1 /*
2 * Copyright (c) 1998, 2009, 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 "incls/_precompiled.incl"
26 #include "incls/_postaloc.cpp.incl"
27
28 // see if this register kind does not requires two registers
29 static bool is_single_register(uint x) {
30 #ifdef _LP64
31 return (x != Op_RegD && x != Op_RegL && x != Op_RegP);
32 #else
33 return (x != Op_RegD && x != Op_RegL);
34 #endif
35 }
36
37 //---------------------------may_be_copy_of_callee-----------------------------
38 // Check to see if we can possibly be a copy of a callee-save value.
39 bool PhaseChaitin::may_be_copy_of_callee( Node *def ) const {
40 // Short circuit if there are no callee save registers
41 if (_matcher.number_of_saved_registers() == 0) return false;
42
43 // Expect only a spill-down and reload on exit for callee-save spills.
44 // Chains of copies cannot be deep.
45 // 5008997 - This is wishful thinking. Register allocator seems to
46 // be splitting live ranges for callee save registers to such
47 // an extent that in large methods the chains can be very long
48 // (50+). The conservative answer is to return true if we don't
49 // know as this prevents optimizations from occurring.
50
51 const int limit = 60;
52 int i;
53 for( i=0; i < limit; i++ ) {
54 if( def->is_Proj() && def->in(0)->is_Start() &&
55 _matcher.is_save_on_entry(lrgs(n2lidx(def)).reg()) )
56 return true; // Direct use of callee-save proj
57 if( def->is_Copy() ) // Copies carry value through
58 def = def->in(def->is_Copy());
59 else if( def->is_Phi() ) // Phis can merge it from any direction
60 def = def->in(1);
61 else
62 break;
63 guarantee(def != NULL, "must not resurrect dead copy");
64 }
65 // If we reached the end and didn't find a callee save proj
66 // then this may be a callee save proj so we return true
67 // as the conservative answer. If we didn't reach then end
68 // we must have discovered that it was not a callee save
69 // else we would have returned.
70 return i == limit;
71 }
72
73
74
75 //------------------------------yank_if_dead-----------------------------------
76 // Removed an edge from 'old'. Yank if dead. Return adjustment counts to
77 // iterators in the current block.
78 int PhaseChaitin::yank_if_dead( Node *old, Block *current_block, Node_List *value, Node_List *regnd ) {
79 int blk_adjust=0;
80 while (old->outcnt() == 0 && old != C->top()) {
81 Block *oldb = _cfg._bbs[old->_idx];
82 oldb->find_remove(old);
83 // Count 1 if deleting an instruction from the current block
84 if( oldb == current_block ) blk_adjust++;
85 _cfg._bbs.map(old->_idx,NULL);
86 OptoReg::Name old_reg = lrgs(n2lidx(old)).reg();
87 if( regnd && (*regnd)[old_reg]==old ) { // Instruction is currently available?
88 value->map(old_reg,NULL); // Yank from value/regnd maps
89 regnd->map(old_reg,NULL); // This register's value is now unknown
90 }
91 assert(old->req() <= 2, "can't handle more inputs");
92 Node *tmp = old->req() > 1 ? old->in(1) : NULL;
93 old->disconnect_inputs(NULL);
94 if( !tmp ) break;
95 old = tmp;
96 }
97 return blk_adjust;
98 }
99
100 //------------------------------use_prior_register-----------------------------
101 // Use the prior value instead of the current value, in an effort to make
102 // the current value go dead. Return block iterator adjustment, in case
103 // we yank some instructions from this block.
104 int PhaseChaitin::use_prior_register( Node *n, uint idx, Node *def, Block *current_block, Node_List &value, Node_List ®nd ) {
105 // No effect?
106 if( def == n->in(idx) ) return 0;
107 // Def is currently dead and can be removed? Do not resurrect
108 if( def->outcnt() == 0 ) return 0;
109
110 // Not every pair of physical registers are assignment compatible,
111 // e.g. on sparc floating point registers are not assignable to integer
112 // registers.
