1 /* 2 * Copyright (c) 1998, 2016, 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 "memory/resourceArea.hpp" 28 #include "opto/chaitin.hpp" 29 #include "opto/machnode.hpp" 30 31 // See if this register (or pairs, or vector) already contains the value. 32 static bool register_contains_value(Node* val, OptoReg::Name reg, int n_regs, 33 Node_List& value) { 34 for (int i = 0; i < n_regs; i++) { 35 OptoReg::Name nreg = OptoReg::add(reg,-i); 36 if (value[nreg] != val) 37 return false; 38 } 39 return true; 40 } 41 42 //---------------------------may_be_copy_of_callee----------------------------- 43 // Check to see if we can possibly be a copy of a callee-save value. 44 bool PhaseChaitin::may_be_copy_of_callee( Node *def ) const { 45 // Short circuit if there are no callee save registers 46 if (_matcher.number_of_saved_registers() == 0) return false; 47 48 // Expect only a spill-down and reload on exit for callee-save spills. 49 // Chains of copies cannot be deep. 50 // 5008997 - This is wishful thinking. Register allocator seems to 51 // be splitting live ranges for callee save registers to such 52 // an extent that in large methods the chains can be very long 53 // (50+). The conservative answer is to return true if we don't 54 // know as this prevents optimizations from occurring. 55 56 const int limit = 60; 57 int i; 58 for( i=0; i < limit; i++ ) { 59 if( def->is_Proj() && def->in(0)->is_Start() && 60 _matcher.is_save_on_entry(lrgs(_lrg_map.live_range_id(def)).reg())) 61 return true; // Direct use of callee-save proj 62 if( def->is_Copy() ) // Copies carry value through 63 def = def->in(def->is_Copy()); 64 else if( def->is_Phi() ) // Phis can merge it from any direction 65 def = def->in(1); 66 else 67 break; 68 guarantee(def != NULL, "must not resurrect dead copy"); 69 } 70 // If we reached the end and didn't find a callee save proj 71 // then this may be a callee save proj so we return true 72 // as the conservative answer. If we didn't reach then end 73 // we must have discovered that it was not a callee save 74 // else we would have returned. 75 return i == limit; 76 } 77 78 //------------------------------yank----------------------------------- 79 // Helper function for yank_if_dead 80 int PhaseChaitin::yank( Node *old, Block *current_block, Node_List *value, Node_List *regnd ) { 81 int blk_adjust=0; 82 Block *oldb = _cfg.get_block_for_node(old); 83 oldb->find_remove(old); 84 // Count 1 if deleting an instruction from the current block 85 if (oldb == current_block) { 86 blk_adjust++; 87 } 88 _cfg.unmap_node_from_block(old); 89 OptoReg::Name old_reg = lrgs(_lrg_map.live_range_id(old)).reg(); 90 if( regnd && (*regnd)[old_reg]==old ) { // Instruction is currently available? 91 value->map(old_reg,NULL); // Yank from value/regnd maps 92 regnd->map(old_reg,NULL); // This register's value is now unknown 93 } 94 return blk_adjust; 95 } 96 97 #ifdef ASSERT 98 static bool expected_yanked_node(Node *old, Node *orig_old) { 99 // This code is expected only next original nodes: 100 // - load from constant table node which may have next data input nodes: 101 // MachConstantBase, MachTemp, MachSpillCopy 102 // - Phi nodes that are considered Junk 103 // - load constant node which may have next data input nodes: 104 // MachTemp, MachSpillCopy 105 // - MachSpillCopy 106 // - MachProj and Copy dead nodes 107 if (old->is_MachSpillCopy()) { 108 return true; 109 } else if (old->is_Con()) { 110 return true; 111 } else if (old->is_MachProj()) { // Dead kills projection of Con node 112 return (old == orig_old); 113 } else if (old->is_Copy()) { // Dead copy of a callee-save value 114 return (old == orig_old); 115 } else if (old->is_MachTemp()) { 116 return orig_old->is_Con(); 117 } else if (old->is_Phi()) { // Junk phi's 118 return true; 119 } else if (old->is_MachConstantBase()) { 120 return (orig_old->is_Con() && orig_old->is_MachConstant()); 121 } 122 return false; 123 } 124 #endif 125 126 //------------------------------yank_if_dead----------------------------------- 127 // Removed edges from 'old'. Yank if dead. Return adjustment counts to 128 // iterators in the current block. 