_if_before_proj(Node* left, bool Signed, BoolTest::mask relop, Node* right, ProjNode* proj);

   // Passed in a Phi merging (recursively) some nearly equivalent Bool/Cmps.

   // "Nearly" because all Nodes have been cloned from the original in the loop,

   // but the fall-in edges to the Cmp are different.  Clone bool/Cmp pairs

   // through the Phi recursively, and return a Bool.

   BoolNode *clone_iff( PhiNode *phi, IdealLoopTree *loop );

   CmpNode *clone_bool( PhiNode *phi, IdealLoopTree *loop );

   // Rework addressing expressions to get the most loop-invariant stuff

   // moved out.  We'd like to do all associative operators, but it's especially

   // important (common) to do address expressions.

   Node *remix_address_expressions( Node *n );

   // Attempt to use a conditional move instead of a phi/branch

   Node *conditional_move( Node *n );

   // Reorganize offset computations to lower register pressure.

   // Mostly prevent loop-fallout uses of the pre-incremented trip counter

   // (which are then alive with the post-incremented trip counter

   // forcing an extra register move)

   void reorg_offsets( IdealLoopTree *loop );

   // Check for aggressive application of 'split-if' optimization,

   // using basic block level info.

   void  split_if_with_blocks     ( VectorSet &visited, Node_Stack &nstack );

   Node *split_if_with_blocks_pre ( Node *n );

   void  split_if_with_blocks_post( Node *n );

   Node *has_local_phi_input( Node *n );

   // Mark an IfNode as being dominated by a prior test,

   // without actually altering the CFG (and hence IDOM info).

   void dominated_by( Node *prevdom, Node *iff );

   // Split Node 'n' through merge point

   Node *split_thru_region( Node *n, Node *region );

   // Split Node 'n' through merge point if there is enough win.

   Node *split_thru_phi( Node *n, Node *region, int policy );

   // Found an If getting its condition-code input from a Phi in the

   // same block.  Split thru the Region.

   void do_split_if( Node *iff );

 private:

   // Return a type based on condition control flow

   const TypeInt* filtered_type( Node *n, Node* n_ctrl);

   const TypeInt* filtered_type( Node *n ) { return filtered_type(n, NULL); }

  // Helpers for filtered type

   const TypeInt* filtered_type_from_dominators( Node* val, Node *val_ctrl);

   // Helper functions

   void register_new_node( Node *n, Node *blk );

   Node *spinup( Node *iff, Node *new_false, Node *new_true, Node *region, Node *phi, small_cache *cache );

   Node *find_use_block( Node *use, Node *def, Node *old_false, Node *new_false, Node *old_true, Node *new_true );

   void handle_use( Node *use, Node *def, small_cache *cache, Node *region_dom, Node *new_false, Node *new_true, Node *old_false, Node *old_true );

   bool split_up( Node *n, Node *blk1, Node *blk2 );

   void sink_use( Node *use, Node *post_loop );

   Node *place_near_use( Node *useblock ) const;

   bool _created_loop_node;

 public:

   void set_created_loop_node() { _created_loop_node = true; }

   bool created_loop_node()     { return _created_loop_node; }

 #ifndef PRODUCT

   void dump( ) const;

   void dump( IdealLoopTree *loop, uint rpo_idx, Node_List &rpo_list ) const;

   void rpo( Node *start, Node_Stack &stk, VectorSet &visited, Node_List &rpo_list ) const;

   void verify() const;          // Major slow  :-)

   void verify_compare( Node *n, const PhaseIdealLoop *loop_verify, VectorSet &visited ) const;

   IdealLoopTree *get_loop_idx(Node* n) const {

     // Dead nodes have no loop, so return the top level loop instead

     return _nodes[n->_idx] ? (IdealLoopTree*)_nodes[n->_idx] : _ltree_root;

   }

   // Print some stats

   static void print_statistics();

   static int _loop_invokes;     // Count of PhaseIdealLoop invokes

   static int _loop_work;        // Sum of PhaseIdealLoop x _unique

 #endif

 };

 inline Node* IdealLoopTree::tail() {

 // Handle lazy update of _tail field

   Node *n = _tail;

   //while( !n->in(0) )  // Skip dead CFG nodes

     //n = n->in(1);

   if (n->in(0) == NULL)

     n = _phase->get_ctrl(n);

   _tail = n;

   return n;

 }

 // Iterate over the loop tree using a preorder, left-to-right traversal.

 //

 // Example that visits all counted loops from within PhaseIdealLoop

 //

 //  for (LoopTreeIterator iter(_ltree_root); !iter.done(); iter.next()) {

 //   IdealLoopTree* lpt = iter.current();

 //   if (!lpt->is_counted()) continue;

 //   ...

 class LoopTreeIterator : public StackObj {

 private:

   IdealLoopTree* _root;

   IdealLoopTree* _curnt;

 public:

   LoopTreeIterator(IdealLoopTree* root) : _root(root), _curnt(root) {}

   bool done() { return _curnt == NULL; }       // Finished iterating?

   void next();                                 // Advance to next loop tree

   IdealLoopTree* current() { return _curnt; }  // Return current value of iterator.

 };