113 const LRG &def_lrg = lrgs(n2lidx(def));
114 OptoReg::Name def_reg = def_lrg.reg();
115 const RegMask &use_mask = n->in_RegMask(idx);
116 bool can_use = ( RegMask::can_represent(def_reg) ? (use_mask.Member(def_reg) != 0)
117 : (use_mask.is_AllStack() != 0));
118 // Check for a copy to or from a misaligned pair.
119 can_use = can_use && !use_mask.is_misaligned_Pair() && !def_lrg.mask().is_misaligned_Pair();
120
121 if (!can_use)
122 return 0;
123
124 // Capture the old def in case it goes dead...
125 Node *old = n->in(idx);
126
127 // Save-on-call copies can only be elided if the entire copy chain can go
128 // away, lest we get the same callee-save value alive in 2 locations at
129 // once. We check for the obvious trivial case here. Although it can
130 // sometimes be elided with cooperation outside our scope, here we will just
131 // miss the opportunity. :-(
132 if( may_be_copy_of_callee(def) ) {
133 if( old->outcnt() > 1 ) return 0; // We're the not last user
134 int idx = old->is_Copy();
135 assert( idx, "chain of copies being removed" );
136 Node *old2 = old->in(idx); // Chain of copies
137 if( old2->outcnt() > 1 ) return 0; // old is not the last user
138 int idx2 = old2->is_Copy();
139 if( !idx2 ) return 0; // Not a chain of 2 copies
140 if( def != old2->in(idx2) ) return 0; // Chain of exactly 2 copies
141 }
142
143 // Use the new def
144 n->set_req(idx,def);
145 _post_alloc++;
146
147 // Is old def now dead? We successfully yanked a copy?
148 return yank_if_dead(old,current_block,&value,®nd);
149 }
150
151
152 //------------------------------skip_copies------------------------------------
153 // Skip through any number of copies (that don't mod oop-i-ness)
154 Node *PhaseChaitin::skip_copies( Node *c ) {
155 int idx = c->is_Copy();
156 uint is_oop = lrgs(n2lidx(c))._is_oop;
157 while (idx != 0) {
158 guarantee(c->in(idx) != NULL, "must not resurrect dead copy");
159 if (lrgs(n2lidx(c->in(idx)))._is_oop != is_oop)
160 break; // casting copy, not the same value
161 c = c->in(idx);
162 idx = c->is_Copy();
163 }
164 return c;
165 }
166
167 //------------------------------elide_copy-------------------------------------
168 // Remove (bypass) copies along Node n, edge k.
169 int PhaseChaitin::elide_copy( Node *n, int k, Block *current_block, Node_List &value, Node_List ®nd, bool can_change_regs ) {
170 int blk_adjust = 0;
171
172 uint nk_idx = n2lidx(n->in(k));
173 OptoReg::Name nk_reg = lrgs(nk_idx ).reg();
174
175 // Remove obvious same-register copies
176 Node *x = n->in(k);
177 int idx;
178 while( (idx=x->is_Copy()) != 0 ) {
179 Node *copy = x->in(idx);
180 guarantee(copy != NULL, "must not resurrect dead copy");
181 if( lrgs(n2lidx(copy)).reg() != nk_reg ) break;
182 blk_adjust += use_prior_register(n,k,copy,current_block,value,regnd);
183 if( n->in(k) != copy ) break; // Failed for some cutout?
184 x = copy; // Progress, try again
185 }
186
187 // Phis and 2-address instructions cannot change registers so easily - their
188 // outputs must match their input.
189 if( !can_change_regs )
190 return blk_adjust; // Only check stupid copies!
191
192 // Loop backedges won't have a value-mapping yet
193 if( &value == NULL ) return blk_adjust;
194
195 // Skip through all copies to the _value_ being used. Do not change from
196 // int to pointer. This attempts to jump through a chain of copies, where
197 // intermediate copies might be illegal, i.e., value is stored down to stack
198 // then reloaded BUT survives in a register the whole way.
