1 /*
2 * Copyright 2002-2008 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
20 * CA 95054 USA or visit www.sun.com if you need additional information or
21 * have any questions.
22 *
23 */
24
25 #include "incls/_precompiled.incl"
26 #include "incls/_buildOopMap.cpp.incl"
27
28 // The functions in this file builds OopMaps after all scheduling is done.
29 //
30 // OopMaps contain a list of all registers and stack-slots containing oops (so
31 // they can be updated by GC). OopMaps also contain a list of derived-pointer
32 // base-pointer pairs. When the base is moved, the derived pointer moves to
33 // follow it. Finally, any registers holding callee-save values are also
34 // recorded. These might contain oops, but only the caller knows.
35 //
36 // BuildOopMaps implements a simple forward reaching-defs solution. At each
37 // GC point we'll have the reaching-def Nodes. If the reaching Nodes are
38 // typed as pointers (no offset), then they are oops. Pointers+offsets are
39 // derived pointers, and bases can be found from them. Finally, we'll also
40 // track reaching callee-save values. Note that a copy of a callee-save value
41 // "kills" it's source, so that only 1 copy of a callee-save value is alive at
42 // a time.
43 //
44 // We run a simple bitvector liveness pass to help trim out dead oops. Due to
45 // irreducible loops, we can have a reaching def of an oop that only reaches
46 // along one path and no way to know if it's valid or not on the other path.
47 // The bitvectors are quite dense and the liveness pass is fast.
48 //
49 // At GC points, we consult this information to build OopMaps. All reaching
50 // defs typed as oops are added to the OopMap. Only 1 instance of a
51 // callee-save register can be recorded. For derived pointers, we'll have to
52 // find and record the register holding the base.
53 //
54 // The reaching def's is a simple 1-pass worklist approach. I tried a clever
55 // breadth-first approach but it was worse (showed O(n^2) in the
56 // pick-next-block code).
57 //
58 // The relevant data is kept in a struct of arrays (it could just as well be
59 // an array of structs, but the struct-of-arrays is generally a little more
60 // efficient). The arrays are indexed by register number (including
61 // stack-slots as registers) and so is bounded by 200 to 300 elements in
62 // practice. One array will map to a reaching def Node (or NULL for
63 // conflict/dead). The other array will map to a callee-saved register or
64 // OptoReg::Bad for not-callee-saved.
65
66
67 //------------------------------OopFlow----------------------------------------
68 // Structure to pass around
69 struct OopFlow : public ResourceObj {
70 short *_callees; // Array mapping register to callee-saved
71 Node **_defs; // array mapping register to reaching def
72 // or NULL if dead/conflict
73 // OopFlow structs, when not being actively modified, describe the _end_ of
74 // this block.
75 Block *_b; // Block for this struct
76 OopFlow *_next; // Next free OopFlow
77
78 OopFlow( short *callees, Node **defs ) : _callees(callees), _defs(defs),
79 _b(NULL), _next(NULL) { }
80
81 // Given reaching-defs for this block start, compute it for this block end
82 void compute_reach( PhaseRegAlloc *regalloc, int max_reg, Dict *safehash );
83
84 // Merge these two OopFlows into the 'this' pointer.
85 void merge( OopFlow *flow, int max_reg );
86
87 // Copy a 'flow' over an existing flow
88 void clone( OopFlow *flow, int max_size);
89
90 // Make a new OopFlow from scratch
91 static OopFlow *make( Arena *A, int max_size );
92
93 // Build an oopmap from the current flow info
94 OopMap *build_oop_map( Node *n, int max_reg, PhaseRegAlloc *regalloc, int* live );
95 };
96
97 //------------------------------compute_reach----------------------------------
98 // Given reaching-defs for this block start, compute it for this block end
99 void OopFlow::compute_reach( PhaseRegAlloc *regalloc, int max_reg, Dict *safehash ) {
100
101 for( uint i=0; i<_b->_nodes.size(); i++ ) {
102 Node *n = _b->_nodes[i];
103
104 if( n->jvms() ) { // Build an OopMap here?
