postaloc.cpp revision 1915:2f644f85485d
1/* 2 * Copyright (c) 1998, 2010, 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 kind does not requires two registers 31static bool is_single_register(uint x) { 32#ifdef _LP64 33 return (x != Op_RegD && x != Op_RegL && x != Op_RegP); 34#else 35 return (x != Op_RegD && x != Op_RegL); 36#endif 37} 38 39//---------------------------may_be_copy_of_callee----------------------------- 40// Check to see if we can possibly be a copy of a callee-save value. 41bool PhaseChaitin::may_be_copy_of_callee( Node *def ) const { 42 // Short circuit if there are no callee save registers 43 if (_matcher.number_of_saved_registers() == 0) return false; 44 45 // Expect only a spill-down and reload on exit for callee-save spills. 46 // Chains of copies cannot be deep. 47 // 5008997 - This is wishful thinking. Register allocator seems to 48 // be splitting live ranges for callee save registers to such 49 // an extent that in large methods the chains can be very long 50 // (50+). The conservative answer is to return true if we don't 51 // know as this prevents optimizations from occurring. 52 53 const int limit = 60; 54 int i; 55 for( i=0; i < limit; i++ ) { 56 if( def->is_Proj() && def->in(0)->is_Start() && 57 _matcher.is_save_on_entry(lrgs(n2lidx(def)).reg()) ) 58 return true; // Direct use of callee-save proj 59 if( def->is_Copy() ) // Copies carry value through 60 def = def->in(def->is_Copy()); 61 else if( def->is_Phi() ) // Phis can merge it from any direction 62 def = def->in(1); 63 else 64 break; 65 guarantee(def != NULL, "must not resurrect dead copy"); 66 } 67 // If we reached the end and didn't find a callee save proj 68 // then this may be a callee save proj so we return true 69 // as the conservative answer. If we didn't reach then end 70 // we must have discovered that it was not a callee save 71 // else we would have returned. 72 return i == limit; 73} 74 75 76 77//------------------------------yank_if_dead----------------------------------- 78// Removed an edge from 'old'. Yank if dead. Return adjustment counts to 79// iterators in the current block. 80int PhaseChaitin::yank_if_dead( Node *old, Block *current_block, Node_List *value, Node_List *regnd ) { 81 int blk_adjust=0; 82 while (old->outcnt() == 0 && old != C->top()) { 83 Block *oldb = _cfg._bbs[old->_idx]; 84 oldb->find_remove(old); 85 // Count 1 if deleting an instruction from the current block 86 if( oldb == current_block ) blk_adjust++; 87 _cfg._bbs.map(old->_idx,NULL); 88 OptoReg::Name old_reg = lrgs(n2lidx(old)).reg(); 89 if( regnd && (*regnd)[old_reg]==old ) { // Instruction is currently available? 90 value->map(old_reg,NULL); // Yank from value/regnd maps 91 regnd->map(old_reg,NULL); // This register's value is now unknown 92 } 93 assert(old->req() <= 2, "can't handle more inputs"); 94 Node *tmp = old->req() > 1 ? old->in(1) : NULL; 95 old->disconnect_inputs(NULL); 96 if( !tmp ) break; 97 old = tmp; 98 } 99 return blk_adjust; 100} 101 102//------------------------------use_prior_register----------------------------- 103// Use the prior value instead of the current value, in an effort to make 104// the current value go dead. Return block iterator adjustment, in case 105// we yank some instructions from this block. 106int PhaseChaitin::use_prior_register( Node *n, uint idx, Node *def, Block *current_block, Node_List &value, Node_List ®nd ) { 107 // No effect? 