199 Node *val = skip_copies(n->in(k));
200
201 if (val == x && nk_idx != 0 &&
202 regnd[nk_reg] != NULL && regnd[nk_reg] != x &&
203 n2lidx(x) == n2lidx(regnd[nk_reg])) {
204 // When rematerialzing nodes and stretching lifetimes, the
205 // allocator will reuse the original def for multidef LRG instead
206 // of the current reaching def because it can't know it's safe to
207 // do so. After allocation completes if they are in the same LRG
208 // then it should use the current reaching def instead.
209 n->set_req(k, regnd[nk_reg]);
210 blk_adjust += yank_if_dead(val, current_block, &value, ®nd);
211 val = skip_copies(n->in(k));
212 }
213
214 if( val == x ) return blk_adjust; // No progress?
215
216 bool single = is_single_register(val->ideal_reg());
217 uint val_idx = n2lidx(val);
218 OptoReg::Name val_reg = lrgs(val_idx).reg();
219
220 // See if it happens to already be in the correct register!
221 // (either Phi's direct register, or the common case of the name
222 // never-clobbered original-def register)
223 if( value[val_reg] == val &&
224 // Doubles check both halves
225 ( single || value[val_reg-1] == val ) ) {
226 blk_adjust += use_prior_register(n,k,regnd[val_reg],current_block,value,regnd);
227 if( n->in(k) == regnd[val_reg] ) // Success! Quit trying
228 return blk_adjust;
229 }
230
231 // See if we can skip the copy by changing registers. Don't change from
232 // using a register to using the stack unless we know we can remove a
233 // copy-load. Otherwise we might end up making a pile of Intel cisc-spill
234 // ops reading from memory instead of just loading once and using the
235 // register.
236
237 // Also handle duplicate copies here.
238 const Type *t = val->is_Con() ? val->bottom_type() : NULL;
239
240 // Scan all registers to see if this value is around already
241 for( uint reg = 0; reg < (uint)_max_reg; reg++ ) {
242 if (reg == (uint)nk_reg) {
243 // Found ourselves so check if there is only one user of this
244 // copy and keep on searching for a better copy if so.
245 bool ignore_self = true;
246 x = n->in(k);
247 DUIterator_Fast imax, i = x->fast_outs(imax);
248 Node* first = x->fast_out(i); i++;
249 while (i < imax && ignore_self) {
250 Node* use = x->fast_out(i); i++;
251 if (use != first) ignore_self = false;
252 }
253 if (ignore_self) continue;
254 }
255
256 Node *vv = value[reg];
257 if( !single ) { // Doubles check for aligned-adjacent pair
258 if( (reg&1)==0 ) continue; // Wrong half of a pair
259 if( vv != value[reg-1] ) continue; // Not a complete pair
260 }
261 if( vv == val || // Got a direct hit?
262 (t && vv && vv->bottom_type() == t && vv->is_Mach() &&
263 vv->as_Mach()->rule() == val->as_Mach()->rule()) ) { // Or same constant?
264 assert( !n->is_Phi(), "cannot change registers at a Phi so easily" );
265 if( OptoReg::is_stack(nk_reg) || // CISC-loading from stack OR
266 OptoReg::is_reg(reg) || // turning into a register use OR
267 regnd[reg]->outcnt()==1 ) { // last use of a spill-load turns into a CISC use
268 blk_adjust += use_prior_register(n,k,regnd[reg],current_block,value,regnd);
269 if( n->in(k) == regnd[reg] ) // Success! Quit trying
270 return blk_adjust;
271 } // End of if not degrading to a stack
272 } // End of if found value in another register
273 } // End of scan all machine registers
274 return blk_adjust;
275 }
276
277
278 //
279 // Check if nreg already contains the constant value val. Normal copy
280 // elimination doesn't doesn't work on constants because multiple
281 // nodes can represent the same constant so the type and rule of the
282 // MachNode must be checked to ensure equivalence.