105 JVMState *jvms = n->jvms();
106 // no map needed for leaf calls
107 if( n->is_MachSafePoint() && !n->is_MachCallLeaf() ) {
108 int *live = (int*) (*safehash)[n];
109 assert( live, "must find live" );
110 n->as_MachSafePoint()->set_oop_map( build_oop_map(n,max_reg,regalloc, live) );
111 }
112 }
113
114 // Assign new reaching def's.
115 // Note that I padded the _defs and _callees arrays so it's legal
116 // to index at _defs[OptoReg::Bad].
117 OptoReg::Name first = regalloc->get_reg_first(n);
118 OptoReg::Name second = regalloc->get_reg_second(n);
119 _defs[first] = n;
120 _defs[second] = n;
121
122 // Pass callee-save info around copies
123 int idx = n->is_Copy();
124 if( idx ) { // Copies move callee-save info
125 OptoReg::Name old_first = regalloc->get_reg_first(n->in(idx));
126 OptoReg::Name old_second = regalloc->get_reg_second(n->in(idx));
127 int tmp_first = _callees[old_first];
128 int tmp_second = _callees[old_second];
129 _callees[old_first] = OptoReg::Bad; // callee-save is moved, dead in old location
130 _callees[old_second] = OptoReg::Bad;
131 _callees[first] = tmp_first;
132 _callees[second] = tmp_second;
133 } else if( n->is_Phi() ) { // Phis do not mod callee-saves
134 assert( _callees[first] == _callees[regalloc->get_reg_first(n->in(1))], "" );
135 assert( _callees[second] == _callees[regalloc->get_reg_second(n->in(1))], "" );
136 assert( _callees[first] == _callees[regalloc->get_reg_first(n->in(n->req()-1))], "" );
137 assert( _callees[second] == _callees[regalloc->get_reg_second(n->in(n->req()-1))], "" );
138 } else {
139 _callees[first] = OptoReg::Bad; // No longer holding a callee-save value
140 _callees[second] = OptoReg::Bad;
141
142 // Find base case for callee saves
143 if( n->is_Proj() && n->in(0)->is_Start() ) {
144 if( OptoReg::is_reg(first) &&
145 regalloc->_matcher.is_save_on_entry(first) )
146 _callees[first] = first;
147 if( OptoReg::is_reg(second) &&
148 regalloc->_matcher.is_save_on_entry(second) )
149 _callees[second] = second;
150 }
151 }
152 }
153 }
154
155 //------------------------------merge------------------------------------------
156 // Merge the given flow into the 'this' flow
157 void OopFlow::merge( OopFlow *flow, int max_reg ) {
158 assert( _b == NULL, "merging into a happy flow" );
159 assert( flow->_b, "this flow is still alive" );
160 assert( flow != this, "no self flow" );
161
162 // Do the merge. If there are any differences, drop to 'bottom' which
163 // is OptoReg::Bad or NULL depending.
