1 /*
2 * Copyright (c) 1998, 2012, 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 "memory/allocation.inline.hpp"
27 #include "opto/chaitin.hpp"
28 #include "opto/machnode.hpp"
29
30 // See if this register (or pairs, or vector) already contains the value.
31 static bool register_contains_value(Node* val, OptoReg::Name reg, int n_regs,
32 Node_List& value) {
33 for (int i = 0; i < n_regs; i++) {
34 OptoReg::Name nreg = OptoReg::add(reg,-i);
35 if (value[nreg] != val)
36 return false;
37 }
38 return true;
39 }
40
41 //---------------------------may_be_copy_of_callee-----------------------------
42 // Check to see if we can possibly be a copy of a callee-save value.
43 bool PhaseChaitin::may_be_copy_of_callee( Node *def ) const {
44 // Short circuit if there are no callee save registers
45 if (_matcher.number_of_saved_registers() == 0) return false;
46
47 // Expect only a spill-down and reload on exit for callee-save spills.
48 // Chains of copies cannot be deep.
49 // 5008997 - This is wishful thinking. Register allocator seems to
50 // be splitting live ranges for callee save registers to such
51 // an extent that in large methods the chains can be very long
52 // (50+). The conservative answer is to return true if we don't
53 // know as this prevents optimizations from occurring.
54
55 const int limit = 60;
56 int i;
57 for( i=0; i < limit; i++ ) {
58 if( def->is_Proj() && def->in(0)->is_Start() &&
59 _matcher.is_save_on_entry(lrgs(n2lidx(def)).reg()) )
60 return true; // Direct use of callee-save proj
61 if( def->is_Copy() ) // Copies carry value through
62 def = def->in(def->is_Copy());
63 else if( def->is_Phi() ) // Phis can merge it from any direction
64 def = def->in(1);
65 else
66 break;
67 guarantee(def != NULL, "must not resurrect dead copy");
68 }
69 // If we reached the end and didn't find a callee save proj
70 // then this may be a callee save proj so we return true
71 // as the conservative answer. If we didn't reach then end
72 // we must have discovered that it was not a callee save
73 // else we would have returned.
74 return i == limit;
75 }
76
77 //------------------------------yank-----------------------------------
78 // Helper function for yank_if_dead
79 int PhaseChaitin::yank( Node *old, Block *current_block, Node_List *value, Node_List *regnd ) {
80 int blk_adjust=0;
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 return blk_adjust;
92 }
93
94 #ifdef ASSERT
95 static bool expected_yanked_node(Node *old, Node *orig_old) {
96 // This code is expected only next original nodes:
97 // - load from constant table node which may have next data input nodes:
98 // MachConstantBase, Phi, MachTemp, MachSpillCopy
99 // - load constant node which may have next data input nodes:
100 // MachTemp, MachSpillCopy
101 // - MachSpillCopy
102 // - MachProj and Copy dead nodes
103 if (old->is_MachSpillCopy()) {
104 return true;
105 } else if (old->is_Con()) {
106 return true;
107 } else if (old->is_MachProj()) { // Dead kills projection of Con node
108 return (old == orig_old);
109 } else if (old->is_Copy()) { // Dead copy of a callee-save value
110 return (old == orig_old);
111 } else if (old->is_MachTemp()) {
112 return orig_old->is_Con();
113 } else if (old->is_Phi() || old->is_MachConstantBase()) {
114 return (orig_old->is_Con() && orig_old->is_MachConstant());
115 }
116 return false;
117 }
118 #endif
119
120 //------------------------------yank_if_dead-----------------------------------
121 // Removed edges from 'old'. Yank if dead. Return adjustment counts to
122 // iterators in the current block.
123 int PhaseChaitin::yank_if_dead_recurse(Node *old, Node *orig_old, Block *current_block,
124 Node_List *value, Node_List *regnd) {
125 int blk_adjust=0;
126 if (old->outcnt() == 0 && old != C->top()) {
127 #ifdef ASSERT
128 if (!expected_yanked_node(old, orig_old)) {
129 tty->print_cr("==============================================");
130 tty->print_cr("orig_old:");
131 orig_old->dump();
132 tty->print_cr("old:");
133 old->dump();
134 assert(false, "unexpected yanked node");
135 }
136 if (old->is_Con())
137 orig_old = old; // Reset to satisfy expected nodes checks.