283 //
284 bool PhaseChaitin::eliminate_copy_of_constant(Node* val, Node* n,
285 Block *current_block,
286 Node_List& value, Node_List& regnd,
287 OptoReg::Name nreg, OptoReg::Name nreg2) {
288 if (value[nreg] != val && val->is_Con() &&
289 value[nreg] != NULL && value[nreg]->is_Con() &&
290 (nreg2 == OptoReg::Bad || value[nreg] == value[nreg2]) &&
291 value[nreg]->bottom_type() == val->bottom_type() &&
292 value[nreg]->as_Mach()->rule() == val->as_Mach()->rule()) {
293 // This code assumes that two MachNodes representing constants
294 // which have the same rule and the same bottom type will produce
295 // identical effects into a register. This seems like it must be
296 // objectively true unless there are hidden inputs to the nodes
297 // but if that were to change this code would need to updated.
298 // Since they are equivalent the second one if redundant and can
299 // be removed.
300 //
301 // n will be replaced with the old value but n might have
302 // kills projections associated with it so remove them now so that
303 // yank_if_dead will be able to eliminate the copy once the uses
304 // have been transferred to the old[value].
305 for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax; i++) {
306 Node* use = n->fast_out(i);
307 if (use->is_Proj() && use->outcnt() == 0) {
308 // Kill projections have no users and one input
309 use->set_req(0, C->top());
310 yank_if_dead(use, current_block, &value, ®nd);
311 --i; --imax;
312 }
313 }
314 _post_alloc++;
315 return true;
316 }
317 return false;
318 }
319
320
321 //------------------------------post_allocate_copy_removal---------------------
322 // Post-Allocation peephole copy removal. We do this in 1 pass over the
323 // basic blocks. We maintain a mapping of registers to Nodes (an array of
324 // Nodes indexed by machine register or stack slot number). NULL means that a
325 // register is not mapped to any Node. We can (want to have!) have several
326 // registers map to the same Node. We walk forward over the instructions
327 // updating the mapping as we go. At merge points we force a NULL if we have
328 // to merge 2 different Nodes into the same register. Phi functions will give
329 // us a new Node if there is a proper value merging. Since the blocks are
330 // arranged in some RPO, we will visit all parent blocks before visiting any
331 // successor blocks (except at loops).
332 //
333 // If we find a Copy we look to see if the Copy's source register is a stack
334 // slot and that value has already been loaded into some machine register; if
335 // so we use machine register directly. This turns a Load into a reg-reg
336 // Move. We also look for reloads of identical constants.
337 //
338 // When we see a use from a reg-reg Copy, we will attempt to use the copy's
339 // source directly and make the copy go dead.
340 void PhaseChaitin::post_allocate_copy_removal() {
341 NOT_PRODUCT( Compile::TracePhase t3("postAllocCopyRemoval", &_t_postAllocCopyRemoval, TimeCompiler); )
342 ResourceMark rm;
343
344 // Need a mapping from basic block Node_Lists. We need a Node_List to
345 // map from register number to value-producing Node.
346 Node_List **blk2value = NEW_RESOURCE_ARRAY( Node_List *, _cfg._num_blocks+1);
347 memset( blk2value, 0, sizeof(Node_List*)*(_cfg._num_blocks+1) );
348 // Need a mapping from basic block Node_Lists. We need a Node_List to
349 // map from register number to register-defining Node.
350 Node_List **blk2regnd = NEW_RESOURCE_ARRAY( Node_List *, _cfg._num_blocks+1);
351 memset( blk2regnd, 0, sizeof(Node_List*)*(_cfg._num_blocks+1) );
352
353 // We keep unused Node_Lists on a free_list to avoid wasting
354 // memory.
