1 /*
2 * Copyright (c) 2002, 2014, 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.
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20 * or visit www.oracle.com if you need additional information or have any
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23 */
24
25 #include "precompiled.hpp"
26 #include "code/vmreg.inline.hpp"
27 #include "compiler/oopMap.hpp"
28 #include "opto/addnode.hpp"
29 #include "opto/callnode.hpp"
30 #include "opto/compile.hpp"
31 #include "opto/machnode.hpp"
32 #include "opto/matcher.hpp"
33 #include "opto/phase.hpp"
34 #include "opto/regalloc.hpp"
35 #include "opto/rootnode.hpp"
36
37 // The functions in this file builds OopMaps after all scheduling is done.
38 //
39 // OopMaps contain a list of all registers and stack-slots containing oops (so
40 // they can be updated by GC). OopMaps also contain a list of derived-pointer
41 // base-pointer pairs. When the base is moved, the derived pointer moves to
42 // follow it. Finally, any registers holding callee-save values are also
43 // recorded. These might contain oops, but only the caller knows.
44 //
45 // BuildOopMaps implements a simple forward reaching-defs solution. At each
46 // GC point we'll have the reaching-def Nodes. If the reaching Nodes are
47 // typed as pointers (no offset), then they are oops. Pointers+offsets are
48 // derived pointers, and bases can be found from them. Finally, we'll also
49 // track reaching callee-save values. Note that a copy of a callee-save value
50 // "kills" it's source, so that only 1 copy of a callee-save value is alive at
51 // a time.
52 //
53 // We run a simple bitvector liveness pass to help trim out dead oops. Due to
54 // irreducible loops, we can have a reaching def of an oop that only reaches
55 // along one path and no way to know if it's valid or not on the other path.
56 // The bitvectors are quite dense and the liveness pass is fast.
57 //
58 // At GC points, we consult this information to build OopMaps. All reaching
59 // defs typed as oops are added to the OopMap. Only 1 instance of a
60 // callee-save register can be recorded. For derived pointers, we'll have to
61 // find and record the register holding the base.
62 //
63 // The reaching def's is a simple 1-pass worklist approach. I tried a clever
64 // breadth-first approach but it was worse (showed O(n^2) in the
65 // pick-next-block code).
66 //
67 // The relevant data is kept in a struct of arrays (it could just as well be
68 // an array of structs, but the struct-of-arrays is generally a little more
69 // efficient). The arrays are indexed by register number (including
70 // stack-slots as registers) and so is bounded by 200 to 300 elements in
71 // practice. One array will map to a reaching def Node (or NULL for
72 // conflict/dead). The other array will map to a callee-saved register or
73 // OptoReg::Bad for not-callee-saved.
74
75
76 // Structure to pass around
77 struct OopFlow : public ResourceObj {
78 short *_callees; // Array mapping register to callee-saved
79 Node **_defs; // array mapping register to reaching def
80 // or NULL if dead/conflict
81 // OopFlow structs, when not being actively modified, describe the _end_ of
82 // this block.
83 Block *_b; // Block for this struct
84 OopFlow *_next; // Next free OopFlow
85 // or NULL if dead/conflict
86 Compile* C;
87
88 OopFlow( short *callees, Node **defs, Compile* c ) : _callees(callees), _defs(defs),
89 _b(NULL), _next(NULL), C(c) { }
90
91 // Given reaching-defs for this block start, compute it for this block end
92 void compute_reach( PhaseRegAlloc *regalloc, int max_reg, Dict *safehash );
93
94 // Merge these two OopFlows into the 'this' pointer.
95 void merge( OopFlow *flow, int max_reg );
96
97 // Copy a 'flow' over an existing flow
98 void clone( OopFlow *flow, int max_size);
99
100 // Make a new OopFlow from scratch
101 static OopFlow *make( Arena *A, int max_size, Compile* C );
102
103 // Build an oopmap from the current flow info
104 OopMap *build_oop_map( Node *n, int max_reg, PhaseRegAlloc *regalloc, int* live );
105 };
106
107 // Given reaching-defs for this block start, compute it for this block end
108 void OopFlow::compute_reach( PhaseRegAlloc *regalloc, int max_reg, Dict *safehash ) {
109
110 for( uint i=0; i<_b->number_of_nodes(); i++ ) {
111 Node *n = _b->get_node(i);
112
113 if( n->jvms() ) { // Build an OopMap here?