129 int PhaseChaitin::yank_if_dead_recurse(Node *old, Node *orig_old, Block *current_block, 130 Node_List *value, Node_List *regnd) { 131 int blk_adjust=0; 132 if (old->outcnt() == 0 && old != C->top()) { 133 #ifdef ASSERT 134 if (!expected_yanked_node(old, orig_old)) { 135 tty->print_cr("=============================================="); 136 tty->print_cr("orig_old:"); 137 orig_old->dump(); 138 tty->print_cr("old:"); 139 old->dump(); 140 assert(false, "unexpected yanked node"); 141 } 142 if (old->is_Con()) 143 orig_old = old; // Reset to satisfy expected nodes checks. 144 #endif 145 blk_adjust += yank(old, current_block, value, regnd); 146 147 for (uint i = 1; i < old->req(); i++) { 148 Node* n = old->in(i); 149 if (n != NULL) { 150 old->set_req(i, NULL); 151 blk_adjust += yank_if_dead_recurse(n, orig_old, current_block, value, regnd); 152 } 153 } 154 // Disconnect control and remove precedence edges if any exist 155 old->disconnect_inputs(NULL, C); 156 } 157 return blk_adjust; 158 } 159 160 //------------------------------use_prior_register----------------------------- 161 // Use the prior value instead of the current value, in an effort to make 162 // the current value go dead. Return block iterator adjustment, in case 163 // we yank some instructions from this block. 164 int PhaseChaitin::use_prior_register( Node *n, uint idx, Node *def, Block *current_block, Node_List &value, Node_List ®nd ) { 165 // No effect? 166 if( def == n->in(idx) ) return 0; 167 // Def is currently dead and can be removed? Do not resurrect 168 if( def->outcnt() == 0 ) return 0; 169 170 // Not every pair of physical registers are assignment compatible, 171 // e.g. on sparc floating point registers are not assignable to integer 172 // registers. 173 const LRG &def_lrg = lrgs(_lrg_map.live_range_id(def)); 174 OptoReg::Name def_reg = def_lrg.reg(); 175 const RegMask &use_mask = n->in_RegMask(idx); 176 bool can_use = ( RegMask::can_represent(def_reg) ? (use_mask.Member(def_reg) != 0) 177 : (use_mask.is_AllStack() != 0)); 178 if (!RegMask::is_vector(def->ideal_reg())) { 179 // Check for a copy to or from a misaligned pair. 180 // It is workaround for a sparc with misaligned pairs. 181 can_use = can_use && !use_mask.is_misaligned_pair() && !def_lrg.mask().is_misaligned_pair(); 182 } 183 if (!can_use) 184 return 0; 185 186 // Capture the old def in case it goes dead... 187 Node *old = n->in(idx); 188 189 // Save-on-call copies can only be elided if the entire copy chain can go 190 // away, lest we get the same callee-save value alive in 2 locations at 191 // once. We check for the obvious trivial case here. Although it can 192 // sometimes be elided with cooperation outside our scope, here we will just 193 // miss the opportunity. :-( 194 if( may_be_copy_of_callee(def) ) { 195 if( old->outcnt() > 1 ) return 0; // We're the not last user 196 int idx = old->is_Copy(); 197 assert( idx, "chain of copies being removed" ); 198 Node *old2 = old->in(idx); // Chain of copies 199 if( old2->outcnt() > 1 ) return 0; // old is not the last user 200 int idx2 = old2->is_Copy(); 201 if( !idx2 ) return 0; // Not a chain of 2 copies 202 if( def != old2->in(idx2) ) return 0; // Chain of exactly 2 copies 203 } 204 205 // Use the new def 206 n->set_req(idx,def); 207 _post_alloc++; 208 209 // Is old def now dead? We successfully yanked a copy? 210 return yank_if_dead(old,current_block,&value,®nd); 211 } 212 213 214 //------------------------------skip_copies------------------------------------ 215 // Skip through any number of copies (that don't mod oop-i-ness) 216 Node *PhaseChaitin::skip_copies( Node *c ) { 217 int idx = c->is_Copy(); 218 uint is_oop = lrgs(_lrg_map.live_range_id(c))._is_oop; 219 while (idx != 0) { 220 guarantee(c->in(idx) != NULL, "must not resurrect dead copy"); 221 if (lrgs(_lrg_map.live_range_id(c->in(idx)))._is_oop != is_oop) { 222 break; // casting copy, not the same value 223 } 224 c = c->in(idx); 225 idx = c->is_Copy(); 226 } 227 return c; 228 } 229 230 //------------------------------elide_copy------------------------------------- 231 // Remove (bypass) copies along Node n, edge k. 232 int PhaseChaitin::elide_copy( Node *n, int k, Block *current_block, Node_List &value, Node_List ®nd, bool can_change_regs ) { 233 int blk_adjust = 0; 234 235 uint nk_idx = _lrg_map.live_range_id(n->in(k)); 236 OptoReg::Name nk_reg = lrgs(nk_idx).reg(); 237 238 // Remove obvious same-register copies 239 Node *x = n->in(k); 240 int idx; 241 while( (idx=x->is_Copy()) != 0 ) { 242 Node *copy = x->in(idx); 243 guarantee(copy != NULL, "must not resurrect dead copy"); 244 if(lrgs(_lrg_map.live_range_id(copy)).reg() != nk_reg) { 245 break; 246 } 247 blk_adjust += use_prior_register(n,k,copy,current_block,value,regnd); 248 if (n->in(k) != copy) { 249 break; // Failed for some cutout? 