108 if( def == n->in(idx) ) return 0; 109 // Def is currently dead and can be removed? Do not resurrect 110 if( def->outcnt() == 0 ) return 0; 111 112 // Not every pair of physical registers are assignment compatible, 113 // e.g. on sparc floating point registers are not assignable to integer 114 // registers. 115 const LRG &def_lrg = lrgs(n2lidx(def)); 116 OptoReg::Name def_reg = def_lrg.reg(); 117 const RegMask &use_mask = n->in_RegMask(idx); 118 bool can_use = ( RegMask::can_represent(def_reg) ? (use_mask.Member(def_reg) != 0) 119 : (use_mask.is_AllStack() != 0)); 120 // Check for a copy to or from a misaligned pair. 121 can_use = can_use && !use_mask.is_misaligned_Pair() && !def_lrg.mask().is_misaligned_Pair(); 122 123 if (!can_use) 124 return 0; 125 126 // Capture the old def in case it goes dead... 127 Node *old = n->in(idx); 128 129 // Save-on-call copies can only be elided if the entire copy chain can go 130 // away, lest we get the same callee-save value alive in 2 locations at 131 // once. We check for the obvious trivial case here. Although it can 132 // sometimes be elided with cooperation outside our scope, here we will just 133 // miss the opportunity. :-( 134 if( may_be_copy_of_callee(def) ) { 135 if( old->outcnt() > 1 ) return 0; // We're the not last user 136 int idx = old->is_Copy(); 137 assert( idx, "chain of copies being removed" ); 138 Node *old2 = old->in(idx); // Chain of copies 139 if( old2->outcnt() > 1 ) return 0; // old is not the last user 140 int idx2 = old2->is_Copy(); 141 if( !idx2 ) return 0; // Not a chain of 2 copies 142 if( def != old2->in(idx2) ) return 0; // Chain of exactly 2 copies 143 } 144 145 // Use the new def 146 n->set_req(idx,def); 147 _post_alloc++; 148 149 // Is old def now dead? We successfully yanked a copy? 150 return yank_if_dead(old,current_block,&value,®nd); 151} 152 153 154//------------------------------skip_copies------------------------------------ 155// Skip through any number of copies (that don't mod oop-i-ness) 156Node *PhaseChaitin::skip_copies( Node *c ) { 157 int idx = c->is_Copy(); 158 uint is_oop = lrgs(n2lidx(c))._is_oop; 159 while (idx != 0) { 160 guarantee(c->in(idx) != NULL, "must not resurrect dead copy"); 161 if (lrgs(n2lidx(c->in(idx)))._is_oop != is_oop) 162 break; // casting copy, not the same value 163 c = c->in(idx); 164 idx = c->is_Copy(); 165 } 166 return c; 167} 168 169//------------------------------elide_copy------------------------------------- 170// Remove (bypass) copies along Node n, edge k. 171int PhaseChaitin::elide_copy( Node *n, int k, Block *current_block, Node_List &value, Node_List ®nd, bool can_change_regs ) { 172 int blk_adjust = 0; 173 174 uint nk_idx = n2lidx(n->in(k)); 175 OptoReg::Name nk_reg = lrgs(nk_idx ).reg(); 176 177 // Remove obvious same-register copies 178 Node *x = n->in(k); 179 int idx; 180 while( (idx=x->is_Copy()) != 0 ) { 181 Node *copy = x->in(idx); 182 guarantee(copy != NULL, "must not resurrect dead copy"); 183 if( lrgs(n2lidx(copy)).reg() != nk_reg ) break; 184 blk_adjust += use_prior_register(n,k,copy,current_block,value,regnd); 185 if( n->in(k) != copy ) break; // Failed for some cutout? 186 x = copy; // Progress, try again 187 } 188 189 // Phis and 2-address instructions cannot change registers so easily - their 190 // outputs must match their input. 191 if( !can_change_regs ) 192 return blk_adjust; // Only check stupid copies! 