114 JVMState *jvms = n->jvms();
115 // no map needed for leaf calls
116 if( n->is_MachSafePoint() && !n->is_MachCallLeaf() ) {
117 int *live = (int*) (*safehash)[n];
118 assert( live, "must find live" );
119 n->as_MachSafePoint()->set_oop_map( build_oop_map(n,max_reg,regalloc, live) );
120 }
121 }
122
123 // Assign new reaching def's.
124 // Note that I padded the _defs and _callees arrays so it's legal
125 // to index at _defs[OptoReg::Bad].
126 OptoReg::Name first = regalloc->get_reg_first(n);
127 OptoReg::Name second = regalloc->get_reg_second(n);
128 _defs[first] = n;
129 _defs[second] = n;
130
131 // Pass callee-save info around copies
132 int idx = n->is_Copy();
133 if( idx ) { // Copies move callee-save info
134 OptoReg::Name old_first = regalloc->get_reg_first(n->in(idx));
135 OptoReg::Name old_second = regalloc->get_reg_second(n->in(idx));
136 int tmp_first = _callees[old_first];
137 int tmp_second = _callees[old_second];
138 _callees[old_first] = OptoReg::Bad; // callee-save is moved, dead in old location
139 _callees[old_second] = OptoReg::Bad;
140 _callees[first] = tmp_first;
141 _callees[second] = tmp_second;
142 } else if( n->is_Phi() ) { // Phis do not mod callee-saves
143 assert( _callees[first] == _callees[regalloc->get_reg_first(n->in(1))], "" );
144 assert( _callees[second] == _callees[regalloc->get_reg_second(n->in(1))], "" );
145 assert( _callees[first] == _callees[regalloc->get_reg_first(n->in(n->req()-1))], "" );
146 assert( _callees[second] == _callees[regalloc->get_reg_second(n->in(n->req()-1))], "" );
147 } else {
148 _callees[first] = OptoReg::Bad; // No longer holding a callee-save value
149 _callees[second] = OptoReg::Bad;
150
151 // Find base case for callee saves
152 if( n->is_Proj() && n->in(0)->is_Start() ) {
153 if( OptoReg::is_reg(first) &&
154 regalloc->_matcher.is_save_on_entry(first) )
155 _callees[first] = first;
156 if( OptoReg::is_reg(second) &&
157 regalloc->_matcher.is_save_on_entry(second) )
158 _callees[second] = second;
159 }
160 }
161 }
162 }
163
164 // Merge the given flow into the 'this' flow
165 void OopFlow::merge( OopFlow *flow, int max_reg ) {
166 assert( _b == NULL, "merging into a happy flow" );
167 assert( flow->_b, "this flow is still alive" );
168 assert( flow != this, "no self flow" );
169
170 // Do the merge. If there are any differences, drop to 'bottom' which
171 // is OptoReg::Bad or NULL depending.