138 #endif
139 blk_adjust += yank(old, current_block, value, regnd);
140
141 for (uint i = 1; i < old->req(); i++) {
142 Node* n = old->in(i);
143 if (n != NULL) {
144 old->set_req(i, NULL);
145 blk_adjust += yank_if_dead_recurse(n, orig_old, current_block, value, regnd);
146 }
147 }
148 // Disconnect control and remove precedence edges if any exist
149 old->disconnect_inputs(NULL);
150 }
151 return blk_adjust;
152 }
153
154 //------------------------------use_prior_register-----------------------------
155 // Use the prior value instead of the current value, in an effort to make
156 // the current value go dead. Return block iterator adjustment, in case
157 // we yank some instructions from this block.
158 int PhaseChaitin::use_prior_register( Node *n, uint idx, Node *def, Block *current_block, Node_List &value, Node_List ®nd ) {
159 // No effect?
160 if( def == n->in(idx) ) return 0;
161 // Def is currently dead and can be removed? Do not resurrect
162 if( def->outcnt() == 0 ) return 0;
163
164 // Not every pair of physical registers are assignment compatible,
165 // e.g. on sparc floating point registers are not assignable to integer
166 // registers.
167 const LRG &def_lrg = lrgs(n2lidx(def));
168 OptoReg::Name def_reg = def_lrg.reg();
169 const RegMask &use_mask = n->in_RegMask(idx);
170 bool can_use = ( RegMask::can_represent(def_reg) ? (use_mask.Member(def_reg) != 0)
171 : (use_mask.is_AllStack() != 0));
172 if (!RegMask::is_vector(def->ideal_reg())) {
173 // Check for a copy to or from a misaligned pair.
174 // It is workaround for a sparc with misaligned pairs.
175 can_use = can_use && !use_mask.is_misaligned_pair() && !def_lrg.mask().is_misaligned_pair();
176 }
177 if (!can_use)
178 return 0;
179
180 // Capture the old def in case it goes dead...
181 Node *old = n->in(idx);
182
183 // Save-on-call copies can only be elided if the entire copy chain can go
184 // away, lest we get the same callee-save value alive in 2 locations at
185 // once. We check for the obvious trivial case here. Although it can
186 // sometimes be elided with cooperation outside our scope, here we will just
187 // miss the opportunity. :-(
188 if( may_be_copy_of_callee(def) ) {
189 if( old->outcnt() > 1 ) return 0; // We're the not last user
190 int idx = old->is_Copy();
191 assert( idx, "chain of copies being removed" );
192 Node *old2 = old->in(idx); // Chain of copies
193 if( old2->outcnt() > 1 ) return 0; // old is not the last user
194 int idx2 = old2->is_Copy();
195 if( !idx2 ) return 0; // Not a chain of 2 copies
196 if( def != old2->in(idx2) ) return 0; // Chain of exactly 2 copies
197 }
198
199 // Use the new def
200 n->set_req(idx,def);
201 _post_alloc++;
202
203 // Is old def now dead? We successfully yanked a copy?
204 return yank_if_dead(old,current_block,&value,®nd);
205 }
206
207
208 //------------------------------skip_copies------------------------------------
209 // Skip through any number of copies (that don't mod oop-i-ness)
210 Node *PhaseChaitin::skip_copies( Node *c ) {
211 int idx = c->is_Copy();
212 uint is_oop = lrgs(n2lidx(c))._is_oop;
213 while (idx != 0) {
214 guarantee(c->in(idx) != NULL, "must not resurrect dead copy");
215 if (lrgs(n2lidx(c->in(idx)))._is_oop != is_oop)
216 break; // casting copy, not the same value
217 c = c->in(idx);
218 idx = c->is_Copy();
219 }
220 return c;
221 }
222
223 //------------------------------elide_copy-------------------------------------
224 // Remove (bypass) copies along Node n, edge k.
225 int PhaseChaitin::elide_copy( Node *n, int k, Block *current_block, Node_List &value, Node_List ®nd, bool can_change_regs ) {
226 int blk_adjust = 0;
227
228 uint nk_idx = n2lidx(n->in(k));
229 OptoReg::Name nk_reg = lrgs(nk_idx ).reg();
230
231 // Remove obvious same-register copies
232 Node *x = n->in(k);
233 int idx;
234 while( (idx=x->is_Copy()) != 0 ) {
235 Node *copy = x->in(idx);
236 guarantee(copy != NULL, "must not resurrect dead copy");
237 if( lrgs(n2lidx(copy)).reg() != nk_reg ) break;
238 blk_adjust += use_prior_register(n,k,copy,current_block,value,regnd);
239 if( n->in(k) != copy ) break; // Failed for some cutout?