193 194 // Loop backedges won't have a value-mapping yet 195 if( &value == NULL ) return blk_adjust; 196 197 // Skip through all copies to the _value_ being used. Do not change from 198 // int to pointer. This attempts to jump through a chain of copies, where 199 // intermediate copies might be illegal, i.e., value is stored down to stack 200 // then reloaded BUT survives in a register the whole way. 201 Node *val = skip_copies(n->in(k)); 202 203 if (val == x && nk_idx != 0 && 204 regnd[nk_reg] != NULL && regnd[nk_reg] != x && 205 n2lidx(x) == n2lidx(regnd[nk_reg])) { 206 // When rematerialzing nodes and stretching lifetimes, the 207 // allocator will reuse the original def for multidef LRG instead 208 // of the current reaching def because it can't know it's safe to 209 // do so. After allocation completes if they are in the same LRG 210 // then it should use the current reaching def instead. 211 n->set_req(k, regnd[nk_reg]); 212 blk_adjust += yank_if_dead(val, current_block, &value, ®nd); 213 val = skip_copies(n->in(k)); 214 } 215 216 if( val == x ) return blk_adjust; // No progress? 217 218 bool single = is_single_register(val->ideal_reg()); 219 uint val_idx = n2lidx(val); 220 OptoReg::Name val_reg = lrgs(val_idx).reg(); 221 222 // See if it happens to already be in the correct register! 223 // (either Phi's direct register, or the common case of the name 224 // never-clobbered original-def register) 225 if( value[val_reg] == val && 226 // Doubles check both halves 227 ( single || value[val_reg-1] == val ) ) { 228 blk_adjust += use_prior_register(n,k,regnd[val_reg],current_block,value,regnd); 229 if( n->in(k) == regnd[val_reg] ) // Success! Quit trying 230 return blk_adjust; 231 } 232 233 // See if we can skip the copy by changing registers. Don't change from 234 // using a register to using the stack unless we know we can remove a 235 // copy-load. Otherwise we might end up making a pile of Intel cisc-spill 236 // ops reading from memory instead of just loading once and using the 237 // register. 238 239 // Also handle duplicate copies here. 240 const Type *t = val->is_Con() ? val->bottom_type() : NULL; 241 242 // Scan all registers to see if this value is around already 243 for( uint reg = 0; reg < (uint)_max_reg; reg++ ) { 244 if (reg == (uint)nk_reg) { 245 // Found ourselves so check if there is only one user of this 246 // copy and keep on searching for a better copy if so. 247 bool ignore_self = true; 248 x = n->in(k); 249 DUIterator_Fast imax, i = x->fast_outs(imax); 250 Node* first = x->fast_out(i); i++; 251 while (i < imax && ignore_self) { 252 Node* use = x->fast_out(i); i++; 253 if (use != first) ignore_self = false; 254 } 255 if (ignore_self) continue; 256 } 257 258 Node *vv = value[reg]; 259 if( !single ) { // Doubles check for aligned-adjacent pair 260 if( (reg&1)==0 ) continue; // Wrong half of a pair 261 if( vv != value[reg-1] ) continue; // Not a complete pair 262 } 263 if( vv == val || // Got a direct hit? 264 (t && vv && vv->bottom_type() == t && vv->is_Mach() && 265 vv->as_Mach()->rule() == val->as_Mach()->rule()) ) { // Or same constant? 266 assert( !n->is_Phi(), "cannot change registers at a Phi so easily" ); 267 if( OptoReg::is_stack(nk_reg) || // CISC-loading from stack OR 268 OptoReg::is_reg(reg) || // turning into a register use OR 269 regnd[reg]->outcnt()==1 ) { // last use of a spill-load turns into a CISC use 270 blk_adjust += use_prior_register(n,k,regnd[reg],current_block,value,regnd); 271 if( n->in(k) == regnd[reg] ) // Success! Quit trying 272 return blk_adjust; 273 } // End of if not degrading to a stack 274 } // End of if found value in another register 275 } // End of scan all machine registers 276 return blk_adjust; 277} 278 279 280// 281// Check if nreg already contains the constant value val. Normal copy 282// elimination doesn't doesn't work on constants because multiple 283// nodes can represent the same constant so the type and rule of the 284// MachNode must be checked to ensure equivalence. 