172 for( int i=0; i<max_reg; i++ ) {
173 // Merge the callee-save's
174 if( _callees[i] != flow->_callees[i] )
175 _callees[i] = OptoReg::Bad;
176 // Merge the reaching defs
177 if( _defs[i] != flow->_defs[i] )
178 _defs[i] = NULL;
179 }
180
181 }
182
183 void OopFlow::clone( OopFlow *flow, int max_size ) {
184 _b = flow->_b;
185 memcpy( _callees, flow->_callees, sizeof(short)*max_size);
186 memcpy( _defs , flow->_defs , sizeof(Node*)*max_size);
187 }
188
189 OopFlow *OopFlow::make( Arena *A, int max_size, Compile* C ) {
190 short *callees = NEW_ARENA_ARRAY(A,short,max_size+1);
191 Node **defs = NEW_ARENA_ARRAY(A,Node*,max_size+1);
192 debug_only( memset(defs,0,(max_size+1)*sizeof(Node*)) );
193 OopFlow *flow = new (A) OopFlow(callees+1, defs+1, C);
194 assert( &flow->_callees[OptoReg::Bad] == callees, "Ok to index at OptoReg::Bad" );
195 assert( &flow->_defs [OptoReg::Bad] == defs , "Ok to index at OptoReg::Bad" );
196 return flow;
197 }
198
199 static int get_live_bit( int *live, int reg ) {
200 return live[reg>>LogBitsPerInt] & (1<<(reg&(BitsPerInt-1))); }
201 static void set_live_bit( int *live, int reg ) {
202 live[reg>>LogBitsPerInt] |= (1<<(reg&(BitsPerInt-1))); }
203 static void clr_live_bit( int *live, int reg ) {
204 live[reg>>LogBitsPerInt] &= ~(1<<(reg&(BitsPerInt-1))); }
205
206 // Build an oopmap from the current flow info
207 OopMap *OopFlow::build_oop_map( Node *n, int max_reg, PhaseRegAlloc *regalloc, int* live ) {
208 int framesize = regalloc->_framesize;
209 int max_inarg_slot = OptoReg::reg2stack(regalloc->_matcher._new_SP);
210 debug_only( char *dup_check = NEW_RESOURCE_ARRAY(char,OptoReg::stack0());
211 memset(dup_check,0,OptoReg::stack0()) );
212
213 OopMap *omap = new OopMap( framesize, max_inarg_slot );
214 MachCallNode *mcall = n->is_MachCall() ? n->as_MachCall() : NULL;
215 JVMState* jvms = n->jvms();
216
217 // For all registers do...
218 for( int reg=0; reg<max_reg; reg++ ) {
219 if( get_live_bit(live,reg) == 0 )
220 continue; // Ignore if not live
221
222 // %%% C2 can use 2 OptoRegs when the physical register is only one 64bit
223 // register in that case we'll get an non-concrete register for the second
224 // half. We only need to tell the map the register once!
225 //
226 // However for the moment we disable this change and leave things as they
227 // were.
228
229 VMReg r = OptoReg::as_VMReg(OptoReg::Name(reg), framesize, max_inarg_slot);
230
231 if (false && r->is_reg() && !r->is_concrete()) {
232 continue;
233 }
234
235 // See if dead (no reaching def).
236 Node *def = _defs[reg]; // Get reaching def
237 assert( def, "since live better have reaching def" );
238
239 // Classify the reaching def as oop, derived, callee-save, dead, or other
240 const Type *t = def->bottom_type();
241 if( t->isa_oop_ptr() ) { // Oop or derived?
242 assert( !OptoReg::is_valid(_callees[reg]), "oop can't be callee save" );
243 #ifdef _LP64
244 // 64-bit pointers record oop-ishness on 2 aligned adjacent registers.
245 // Make sure both are record from the same reaching def, but do not
246 // put both into the oopmap.
247 if( (reg&1) == 1 ) { // High half of oop-pair?
248 assert( _defs[reg-1] == _defs[reg], "both halves from same reaching def" );
249 continue; // Do not record high parts in oopmap
250 }
251 #endif
252
253 // Check for a legal reg name in the oopMap and bailout if it is not.
254 if (!omap->legal_vm_reg_name(r)) {
255 regalloc->C->record_method_not_compilable("illegal oopMap register name");
256 continue;
257 }
258 if( t->is_ptr()->_offset == 0 ) { // Not derived?
259 if( mcall ) {
260 // Outgoing argument GC mask responsibility belongs to the callee,
261 // not the caller. Inspect the inputs to the call, to see if
262 // this live-range is one of them.
263 uint cnt = mcall->tf()->domain()->cnt();
264 uint j;
265 for( j = TypeFunc::Parms; j < cnt; j++)
266 if( mcall->in(j) == def )
267 break; // reaching def is an argument oop
268 if( j < cnt ) // arg oops dont go in GC map
269 continue; // Continue on to the next register
270 }
271 omap->set_oop(r);
272 } else { // Else it's derived.
273 // Find the base of the derived value.
