1 /* 2 * Copyright (c) 1998, 2013, 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(_lrg_map.live_range_id(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.get_block_for_node(old); 82 oldb->find_remove(old); 83 // Count 1 if deleting an instruction from the current block 84 if (oldb == current_block) { 85 blk_adjust++; 86 } 87 _cfg.unmap_node_from_block(old); 88 OptoReg::Name old_reg = lrgs(_lrg_map.live_range_id(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 return blk_adjust; 94 } 95 96 #ifdef ASSERT 97 static bool expected_yanked_node(Node *old, Node *orig_old) { 98 // This code is expected only next original nodes: 99 // - load from constant table node which may have next data input nodes: 100 // MachConstantBase, MachTemp, MachSpillCopy 101 // - Phi nodes that are considered Junk 102 // - load constant node which may have next data input nodes: 103 // MachTemp, MachSpillCopy 104 // - MachSpillCopy 105 // - MachProj and Copy dead nodes 106 if (old->is_MachSpillCopy()) { 107 return true; 108 } else if (old->is_Con()) { 109 return true; 110 } else if (old->is_MachProj()) { // Dead kills projection of Con node 111 return (old == orig_old); 112 } else if (old->is_Copy()) { // Dead copy of a callee-save value 113 return (old == orig_old); 114 } else if (old->is_MachTemp()) { 115 return orig_old->is_Con(); 116 } else if (old->is_Phi()) { // Junk phi's 117 return true; 118 } else if (old->is_MachConstantBase()) { 119 return (orig_old->is_Con() && orig_old->is_MachConstant()); 120 } 121 return false; 122 } 123 #endif 124 125 //------------------------------yank_if_dead----------------------------------- 126 // Removed edges from 'old'. Yank if dead. Return adjustment counts to 127 // iterators in the current block. 128 int PhaseChaitin::yank_if_dead_recurse(Node *old, Node *orig_old, Block *current_block, 129 Node_List *value, Node_List *regnd) { 130 int blk_adjust=0; 131 if (old->outcnt() == 0 && old != C->top()) { 132 #ifdef ASSERT 133 if (!expected_yanked_node(old, orig_old)) { 134 tty->print_cr("=============================================="); 135 tty->print_cr("orig_old:"); 136 orig_old->dump(); 137 tty->print_cr("old:"); 138 old->dump(); 139 assert(false, "unexpected yanked node"); 140 } 141 if (old->is_Con()) 142 orig_old = old; // Reset to satisfy expected nodes checks. 143 #endif 144 blk_adjust += yank(old, current_block, value, regnd); 145 146 for (uint i = 1; i < old->req(); i++) { 147 Node* n = old->in(i); 148 if (n != NULL) { 149 old->set_req(i, NULL); 150 blk_adjust += yank_if_dead_recurse(n, orig_old, current_block, value, regnd); 151 } 152 } 153 // Disconnect control and remove precedence edges if any exist 154 old->disconnect_inputs(NULL, C); 155 } 156 return blk_adjust; 157 } 158 159 //------------------------------use_prior_register----------------------------- 160 // Use the prior value instead of the current value, in an effort to make 161 // the current value go dead. Return block iterator adjustment, in case 162 // we yank some instructions from this block. 163 int PhaseChaitin::use_prior_register( Node *n, uint idx, Node *def, Block *current_block, Node_List &value, Node_List ®nd ) { 164 // No effect? 165 if( def == n->in(idx) ) return 0; 166 // Def is currently dead and can be removed? Do not resurrect 167 if( def->outcnt() == 0 ) return 0; 168 169 // Not every pair of physical registers are assignment compatible, 170 // e.g. on sparc floating point registers are not assignable to integer 171 // registers. 