355 GrowableArray<Node_List*> free_list = GrowableArray<Node_List*>(16);
356
357 // For all blocks
358 for( uint i = 0; i < _cfg._num_blocks; i++ ) {
359 uint j;
360 Block *b = _cfg._blocks[i];
361
362 // Count of Phis in block
363 uint phi_dex;
364 for( phi_dex = 1; phi_dex < b->_nodes.size(); phi_dex++ ) {
365 Node *phi = b->_nodes[phi_dex];
366 if( !phi->is_Phi() )
367 break;
368 }
369
370 // If any predecessor has not been visited, we do not know the state
371 // of registers at the start. Check for this, while updating copies
372 // along Phi input edges
373 bool missing_some_inputs = false;
374 Block *freed = NULL;
375 for( j = 1; j < b->num_preds(); j++ ) {
376 Block *pb = _cfg._bbs[b->pred(j)->_idx];
377 // Remove copies along phi edges
378 for( uint k=1; k<phi_dex; k++ )
379 elide_copy( b->_nodes[k], j, b, *blk2value[pb->_pre_order], *blk2regnd[pb->_pre_order], false );
380 if( blk2value[pb->_pre_order] ) { // Have a mapping on this edge?
381 // See if this predecessor's mappings have been used by everybody
382 // who wants them. If so, free 'em.
383 uint k;
384 for( k=0; k<pb->_num_succs; k++ ) {
385 Block *pbsucc = pb->_succs[k];
386 if( !blk2value[pbsucc->_pre_order] && pbsucc != b )
387 break; // Found a future user
388 }
389 if( k >= pb->_num_succs ) { // No more uses, free!
390 freed = pb; // Record last block freed
391 free_list.push(blk2value[pb->_pre_order]);
392 free_list.push(blk2regnd[pb->_pre_order]);
393 }
394 } else { // This block has unvisited (loopback) inputs
395 missing_some_inputs = true;
396 }
397 }
398
399
400 // Extract Node_List mappings. If 'freed' is non-zero, we just popped
401 // 'freed's blocks off the list
402 Node_List ®nd = *(free_list.is_empty() ? new Node_List() : free_list.pop());
403 Node_List &value = *(free_list.is_empty() ? new Node_List() : free_list.pop());
404 assert( !freed || blk2value[freed->_pre_order] == &value, "" );
405 value.map(_max_reg,NULL);
406 regnd.map(_max_reg,NULL);
407 // Set mappings as OUR mappings
408 blk2value[b->_pre_order] = &value;
409 blk2regnd[b->_pre_order] = ®nd;
410
411 // Initialize value & regnd for this block
412 if( missing_some_inputs ) {
413 // Some predecessor has not yet been visited; zap map to empty
414 for( uint k = 0; k < (uint)_max_reg; k++ ) {
415 value.map(k,NULL);
416 regnd.map(k,NULL);
417 }
418 } else {
419 if( !freed ) { // Didn't get a freebie prior block
420 // Must clone some data
421 freed = _cfg._bbs[b->pred(1)->_idx];
422 Node_List &f_value = *blk2value[freed->_pre_order];
423 Node_List &f_regnd = *blk2regnd[freed->_pre_order];
424 for( uint k = 0; k < (uint)_max_reg; k++ ) {
425 value.map(k,f_value[k]);
426 regnd.map(k,f_regnd[k]);
427 }
428 }
429 // Merge all inputs together, setting to NULL any conflicts.
430 for( j = 1; j < b->num_preds(); j++ ) {
431 Block *pb = _cfg._bbs[b->pred(j)->_idx];
432 if( pb == freed ) continue; // Did self already via freelist
433 Node_List &p_regnd = *blk2regnd[pb->_pre_order];
434 for( uint k = 0; k < (uint)_max_reg; k++ ) {
435 if( regnd[k] != p_regnd[k] ) { // Conflict on reaching defs?