274 uint i;
275 // Fast, common case, scan
276 for( i = jvms->oopoff(); i < n->req(); i+=2 )
277 if( n->in(i) == def ) break; // Common case
278 if( i == n->req() ) { // Missed, try a more generous scan
279 // Scan again, but this time peek through copies
280 for( i = jvms->oopoff(); i < n->req(); i+=2 ) {
281 Node *m = n->in(i); // Get initial derived value
282 while( 1 ) {
283 Node *d = def; // Get initial reaching def
284 while( 1 ) { // Follow copies of reaching def to end
285 if( m == d ) goto found; // breaks 3 loops
286 int idx = d->is_Copy();
287 if( !idx ) break;
288 d = d->in(idx); // Link through copy
289 }
290 int idx = m->is_Copy();
291 if( !idx ) break;
292 m = m->in(idx);
293 }
294 }
295 guarantee( 0, "must find derived/base pair" );
296 }
297 found: ;
298 Node *base = n->in(i+1); // Base is other half of pair
299 int breg = regalloc->get_reg_first(base);
300 VMReg b = OptoReg::as_VMReg(OptoReg::Name(breg), framesize, max_inarg_slot);
301
302 // I record liveness at safepoints BEFORE I make the inputs
303 // live. This is because argument oops are NOT live at a
304 // safepoint (or at least they cannot appear in the oopmap).
305 // Thus bases of base/derived pairs might not be in the
306 // liveness data but they need to appear in the oopmap.
307 if( get_live_bit(live,breg) == 0 ) {// Not live?
308 // Flag it, so next derived pointer won't re-insert into oopmap
309 set_live_bit(live,breg);
310 // Already missed our turn?
311 if( breg < reg ) {
312 if (b->is_stack() || b->is_concrete() || true ) {
313 omap->set_oop( b);
314 }
315 }
316 }
317 if (b->is_stack() || b->is_concrete() || true ) {
318 omap->set_derived_oop( r, b);
319 }
320 }
321
322 } else if( t->isa_narrowoop() ) {
323 assert( !OptoReg::is_valid(_callees[reg]), "oop can't be callee save" );
324 // Check for a legal reg name in the oopMap and bailout if it is not.
325 if (!omap->legal_vm_reg_name(r)) {
326 regalloc->C->record_method_not_compilable("illegal oopMap register name");
327 continue;
328 }
329 if( mcall ) {
330 // Outgoing argument GC mask responsibility belongs to the callee,
331 // not the caller. Inspect the inputs to the call, to see if
332 // this live-range is one of them.
333 uint cnt = mcall->tf()->domain()->cnt();
334 uint j;
335 for( j = TypeFunc::Parms; j < cnt; j++)
336 if( mcall->in(j) == def )
337 break; // reaching def is an argument oop
338 if( j < cnt ) // arg oops dont go in GC map
339 continue; // Continue on to the next register
340 }
341 omap->set_narrowoop(r);
342 } else if( OptoReg::is_valid(_callees[reg])) { // callee-save?
343 // It's a callee-save value
344 assert( dup_check[_callees[reg]]==0, "trying to callee save same reg twice" );
345 debug_only( dup_check[_callees[reg]]=1; )
346 VMReg callee = OptoReg::as_VMReg(OptoReg::Name(_callees[reg]));
347 if ( callee->is_concrete() || true ) {
348 omap->set_callee_saved( r, callee);
349 }
350
351 } else {
352 // Other - some reaching non-oop value
353 omap->set_value( r);
354 #ifdef ASSERT
355 if( t->isa_rawptr() && C->cfg()->_raw_oops.member(def) ) {
356 def->dump();
357 n->dump();
358 assert(false, "there should be a oop in OopMap instead of a live raw oop at safepoint");
359 }
360 #endif
361 }
362
363 }
364
365 #ifdef ASSERT
366 /* Nice, Intel-only assert
367 int cnt_callee_saves=0;
368 int reg2 = 0;
369 while (OptoReg::is_reg(reg2)) {
370 if( dup_check[reg2] != 0) cnt_callee_saves++;
371 assert( cnt_callee_saves==3 || cnt_callee_saves==5, "missed some callee-save" );
372 reg2++;
373 }
374 */
375 #endif
376
377 #ifdef ASSERT
378 for( OopMapStream oms1(omap, OopMapValue::derived_oop_value); !oms1.is_done(); oms1.next()) {
379 OopMapValue omv1 = oms1.current();
380 bool found = false;