172 const LRG &def_lrg = lrgs(_lrg_map.live_range_id(def)); 173 OptoReg::Name def_reg = def_lrg.reg(); 174 const RegMask &use_mask = n->in_RegMask(idx); 175 bool can_use = ( RegMask::can_represent(def_reg) ? (use_mask.Member(def_reg) != 0) 176 : (use_mask.is_AllStack() != 0)); 177 if (!RegMask::is_vector(def->ideal_reg())) { 178 // Check for a copy to or from a misaligned pair. 179 // It is workaround for a sparc with misaligned pairs. 180 can_use = can_use && !use_mask.is_misaligned_pair() && !def_lrg.mask().is_misaligned_pair(); 181 } 182 if (!can_use) 183 return 0; 184 185 // Capture the old def in case it goes dead... 186 Node *old = n->in(idx); 187 188 // Save-on-call copies can only be elided if the entire copy chain can go 189 // away, lest we get the same callee-save value alive in 2 locations at 190 // once. We check for the obvious trivial case here. Although it can 191 // sometimes be elided with cooperation outside our scope, here we will just 192 // miss the opportunity. :-( 193 if( may_be_copy_of_callee(def) ) { 194 if( old->outcnt() > 1 ) return 0; // We're the not last user 195 int idx = old->is_Copy(); 196 assert( idx, "chain of copies being removed" ); 197 Node *old2 = old->in(idx); // Chain of copies 198 if( old2->outcnt() > 1 ) return 0; // old is not the last user 199 int idx2 = old2->is_Copy(); 200 if( !idx2 ) return 0; // Not a chain of 2 copies 201 if( def != old2->in(idx2) ) return 0; // Chain of exactly 2 copies 202 } 203 204 // Use the new def 205 n->set_req(idx,def); 206 _post_alloc++; 207 208 // Is old def now dead? We successfully yanked a copy? 209 return yank_if_dead(old,current_block,&value,®nd); 210 } 211 212 213 //------------------------------skip_copies------------------------------------ 214 // Skip through any number of copies (that don't mod oop-i-ness) 215 Node *PhaseChaitin::skip_copies( Node *c ) { 216 int idx = c->is_Copy(); 217 uint is_oop = lrgs(_lrg_map.live_range_id(c))._is_oop; 218 while (idx != 0) { 219 guarantee(c->in(idx) != NULL, "must not resurrect dead copy"); 220 if (lrgs(_lrg_map.live_range_id(c->in(idx)))._is_oop != is_oop) { 221 break; // casting copy, not the same value 222 } 223 c = c->in(idx); 224 idx = c->is_Copy(); 225 } 226 return c; 227 } 228 229 //------------------------------elide_copy------------------------------------- 230 // Remove (bypass) copies along Node n, edge k. 231 int PhaseChaitin::elide_copy( Node *n, int k, Block *current_block, Node_List &value, Node_List ®nd, bool can_change_regs ) { 232 int blk_adjust = 0; 233 234 uint nk_idx = _lrg_map.live_range_id(n->in(k)); 235 OptoReg::Name nk_reg = lrgs(nk_idx).reg(); 236 237 // Remove obvious same-register copies 238 Node *x = n->in(k); 239 int idx; 240 while( (idx=x->is_Copy()) != 0 ) { 241 Node *copy = x->in(idx); 242 guarantee(copy != NULL, "must not resurrect dead copy"); 243 if(lrgs(_lrg_map.live_range_id(copy)).reg() != nk_reg) { 244 break; 245 } 246 blk_adjust += use_prior_register(n,k,copy,current_block,value,regnd); 247 if (n->in(k) != copy) { 248 break; // Failed for some cutout? 249 } 250 x = copy; // Progress, try again 251 } 252 253 // Phis and 2-address instructions cannot change registers so easily - their 254 // outputs must match their input. 255 if( !can_change_regs ) 256 return blk_adjust; // Only check stupid copies! 257 258 // Loop backedges won't have a value-mapping yet 259 if( &value == NULL ) return blk_adjust; 260 261 // Skip through all copies to the _value_ being used. Do not change from 262 // int to pointer. This attempts to jump through a chain of copies, where 263 // intermediate copies might be illegal, i.e., value is stored down to stack 264 // then reloaded BUT survives in a register the whole way. 265 Node *val = skip_copies(n->in(k)); 266 267 if (val == x && nk_idx != 0 && 268 regnd[nk_reg] != NULL && regnd[nk_reg] != x && 269 _lrg_map.live_range_id(x) == _lrg_map.live_range_id(regnd[nk_reg])) { 270 // When rematerialzing nodes and stretching lifetimes, the 271 // allocator will reuse the original def for multidef LRG instead 272 // of the current reaching def because it can't know it's safe to 273 // do so. After allocation completes if they are in the same LRG 274 // then it should use the current reaching def instead. 