1 /*
  2  * Copyright (c) 2002, 2021, Oracle and/or its affiliates. All rights reserved.
  3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  4  *
  5  * This code is free software; you can redistribute it and/or modify it
  6  * under the terms of the GNU General Public License version 2 only, as
  7  * published by the Free Software Foundation.
  8  *
  9  * This code is distributed in the hope that it will be useful, but WITHOUT
 10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 12  * version 2 for more details (a copy is included in the LICENSE file that
 13  * accompanied this code).
 14  *
 15  * You should have received a copy of the GNU General Public License version
 16  * 2 along with this work; if not, write to the Free Software Foundation,
 17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 18  *
 19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 20  * or visit www.oracle.com if you need additional information or have any
 21  * questions.
 22  *
 23  */
 24 
 25 #include "precompiled.hpp"
 26 #include "code/vmreg.inline.hpp"
 27 #include "compiler/oopMap.hpp"
 28 #include "memory/resourceArea.hpp"
 29 #include "opto/addnode.hpp"
 30 #include "opto/callnode.hpp"
 31 #include "opto/compile.hpp"
 32 #include "opto/machnode.hpp"
 33 #include "opto/matcher.hpp"
 34 #include "opto/output.hpp"
 35 #include "opto/phase.hpp"
 36 #include "opto/regalloc.hpp"
 37 #include "opto/rootnode.hpp"
 38 #include "utilities/align.hpp"
 39 
 40 // The functions in this file builds OopMaps after all scheduling is done.
 41 //
 42 // OopMaps contain a list of all registers and stack-slots containing oops (so
 43 // they can be updated by GC).  OopMaps also contain a list of derived-pointer
 44 // base-pointer pairs.  When the base is moved, the derived pointer moves to
 45 // follow it.  Finally, any registers holding callee-save values are also
 46 // recorded.  These might contain oops, but only the caller knows.
 47 //
 48 // BuildOopMaps implements a simple forward reaching-defs solution.  At each
 49 // GC point we'll have the reaching-def Nodes.  If the reaching Nodes are
 50 // typed as pointers (no offset), then they are oops.  Pointers+offsets are
 51 // derived pointers, and bases can be found from them.  Finally, we'll also
 52 // track reaching callee-save values.  Note that a copy of a callee-save value
 53 // "kills" it's source, so that only 1 copy of a callee-save value is alive at
 54 // a time.
 55 //
 56 // We run a simple bitvector liveness pass to help trim out dead oops.  Due to
 57 // irreducible loops, we can have a reaching def of an oop that only reaches
 58 // along one path and no way to know if it's valid or not on the other path.
 59 // The bitvectors are quite dense and the liveness pass is fast.
 60 //
 61 // At GC points, we consult this information to build OopMaps.  All reaching
 62 // defs typed as oops are added to the OopMap.  Only 1 instance of a
 63 // callee-save register can be recorded.  For derived pointers, we'll have to
 64 // find and record the register holding the base.
 65 //
 66 // The reaching def's is a simple 1-pass worklist approach.  I tried a clever
 67 // breadth-first approach but it was worse (showed O(n^2) in the
 68 // pick-next-block code).
 69 //
 70 // The relevant data is kept in a struct of arrays (it could just as well be
 71 // an array of structs, but the struct-of-arrays is generally a little more
 72 // efficient).  The arrays are indexed by register number (including
 73 // stack-slots as registers) and so is bounded by 200 to 300 elements in
 74 // practice.  One array will map to a reaching def Node (or NULL for
 75 // conflict/dead).  The other array will map to a callee-saved register or
 76 // OptoReg::Bad for not-callee-saved.
 77 
 78 
 79 // Structure to pass around
 80 struct OopFlow : public ResourceObj {
 81   short *_callees;              // Array mapping register to callee-saved
 82   Node **_defs;                 // array mapping register to reaching def
 83                                 // or NULL if dead/conflict
 84   // OopFlow structs, when not being actively modified, describe the _end_ of
 85   // this block.