285// 286bool PhaseChaitin::eliminate_copy_of_constant(Node* val, Node* n, 287 Block *current_block, 288 Node_List& value, Node_List& regnd, 289 OptoReg::Name nreg, OptoReg::Name nreg2) { 290 if (value[nreg] != val && val->is_Con() && 291 value[nreg] != NULL && value[nreg]->is_Con() && 292 (nreg2 == OptoReg::Bad || value[nreg] == value[nreg2]) && 293 value[nreg]->bottom_type() == val->bottom_type() && 294 value[nreg]->as_Mach()->rule() == val->as_Mach()->rule()) { 295 // This code assumes that two MachNodes representing constants 296 // which have the same rule and the same bottom type will produce 297 // identical effects into a register. This seems like it must be 298 // objectively true unless there are hidden inputs to the nodes 299 // but if that were to change this code would need to updated. 300 // Since they are equivalent the second one if redundant and can 301 // be removed. 302 // 303 // n will be replaced with the old value but n might have 304 // kills projections associated with it so remove them now so that 305 // yank_if_dead will be able to eliminate the copy once the uses 306 // have been transferred to the old[value]. 307 for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax; i++) { 308 Node* use = n->fast_out(i); 309 if (use->is_Proj() && use->outcnt() == 0) { 310 // Kill projections have no users and one input 311 use->set_req(0, C->top()); 312 yank_if_dead(use, current_block, &value, ®nd); 313 --i; --imax; 314 } 315 } 316 _post_alloc++; 317 return true; 318 } 319 return false; 320} 321 322 323//------------------------------post_allocate_copy_removal--------------------- 324// Post-Allocation peephole copy removal. We do this in 1 pass over the 325// basic blocks. We maintain a mapping of registers to Nodes (an array of 326// Nodes indexed by machine register or stack slot number). NULL means that a 327// register is not mapped to any Node. We can (want to have!) have several 328// registers map to the same Node. We walk forward over the instructions 329// updating the mapping as we go. At merge points we force a NULL if we have 330// to merge 2 different Nodes into the same register. Phi functions will give 331// us a new Node if there is a proper value merging. Since the blocks are 332// arranged in some RPO, we will visit all parent blocks before visiting any 333// successor blocks (except at loops). 334// 335// If we find a Copy we look to see if the Copy's source register is a stack 336// slot and that value has already been loaded into some machine register; if 337// so we use machine register directly. This turns a Load into a reg-reg 338// Move. We also look for reloads of identical constants. 