164 for( int i=0; i<max_reg; i++ ) {
165 // Merge the callee-save's
166 if( _callees[i] != flow->_callees[i] )
167 _callees[i] = OptoReg::Bad;
168 // Merge the reaching defs
169 if( _defs[i] != flow->_defs[i] )
170 _defs[i] = NULL;
171 }
172
173 }
174
175 //------------------------------clone------------------------------------------
176 void OopFlow::clone( OopFlow *flow, int max_size ) {
177 _b = flow->_b;
178 memcpy( _callees, flow->_callees, sizeof(short)*max_size);
179 memcpy( _defs , flow->_defs , sizeof(Node*)*max_size);
180 }
181
182 //------------------------------make-------------------------------------------
183 OopFlow *OopFlow::make( Arena *A, int max_size ) {
184 short *callees = NEW_ARENA_ARRAY(A,short,max_size+1);
185 Node **defs = NEW_ARENA_ARRAY(A,Node*,max_size+1);
186 debug_only( memset(defs,0,(max_size+1)*sizeof(Node*)) );
187 OopFlow *flow = new (A) OopFlow(callees+1, defs+1);
188 assert( &flow->_callees[OptoReg::Bad] == callees, "Ok to index at OptoReg::Bad" );
189 assert( &flow->_defs [OptoReg::Bad] == defs , "Ok to index at OptoReg::Bad" );
190 return flow;
191 }
192
193 //------------------------------bit twiddlers----------------------------------
194 static int get_live_bit( int *live, int reg ) {
195 return live[reg>>LogBitsPerInt] & (1<<(reg&(BitsPerInt-1))); }
196 static void set_live_bit( int *live, int reg ) {
197 live[reg>>LogBitsPerInt] |= (1<<(reg&(BitsPerInt-1))); }
198 static void clr_live_bit( int *live, int reg ) {
199 live[reg>>LogBitsPerInt] &= ~(1<<(reg&(BitsPerInt-1))); }
200
201 //------------------------------build_oop_map----------------------------------
202 // Build an oopmap from the current flow info
203 OopMap *OopFlow::build_oop_map( Node *n, int max_reg, PhaseRegAlloc *regalloc, int* live ) {
204 int framesize = regalloc->_framesize;
205 int max_inarg_slot = OptoReg::reg2stack(regalloc->_matcher._new_SP);
206 debug_only( char *dup_check = NEW_RESOURCE_ARRAY(char,OptoReg::stack0());
207 memset(dup_check,0,OptoReg::stack0()) );
208
209 OopMap *omap = new OopMap( framesize, max_inarg_slot );
210 MachCallNode *mcall = n->is_MachCall() ? n->as_MachCall() : NULL;
211 JVMState* jvms = n->jvms();
212
213 // For all registers do...
214 for( int reg=0; reg<max_reg; reg++ ) {
215 if( get_live_bit(live,reg) == 0 )
216 continue; // Ignore if not live
217
218 // %%% C2 can use 2 OptoRegs when the physical register is only one 64bit
219 // register in that case we'll get an non-concrete register for the second
220 // half. We only need to tell the map the register once!
221 //
222 // However for the moment we disable this change and leave things as they
223 // were.
224
225 VMReg r = OptoReg::as_VMReg(OptoReg::Name(reg), framesize, max_inarg_slot);
226
227 if (false && r->is_reg() && !r->is_concrete()) {
228 continue;
229 }
230
231 // See if dead (no reaching def).
232 Node *def = _defs[reg]; // Get reaching def
233 assert( def, "since live better have reaching def" );
234
235 // Classify the reaching def as oop, derived, callee-save, dead, or other
236 const Type *t = def->bottom_type();
237 if( t->isa_oop_ptr() ) { // Oop or derived?
238 assert( !OptoReg::is_valid(_callees[reg]), "oop can't be callee save" );
239 #ifdef _LP64
240 // 64-bit pointers record oop-ishness on 2 aligned adjacent registers.
241 // Make sure both are record from the same reaching def, but do not
242 // put both into the oopmap.
243 if( (reg&1) == 1 ) { // High half of oop-pair?
244 assert( _defs[reg-1] == _defs[reg], "both halves from same reaching def" );
245 continue; // Do not record high parts in oopmap
246 }
247 #endif
248
249 // Check for a legal reg name in the oopMap and bailout if it is not.
250 if (!omap->legal_vm_reg_name(r)) {
251 regalloc->C->record_method_not_compilable("illegal oopMap register name");
252 continue;
253 }
254 if( t->is_ptr()->_offset == 0 ) { // Not derived?
255 if( mcall ) {
256 // Outgoing argument GC mask responsibility belongs to the callee,
257 // not the caller. Inspect the inputs to the call, to see if
258 // this live-range is one of them.
259 uint cnt = mcall->tf()->domain()->cnt();
260 uint j;
261 for( j = TypeFunc::Parms; j < cnt; j++)
262 if( mcall->in(j) == def )
263 break; // reaching def is an argument oop
264 if( j < cnt ) // arg oops dont go in GC map
265 continue; // Continue on to the next register
266 }
267 omap->set_oop(r);
268 } else { // Else it's derived.
269 // Find the base of the derived value.