 86   Block *_b;                    // Block for this struct
 87   OopFlow *_next;               // Next free OopFlow
 88                                 // or NULL if dead/conflict
 89   Compile* C;
 90 
 91   OopFlow( short *callees, Node **defs, Compile* c ) : _callees(callees), _defs(defs),
 92     _b(NULL), _next(NULL), C(c) { }
 93 
 94   // Given reaching-defs for this block start, compute it for this block end
 95   void compute_reach( PhaseRegAlloc *regalloc, int max_reg, Dict *safehash );
 96 
 97   // Merge these two OopFlows into the 'this' pointer.
 98   void merge( OopFlow *flow, int max_reg );
 99 
100   // Copy a 'flow' over an existing flow
101   void clone( OopFlow *flow, int max_size);
102 
103   // Make a new OopFlow from scratch
104   static OopFlow *make( Arena *A, int max_size, Compile* C );
105 
106   // Build an oopmap from the current flow info
107   OopMap *build_oop_map( Node *n, int max_reg, PhaseRegAlloc *regalloc, int* live );
108 };
109 
110 // Given reaching-defs for this block start, compute it for this block end
111 void OopFlow::compute_reach( PhaseRegAlloc *regalloc, int max_reg, Dict *safehash ) {
112 
113   for( uint i=0; i<_b->number_of_nodes(); i++ ) {
114     Node *n = _b->get_node(i);
115 
116     if( n->jvms() ) {           // Build an OopMap here?
117       JVMState *jvms = n->jvms();
118       // no map needed for leaf calls
119       if( n->is_MachSafePoint() && !n->is_MachCallLeaf() ) {
120         int *live = (int*) (*safehash)[n];
121         assert( live, "must find live" );
122         n->as_MachSafePoint()->set_oop_map( build_oop_map(n,max_reg,regalloc, live) );
123       }
124     }
125 
126     // Assign new reaching def's.
127     // Note that I padded the _defs and _callees arrays so it's legal
128     // to index at _defs[OptoReg::Bad].
129     OptoReg::Name first = regalloc->get_reg_first(n);
130     OptoReg::Name second = regalloc->get_reg_second(n);
131     _defs[first] = n;
132     _defs[second] = n;
133 
134     // Pass callee-save info around copies
135     int idx = n->is_Copy();
136     if( idx ) {                 // Copies move callee-save info
137       OptoReg::Name old_first = regalloc->get_reg_first(n->in(idx));
138       OptoReg::Name old_second = regalloc->get_reg_second(n->in(idx));
139       int tmp_first = _callees[old_first];
140       int tmp_second = _callees[old_second];
141       _callees[old_first] = OptoReg::Bad; // callee-save is moved, dead in old location
142       _callees[old_second] = OptoReg::Bad;
143       _callees[first] = tmp_first;
144       _callees[second] = tmp_second;
145     } else if( n->is_Phi() ) {  // Phis do not mod callee-saves
146       assert( _callees[first] == _callees[regalloc->get_reg_first(n->in(1))], "" );
147       assert( _callees[second] == _callees[regalloc->get_reg_second(n->in(1))], "" );
148       assert( _callees[first] == _callees[regalloc->get_reg_first(n->in(n->req()-1))], "" );
149       assert( _callees[second] == _callees[regalloc->get_reg_second(n->in(n->req()-1))], "" );
150     } else {
151       _callees[first] = OptoReg::Bad; // No longer holding a callee-save value
152       _callees[second] = OptoReg::Bad;
153 
154       // Find base case for callee saves
155       if( n->is_Proj() && n->in(0)->is_Start() ) {
156         if( OptoReg::is_reg(first) &&
157             regalloc->_matcher.is_save_on_entry(first) )
158           _callees[first] = first;
159         if( OptoReg::is_reg(second) &&
160             regalloc->_matcher.is_save_on_entry(second) )
161           _callees[second] = second;
162       }
163     }
164   }
165 }
166 
167 // Merge the given flow into the 'this' flow
168 void OopFlow::merge( OopFlow *flow, int max_reg ) {
169   assert( _b == NULL, "merging into a happy flow" );
170   assert( flow->_b, "this flow is still alive" );
171   assert( flow != this, "no self flow" );
172 
173   // Do the merge.  If there are any differences, drop to 'bottom' which
174   // is OptoReg::Bad or NULL depending.