240 x = copy; // Progress, try again
241 }
242
243 // Phis and 2-address instructions cannot change registers so easily - their
244 // outputs must match their input.
245 if( !can_change_regs )
246 return blk_adjust; // Only check stupid copies!
247
248 // Loop backedges won't have a value-mapping yet
249 if( &value == NULL ) return blk_adjust;
250
251 // Skip through all copies to the _value_ being used. Do not change from
252 // int to pointer. This attempts to jump through a chain of copies, where
253 // intermediate copies might be illegal, i.e., value is stored down to stack
254 // then reloaded BUT survives in a register the whole way.
255 Node *val = skip_copies(n->in(k));
256
257 if (val == x && nk_idx != 0 &&
258 regnd[nk_reg] != NULL && regnd[nk_reg] != x &&
259 n2lidx(x) == n2lidx(regnd[nk_reg])) {
260 // When rematerialzing nodes and stretching lifetimes, the
261 // allocator will reuse the original def for multidef LRG instead
262 // of the current reaching def because it can't know it's safe to
263 // do so. After allocation completes if they are in the same LRG
264 // then it should use the current reaching def instead.
265 n->set_req(k, regnd[nk_reg]);
266 blk_adjust += yank_if_dead(val, current_block, &value, ®nd);
267 val = skip_copies(n->in(k));
268 }
269
270 if (val == x) return blk_adjust; // No progress?
271
272 int n_regs = RegMask::num_registers(val->ideal_reg());
273 uint val_idx = n2lidx(val);
274 OptoReg::Name val_reg = lrgs(val_idx).reg();
275
276 // See if it happens to already be in the correct register!
277 // (either Phi's direct register, or the common case of the name
278 // never-clobbered original-def register)
279 if (register_contains_value(val, val_reg, n_regs, value)) {
280 blk_adjust += use_prior_register(n,k,regnd[val_reg],current_block,value,regnd);
281 if( n->in(k) == regnd[val_reg] ) // Success! Quit trying
282 return blk_adjust;
283 }
284
285 // See if we can skip the copy by changing registers. Don't change from
286 // using a register to using the stack unless we know we can remove a
287 // copy-load. Otherwise we might end up making a pile of Intel cisc-spill
288 // ops reading from memory instead of just loading once and using the
289 // register.
290
291 // Also handle duplicate copies here.
292 const Type *t = val->is_Con() ? val->bottom_type() : NULL;
293
294 // Scan all registers to see if this value is around already
295 for( uint reg = 0; reg < (uint)_max_reg; reg++ ) {
296 if (reg == (uint)nk_reg) {
297 // Found ourselves so check if there is only one user of this
298 // copy and keep on searching for a better copy if so.
299 bool ignore_self = true;
300 x = n->in(k);
301 DUIterator_Fast imax, i = x->fast_outs(imax);
302 Node* first = x->fast_out(i); i++;
303 while (i < imax && ignore_self) {
304 Node* use = x->fast_out(i); i++;
305 if (use != first) ignore_self = false;
306 }
307 if (ignore_self) continue;
308 }
309
310 Node *vv = value[reg];
311 if (n_regs > 1) { // Doubles and vectors check for aligned-adjacent set
312 uint last = (n_regs-1); // Looking for the last part of a set
313 if ((reg&last) != last) continue; // Wrong part of a set
314 if (!register_contains_value(vv, reg, n_regs, value)) continue; // Different value
315 }
316 if( vv == val || // Got a direct hit?
317 (t && vv && vv->bottom_type() == t && vv->is_Mach() &&
318 vv->as_Mach()->rule() == val->as_Mach()->rule()) ) { // Or same constant?