381 for( OopMapStream oms2(omap,OopMapValue::oop_value); !oms2.is_done(); oms2.next()) {
382 if( omv1.content_reg() == oms2.current().reg() ) {
383 found = true;
384 break;
385 }
386 }
387 assert( found, "derived with no base in oopmap" );
388 }
389 #endif
390
391 return omap;
392 }
393
394 // Compute backwards liveness on registers
395 static void do_liveness(PhaseRegAlloc* regalloc, PhaseCFG* cfg, Block_List* worklist, int max_reg_ints, Arena* A, Dict* safehash) {
396 int* live = NEW_ARENA_ARRAY(A, int, (cfg->number_of_blocks() + 1) * max_reg_ints);
397 int* tmp_live = &live[cfg->number_of_blocks() * max_reg_ints];
398 Node* root = cfg->get_root_node();
399 // On CISC platforms, get the node representing the stack pointer that regalloc
400 // used for spills
401 Node *fp = NodeSentinel;
402 if (UseCISCSpill && root->req() > 1) {
403 fp = root->in(1)->in(TypeFunc::FramePtr);
404 }
405 memset(live, 0, cfg->number_of_blocks() * (max_reg_ints << LogBytesPerInt));
406 // Push preds onto worklist
407 for (uint i = 1; i < root->req(); i++) {
408 Block* block = cfg->get_block_for_node(root->in(i));
409 worklist->push(block);
410 }
411
412 // ZKM.jar includes tiny infinite loops which are unreached from below.
413 // If we missed any blocks, we'll retry here after pushing all missed
414 // blocks on the worklist. Normally this outer loop never trips more
415 // than once.
416 while (1) {
417
418 while( worklist->size() ) { // Standard worklist algorithm
419 Block *b = worklist->rpop();
420
421 // Copy first successor into my tmp_live space
422 int s0num = b->_succs[0]->_pre_order;
423 int *t = &live[s0num*max_reg_ints];
424 for( int i=0; i<max_reg_ints; i++ )
425 tmp_live[i] = t[i];
426
427 // OR in the remaining live registers
428 for( uint j=1; j<b->_num_succs; j++ ) {
429 uint sjnum = b->_succs[j]->_pre_order;
430 int *t = &live[sjnum*max_reg_ints];
431 for( int i=0; i<max_reg_ints; i++ )
432 tmp_live[i] |= t[i];
433 }
434
435 // Now walk tmp_live up the block backwards, computing live
436 for( int k=b->number_of_nodes()-1; k>=0; k-- ) {
437 Node *n = b->get_node(k);
438 // KILL def'd bits
439 int first = regalloc->get_reg_first(n);
440 int second = regalloc->get_reg_second(n);
441 if( OptoReg::is_valid(first) ) clr_live_bit(tmp_live,first);
442 if( OptoReg::is_valid(second) ) clr_live_bit(tmp_live,second);
443
444 MachNode *m = n->is_Mach() ? n->as_Mach() : NULL;
445
446 // Check if m is potentially a CISC alternate instruction (i.e, possibly
447 // synthesized by RegAlloc from a conventional instruction and a
448 // spilled input)
449 bool is_cisc_alternate = false;
450 if (UseCISCSpill && m) {
451 is_cisc_alternate = m->is_cisc_alternate();
452 }
453
454 // GEN use'd bits
455 for( uint l=1; l<n->req(); l++ ) {
456 Node *def = n->in(l);
457 assert(def != 0, "input edge required");
458 int first = regalloc->get_reg_first(def);
459 int second = regalloc->get_reg_second(def);
460 if( OptoReg::is_valid(first) ) set_live_bit(tmp_live,first);
461 if( OptoReg::is_valid(second) ) set_live_bit(tmp_live,second);
462 // If we use the stack pointer in a cisc-alternative instruction,
463 // check for use as a memory operand. Then reconstruct the RegName
464 // for this stack location, and set the appropriate bit in the
465 // live vector 4987749.
466 if (is_cisc_alternate && def == fp) {
467 const TypePtr *adr_type = NULL;
468 intptr_t offset;
469 const Node* base = m->get_base_and_disp(offset, adr_type);
470 if (base == NodeSentinel) {
471 // Machnode has multiple memory inputs. We are unable to reason
472 // with these, but are presuming (with trepidation) that not any of
473 // them are oops. This can be fixed by making get_base_and_disp()
474 // look at a specific input instead of all inputs.