436 value.map(k,NULL); // Then no value handy
437 regnd.map(k,NULL);
438 }
439 }
440 }
441 }
442
443 // For all Phi's
444 for( j = 1; j < phi_dex; j++ ) {
445 uint k;
446 Node *phi = b->_nodes[j];
447 uint pidx = n2lidx(phi);
448 OptoReg::Name preg = lrgs(n2lidx(phi)).reg();
449
450 // Remove copies remaining on edges. Check for junk phi.
451 Node *u = NULL;
452 for( k=1; k<phi->req(); k++ ) {
453 Node *x = phi->in(k);
454 if( phi != x && u != x ) // Found a different input
455 u = u ? NodeSentinel : x; // Capture unique input, or NodeSentinel for 2nd input
456 }
457 if( u != NodeSentinel ) { // Junk Phi. Remove
458 b->_nodes.remove(j--); phi_dex--;
459 _cfg._bbs.map(phi->_idx,NULL);
460 phi->replace_by(u);
461 phi->disconnect_inputs(NULL);
462 continue;
463 }
464 // Note that if value[pidx] exists, then we merged no new values here
465 // and the phi is useless. This can happen even with the above phi
466 // removal for complex flows. I cannot keep the better known value here
467 // because locally the phi appears to define a new merged value. If I
468 // keep the better value then a copy of the phi, being unable to use the
469 // global flow analysis, can't "peek through" the phi to the original
470 // reaching value and so will act like it's defining a new value. This
471 // can lead to situations where some uses are from the old and some from
472 // the new values. Not illegal by itself but throws the over-strong
473 // assert in scheduling.
474 if( pidx ) {
475 value.map(preg,phi);
476 regnd.map(preg,phi);
477 OptoReg::Name preg_lo = OptoReg::add(preg,-1);
478 if( !is_single_register(phi->ideal_reg()) ) {
479 value.map(preg_lo,phi);
480 regnd.map(preg_lo,phi);
481 }
482 }
483 }
484
485 // For all remaining instructions
486 for( j = phi_dex; j < b->_nodes.size(); j++ ) {
487 Node *n = b->_nodes[j];
488
489 if( n->outcnt() == 0 && // Dead?
490 n != C->top() && // (ignore TOP, it has no du info)
491 !n->is_Proj() ) { // fat-proj kills
492 j -= yank_if_dead(n,b,&value,®nd);
493 continue;
494 }
495
496 // Improve reaching-def info. Occasionally post-alloc's liveness gives
497 // up (at loop backedges, because we aren't doing a full flow pass).
498 // The presence of a live use essentially asserts that the use's def is
499 // alive and well at the use (or else the allocator fubar'd). Take
500 // advantage of this info to set a reaching def for the use-reg.
501 uint k;
502 for( k = 1; k < n->req(); k++ ) {
503 Node *def = n->in(k); // n->in(k) is a USE; def is the DEF for this USE
504 guarantee(def != NULL, "no disconnected nodes at this point");
505 uint useidx = n2lidx(def); // useidx is the live range index for this USE
506
507 if( useidx ) {
508 OptoReg::Name ureg = lrgs(useidx).reg();
509 if( !value[ureg] ) {
510 int idx; // Skip occasional useless copy
511 while( (idx=def->is_Copy()) != 0 &&
512 def->in(idx) != NULL && // NULL should not happen
513 ureg == lrgs(n2lidx(def->in(idx))).reg() )
514 def = def->in(idx);
515 Node *valdef = skip_copies(def); // tighten up val through non-useless copies
516 value.map(ureg,valdef); // record improved reaching-def info
517 regnd.map(ureg, def);
518 // Record other half of doubles
519 OptoReg::Name ureg_lo = OptoReg::add(ureg,-1);
520 if( !is_single_register(def->ideal_reg()) &&
521 ( !RegMask::can_represent(ureg_lo) ||
522 lrgs(useidx).mask().Member(ureg_lo) ) && // Nearly always adjacent
523 !value[ureg_lo] ) {
524 value.map(ureg_lo,valdef); // record improved reaching-def info
525 regnd.map(ureg_lo, def);
526 }
527 }
528 }
529 }
530
531 const uint two_adr = n->is_Mach() ? n->as_Mach()->two_adr() : 0;
532
533 // Remove copies along input edges
534 for( k = 1; k < n->req(); k++ )
535 j -= elide_copy( n, k, b, value, regnd, two_adr!=k );
536
537 // Unallocated Nodes define no registers
538 uint lidx = n2lidx(n);
539 if( !lidx ) continue;
540
541 // Update the register defined by this instruction
542 OptoReg::Name nreg = lrgs(lidx).reg();
543 // Skip through all copies to the _value_ being defined.