339// 340// When we see a use from a reg-reg Copy, we will attempt to use the copy's 341// source directly and make the copy go dead. 342void PhaseChaitin::post_allocate_copy_removal() { 343 NOT_PRODUCT( Compile::TracePhase t3("postAllocCopyRemoval", &_t_postAllocCopyRemoval, TimeCompiler); ) 344 ResourceMark rm; 345 346 // Need a mapping from basic block Node_Lists. We need a Node_List to 347 // map from register number to value-producing Node. 348 Node_List **blk2value = NEW_RESOURCE_ARRAY( Node_List *, _cfg._num_blocks+1); 349 memset( blk2value, 0, sizeof(Node_List*)*(_cfg._num_blocks+1) ); 350 // Need a mapping from basic block Node_Lists. We need a Node_List to 351 // map from register number to register-defining Node. 352 Node_List **blk2regnd = NEW_RESOURCE_ARRAY( Node_List *, _cfg._num_blocks+1); 353 memset( blk2regnd, 0, sizeof(Node_List*)*(_cfg._num_blocks+1) ); 354 355 // We keep unused Node_Lists on a free_list to avoid wasting 356 // memory. 357 GrowableArray<Node_List*> free_list = GrowableArray<Node_List*>(16); 358 359 // For all blocks 360 for( uint i = 0; i < _cfg._num_blocks; i++ ) { 361 uint j; 362 Block *b = _cfg._blocks[i]; 363 364 // Count of Phis in block 365 uint phi_dex; 366 for( phi_dex = 1; phi_dex < b->_nodes.size(); phi_dex++ ) { 367 Node *phi = b->_nodes[phi_dex]; 368 if( !phi->is_Phi() ) 369 break; 370 } 371 372 // If any predecessor has not been visited, we do not know the state 373 // of registers at the start. Check for this, while updating copies 374 // along Phi input edges 375 bool missing_some_inputs = false; 376 Block *freed = NULL; 377 for( j = 1; j < b->num_preds(); j++ ) { 378 Block *pb = _cfg._bbs[b->pred(j)->_idx]; 379 // Remove copies along phi edges 380 for( uint k=1; k<phi_dex; k++ ) 381 elide_copy( b->_nodes[k], j, b, *blk2value[pb->_pre_order], *blk2regnd[pb->_pre_order], false ); 382 if( blk2value[pb->_pre_order] ) { // Have a mapping on this edge? 383 // See if this predecessor's mappings have been used by everybody 384 // who wants them. If so, free 'em. 385 uint k; 386 for( k=0; k<pb->_num_succs; k++ ) { 387 Block *pbsucc = pb->_succs[k]; 388 if( !blk2value[pbsucc->_pre_order] && pbsucc != b ) 389 break; // Found a future user 390 } 391 if( k >= pb->_num_succs ) { // No more uses, free! 392 freed = pb; // Record last block freed 393 free_list.push(blk2value[pb->_pre_order]); 394 free_list.push(blk2regnd[pb->_pre_order]); 395 } 396 } else { // This block has unvisited (loopback) inputs 397 missing_some_inputs = true; 398 } 399 } 400 401 402 // Extract Node_List mappings. If 'freed' is non-zero, we just popped 403 // 'freed's blocks off the list 404 Node_List ®nd = *(free_list.is_empty() ? new Node_List() : free_list.pop()); 405 Node_List &value = *(free_list.is_empty() ? new Node_List() : free_list.pop()); 406 assert( !freed || blk2value[freed->_pre_order] == &value, "" ); 407 value.map(_max_reg,NULL); 408 regnd.map(_max_reg,NULL); 409 // Set mappings as OUR mappings 410 blk2value[b->_pre_order] = &value; 411 blk2regnd[b->_pre_order] = ®nd; 412 413 // Initialize value & regnd for this block 414 if( missing_some_inputs ) { 415 // Some predecessor has not yet been visited; zap map to empty 416 for( uint k = 0; k < (uint)_max_reg; k++ ) { 417 value.map(k,NULL); 418 regnd.map(k,NULL); 419 } 420 } else { 421 if( !freed ) { // Didn't get a freebie prior block 422 // Must clone some data 423 freed = _cfg._bbs[b->pred(1)->_idx]; 424 Node_List &f_value = *blk2value[freed->_pre_order]; 425 Node_List &f_regnd = *blk2regnd[freed->_pre_order]; 426 for( uint k = 0; k < (uint)_max_reg; k++ ) { 427 value.map(k,f_value[k]); 428 regnd.map(k,f_regnd[k]); 429 } 430 } 431 // Merge all inputs together, setting to NULL any conflicts. 