270 uint i;
271 // Fast, common case, scan
272 for( i = jvms->oopoff(); i < n->req(); i+=2 )
273 if( n->in(i) == def ) break; // Common case
274 if( i == n->req() ) { // Missed, try a more generous scan
275 // Scan again, but this time peek through copies
276 for( i = jvms->oopoff(); i < n->req(); i+=2 ) {
277 Node *m = n->in(i); // Get initial derived value
278 while( 1 ) {
279 Node *d = def; // Get initial reaching def
280 while( 1 ) { // Follow copies of reaching def to end
281 if( m == d ) goto found; // breaks 3 loops
282 int idx = d->is_Copy();
283 if( !idx ) break;
284 d = d->in(idx); // Link through copy
285 }
286 int idx = m->is_Copy();
287 if( !idx ) break;
288 m = m->in(idx);
289 }
290 }
291 guarantee( 0, "must find derived/base pair" );
292 }
293 found: ;
294 Node *base = n->in(i+1); // Base is other half of pair
295 int breg = regalloc->get_reg_first(base);
296 VMReg b = OptoReg::as_VMReg(OptoReg::Name(breg), framesize, max_inarg_slot);
297
298 // I record liveness at safepoints BEFORE I make the inputs
299 // live. This is because argument oops are NOT live at a
300 // safepoint (or at least they cannot appear in the oopmap).
301 // Thus bases of base/derived pairs might not be in the
302 // liveness data but they need to appear in the oopmap.
303 if( get_live_bit(live,breg) == 0 ) {// Not live?
304 // Flag it, so next derived pointer won't re-insert into oopmap
305 set_live_bit(live,breg);
306 // Already missed our turn?
307 if( breg < reg ) {
308 if (b->is_stack() || b->is_concrete() || true ) {
309 omap->set_oop( b);
310 }
311 }
312 }
313 if (b->is_stack() || b->is_concrete() || true ) {
314 omap->set_derived_oop( r, b);
315 }
316 }
317
318 } else if( t->isa_narrowoop() ) {
319 assert( !OptoReg::is_valid(_callees[reg]), "oop can't be callee save" );
320 // Check for a legal reg name in the oopMap and bailout if it is not.
321 if (!omap->legal_vm_reg_name(r)) {
322 regalloc->C->record_method_not_compilable("illegal oopMap register name");
323 continue;
324 }
325 if( mcall ) {
326 // Outgoing argument GC mask responsibility belongs to the callee,
327 // not the caller. Inspect the inputs to the call, to see if
328 // this live-range is one of them.
329 uint cnt = mcall->tf()->domain()->cnt();
330 uint j;
331 for( j = TypeFunc::Parms; j < cnt; j++)
332 if( mcall->in(j) == def )
333 break; // reaching def is an argument oop
334 if( j < cnt ) // arg oops dont go in GC map
335 continue; // Continue on to the next register
336 }
337 omap->set_narrowoop(r);
338 } else if( OptoReg::is_valid(_callees[reg])) { // callee-save?
339 // It's a callee-save value
340 assert( dup_check[_callees[reg]]==0, "trying to callee save same reg twice" );
341 debug_only( dup_check[_callees[reg]]=1; )
342 VMReg callee = OptoReg::as_VMReg(OptoReg::Name(_callees[reg]));
343 if ( callee->is_concrete() || true ) {
344 omap->set_callee_saved( r, callee);
345 }
346
347 } else {
348 // Other - some reaching non-oop value
349 omap->set_value( r);
350 }
351
352 }
353
354 #ifdef ASSERT
355 /* Nice, Intel-only assert
356 int cnt_callee_saves=0;
357 int reg2 = 0;
358 while (OptoReg::is_reg(reg2)) {
359 if( dup_check[reg2] != 0) cnt_callee_saves++;
360 assert( cnt_callee_saves==3 || cnt_callee_saves==5, "missed some callee-save" );
361 reg2++;
362 }
363 */
364 #endif
365
366 return omap;
367 }
368
369 //------------------------------do_liveness------------------------------------
370 // Compute backwards liveness on registers
371 static void do_liveness( PhaseRegAlloc *regalloc, PhaseCFG *cfg, Block_List *worklist, int max_reg_ints, Arena *A, Dict *safehash ) {
372 int *live = NEW_ARENA_ARRAY(A, int, (cfg->_num_blocks+1) * max_reg_ints);
373 int *tmp_live = &live[cfg->_num_blocks * max_reg_ints];
374 Node *root = cfg->C->root();
375 // On CISC platforms, get the node representing the stack pointer that regalloc
376 // used for spills
377 Node *fp = NodeSentinel;
378 if (UseCISCSpill && root->req() > 1) {
379 fp = root->in(1)->in(TypeFunc::FramePtr);
380 }
381 memset( live, 0, cfg->_num_blocks * (max_reg_ints<<LogBytesPerInt) );
382 // Push preds onto worklist
383 for( uint i=1; i<root->req(); i++ )
384 worklist->push(cfg->_bbs[root->in(i)->_idx]);
385
386 // ZKM.jar includes tiny infinite loops which are unreached from below.