275 n->set_req(k, regnd[nk_reg]); 276 blk_adjust += yank_if_dead(val, current_block, &value, ®nd); 277 val = skip_copies(n->in(k)); 278 } 279 280 if (val == x) return blk_adjust; // No progress? 281 282 int n_regs = RegMask::num_registers(val->ideal_reg()); 283 uint val_idx = _lrg_map.live_range_id(val); 284 OptoReg::Name val_reg = lrgs(val_idx).reg(); 285 286 // See if it happens to already be in the correct register! 287 // (either Phi's direct register, or the common case of the name 288 // never-clobbered original-def register) 289 if (register_contains_value(val, val_reg, n_regs, value)) { 290 blk_adjust += use_prior_register(n,k,regnd[val_reg],current_block,value,regnd); 291 if( n->in(k) == regnd[val_reg] ) // Success! Quit trying 292 return blk_adjust; 293 } 294 295 // See if we can skip the copy by changing registers. Don't change from 296 // using a register to using the stack unless we know we can remove a 297 // copy-load. Otherwise we might end up making a pile of Intel cisc-spill 298 // ops reading from memory instead of just loading once and using the 299 // register. 300 301 // Also handle duplicate copies here. 302 const Type *t = val->is_Con() ? val->bottom_type() : NULL; 303 304 // Scan all registers to see if this value is around already 305 for( uint reg = 0; reg < (uint)_max_reg; reg++ ) { 306 if (reg == (uint)nk_reg) { 307 // Found ourselves so check if there is only one user of this 308 // copy and keep on searching for a better copy if so. 309 bool ignore_self = true; 310 x = n->in(k); 311 DUIterator_Fast imax, i = x->fast_outs(imax); 312 Node* first = x->fast_out(i); i++; 313 while (i < imax && ignore_self) { 314 Node* use = x->fast_out(i); i++; 315 if (use != first) ignore_self = false; 316 } 317 if (ignore_self) continue; 318 } 319 320 Node *vv = value[reg]; 321 if (n_regs > 1) { // Doubles and vectors check for aligned-adjacent set 322 uint last = (n_regs-1); // Looking for the last part of a set 323 if ((reg&last) != last) continue; // Wrong part of a set 324 if (!register_contains_value(vv, reg, n_regs, value)) continue; // Different value 325 } 326 if( vv == val || // Got a direct hit? 327 (t && vv && vv->bottom_type() == t && vv->is_Mach() && 328 vv->as_Mach()->rule() == val->as_Mach()->rule()) ) { // Or same constant? 329 assert( !n->is_Phi(), "cannot change registers at a Phi so easily" ); 330 if( OptoReg::is_stack(nk_reg) || // CISC-loading from stack OR 331 OptoReg::is_reg(reg) || // turning into a register use OR 332 regnd[reg]->outcnt()==1 ) { // last use of a spill-load turns into a CISC use 333 blk_adjust += use_prior_register(n,k,regnd[reg],current_block,value,regnd); 334 if( n->in(k) == regnd[reg] ) // Success! Quit trying 335 return blk_adjust; 336 } // End of if not degrading to a stack 337 } // End of if found value in another register 338 } // End of scan all machine registers 339 return blk_adjust; 340 } 341 342 343 // 344 // Check if nreg already contains the constant value val. Normal copy 345 // elimination doesn't doesn't work on constants because multiple 346 // nodes can represent the same constant so the type and rule of the 347 // MachNode must be checked to ensure equivalence. 