432 for( j = 1; j < b->num_preds(); j++ ) { 433 Block *pb = _cfg._bbs[b->pred(j)->_idx]; 434 if( pb == freed ) continue; // Did self already via freelist 435 Node_List &p_regnd = *blk2regnd[pb->_pre_order]; 436 for( uint k = 0; k < (uint)_max_reg; k++ ) { 437 if( regnd[k] != p_regnd[k] ) { // Conflict on reaching defs? 438 value.map(k,NULL); // Then no value handy 439 regnd.map(k,NULL); 440 } 441 } 442 } 443 } 444 445 // For all Phi's 446 for( j = 1; j < phi_dex; j++ ) { 447 uint k; 448 Node *phi = b->_nodes[j]; 449 uint pidx = n2lidx(phi); 450 OptoReg::Name preg = lrgs(n2lidx(phi)).reg(); 451 452 // Remove copies remaining on edges. Check for junk phi. 453 Node *u = NULL; 454 for( k=1; k<phi->req(); k++ ) { 455 Node *x = phi->in(k); 456 if( phi != x && u != x ) // Found a different input 457 u = u ? NodeSentinel : x; // Capture unique input, or NodeSentinel for 2nd input 458 } 459 if( u != NodeSentinel ) { // Junk Phi. Remove 460 b->_nodes.remove(j--); phi_dex--; 461 _cfg._bbs.map(phi->_idx,NULL); 462 phi->replace_by(u); 463 phi->disconnect_inputs(NULL); 464 continue; 465 } 466 // Note that if value[pidx] exists, then we merged no new values here 467 // and the phi is useless. This can happen even with the above phi 468 // removal for complex flows. I cannot keep the better known value here 469 // because locally the phi appears to define a new merged value. If I 470 // keep the better value then a copy of the phi, being unable to use the 471 // global flow analysis, can't "peek through" the phi to the original 472 // reaching value and so will act like it's defining a new value. This 473 // can lead to situations where some uses are from the old and some from 474 // the new values. Not illegal by itself but throws the over-strong 475 // assert in scheduling. 476 if( pidx ) { 477 value.map(preg,phi); 478 regnd.map(preg,phi); 479 OptoReg::Name preg_lo = OptoReg::add(preg,-1); 480 if( !is_single_register(phi->ideal_reg()) ) { 481 value.map(preg_lo,phi); 482 regnd.map(preg_lo,phi); 483 } 484 } 485 } 486 487 // For all remaining instructions 488 for( j = phi_dex; j < b->_nodes.size(); j++ ) { 489 Node *n = b->_nodes[j]; 490 491 if( n->outcnt() == 0 && // Dead? 492 n != C->top() && // (ignore TOP, it has no du info) 493 !n->is_Proj() ) { // fat-proj kills 494 j -= yank_if_dead(n,b,&value,®nd); 495 continue; 496 } 497 498 // Improve reaching-def info. Occasionally post-alloc's liveness gives 499 // up (at loop backedges, because we aren't doing a full flow pass). 500 // The presence of a live use essentially asserts that the use's def is 501 // alive and well at the use (or else the allocator fubar'd). Take 502 // advantage of this info to set a reaching def for the use-reg. 503 uint k; 504 for( k = 1; k < n->req(); k++ ) { 505 Node *def = n->in(k); // n->in(k) is a USE; def is the DEF for this USE 506 guarantee(def != NULL, "no disconnected nodes at this point"); 507 uint useidx = n2lidx(def); // useidx is the live range index for this USE 508 509 if( useidx ) { 510 OptoReg::Name ureg = lrgs(useidx).reg(); 511 if( !value[ureg] ) { 512 int idx; // Skip occasional useless copy 513 while( (idx=def->is_Copy()) != 0 && 514 def->in(idx) != NULL && // NULL should not happen 515 ureg == lrgs(n2lidx(def->in(idx))).reg() ) 516 def = def->in(idx); 517 Node *valdef = skip_copies(def); // tighten up val through non-useless copies 518 value.map(ureg,valdef); // record improved reaching-def info 519 regnd.map(ureg, def); 520 // Record other half of doubles 521 OptoReg::Name ureg_lo = OptoReg::add(ureg,-1); 522 if( !is_single_register(def->ideal_reg()) && 523 ( !RegMask::can_represent(ureg_lo) || 524 lrgs(useidx).mask().Member(ureg_lo) ) && // Nearly always adjacent 525 !value[ureg_lo] ) { 526 value.map(ureg_lo,valdef); // record improved reaching-def info 527 regnd.map(ureg_lo, def); 528 } 529 } 530 } 531 } 532 533 const uint two_adr = n->is_Mach() ? n->as_Mach()->two_adr() : 0; 534 535 // Remove copies along input edges 536 for( k = 1; k < n->req(); k++ ) 537 j -= elide_copy( n, k, b, value, regnd, two_adr!