175   for( int i=0; i<max_reg; i++ ) {
176     // Merge the callee-save's
177     if( _callees[i] != flow->_callees[i] )
178       _callees[i] = OptoReg::Bad;
179     // Merge the reaching defs
180     if( _defs[i] != flow->_defs[i] )
181       _defs[i] = NULL;
182   }
183 
184 }
185 
186 void OopFlow::clone( OopFlow *flow, int max_size ) {
187   _b = flow->_b;
188   memcpy( _callees, flow->_callees, sizeof(short)*max_size);
189   memcpy( _defs   , flow->_defs   , sizeof(Node*)*max_size);
190 }
191 
192 OopFlow *OopFlow::make( Arena *A, int max_size, Compile* C ) {
193   short *callees = NEW_ARENA_ARRAY(A,short,max_size+1);
194   Node **defs    = NEW_ARENA_ARRAY(A,Node*,max_size+1);
195   debug_only( memset(defs,0,(max_size+1)*sizeof(Node*)) );
196   OopFlow *flow = new (A) OopFlow(callees+1, defs+1, C);
197   assert( &flow->_callees[OptoReg::Bad] == callees, "Ok to index at OptoReg::Bad" );
198   assert( &flow->_defs   [OptoReg::Bad] == defs   , "Ok to index at OptoReg::Bad" );
199   return flow;
200 }
201 
202 static int get_live_bit( int *live, int reg ) {
203   return live[reg>>LogBitsPerInt] &   (1<<(reg&(BitsPerInt-1))); }
204 static void set_live_bit( int *live, int reg ) {
205          live[reg>>LogBitsPerInt] |=  (1<<(reg&(BitsPerInt-1))); }
206 static void clr_live_bit( int *live, int reg ) {
207          live[reg>>LogBitsPerInt] &= ~(1<<(reg&(BitsPerInt-1))); }
208 
209 // Build an oopmap from the current flow info
210 OopMap *OopFlow::build_oop_map( Node *n, int max_reg, PhaseRegAlloc *regalloc, int* live ) {
211   int framesize = regalloc->_framesize;
212   int max_inarg_slot = OptoReg::reg2stack(regalloc->_matcher._new_SP);
213   debug_only( char *dup_check = NEW_RESOURCE_ARRAY(char,OptoReg::stack0());
214               memset(dup_check,0,OptoReg::stack0()) );
215 
216   OopMap *omap = new OopMap( framesize,  max_inarg_slot );
217   MachCallNode *mcall = n->is_MachCall() ? n->as_MachCall() : NULL;
218   JVMState* jvms = n->jvms();
219 
220   // For all registers do...
221   for( int reg=0; reg<max_reg; reg++ ) {
222     if( get_live_bit(live,reg) == 0 )
223       continue;                 // Ignore if not live
224 
225     // %%% C2 can use 2 OptoRegs when the physical register is only one 64bit
226     // register in that case we'll get an non-concrete register for the second
227     // half. We only need to tell the map the register once!
228     //
229     // However for the moment we disable this change and leave things as they
230     // were.
231 
232     VMReg r = OptoReg::as_VMReg(OptoReg::Name(reg), framesize, max_inarg_slot);
233 
234     // See if dead (no reaching def).