319 assert( !n->is_Phi(), "cannot change registers at a Phi so easily" );
320 if( OptoReg::is_stack(nk_reg) || // CISC-loading from stack OR
321 OptoReg::is_reg(reg) || // turning into a register use OR
322 regnd[reg]->outcnt()==1 ) { // last use of a spill-load turns into a CISC use
323 blk_adjust += use_prior_register(n,k,regnd[reg],current_block,value,regnd);
324 if( n->in(k) == regnd[reg] ) // Success! Quit trying
325 return blk_adjust;
326 } // End of if not degrading to a stack
327 } // End of if found value in another register
328 } // End of scan all machine registers
329 return blk_adjust;
330 }
331
332
333 //
334 // Check if nreg already contains the constant value val. Normal copy
335 // elimination doesn't doesn't work on constants because multiple
336 // nodes can represent the same constant so the type and rule of the
337 // MachNode must be checked to ensure equivalence.
338 //
339 bool PhaseChaitin::eliminate_copy_of_constant(Node* val, Node* n,
340 Block *current_block,
341 Node_List& value, Node_List& regnd,
342 OptoReg::Name nreg, OptoReg::Name nreg2) {
343 if (value[nreg] != val && val->is_Con() &&
344 value[nreg] != NULL && value[nreg]->is_Con() &&
345 (nreg2 == OptoReg::Bad || value[nreg] == value[nreg2]) &&
346 value[nreg]->bottom_type() == val->bottom_type() &&
347 value[nreg]->as_Mach()->rule() == val->as_Mach()->rule()) {
348 // This code assumes that two MachNodes representing constants
349 // which have the same rule and the same bottom type will produce
350 // identical effects into a register. This seems like it must be
351 // objectively true unless there are hidden inputs to the nodes
352 // but if that were to change this code would need to updated.
353 // Since they are equivalent the second one if redundant and can
354 // be removed.
355 //
356 // n will be replaced with the old value but n might have
357 // kills projections associated with it so remove them now so that
358 // yank_if_dead will be able to eliminate the copy once the uses
359 // have been transferred to the old[value].
360 for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax; i++) {
361 Node* use = n->fast_out(i);
362 if (use->is_Proj() && use->outcnt() == 0) {
363 // Kill projections have no users and one input
364 use->set_req(0, C->top());
365 yank_if_dead(use, current_block, &value, ®nd);
366 --i; --imax;
367 }
368 }
369 _post_alloc++;
370 return true;
371 }
372 return false;
373 }
374
375
376 //------------------------------post_allocate_copy_removal---------------------
377 // Post-Allocation peephole copy removal. We do this in 1 pass over the
378 // basic blocks. We maintain a mapping of registers to Nodes (an array of
379 // Nodes indexed by machine register or stack slot number). NULL means that a
380 // register is not mapped to any Node. We can (want to have!) have several
381 // registers map to the same Node. We walk forward over the instructions
382 // updating the mapping as we go. At merge points we force a NULL if we have
383 // to merge 2 different Nodes into the same register. Phi functions will give
384 // us a new Node if there is a proper value merging. Since the blocks are
385 // arranged in some RPO, we will visit all parent blocks before visiting any
386 // successor blocks (except at loops).
387 //
388 // If we find a Copy we look to see if the Copy's source register is a stack
389 // slot and that value has already been loaded into some machine register; if
390 // so we use machine register directly. This turns a Load into a reg-reg
391 // Move. We also look for reloads of identical constants.
392 //
393 // When we see a use from a reg-reg Copy, we will attempt to use the copy's
394 // source directly and make the copy go dead.
395 void PhaseChaitin::post_allocate_copy_removal() {
396 NOT_PRODUCT( Compile::TracePhase t3("postAllocCopyRemoval", &_t_postAllocCopyRemoval, TimeCompiler); )
397 ResourceMark rm;
398
399 // Need a mapping from basic block Node_Lists. We need a Node_List to
400 // map from register number to value-producing Node.
401 Node_List **blk2value = NEW_RESOURCE_ARRAY( Node_List *, _cfg._num_blocks+1);
402 memset( blk2value, 0, sizeof(Node_List*)*(_cfg._num_blocks+1) );
403 // Need a mapping from basic block Node_Lists. We need a Node_List to
404 // map from register number to register-defining Node.
405 Node_List **blk2regnd = NEW_RESOURCE_ARRAY( Node_List *, _cfg._num_blocks+1);
406 memset( blk2regnd, 0, sizeof(Node_List*)*(_cfg._num_blocks+1) );
407
408 // We keep unused Node_Lists on a free_list to avoid wasting
409 // memory.