387 // If we missed any blocks, we'll retry here after pushing all missed
388 // blocks on the worklist. Normally this outer loop never trips more
389 // than once.
390 while( 1 ) {
391
392 while( worklist->size() ) { // Standard worklist algorithm
393 Block *b = worklist->rpop();
394
395 // Copy first successor into my tmp_live space
396 int s0num = b->_succs[0]->_pre_order;
397 int *t = &live[s0num*max_reg_ints];
398 for( int i=0; i<max_reg_ints; i++ )
399 tmp_live[i] = t[i];
400
401 // OR in the remaining live registers
402 for( uint j=1; j<b->_num_succs; j++ ) {
403 uint sjnum = b->_succs[j]->_pre_order;
404 int *t = &live[sjnum*max_reg_ints];
405 for( int i=0; i<max_reg_ints; i++ )
406 tmp_live[i] |= t[i];
407 }
408
409 // Now walk tmp_live up the block backwards, computing live
410 for( int k=b->_nodes.size()-1; k>=0; k-- ) {
411 Node *n = b->_nodes[k];
412 // KILL def'd bits
413 int first = regalloc->get_reg_first(n);
414 int second = regalloc->get_reg_second(n);
415 if( OptoReg::is_valid(first) ) clr_live_bit(tmp_live,first);
416 if( OptoReg::is_valid(second) ) clr_live_bit(tmp_live,second);
417
418 MachNode *m = n->is_Mach() ? n->as_Mach() : NULL;
419
420 // Check if m is potentially a CISC alternate instruction (i.e, possibly
421 // synthesized by RegAlloc from a conventional instruction and a
422 // spilled input)
423 bool is_cisc_alternate = false;
424 if (UseCISCSpill && m) {
425 is_cisc_alternate = m->is_cisc_alternate();
426 }
427
428 // GEN use'd bits
429 for( uint l=1; l<n->req(); l++ ) {
430 Node *def = n->in(l);
431 assert(def != 0, "input edge required");
432 int first = regalloc->get_reg_first(def);
433 int second = regalloc->get_reg_second(def);
434 if( OptoReg::is_valid(first) ) set_live_bit(tmp_live,first);
435 if( OptoReg::is_valid(second) ) set_live_bit(tmp_live,second);
436 // If we use the stack pointer in a cisc-alternative instruction,
437 // check for use as a memory operand. Then reconstruct the RegName
438 // for this stack location, and set the appropriate bit in the
439 // live vector 4987749.
440 if (is_cisc_alternate && def == fp) {
441 const TypePtr *adr_type = NULL;
442 intptr_t offset;
443 const Node* base = m->get_base_and_disp(offset, adr_type);
444 if (base == NodeSentinel) {
445 // Machnode has multiple memory inputs. We are unable to reason
446 // with these, but are presuming (with trepidation) that not any of
447 // them are oops. This can be fixed by making get_base_and_disp()
448 // look at a specific input instead of all inputs.
449 assert(!def->bottom_type()->isa_oop_ptr(), "expecting non-oop mem input");
450 } else if (base != fp || offset == Type::OffsetBot) {
451 // Do nothing: the fp operand is either not from a memory use
452 // (base == NULL) OR the fp is used in a non-memory context
453 // (base is some other register) OR the offset is not constant,
454 // so it is not a stack slot.