235     Node *def = _defs[reg];     // Get reaching def
236     assert( def, "since live better have reaching def" );
237 
238     // Classify the reaching def as oop, derived, callee-save, dead, or other
239     const Type *t = def->bottom_type();
240     if( t->isa_oop_ptr() ) {    // Oop or derived?
241       assert( !OptoReg::is_valid(_callees[reg]), "oop can't be callee save" );
242 #ifdef _LP64
243       // 64-bit pointers record oop-ishness on 2 aligned adjacent registers.
244       // Make sure both are record from the same reaching def, but do not
245       // put both into the oopmap.
246       if( (reg&1) == 1 ) {      // High half of oop-pair?
247         assert( _defs[reg-1] == _defs[reg], "both halves from same reaching def" );
248         continue;               // Do not record high parts in oopmap
249       }
250 #endif
251 
252       // Check for a legal reg name in the oopMap and bailout if it is not.
253       if (!omap->legal_vm_reg_name(r)) {
254         regalloc->C->record_method_not_compilable("illegal oopMap register name");
255         continue;
256       }
257       if (t->is_ptr()->offset() == 0) { // Not derived?
258         if( mcall ) {
259           // Outgoing argument GC mask responsibility belongs to the callee,
260           // not the caller.  Inspect the inputs to the call, to see if
261           // this live-range is one of them.
262           uint cnt = mcall->tf()->domain_cc()->cnt();
263           uint j;
264           for( j = TypeFunc::Parms; j < cnt; j++)
265             if( mcall->in(j) == def )
266               break;            // reaching def is an argument oop
267           if( j < cnt )         // arg oops dont go in GC map
268             continue;           // Continue on to the next register
269         }
270         omap->set_oop(r);
271       } else {                  // Else it's derived.
272         // Find the base of the derived value.
273         uint i;
274         // Fast, common case, scan
275         for( i = jvms->oopoff(); i < n->req(); i+=2 )
276           if( n->in(i) == def ) break; // Common case
277         if( i == n->req() ) {   // Missed, try a more generous scan
278           // Scan again, but this time peek through copies
279           for( i = jvms->oopoff(); i < n->req(); i+=2 ) {
280             Node *m = n->in(i); // Get initial derived value
281             while( 1 ) {
282               Node *d = def;    // Get initial reaching def
283               while( 1 ) {      // Follow copies of reaching def to end
284                 if( m == d ) goto found; // breaks 3 loops
285                 int idx = d->is_Copy();
286                 if( !idx ) break;
287                 d = d->in(idx);     // Link through copy
288               }
289               int idx = m->is_Copy();
290               if( !idx ) break;
291               m = m->in(idx);
292             }
293           }
294           guarantee( 0, "must find derived/base pair" );
295         }
296       found: ;
297         Node *base = n->in(i+1); // Base is other half of pair
298         int breg = regalloc->get_reg_first(base);
299         VMReg b = OptoReg::as_VMReg(OptoReg::Name(breg), framesize, max_inarg_slot);
300 
301         // I record liveness at safepoints BEFORE I make the inputs
302         // live.  This is because argument oops are NOT live at a
303         // safepoint (or at least they cannot appear in the oopmap).
304         // Thus bases of base/derived pairs might not be in the
305         // liveness data but they need to appear in the oopmap.
306         if( get_live_bit(live,breg) == 0 ) {// Not live?
307           // Flag it, so next derived pointer won't re-insert into oopmap
308           set_live_bit(live,breg);
309           // Already missed our turn?
310           if( breg < reg ) {
311             omap->set_oop(b);
312           }
313         }
314         omap->set_derived_oop(r, b);
315       }
316 
317     } else if( t->isa_narrowoop() ) {
318       assert( !OptoReg::is_valid(_callees[reg]), "oop can't be callee save" );
319       // Check for a legal reg name in the oopMap and bailout if it is not.