410 GrowableArray<Node_List*> free_list = GrowableArray<Node_List*>(16);
411
412 // For all blocks
413 for( uint i = 0; i < _cfg._num_blocks; i++ ) {
414 uint j;
415 Block *b = _cfg._blocks[i];
416
417 // Count of Phis in block
418 uint phi_dex;
419 for( phi_dex = 1; phi_dex < b->_nodes.size(); phi_dex++ ) {
420 Node *phi = b->_nodes[phi_dex];
421 if( !phi->is_Phi() )
422 break;
423 }
424
425 // If any predecessor has not been visited, we do not know the state
426 // of registers at the start. Check for this, while updating copies
427 // along Phi input edges
428 bool missing_some_inputs = false;
429 Block *freed = NULL;
430 for( j = 1; j < b->num_preds(); j++ ) {
431 Block *pb = _cfg._bbs[b->pred(j)->_idx];
432 // Remove copies along phi edges
433 for( uint k=1; k<phi_dex; k++ )
434 elide_copy( b->_nodes[k], j, b, *blk2value[pb->_pre_order], *blk2regnd[pb->_pre_order], false );
435 if( blk2value[pb->_pre_order] ) { // Have a mapping on this edge?
436 // See if this predecessor's mappings have been used by everybody
437 // who wants them. If so, free 'em.
438 uint k;
439 for( k=0; k<pb->_num_succs; k++ ) {
440 Block *pbsucc = pb->_succs[k];
441 if( !blk2value[pbsucc->_pre_order] && pbsucc != b )
442 break; // Found a future user
443 }
444 if( k >= pb->_num_succs ) { // No more uses, free!
445 freed = pb; // Record last block freed
446 free_list.push(blk2value[pb->_pre_order]);
447 free_list.push(blk2regnd[pb->_pre_order]);
448 }
449 } else { // This block has unvisited (loopback) inputs
450 missing_some_inputs = true;
451 }
452 }
453
454
455 // Extract Node_List mappings. If 'freed' is non-zero, we just popped
456 // 'freed's blocks off the list
457 Node_List ®nd = *(free_list.is_empty() ? new Node_List() : free_list.pop());
458 Node_List &value = *(free_list.is_empty() ? new Node_List() : free_list.pop());
459 assert( !freed || blk2value[freed->_pre_order] == &value, "" );
460 value.map(_max_reg,NULL);
461 regnd.map(_max_reg,NULL);
462 // Set mappings as OUR mappings
463 blk2value[b->_pre_order] = &value;
464 blk2regnd[b->_pre_order] = ®nd;
465
466 // Initialize value & regnd for this block
467 if( missing_some_inputs ) {
468 // Some predecessor has not yet been visited; zap map to empty
469 for( uint k = 0; k < (uint)_max_reg; k++ ) {
470 value.map(k,NULL);
471 regnd.map(k,NULL);
472 }
473 } else {
474 if( !freed ) { // Didn't get a freebie prior block
475 // Must clone some data
476 freed = _cfg._bbs[b->pred(1)->_idx];
477 Node_List &f_value = *blk2value[freed->_pre_order];
478 Node_List &f_regnd = *blk2regnd[freed->_pre_order];
479 for( uint k = 0; k < (uint)_max_reg; k++ ) {
480 value.map(k,f_value[k]);
481 regnd.map(k,f_regnd[k]);
482 }
483 }
484 // Merge all inputs together, setting to NULL any conflicts.
485 for( j = 1; j < b->num_preds(); j++ ) {
486 Block *pb = _cfg._bbs[b->pred(j)->_idx];
487 if( pb == freed ) continue; // Did self already via freelist
488 Node_List &p_regnd = *blk2regnd[pb->_pre_order];
489 for( uint k = 0; k < (uint)_max_reg; k++ ) {
490 if( regnd[k] != p_regnd[k] ) { // Conflict on reaching defs?
491 value.map(k,NULL); // Then no value handy
492 regnd.map(k,NULL);
493 }
494 }
495 }
496 }
497
498 // For all Phi's
499 for( j = 1; j < phi_dex; j++ ) {
500 uint k;
501 Node *phi = b->_nodes[j];
502 uint pidx = n2lidx(phi);
503 OptoReg::Name preg = lrgs(n2lidx(phi)).reg();
504
505 // Remove copies remaining on edges. Check for junk phi.