455 } else {
456 assert(offset >= 0, "unexpected negative offset");
457 offset -= (offset % jintSize); // count the whole word
458 int stack_reg = regalloc->offset2reg(offset);
459 if (OptoReg::is_stack(stack_reg)) {
460 set_live_bit(tmp_live, stack_reg);
461 } else {
462 assert(false, "stack_reg not on stack?");
463 }
464 }
465 }
466 }
467
468 if( n->jvms() ) { // Record liveness at safepoint
469
470 // This placement of this stanza means inputs to calls are
471 // considered live at the callsite's OopMap. Argument oops are
472 // hence live, but NOT included in the oopmap. See cutout in
473 // build_oop_map. Debug oops are live (and in OopMap).
474 int *n_live = NEW_ARENA_ARRAY(A, int, max_reg_ints);
475 for( int l=0; l<max_reg_ints; l++ )
476 n_live[l] = tmp_live[l];
477 safehash->Insert(n,n_live);
478 }
479
480 }
481
482 // Now at block top, see if we have any changes. If so, propagate
483 // to prior blocks.
484 int *old_live = &live[b->_pre_order*max_reg_ints];
485 int l;
486 for( l=0; l<max_reg_ints; l++ )
487 if( tmp_live[l] != old_live[l] )
488 break;
489 if( l<max_reg_ints ) { // Change!
490 // Copy in new value
491 for( l=0; l<max_reg_ints; l++ )
492 old_live[l] = tmp_live[l];
493 // Push preds onto worklist
494 for( l=1; l<(int)b->num_preds(); l++ )
495 worklist->push(cfg->_bbs[b->pred(l)->_idx]);
496 }
497 }
498
499 // Scan for any missing safepoints. Happens to infinite loops
500 // ala ZKM.jar
501 uint i;
502 for( i=1; i<cfg->_num_blocks; i++ ) {
503 Block *b = cfg->_blocks[i];
504 uint j;
505 for( j=1; j<b->_nodes.size(); j++ )
506 if( b->_nodes[j]->jvms() &&
507 (*safehash)[b->_nodes[j]] == NULL )
508 break;
509 if( j<b->_nodes.size() ) break;
510 }
511 if( i == cfg->_num_blocks )
512 break; // Got 'em all
513 #ifndef PRODUCT
514 if( PrintOpto && Verbose )
515 tty->print_cr("retripping live calc");
516 #endif
517 // Force the issue (expensively): recheck everybody
518 for( i=1; i<cfg->_num_blocks; i++ )
519 worklist->push(cfg->_blocks[i]);
520 }
521
522 }
523
524 //------------------------------BuildOopMaps-----------------------------------
525 // Collect GC mask info - where are all the OOPs?
526 void Compile::BuildOopMaps() {
527 NOT_PRODUCT( TracePhase t3("bldOopMaps", &_t_buildOopMaps, TimeCompiler); )
528 // Can't resource-mark because I need to leave all those OopMaps around,
529 // or else I need to resource-mark some arena other than the default.