320       if (!omap->legal_vm_reg_name(r)) {
321         regalloc->C->record_method_not_compilable("illegal oopMap register name");
322         continue;
323       }
324       if( mcall ) {
325           // Outgoing argument GC mask responsibility belongs to the callee,
326           // not the caller.  Inspect the inputs to the call, to see if
327           // this live-range is one of them.
328         uint cnt = mcall->tf()->domain_cc()->cnt();
329         uint j;
330         for( j = TypeFunc::Parms; j < cnt; j++)
331           if( mcall->in(j) == def )
332             break;            // reaching def is an argument oop
333         if( j < cnt )         // arg oops dont go in GC map
334           continue;           // Continue on to the next register
335       }
336       omap->set_narrowoop(r);
337     } else if( OptoReg::is_valid(_callees[reg])) { // callee-save?
338       // It's a callee-save value
339       assert( dup_check[_callees[reg]]==0, "trying to callee save same reg twice" );
340       debug_only( dup_check[_callees[reg]]=1; )
341       VMReg callee = OptoReg::as_VMReg(OptoReg::Name(_callees[reg]));
342       omap->set_callee_saved(r, callee);
343 
344     } else {
345       // Other - some reaching non-oop value
346 #ifdef ASSERT
347       if( t->isa_rawptr() && C->cfg()->_raw_oops.member(def) ) {
348         def->dump();
349         n->dump();
350         assert(false, "there should be a oop in OopMap instead of a live raw oop at safepoint");
351       }
352 #endif
353     }
354 
355   }
356 
357 #ifdef ASSERT
358   /* Nice, Intel-only assert
359   int cnt_callee_saves=0;
360   int reg2 = 0;
361   while (OptoReg::is_reg(reg2)) {
362     if( dup_check[reg2] != 0) cnt_callee_saves++;
363     assert( cnt_callee_saves==3 || cnt_callee_saves==5, "missed some callee-save" );
364     reg2++;
365   }
366   */
367 #endif
368 
369 #ifdef ASSERT
370   for( OopMapStream oms1(omap); !oms1.is_done(); oms1.next()) {
371     OopMapValue omv1 = oms1.current();
372     if (omv1.type() != OopMapValue::derived_oop_value) {
373       continue;
374     }
375     bool found = false;
376     for( OopMapStream oms2(omap); !oms2.is_done(); oms2.next()) {
377       OopMapValue omv2 = oms2.current();
378       if (omv2.type() != OopMapValue::oop_value) {
379         continue;
380       }
381       if( omv1.content_reg() == omv2.reg() ) {
382         found = true;
383         break;
384       }
385     }
386     assert( found, "derived with no base in oopmap" );
387   }
388 #endif
389 
390   return omap;
391 }
392 
393 // Compute backwards liveness on registers
394 static void do_liveness(PhaseRegAlloc* regalloc, PhaseCFG* cfg, Block_List* worklist, int max_reg_ints, Arena* A, Dict* safehash) {
395   int* live = NEW_ARENA_ARRAY(A, int, (cfg->number_of_blocks() + 1) * max_reg_ints);
396   int* tmp_live = &live[cfg->number_of_blocks() * max_reg_ints];
397   Node* root = cfg->get_root_node();
398   // On CISC platforms, get the node representing the stack pointer  that regalloc
399   // used for spills
400   Node *fp = NodeSentinel;
401   if (UseCISCSpill && root->req() > 1) {
402     fp = root->in(1)->in(TypeFunc::FramePtr);
403   }
404   memset(live, 0, cfg->number_of_blocks() * (max_reg_ints << LogBytesPerInt));
405   // Push preds onto worklist
406   for (uint i = 1; i < root->req(); i++) {
407     Block* block = cfg->get_block_for_node(root->in(i));
408     worklist->push(block);
409   }
410 
411   // ZKM.jar includes tiny infinite loops which are unreached from below.
412   // If we missed any blocks, we'll retry here after pushing all missed
413   // blocks on the worklist.  Normally this outer loop never trips more
414   // than once.