506 Node *u = NULL;
507 for( k=1; k<phi->req(); k++ ) {
508 Node *x = phi->in(k);
509 if( phi != x && u != x ) // Found a different input
510 u = u ? NodeSentinel : x; // Capture unique input, or NodeSentinel for 2nd input
511 }
512 if( u != NodeSentinel ) { // Junk Phi. Remove
513 b->_nodes.remove(j--); phi_dex--;
514 _cfg._bbs.map(phi->_idx,NULL);
515 phi->replace_by(u);
516 phi->disconnect_inputs(NULL);
517 continue;
518 }
519 // Note that if value[pidx] exists, then we merged no new values here
520 // and the phi is useless. This can happen even with the above phi
521 // removal for complex flows. I cannot keep the better known value here
522 // because locally the phi appears to define a new merged value. If I
523 // keep the better value then a copy of the phi, being unable to use the
524 // global flow analysis, can't "peek through" the phi to the original
525 // reaching value and so will act like it's defining a new value. This
526 // can lead to situations where some uses are from the old and some from
527 // the new values. Not illegal by itself but throws the over-strong
528 // assert in scheduling.
529 if( pidx ) {
530 value.map(preg,phi);
531 regnd.map(preg,phi);
532 int n_regs = RegMask::num_registers(phi->ideal_reg());
533 for (int l = 1; l < n_regs; l++) {
534 OptoReg::Name preg_lo = OptoReg::add(preg,-l);
535 value.map(preg_lo,phi);
536 regnd.map(preg_lo,phi);
537 }
538 }
539 }
540
541 // For all remaining instructions
542 for( j = phi_dex; j < b->_nodes.size(); j++ ) {
543 Node *n = b->_nodes[j];
544
545 if( n->outcnt() == 0 && // Dead?
546 n != C->top() && // (ignore TOP, it has no du info)
547 !n->is_Proj() ) { // fat-proj kills
548 j -= yank_if_dead(n,b,&value,®nd);
549 continue;
550 }
551
552 // Improve reaching-def info. Occasionally post-alloc's liveness gives
553 // up (at loop backedges, because we aren't doing a full flow pass).
554 // The presence of a live use essentially asserts that the use's def is
555 // alive and well at the use (or else the allocator fubar'd). Take
556 // advantage of this info to set a reaching def for the use-reg.
557 uint k;
558 for( k = 1; k < n->req(); k++ ) {
559 Node *def = n->in(k); // n->in(k) is a USE; def is the DEF for this USE
560 guarantee(def != NULL, "no disconnected nodes at this point");
561 uint useidx = n2lidx(def); // useidx is the live range index for this USE
562
563 if( useidx ) {
564 OptoReg::Name ureg = lrgs(useidx).reg();
565 if( !value[ureg] ) {
566 int idx; // Skip occasional useless copy
567 while( (idx=def->is_Copy()) != 0 &&
568 def->in(idx) != NULL && // NULL should not happen
569 ureg == lrgs(n2lidx(def->in(idx))).reg() )
570 def = def->in(idx);
571 Node *valdef = skip_copies(def); // tighten up val through non-useless copies
572 value.map(ureg,valdef); // record improved reaching-def info
573 regnd.map(ureg, def);
574 // Record other half of doubles
575 uint def_ideal_reg = def->ideal_reg();
576 int n_regs = RegMask::num_registers(def_ideal_reg);
577 for (int l = 1; l < n_regs; l++) {
578 OptoReg::Name ureg_lo = OptoReg::add(ureg,-l);
579 if (!value[ureg_lo] &&
580 (!RegMask::can_represent(ureg_lo) ||
581 lrgs(useidx).mask().Member(ureg_lo))) { // Nearly always adjacent
582 value.map(ureg_lo,valdef); // record improved reaching-def info
583 regnd.map(ureg_lo, def);
584 }
585 }
586 }
587 }
588 }
589
590 const uint two_adr = n->is_Mach() ? n->as_Mach()->two_adr() : 0;
591
592 // Remove copies along input edges
593 for( k = 1; k < n->req(); k++ )
594 j -= elide_copy( n, k, b, value, regnd, two_adr!=k );
595
596 // Unallocated Nodes define no registers
597 uint lidx = n2lidx(n);
598 if( !lidx ) continue;
599
600 // Update the register defined by this instruction
601 OptoReg::Name nreg = lrgs(lidx).reg();
602 // Skip through all copies to the _value_ being defined.