530 // ResourceMark rm; // Reclaim all OopFlows when done
531 int max_reg = _regalloc->_max_reg; // Current array extent
532
533 Arena *A = Thread::current()->resource_area();
534 Block_List worklist; // Worklist of pending blocks
535
536 int max_reg_ints = round_to(max_reg, BitsPerInt)>>LogBitsPerInt;
537 Dict *safehash = NULL; // Used for assert only
538 // Compute a backwards liveness per register. Needs a bitarray of
539 // #blocks x (#registers, rounded up to ints)
540 safehash = new Dict(cmpkey,hashkey,A);
541 do_liveness( _regalloc, _cfg, &worklist, max_reg_ints, A, safehash );
542 OopFlow *free_list = NULL; // Free, unused
543
544 // Array mapping blocks to completed oopflows
545 OopFlow **flows = NEW_ARENA_ARRAY(A, OopFlow*, _cfg->_num_blocks);
546 memset( flows, 0, _cfg->_num_blocks*sizeof(OopFlow*) );
547
548
549 // Do the first block 'by hand' to prime the worklist
550 Block *entry = _cfg->_blocks[1];
551 OopFlow *rootflow = OopFlow::make(A,max_reg);
552 // Initialize to 'bottom' (not 'top')
553 memset( rootflow->_callees, OptoReg::Bad, max_reg*sizeof(short) );
554 memset( rootflow->_defs , 0, max_reg*sizeof(Node*) );
555 flows[entry->_pre_order] = rootflow;
556
557 // Do the first block 'by hand' to prime the worklist
558 rootflow->_b = entry;
559 rootflow->compute_reach( _regalloc, max_reg, safehash );
560 for( uint i=0; i<entry->_num_succs; i++ )
561 worklist.push(entry->_succs[i]);
562
563 // Now worklist contains blocks which have some, but perhaps not all,
564 // predecessors visited.
565 while( worklist.size() ) {
566 // Scan for a block with all predecessors visited, or any randoms slob
567 // otherwise. All-preds-visited order allows me to recycle OopFlow
568 // structures rapidly and cut down on the memory footprint.
569 // Note: not all predecessors might be visited yet (must happen for
570 // irreducible loops). This is OK, since every live value must have the
571 // SAME reaching def for the block, so any reaching def is OK.
572 uint i;
573
574 Block *b = worklist.pop();
575 // Ignore root block
576 if( b == _cfg->_broot ) continue;
577 // Block is already done? Happens if block has several predecessors,
578 // he can get on the worklist more than once.
579 if( flows[b->_pre_order] ) continue;
580
581 // If this block has a visited predecessor AND that predecessor has this
582 // last block as his only undone child, we can move the OopFlow from the
583 // pred to this block. Otherwise we have to grab a new OopFlow.
584 OopFlow *flow = NULL; // Flag for finding optimized flow
585 Block *pred = (Block*)0xdeadbeef;
586 uint j;
587 // Scan this block's preds to find a done predecessor
588 for( j=1; j<b->num_preds(); j++ ) {
589 Block *p = _cfg->_bbs[b->pred(j)->_idx];
590 OopFlow *p_flow = flows[p->_pre_order];
591 if( p_flow ) { // Predecessor is done
592 assert( p_flow->_b == p, "cross check" );
593 pred = p; // Record some predecessor
594 // If all successors of p are done except for 'b', then we can carry
595 // p_flow forward to 'b' without copying, otherwise we have to draw
596 // from the free_list and clone data.
597 uint k;
598 for( k=0; k<p->_num_succs; k++ )
599 if( !flows[p->_succs[k]->_pre_order] &&
600 p->_succs[k] != b )
601 break;
602
603 // Either carry-forward the now-unused OopFlow for b's use
604 // or draw a new one from the free list
605 if( k==p->_num_succs ) {
606 flow = p_flow;
607 break; // Found an ideal pred, use him
608 }
609 }
610 }
611
612 if( flow ) {
613 // We have an OopFlow that's the last-use of a predecessor.
614 // Carry it forward.
615 } else { // Draw a new OopFlow from the freelist
616 if( !free_list )
617 free_list = OopFlow::make(A,max_reg);
618 flow = free_list;
619 assert( flow->_b == NULL, "oopFlow is not free" );
620 free_list = flow->_next;
621 flow->_next = NULL;
622
623 // Copy/clone over the data
624 flow->clone(flows[pred->_pre_order], max_reg);
625 }
626
627 // Mark flow for block. Blocks can only be flowed over once,
628 // because after the first time they are guarded from entering
629 // this code again.
630 assert( flow->_b == pred, "have some prior flow" );
631 flow->_b = NULL;
632
633 // Now push flow forward
634 flows[b->_pre_order] = flow;// Mark flow for this block
635 flow->_b = b;
636 flow->compute_reach( _regalloc, max_reg, safehash );
637
638 // Now push children onto worklist
639 for( i=0; i<b->_num_succs; i++ )
640 worklist.push(b->_succs[i]);
641
642 }
643 }