348 // 349 bool PhaseChaitin::eliminate_copy_of_constant(Node* val, Node* n, 350 Block *current_block, 351 Node_List& value, Node_List& regnd, 352 OptoReg::Name nreg, OptoReg::Name nreg2) { 353 if (value[nreg] != val && val->is_Con() && 354 value[nreg] != NULL && value[nreg]->is_Con() && 355 (nreg2 == OptoReg::Bad || value[nreg] == value[nreg2]) && 356 value[nreg]->bottom_type() == val->bottom_type() && 357 value[nreg]->as_Mach()->rule() == val->as_Mach()->rule()) { 358 // This code assumes that two MachNodes representing constants 359 // which have the same rule and the same bottom type will produce 360 // identical effects into a register. This seems like it must be 361 // objectively true unless there are hidden inputs to the nodes 362 // but if that were to change this code would need to updated. 363 // Since they are equivalent the second one if redundant and can 364 // be removed. 365 // 366 // n will be replaced with the old value but n might have 367 // kills projections associated with it so remove them now so that 368 // yank_if_dead will be able to eliminate the copy once the uses 369 // have been transferred to the old[value]. 370 for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax; i++) { 371 Node* use = n->fast_out(i); 372 if (use->is_Proj() && use->outcnt() == 0) { 373 // Kill projections have no users and one input 374 use->set_req(0, C->top()); 375 yank_if_dead(use, current_block, &value, ®nd); 376 --i; --imax; 377 } 378 } 379 _post_alloc++; 380 return true; 381 } 382 return false; 383 } 384 385 386 //------------------------------post_allocate_copy_removal--------------------- 387 // Post-Allocation peephole copy removal. We do this in 1 pass over the 388 // basic blocks. We maintain a mapping of registers to Nodes (an array of 389 // Nodes indexed by machine register or stack slot number). NULL means that a 390 // register is not mapped to any Node. We can (want to have!) have several 391 // registers map to the same Node. We walk forward over the instructions 392 // updating the mapping as we go. At merge points we force a NULL if we have 393 // to merge 2 different Nodes into the same register. Phi functions will give 394 // us a new Node if there is a proper value merging. Since the blocks are 395 // arranged in some RPO, we will visit all parent blocks before visiting any 396 // successor blocks (except at loops). 397 // 398 // If we find a Copy we look to see if the Copy's source register is a stack 399 // slot and that value has already been loaded into some machine register; if 400 // so we use machine register directly. This turns a Load into a reg-reg 401 // Move. We also look for reloads of identical constants. 402 // 403 // When we see a use from a reg-reg Copy, we will attempt to use the copy's 404 // source directly and make the copy go dead. 405 void PhaseChaitin::post_allocate_copy_removal() { 406 Compile::TracePhase tp("postAllocCopyRemoval", &timers[_t_postAllocCopyRemoval]); 407 ResourceMark rm; 408 409 // Need a mapping from basic block Node_Lists. We need a Node_List to 410 // map from register number to value-producing Node. 411 Node_List **blk2value = NEW_RESOURCE_ARRAY( Node_List *, _cfg.number_of_blocks() + 1); 412 memset(blk2value, 0, sizeof(Node_List*) * (_cfg.number_of_blocks() + 1)); 413 // Need a mapping from basic block Node_Lists. We need a Node_List to 414 // map from register number to register-defining Node. 415 Node_List **blk2regnd = NEW_RESOURCE_ARRAY( Node_List *, _cfg.number_of_blocks() + 1); 416 memset(blk2regnd, 0, sizeof(Node_List*) * (_cfg.number_of_blocks() + 1)); 417 418 // We keep unused Node_Lists on a free_list to avoid wasting 419 // memory. 