603 // Do not change from int to pointer
604 Node *val = skip_copies(n);
605
606 // Clear out a dead definition before starting so that the
607 // elimination code doesn't have to guard against it. The
608 // definition could in fact be a kill projection with a count of
609 // 0 which is safe but since those are uninteresting for copy
610 // elimination just delete them as well.
611 if (regnd[nreg] != NULL && regnd[nreg]->outcnt() == 0) {
612 regnd.map(nreg, NULL);
613 value.map(nreg, NULL);
614 }
615
616 uint n_ideal_reg = n->ideal_reg();
617 int n_regs = RegMask::num_registers(n_ideal_reg);
618 if (n_regs == 1) {
619 // If Node 'n' does not change the value mapped by the register,
620 // then 'n' is a useless copy. Do not update the register->node
621 // mapping so 'n' will go dead.
622 if( value[nreg] != val ) {
623 if (eliminate_copy_of_constant(val, n, b, value, regnd, nreg, OptoReg::Bad)) {
624 j -= replace_and_yank_if_dead(n, nreg, b, value, regnd);
625 } else {
626 // Update the mapping: record new Node defined by the register
627 regnd.map(nreg,n);
628 // Update mapping for defined *value*, which is the defined
629 // Node after skipping all copies.
630 value.map(nreg,val);
631 }
632 } else if( !may_be_copy_of_callee(n) ) {
633 assert( n->is_Copy(), "" );
634 j -= replace_and_yank_if_dead(n, nreg, b, value, regnd);
635 }
636 } else if (RegMask::is_vector(n_ideal_reg)) {
637 // If Node 'n' does not change the value mapped by the register,
638 // then 'n' is a useless copy. Do not update the register->node
639 // mapping so 'n' will go dead.
640 if (!register_contains_value(val, nreg, n_regs, value)) {
641 // Update the mapping: record new Node defined by the register
642 regnd.map(nreg,n);
643 // Update mapping for defined *value*, which is the defined
644 // Node after skipping all copies.
645 value.map(nreg,val);
646 for (int l = 1; l < n_regs; l++) {
647 OptoReg::Name nreg_lo = OptoReg::add(nreg,-l);
648 regnd.map(nreg_lo, n );
649 value.map(nreg_lo,val);
650 }
651 } else if (n->is_Copy()) {
652 // Note: vector can't be constant and can't be copy of calee.
653 j -= replace_and_yank_if_dead(n, nreg, b, value, regnd);
654 }
655 } else {
656 // If the value occupies a register pair, record same info
657 // in both registers.
658 OptoReg::Name nreg_lo = OptoReg::add(nreg,-1);
659 if( RegMask::can_represent(nreg_lo) && // Either a spill slot, or
660 !lrgs(lidx).mask().Member(nreg_lo) ) { // Nearly always adjacent
661 // Sparc occasionally has non-adjacent pairs.
662 // Find the actual other value
663 RegMask tmp = lrgs(lidx).mask();
664 tmp.Remove(nreg);
665 nreg_lo = tmp.find_first_elem();
666 }
667 if( value[nreg] != val || value[nreg_lo] != val ) {
668 if (eliminate_copy_of_constant(val, n, b, value, regnd, nreg, nreg_lo)) {
669 j -= replace_and_yank_if_dead(n, nreg, b, value, regnd);
670 } else {
671 regnd.map(nreg , n );
672 regnd.map(nreg_lo, n );
673 value.map(nreg ,val);
674 value.map(nreg_lo,val);
675 }
676 } else if( !may_be_copy_of_callee(n) ) {
677 assert( n->is_Copy(), "" );
678 j -= replace_and_yank_if_dead(n, nreg, b, value, regnd);
679 }
680 }
681
682 // Fat projections kill many registers
683 if( n_ideal_reg == MachProjNode::fat_proj ) {
684 RegMask rm = n->out_RegMask();
685 // wow, what an expensive iterator...
686 nreg = rm.find_first_elem();
687 while( OptoReg::is_valid(nreg)) {
688 rm.Remove(nreg);
689 value.map(nreg,n);
690 regnd.map(nreg,n);
691 nreg = rm.find_first_elem();
692 }
693 }
694
695 } // End of for all instructions in the block
696
697 } // End for all blocks
698 }