475 assert(!def->bottom_type()->isa_oop_ptr(), "expecting non-oop mem input");
476 } else if (base != fp || offset == Type::OffsetBot) {
477 // Do nothing: the fp operand is either not from a memory use
478 // (base == NULL) OR the fp is used in a non-memory context
479 // (base is some other register) OR the offset is not constant,
480 // so it is not a stack slot.
481 } else {
482 assert(offset >= 0, "unexpected negative offset");
483 offset -= (offset % jintSize); // count the whole word
484 int stack_reg = regalloc->offset2reg(offset);
485 if (OptoReg::is_stack(stack_reg)) {
486 set_live_bit(tmp_live, stack_reg);
487 } else {
488 assert(false, "stack_reg not on stack?");
489 }
490 }
491 }
492 }
493
494 if( n->jvms() ) { // Record liveness at safepoint
495
496 // This placement of this stanza means inputs to calls are
497 // considered live at the callsite's OopMap. Argument oops are
498 // hence live, but NOT included in the oopmap. See cutout in
499 // build_oop_map. Debug oops are live (and in OopMap).
500 int *n_live = NEW_ARENA_ARRAY(A, int, max_reg_ints);
501 for( int l=0; l<max_reg_ints; l++ )
502 n_live[l] = tmp_live[l];
503 safehash->Insert(n,n_live);
504 }
505
506 }
507
508 // Now at block top, see if we have any changes. If so, propagate
509 // to prior blocks.
510 int *old_live = &live[b->_pre_order*max_reg_ints];
511 int l;
512 for( l=0; l<max_reg_ints; l++ )
513 if( tmp_live[l] != old_live[l] )
514 break;
515 if( l<max_reg_ints ) { // Change!
516 // Copy in new value
517 for( l=0; l<max_reg_ints; l++ )
518 old_live[l] = tmp_live[l];
519 // Push preds onto worklist
520 for (l = 1; l < (int)b->num_preds(); l++) {
521 Block* block = cfg->get_block_for_node(b->pred(l));
522 worklist->push(block);
523 }
524 }
525 }
526
527 // Scan for any missing safepoints. Happens to infinite loops
528 // ala ZKM.jar
529 uint i;
530 for (i = 1; i < cfg->number_of_blocks(); i++) {
531 Block* block = cfg->get_block(i);
532 uint j;
533 for (j = 1; j < block->number_of_nodes(); j++) {
534 if (block->get_node(j)->jvms() && (*safehash)[block->get_node(j)] == NULL) {
535 break;
536 }
537 }
538 if (j < block->number_of_nodes()) {
539 break;
540 }
541 }
542 if (i == cfg->number_of_blocks()) {
543 break; // Got 'em all
544 }
545 #ifndef PRODUCT
546 if( PrintOpto && Verbose )
547 tty->print_cr("retripping live calc");
548 #endif
549 // Force the issue (expensively): recheck everybody
550 for (i = 1; i < cfg->number_of_blocks(); i++) {
551 worklist->push(cfg->get_block(i));
552 }
553 }
554 }
555
556 // Collect GC mask info - where are all the OOPs?
557 void Compile::BuildOopMaps() {
558 NOT_PRODUCT( TracePhase t3("bldOopMaps", &_t_buildOopMaps, TimeCompiler); )
559 // Can't resource-mark because I need to leave all those OopMaps around,
560 // or else I need to resource-mark some arena other than the default.