=k ); 538 539 // Unallocated Nodes define no registers 540 uint lidx = n2lidx(n); 541 if( !lidx ) continue; 542 543 // Update the register defined by this instruction 544 OptoReg::Name nreg = lrgs(lidx).reg(); 545 // Skip through all copies to the _value_ being defined. 546 // Do not change from int to pointer 547 Node *val = skip_copies(n); 548 549 // Clear out a dead definition before starting so that the 550 // elimination code doesn't have to guard against it. The 551 // definition could in fact be a kill projection with a count of 552 // 0 which is safe but since those are uninteresting for copy 553 // elimination just delete them as well. 554 if (regnd[nreg] != NULL && regnd[nreg]->outcnt() == 0) { 555 regnd.map(nreg, NULL); 556 value.map(nreg, NULL); 557 } 558 559 uint n_ideal_reg = n->ideal_reg(); 560 if( is_single_register(n_ideal_reg) ) { 561 // If Node 'n' does not change the value mapped by the register, 562 // then 'n' is a useless copy. Do not update the register->node 563 // mapping so 'n' will go dead. 564 if( value[nreg] != val ) { 565 if (eliminate_copy_of_constant(val, n, b, value, regnd, nreg, OptoReg::Bad)) { 566 j -= replace_and_yank_if_dead(n, nreg, b, value, regnd); 567 } else { 568 // Update the mapping: record new Node defined by the register 569 regnd.map(nreg,n); 570 // Update mapping for defined *value*, which is the defined 571 // Node after skipping all copies. 572 value.map(nreg,val); 573 } 574 } else if( !may_be_copy_of_callee(n) ) { 575 assert( n->is_Copy(), "" ); 576 j -= replace_and_yank_if_dead(n, nreg, b, value, regnd); 577 } 578 } else { 579 // If the value occupies a register pair, record same info 580 // in both registers. 581 OptoReg::Name nreg_lo = OptoReg::add(nreg,-1); 582 if( RegMask::can_represent(nreg_lo) && // Either a spill slot, or 583 !lrgs(lidx).mask().Member(nreg_lo) ) { // Nearly always adjacent 584 // Sparc occasionally has non-adjacent pairs. 585 // Find the actual other value 586 RegMask tmp = lrgs(lidx).mask(); 587 tmp.Remove(nreg); 588 nreg_lo = tmp.find_first_elem(); 589 } 590 if( value[nreg] != val || value[nreg_lo] != val ) { 591 if (eliminate_copy_of_constant(val, n, b, value, regnd, nreg, nreg_lo)) { 592 j -= replace_and_yank_if_dead(n, nreg, b, value, regnd); 593 } else { 594 regnd.map(nreg , n ); 595 regnd.map(nreg_lo, n ); 596 value.map(nreg ,val); 597 value.map(nreg_lo,val); 598 } 599 } else if( !may_be_copy_of_callee(n) ) { 600 assert( n->is_Copy(), "" ); 601 j -= replace_and_yank_if_dead(n, nreg, b, value, regnd); 602 } 603 } 604 605 // Fat projections kill many registers 606 if( n_ideal_reg == MachProjNode::fat_proj ) { 607 RegMask rm = n->out_RegMask(); 608 // wow, what an expensive iterator... 609 nreg = rm.find_first_elem(); 610 while( OptoReg::is_valid(nreg)) { 611 rm.Remove(nreg); 612 value.map(nreg,n); 613 regnd.map(nreg,n); 614 nreg = rm.find_first_elem(); 615 } 616 } 617 618 } // End of for all instructions in the block 619 620 } // End for all blocks 621} 622