415   while (1) {
416 
417     while( worklist->size() ) { // Standard worklist algorithm
418       Block *b = worklist->rpop();
419 
420       // Copy first successor into my tmp_live space
421       int s0num = b->_succs[0]->_pre_order;
422       int *t = &live[s0num*max_reg_ints];
423       for( int i=0; i<max_reg_ints; i++ )
424         tmp_live[i] = t[i];
425 
426       // OR in the remaining live registers
427       for( uint j=1; j<b->_num_succs; j++ ) {
428         uint sjnum = b->_succs[j]->_pre_order;
429         int *t = &live[sjnum*max_reg_ints];
430         for( int i=0; i<max_reg_ints; i++ )
431           tmp_live[i] |= t[i];
432       }
433 
434       // Now walk tmp_live up the block backwards, computing live
435       for( int k=b->number_of_nodes()-1; k>=0; k-- ) {
436         Node *n = b->get_node(k);
437         // KILL def'd bits
438         int first = regalloc->get_reg_first(n);
439         int second = regalloc->get_reg_second(n);
440         if( OptoReg::is_valid(first) ) clr_live_bit(tmp_live,first);
441         if( OptoReg::is_valid(second) ) clr_live_bit(tmp_live,second);
442 
443         MachNode *m = n->is_Mach() ? n->as_Mach() : NULL;
444 
445         // Check if m is potentially a CISC alternate instruction (i.e, possibly
446         // synthesized by RegAlloc from a conventional instruction and a
447         // spilled input)
448         bool is_cisc_alternate = false;
449         if (UseCISCSpill && m) {
450           is_cisc_alternate = m->is_cisc_alternate();
451         }
452 
453         // GEN use'd bits
454         for( uint l=1; l<n->req(); l++ ) {
455           Node *def = n->in(l);
456           assert(def != 0, "input edge required");
457           int first = regalloc->get_reg_first(def);
458           int second = regalloc->get_reg_second(def);
459           //If peephole had removed the node,do not set live bit for it.
460           if (!(def->is_Mach() && def->as_Mach()->get_removed())) {
461             if (OptoReg::is_valid(first)) set_live_bit(tmp_live,first);
462             if (OptoReg::is_valid(second)) set_live_bit(tmp_live,second);
463           }
464           // If we use the stack pointer in a cisc-alternative instruction,
465           // check for use as a memory operand.  Then reconstruct the RegName
466           // for this stack location, and set the appropriate bit in the
467           // live vector 4987749.
468           if (is_cisc_alternate && def == fp) {
469             const TypePtr *adr_type = NULL;
470             intptr_t offset;
471             const Node* base = m->get_base_and_disp(offset, adr_type);
472             if (base == NodeSentinel) {
473               // Machnode has multiple memory inputs. We are unable to reason
474               // with these, but are presuming (with trepidation) that not any of
475               // them are oops. This can be fixed by making get_base_and_disp()
476               // look at a specific input instead of all inputs.
477               assert(!def->bottom_type()->isa_oop_ptr(), "expecting non-oop mem input");
478             } else if (base != fp || offset == Type::OffsetBot) {
479               // Do nothing: the fp operand is either not from a memory use
480               // (base == NULL) OR the fp is used in a non-memory context
481               // (base is some other register) OR the offset is not constant,
482               // so it is not a stack slot.
483             } else {
484               assert(offset >= 0, "unexpected negative offset");
485               offset -= (offset % jintSize);  // count the whole word
486               int stack_reg = regalloc->offset2reg(offset);
487               if (OptoReg::is_stack(stack_reg)) {
488                 set_live_bit(tmp_live, stack_reg);
489               } else {
490                 assert(false, "stack_reg not on stack?");
491               }
492             }
493           }
494         }
495 
496         if( n->jvms() ) {       // Record liveness at safepoint
497 
498           // This placement of this stanza means inputs to calls are
499           // considered live at the callsite's OopMap.  Argument oops are
500           // hence live, but NOT included in the oopmap.  See cutout in
501           // build_oop_map.  Debug oops are live (and in OopMap).