561 // ResourceMark rm; // Reclaim all OopFlows when done
562 int max_reg = _regalloc->_max_reg; // Current array extent
563
564 Arena *A = Thread::current()->resource_area();
565 Block_List worklist; // Worklist of pending blocks
566
567 int max_reg_ints = round_to(max_reg, BitsPerInt)>>LogBitsPerInt;
568 Dict *safehash = NULL; // Used for assert only
569 // Compute a backwards liveness per register. Needs a bitarray of
570 // #blocks x (#registers, rounded up to ints)
571 safehash = new Dict(cmpkey,hashkey,A);
572 do_liveness( _regalloc, _cfg, &worklist, max_reg_ints, A, safehash );
573 OopFlow *free_list = NULL; // Free, unused
574
575 // Array mapping blocks to completed oopflows
576 OopFlow **flows = NEW_ARENA_ARRAY(A, OopFlow*, _cfg->number_of_blocks());
577 memset( flows, 0, _cfg->number_of_blocks() * sizeof(OopFlow*) );
578
579
580 // Do the first block 'by hand' to prime the worklist
581 Block *entry = _cfg->get_block(1);
582 OopFlow *rootflow = OopFlow::make(A,max_reg,this);
583 // Initialize to 'bottom' (not 'top')
584 memset( rootflow->_callees, OptoReg::Bad, max_reg*sizeof(short) );
585 memset( rootflow->_defs , 0, max_reg*sizeof(Node*) );
586 flows[entry->_pre_order] = rootflow;
587
588 // Do the first block 'by hand' to prime the worklist
589 rootflow->_b = entry;
590 rootflow->compute_reach( _regalloc, max_reg, safehash );
591 for( uint i=0; i<entry->_num_succs; i++ )
592 worklist.push(entry->_succs[i]);
593
594 // Now worklist contains blocks which have some, but perhaps not all,
595 // predecessors visited.
596 while( worklist.size() ) {
597 // Scan for a block with all predecessors visited, or any randoms slob
598 // otherwise. All-preds-visited order allows me to recycle OopFlow
599 // structures rapidly and cut down on the memory footprint.
600 // Note: not all predecessors might be visited yet (must happen for
601 // irreducible loops). This is OK, since every live value must have the
602 // SAME reaching def for the block, so any reaching def is OK.
603 uint i;
604
605 Block *b = worklist.pop();
606 // Ignore root block
607 if (b == _cfg->get_root_block()) {
608 continue;
609 }
610 // Block is already done? Happens if block has several predecessors,
611 // he can get on the worklist more than once.
612 if( flows[b->_pre_order] ) continue;
613
614 // If this block has a visited predecessor AND that predecessor has this
615 // last block as his only undone child, we can move the OopFlow from the
616 // pred to this block. Otherwise we have to grab a new OopFlow.
617 OopFlow *flow = NULL; // Flag for finding optimized flow
618 Block *pred = (Block*)0xdeadbeef;
619 // Scan this block's preds to find a done predecessor
620 for (uint j = 1; j < b->num_preds(); j++) {
621 Block* p = _cfg->get_block_for_node(b->pred(j));
622 OopFlow *p_flow = flows[p->_pre_order];
623 if( p_flow ) { // Predecessor is done
624 assert( p_flow->_b == p, "cross check" );
625 pred = p; // Record some predecessor
626 // If all successors of p are done except for 'b', then we can carry
627 // p_flow forward to 'b' without copying, otherwise we have to draw
628 // from the free_list and clone data.
629 uint k;
630 for( k=0; k<p->_num_succs; k++ )
631 if( !flows[p->_succs[k]->_pre_order] &&
632 p->_succs[k] != b )
633 break;
634
635 // Either carry-forward the now-unused OopFlow for b's use
636 // or draw a new one from the free list
637 if( k==p->_num_succs ) {
638 flow = p_flow;
639 break; // Found an ideal pred, use him
640 }
641 }
642 }
643
644 if( flow ) {
645 // We have an OopFlow that's the last-use of a predecessor.
646 // Carry it forward.
647 } else { // Draw a new OopFlow from the freelist
648 if( !free_list )
649 free_list = OopFlow::make(A,max_reg,C);
650 flow = free_list;
651 assert( flow->_b == NULL, "oopFlow is not free" );
652 free_list = flow->_next;
653 flow->_next = NULL;
654
655 // Copy/clone over the data
656 flow->clone(flows[pred->_pre_order], max_reg);
657 }
658
659 // Mark flow for block. Blocks can only be flowed over once,
660 // because after the first time they are guarded from entering
661 // this code again.
662 assert( flow->_b == pred, "have some prior flow" );
663 flow->_b = NULL;
664
665 // Now push flow forward
666 flows[b->_pre_order] = flow;// Mark flow for this block
667 flow->_b = b;
668 flow->compute_reach( _regalloc, max_reg, safehash );
669
670 // Now push children onto worklist
671 for( i=0; i<b->_num_succs; i++ )
672 worklist.push(b->_succs[i]);
673
674 }
675 }