544 // Do not change from int to pointer
545 Node *val = skip_copies(n);
546
547 // Clear out a dead definition before starting so that the
548 // elimination code doesn't have to guard against it. The
549 // definition could in fact be a kill projection with a count of
550 // 0 which is safe but since those are uninteresting for copy
551 // elimination just delete them as well.
552 if (regnd[nreg] != NULL && regnd[nreg]->outcnt() == 0) {
553 regnd.map(nreg, NULL);
554 value.map(nreg, NULL);
555 }
556
557 uint n_ideal_reg = n->ideal_reg();
558 if( is_single_register(n_ideal_reg) ) {
559 // If Node 'n' does not change the value mapped by the register,
560 // then 'n' is a useless copy. Do not update the register->node
561 // mapping so 'n' will go dead.
562 if( value[nreg] != val ) {
563 if (eliminate_copy_of_constant(val, n, b, value, regnd, nreg, OptoReg::Bad)) {
564 j -= replace_and_yank_if_dead(n, nreg, b, value, regnd);
565 } else {
566 // Update the mapping: record new Node defined by the register
567 regnd.map(nreg,n);
568 // Update mapping for defined *value*, which is the defined
569 // Node after skipping all copies.
570 value.map(nreg,val);
571 }
572 } else if( !may_be_copy_of_callee(n) ) {
573 assert( n->is_Copy(), "" );
574 j -= replace_and_yank_if_dead(n, nreg, b, value, regnd);
575 }
576 } else {
577 // If the value occupies a register pair, record same info
578 // in both registers.
579 OptoReg::Name nreg_lo = OptoReg::add(nreg,-1);
580 if( RegMask::can_represent(nreg_lo) && // Either a spill slot, or
581 !lrgs(lidx).mask().Member(nreg_lo) ) { // Nearly always adjacent
582 // Sparc occasionally has non-adjacent pairs.
583 // Find the actual other value
584 RegMask tmp = lrgs(lidx).mask();
585 tmp.Remove(nreg);
586 nreg_lo = tmp.find_first_elem();
587 }
588 if( value[nreg] != val || value[nreg_lo] != val ) {
589 if (eliminate_copy_of_constant(val, n, b, value, regnd, nreg, nreg_lo)) {
590 j -= replace_and_yank_if_dead(n, nreg, b, value, regnd);
591 } else {
592 regnd.map(nreg , n );
593 regnd.map(nreg_lo, n );
594 value.map(nreg ,val);
595 value.map(nreg_lo,val);
596 }
597 } else if( !may_be_copy_of_callee(n) ) {
598 assert( n->is_Copy(), "" );
599 j -= replace_and_yank_if_dead(n, nreg, b, value, regnd);
600 }
601 }
602
603 // Fat projections kill many registers
604 if( n_ideal_reg == MachProjNode::fat_proj ) {
605 RegMask rm = n->out_RegMask();
606 // wow, what an expensive iterator...
607 nreg = rm.find_first_elem();
608 while( OptoReg::is_valid(nreg)) {
609 rm.Remove(nreg);
610 value.map(nreg,n);
611 regnd.map(nreg,n);
612 nreg = rm.find_first_elem();
613 }
614 }
615
616 } // End of for all instructions in the block
617
618 } // End for all blocks
619 }