502           int *n_live = NEW_ARENA_ARRAY(A, int, max_reg_ints);
503           for( int l=0; l<max_reg_ints; l++ )
504             n_live[l] = tmp_live[l];
505           safehash->Insert(n,n_live);
506         }
507 
508       }
509 
510       // Now at block top, see if we have any changes.  If so, propagate
511       // to prior blocks.
512       int *old_live = &live[b->_pre_order*max_reg_ints];
513       int l;
514       for( l=0; l<max_reg_ints; l++ )
515         if( tmp_live[l] != old_live[l] )
516           break;
517       if( l<max_reg_ints ) {     // Change!
518         // Copy in new value
519         for( l=0; l<max_reg_ints; l++ )
520           old_live[l] = tmp_live[l];
521         // Push preds onto worklist
522         for (l = 1; l < (int)b->num_preds(); l++) {
523           Block* block = cfg->get_block_for_node(b->pred(l));
524           worklist->push(block);
525         }
526       }
527     }
528 
529     // Scan for any missing safepoints.  Happens to infinite loops
530     // ala ZKM.jar
531     uint i;
532     for (i = 1; i < cfg->number_of_blocks(); i++) {
533       Block* block = cfg->get_block(i);
534       uint j;
535       for (j = 1; j < block->number_of_nodes(); j++) {
536         if (block->get_node(j)->jvms() && (*safehash)[block->get_node(j)] == NULL) {
537            break;
538         }
539       }
540       if (j < block->number_of_nodes()) {
541         break;
542       }
543     }
544     if (i == cfg->number_of_blocks()) {
545       break;                    // Got 'em all
546     }
547 
548     if (PrintOpto && Verbose) {
549       tty->print_cr("retripping live calc");
550     }
551 
552     // Force the issue (expensively): recheck everybody
553     for (i = 1; i < cfg->number_of_blocks(); i++) {
554       worklist->push(cfg->get_block(i));
555     }
556   }
557 }
558 
559 // Collect GC mask info - where are all the OOPs?
560 void PhaseOutput::BuildOopMaps() {
561   Compile::TracePhase tp("bldOopMaps", &timers[_t_buildOopMaps]);
562   // Can't resource-mark because I need to leave all those OopMaps around,
563   // or else I need to resource-mark some arena other than the default.
564   // ResourceMark rm;              // Reclaim all OopFlows when done
565   int max_reg = C->regalloc()->_max_reg; // Current array extent
566 
567   Arena *A = Thread::current()->resource_area();
568   Block_List worklist;          // Worklist of pending blocks
569 
570   int max_reg_ints = align_up(max_reg, BitsPerInt)>>LogBitsPerInt;
571   Dict *safehash = NULL;        // Used for assert only
572   // Compute a backwards liveness per register.  Needs a bitarray of
573   // #blocks x (#registers, rounded up to ints)
574   safehash = new Dict(cmpkey,hashkey,A);
575   do_liveness( C->regalloc(), C->cfg(), &worklist, max_reg_ints, A, safehash );
576   OopFlow *free_list = NULL;    // Free, unused
577 
578   // Array mapping blocks to completed oopflows
579   OopFlow **flows = NEW_ARENA_ARRAY(A, OopFlow*, C->cfg()->number_of_blocks());
580   memset( flows, 0, C->cfg()->number_of_blocks() * sizeof(OopFlow*) );
581 
582 
583   // Do the first block 'by hand' to prime the worklist
584   Block *entry = C->cfg()->get_block(1);
585   OopFlow *rootflow = OopFlow::make(A,max_reg,C);
586   // Initialize to 'bottom' (not 'top')
587   memset( rootflow->_callees, OptoReg::Bad, max_reg*sizeof(short) );
588   memset( rootflow->_defs   ,            0, max_reg*sizeof(Node*) );
589   flows[entry->_pre_order] = rootflow;
590 
591   // Do the first block 'by hand' to prime the worklist
592   rootflow->_b = entry;
593   rootflow->compute_reach( C->regalloc(), max_reg, safehash );
594   for( uint i=0; i<entry->_num_succs; i++ )
595     worklist.push(entry->_succs[i]);
596 
597   // Now worklist contains blocks which have some, but perhaps not all,
598   // predecessors visited.