420 GrowableArray<Node_List*> free_list = GrowableArray<Node_List*>(16); 421 422 // For all blocks 423 for (uint i = 0; i < _cfg.number_of_blocks(); i++) { 424 uint j; 425 Block* block = _cfg.get_block(i); 426 427 // Count of Phis in block 428 uint phi_dex; 429 for (phi_dex = 1; phi_dex < block->number_of_nodes(); phi_dex++) { 430 Node* phi = block->get_node(phi_dex); 431 if (!phi->is_Phi()) { 432 break; 433 } 434 } 435 436 // If any predecessor has not been visited, we do not know the state 437 // of registers at the start. Check for this, while updating copies 438 // along Phi input edges 439 bool missing_some_inputs = false; 440 Block *freed = NULL; 441 for (j = 1; j < block->num_preds(); j++) { 442 Block* pb = _cfg.get_block_for_node(block->pred(j)); 443 // Remove copies along phi edges 444 for (uint k = 1; k < phi_dex; k++) { 445 elide_copy(block->get_node(k), j, block, *blk2value[pb->_pre_order], *blk2regnd[pb->_pre_order], false); 446 } 447 if (blk2value[pb->_pre_order]) { // Have a mapping on this edge? 448 // See if this predecessor's mappings have been used by everybody 449 // who wants them. If so, free 'em. 450 uint k; 451 for (k = 0; k < pb->_num_succs; k++) { 452 Block* pbsucc = pb->_succs[k]; 453 if (!blk2value[pbsucc->_pre_order] && pbsucc != block) { 454 break; // Found a future user 455 } 456 } 457 if (k >= pb->_num_succs) { // No more uses, free! 458 freed = pb; // Record last block freed 459 free_list.push(blk2value[pb->_pre_order]); 460 free_list.push(blk2regnd[pb->_pre_order]); 461 } 462 } else { // This block has unvisited (loopback) inputs 463 missing_some_inputs = true; 464 } 465 } 466 467 468 // Extract Node_List mappings. If 'freed' is non-zero, we just popped 469 // 'freed's blocks off the list 470 Node_List ®nd = *(free_list.is_empty() ? new Node_List() : free_list.pop()); 471 Node_List &value = *(free_list.is_empty() ? new Node_List() : free_list.pop()); 472 assert( !freed || blk2value[freed->_pre_order] == &value, "" ); 473 value.map(_max_reg,NULL); 474 regnd.map(_max_reg,NULL); 475 // Set mappings as OUR mappings 476 blk2value[block->_pre_order] = &value; 477 blk2regnd[block->_pre_order] = ®nd; 478 479 // Initialize value & regnd for this block 480 if (missing_some_inputs) { 481 // Some predecessor has not yet been visited; zap map to empty 482 for (uint k = 0; k < (uint)_max_reg; k++) { 483 value.map(k,NULL); 484 regnd.map(k,NULL); 485 } 486 } else { 487 if( !freed ) { // Didn't get a freebie prior block 488 // Must clone some data 489 freed = _cfg.get_block_for_node(block->pred(1)); 490 Node_List &f_value = *blk2value[freed->_pre_order]; 491 Node_List &f_regnd = *blk2regnd[freed->_pre_order]; 492 for( uint k = 0; k < (uint)_max_reg; k++ ) { 493 value.map(k,f_value[k]); 494 regnd.map(k,f_regnd[k]); 495 } 496 } 497 // Merge all inputs together, setting to NULL any conflicts. 498 for (j = 1; j < block->num_preds(); j++) { 499 Block* pb = _cfg.get_block_for_node(block->pred(j)); 500 if (pb == freed) { 501 continue; // Did self already via freelist 502 } 503 Node_List &p_regnd = *blk2regnd[pb->_pre_order]; 504 for( uint k = 0; k < (uint)_max_reg; k++ ) { 505 if( regnd[k] != p_regnd[k] ) { // Conflict on reaching defs? 506 value.map(k,NULL); // Then no value handy 507 regnd.map(k,NULL); 508 } 509 } 510 } 511 } 512 513 // For all Phi's 514 for (j = 1; j < phi_dex; j++) { 515 uint k; 516 Node *phi = block->get_node(j); 517 uint pidx = _lrg_map.live_range_id(phi); 518 OptoReg::Name preg = lrgs(_lrg_map.live_range_id(phi)).reg(); 519 520 // Remove copies remaining on edges. Check for junk phi. 521 Node *u = NULL; 522 for (k = 1; k < phi->req(); k++) { 523 Node *x = phi->in(k); 524 if( phi != x && u != x ) // Found a different input 525 u = u ? NodeSentinel : x; // Capture unique input, or NodeSentinel for 2nd input 526 } 527 if (u != NodeSentinel) { // Junk Phi. Remove 528 phi->replace_by(u); 529 j -= yank_if_dead(phi, block, &value, ®nd); 530 phi_dex--; 531 continue; 532 } 533 // Note that if value[pidx] exists, then we merged no new values here 534 // and the phi is useless. This can happen even with the above phi 535 // removal for complex flows. I cannot keep the better known value here 536 // because locally the phi appears to define a new merged value. If I 537 // keep the better value then a copy of the phi, being unable to use the 538 // global flow analysis, can't "peek through" the phi to the original 539 // reaching value and so will act like it's defining a new value. This 540 // can lead to situations where some uses are from the old and some from 541 // the new values. Not illegal by itself but throws the over-strong 542 // assert in scheduling. 543 if( pidx ) { 544 value.map(preg,phi); 545 regnd.map(preg,phi); 546 int n_regs = RegMask::num_registers(phi->ideal_reg()); 547 for (int l = 1; l < n_regs; l++) { 548 OptoReg::Name preg_lo = OptoReg::add(preg,-l); 549 value.map(preg_lo,phi); 550 regnd.map(preg_lo,phi); 551 } 552 } 553 } 554 555 // For all remaining instructions 556 for (j = phi_dex; j < block->number_of_nodes(); j++) { 557 Node* n = block->get_node(j); 558 559 if(n->outcnt() == 0 && // Dead? 560 n != C->top() && // (ignore TOP, it has no du info) 561 !n->is_Proj() ) { // fat-proj kills 562 j -= yank_if_dead(n, block, &value, ®nd); 563 continue; 564 } 565 566 // Improve reaching-def info. Occasionally post-alloc's liveness gives 567 // up (at loop backedges, because we aren't doing a full flow pass). 568 // The presence of a live use essentially asserts that the use's def is 569 // alive and well at the use (or else the allocator fubar'd). Take 570 // advantage of this info to set a reaching def for the use-reg. 571 uint k; 572 for (k = 1; k < n->req(); k++) { 573 Node *def = n->in(k); // n->in(k) is a USE; def is the DEF for this USE 574 guarantee(def != NULL, "no disconnected nodes at this point"); 575 uint useidx = _lrg_map.live_range_id(def); // useidx is the live range index for this USE 576 577 if( useidx ) { 578 OptoReg::Name ureg = lrgs(useidx).reg(); 579 if( !value[ureg] ) { 580 int idx; // Skip occasional useless copy 581 while( (idx=def->is_Copy()) != 0 && 582 def->in(idx) != NULL && // NULL should not happen 583 ureg == lrgs(_lrg_map.live_range_id(def->in(idx))).reg()) 584 def = def->in(idx); 585 Node *valdef = skip_copies(def); // tighten up val through non-useless copies 586 value.map(ureg,valdef); // record improved reaching-def info 587 regnd.map(ureg, def); 588 // Record other half of doubles 589 uint def_ideal_reg = def->ideal_reg(); 590 int n_regs = RegMask::num_registers(def_ideal_reg); 591 for (int l = 1; l < n_regs; l++) { 592 OptoReg::Name ureg_lo = OptoReg::add(ureg,-l); 593 if (!value[ureg_lo] && 594 (!RegMask::can_represent(ureg_lo) || 595 lrgs(useidx).mask().Member(ureg_lo))) { // Nearly always adjacent 596 value.map(ureg_lo,valdef); // record improved reaching-def info 597 regnd.map(ureg_lo, def); 598 } 599 } 600 } 601 } 602 } 603 604 const uint two_adr = n->is_Mach() ? n->as_Mach()->two_adr() : 0; 605 606 // Remove copies along input edges 607 for (k = 1; k < n->req(); k++) { 608 j -= elide_copy(n, k, block, value, regnd, two_adr != k); 609 } 610 611 // Unallocated Nodes define no registers 612 uint lidx = _lrg_map.live_range_id(n); 613 if (!lidx) { 614 continue; 615 } 616 617 // Update the register defined by this instruction 618 OptoReg::Name nreg = lrgs(lidx).reg(); 619 // Skip through all copies to the _value_ being defined. 620 // Do not change from int to pointer 621 Node *val = skip_copies(n); 622 623 // Clear out a dead definition before starting so that the 624 // elimination code doesn't have to guard against it. The 625 // definition could in fact be a kill projection with a count of 626 // 0 which is safe but since those are uninteresting for copy 627 // elimination just delete them as well. 628 if (regnd[nreg] != NULL && regnd[nreg]->outcnt() == 0) { 629 regnd.map(nreg, NULL); 630 value.map(nreg, NULL); 631 } 632 633 uint n_ideal_reg = n->ideal_reg(); 634 int n_regs = RegMask::num_registers(n_ideal_reg); 635 if (n_regs == 1) { 636 // If Node 'n' does not change the value mapped by the register, 637 // then 'n' is a useless copy. Do not update the register->node 638 // mapping so 'n' will go dead. 639 if( value[nreg] != val ) { 640 if (eliminate_copy_of_constant(val, n, block, value, regnd, nreg, OptoReg::Bad)) { 641 j -= replace_and_yank_if_dead(n, nreg, block, value, regnd); 642 } else { 643 // Update the mapping: record new Node defined by the register 644 regnd.map(nreg,n); 645 // Update mapping for defined *value*, which is the defined 646 // Node after skipping all copies. 647 value.map(nreg,val); 648 } 649 } else if( !may_be_copy_of_callee(n) ) { 650 assert(n->is_Copy(), ""); 651 j -= replace_and_yank_if_dead(n, nreg, block, value, regnd); 652 } 653 } else if (RegMask::is_vector(n_ideal_reg)) { 654 // If Node 'n' does not change the value mapped by the register, 655 // then 'n' is a useless copy. Do not update the register->node 656 // mapping so 'n' will go dead. 657 if (!register_contains_value(val, nreg, n_regs, value)) { 658 // Update the mapping: record new Node defined by the register 659 regnd.map(nreg,n); 660 // Update mapping for defined *value*, which is the defined 661 // Node after skipping all copies. 662 value.map(nreg,val); 663 for (int l = 1; l < n_regs; l++) { 664 OptoReg::Name nreg_lo = OptoReg::add(nreg,-l); 665 regnd.map(nreg_lo, n ); 666 value.map(nreg_lo,val); 667 } 668 } else if (n->is_Copy()) { 669 // Note: vector can't be constant and can't be copy of calee. 670 j -= replace_and_yank_if_dead(n, nreg, block, value, regnd); 671 } 672 } else { 673 // If the value occupies a register pair, record same info 674 // in both registers. 675 OptoReg::Name nreg_lo = OptoReg::add(nreg,-1); 676 if( RegMask::can_represent(nreg_lo) && // Either a spill slot, or 677 !lrgs(lidx).mask().Member(nreg_lo) ) { // Nearly always adjacent 678 // Sparc occasionally has non-adjacent pairs. 679 // Find the actual other value 680 RegMask tmp = lrgs(lidx).mask(); 681 tmp.Remove(nreg); 682 nreg_lo = tmp.find_first_elem(); 683 } 684 if (value[nreg] != val || value[nreg_lo] != val) { 685 if (eliminate_copy_of_constant(val, n, block, value, regnd, nreg, nreg_lo)) { 686 j -= replace_and_yank_if_dead(n, nreg, block, value, regnd); 687 } else { 688 regnd.map(nreg , n ); 689 regnd.map(nreg_lo, n ); 690 value.map(nreg ,val); 691 value.map(nreg_lo,val); 692 } 693 } else if (!may_be_copy_of_callee(n)) { 694 assert(n->is_Copy(), ""); 695 j -= replace_and_yank_if_dead(n, nreg, block, value, regnd); 696 } 697 } 698 699 // Fat projections kill many registers 700 if( n_ideal_reg == MachProjNode::fat_proj ) { 701 RegMask rm = n->out_RegMask(); 702 // wow, what an expensive iterator... 703 nreg = rm.find_first_elem(); 704 while( OptoReg::is_valid(nreg)) { 705 rm.Remove(nreg); 706 value.map(nreg,n); 707 regnd.map(nreg,n); 708 nreg = rm.find_first_elem(); 709 } 710 } 711 712 } // End of for all instructions in the block 713 714 } // End for all blocks 715 }