599   while( worklist.size() ) {
600     // Scan for a block with all predecessors visited, or any randoms slob
601     // otherwise.  All-preds-visited order allows me to recycle OopFlow
602     // structures rapidly and cut down on the memory footprint.
603     // Note: not all predecessors might be visited yet (must happen for
604     // irreducible loops).  This is OK, since every live value must have the
605     // SAME reaching def for the block, so any reaching def is OK.
606     uint i;
607 
608     Block *b = worklist.pop();
609     // Ignore root block
610     if (b == C->cfg()->get_root_block()) {
611       continue;
612     }
613     // Block is already done?  Happens if block has several predecessors,
614     // he can get on the worklist more than once.
615     if( flows[b->_pre_order] ) continue;
616 
617     // If this block has a visited predecessor AND that predecessor has this
618     // last block as his only undone child, we can move the OopFlow from the
619     // pred to this block.  Otherwise we have to grab a new OopFlow.
620     OopFlow *flow = NULL;       // Flag for finding optimized flow
621     Block *pred = (Block*)((intptr_t)0xdeadbeef);
622     // Scan this block's preds to find a done predecessor
623     for (uint j = 1; j < b->num_preds(); j++) {
624       Block* p = C->cfg()->get_block_for_node(b->pred(j));
625       OopFlow *p_flow = flows[p->_pre_order];
626       if( p_flow ) {            // Predecessor is done
627         assert( p_flow->_b == p, "cross check" );
628         pred = p;               // Record some predecessor
629         // If all successors of p are done except for 'b', then we can carry
630         // p_flow forward to 'b' without copying, otherwise we have to draw
631         // from the free_list and clone data.
632         uint k;
633         for( k=0; k<p->_num_succs; k++ )
634           if( !flows[p->_succs[k]->_pre_order] &&
635               p->_succs[k] != b )
636             break;
637 
638         // Either carry-forward the now-unused OopFlow for b's use
639         // or draw a new one from the free list
640         if( k==p->_num_succs ) {
641           flow = p_flow;
642           break;                // Found an ideal pred, use him
643         }
644       }
645     }
646 
647     if( flow ) {
648       // We have an OopFlow that's the last-use of a predecessor.
649       // Carry it forward.
650     } else {                    // Draw a new OopFlow from the freelist
651       if( !free_list )
652         free_list = OopFlow::make(A,max_reg,C);
653       flow = free_list;
654       assert( flow->_b == NULL, "oopFlow is not free" );
655       free_list = flow->_next;
656       flow->_next = NULL;
657 
658       // Copy/clone over the data
659       flow->clone(flows[pred->_pre_order], max_reg);
660     }
661 
662     // Mark flow for block.  Blocks can only be flowed over once,
663     // because after the first time they are guarded from entering
664     // this code again.
665     assert( flow->_b == pred, "have some prior flow" );
666     flow->_b = NULL;
667 
668     // Now push flow forward
669     flows[b->_pre_order] = flow;// Mark flow for this block
670     flow->_b = b;
671     flow->compute_reach( C->regalloc(), max_reg, safehash );
672 
673     // Now push children onto worklist
674     for( i=0; i<b->_num_succs; i++ )
675       worklist.push(b->_succs[i]);
676 
677   }
678 }
--- EOF ---