250 } 251 x = copy; // Progress, try again 252 } 253 254 // Phis and 2-address instructions cannot change registers so easily - their 255 // outputs must match their input. 256 if( !can_change_regs ) 257 return blk_adjust; // Only check stupid copies! 258 259 // Loop backedges won't have a value-mapping yet 260 if( &value == NULL ) return blk_adjust; 261 262 // Skip through all copies to the _value_ being used. Do not change from 263 // int to pointer. This attempts to jump through a chain of copies, where 264 // intermediate copies might be illegal, i.e., value is stored down to stack 265 // then reloaded BUT survives in a register the whole way. 266 Node *val = skip_copies(n->in(k)); 267 if (val == x) return blk_adjust; // No progress? 268 269 int n_regs = RegMask::num_registers(val->ideal_reg()); 270 uint val_idx = _lrg_map.live_range_id(val); 271 OptoReg::Name val_reg = lrgs(val_idx).reg(); 272 273 // See if it happens to already be in the correct register! 274 // (either Phi's direct register, or the common case of the name 275 // never-clobbered original-def register) 276 if (register_contains_value(val, val_reg, n_regs, value)) { 277 blk_adjust += use_prior_register(n,k,regnd[val_reg],current_block,value,regnd); 278 if( n->in(k) == regnd[val_reg] ) // Success! Quit trying 279 return blk_adjust; 280 } 281 282 // See if we can skip the copy by changing registers. Don't change from 283 // using a register to using the stack unless we know we can remove a 284 // copy-load. Otherwise we might end up making a pile of Intel cisc-spill 285 // ops reading from memory instead of just loading once and using the 286 // register. 287 288 // Also handle duplicate copies here. 289 const Type *t = val->is_Con() ? val->bottom_type() : NULL; 290 291 // Scan all registers to see if this value is around already 292 for( uint reg = 0; reg < (uint)_max_reg; reg++ ) { 293 if (reg == (uint)nk_reg) { 294 // Found ourselves so check if there is only one user of this 295 // copy and keep on searching for a better copy if so. 296 bool ignore_self = true; 297 x = n->in(k); 298 DUIterator_Fast imax, i = x->fast_outs(imax); 299 Node* first = x->fast_out(i); i++; 300 while (i < imax && ignore_self) { 301 Node* use = x->fast_out(i); i++; 302 if (use != first) ignore_self = false; 303 } 304 if (ignore_self) continue; 305 } 306 307 Node *vv = value[reg]; 308 if (n_regs > 1) { // Doubles and vectors check for aligned-adjacent set 309 uint last = (n_regs-1); // Looking for the last part of a set 310 if ((reg&last) != last) continue; // Wrong part of a set 311 if (!register_contains_value(vv, reg, n_regs, value)) continue; // Different value 312 } 313 if( vv == val || // Got a direct hit? 314 (t && vv && vv->bottom_type() == t && vv->is_Mach() && 315 vv->as_Mach()->rule() == val->as_Mach()->rule()) ) { // Or same constant? 316 assert( !n->is_Phi(), "cannot change registers at a Phi so easily" ); 317 if( OptoReg::is_stack(nk_reg) || // CISC-loading from stack OR 318 OptoReg::is_reg(reg) || // turning into a register use OR 319 regnd[reg]->outcnt()==1 ) { // last use of a spill-load turns into a CISC use 320 blk_adjust += use_prior_register(n,k,regnd[reg],current_block,value,regnd); 321 if( n->in(k) == regnd[reg] ) // Success! Quit trying 322 return blk_adjust; 323 } // End of if not degrading to a stack 324 } // End of if found value in another register 325 } // End of scan all machine registers 326 return blk_adjust; 327 } 328 329 330 // 331 // Check if nreg already contains the constant value val. Normal copy 332 // elimination doesn't doesn't work on constants because multiple 333 // nodes can represent the same constant so the type and rule of the 334 // MachNode must be checked to ensure equivalence. 335 // 336 bool PhaseChaitin::eliminate_copy_of_constant(Node* val, Node* n, 337 Block *current_block, 338 Node_List& value, Node_List& regnd, 339 OptoReg::Name nreg, OptoReg::Name nreg2) { 340 if (value[nreg] != val && val->is_Con() && 341 value[nreg] != NULL && value[nreg]->is_Con() && 342 (nreg2 == OptoReg::Bad || value[nreg] == value[nreg2]) && 343 value[nreg]->bottom_type() == val->bottom_type() && 344 value[nreg]->as_Mach()->rule() == val->as_Mach()->rule()) { 345 // This code assumes that two MachNodes representing constants 346 // which have the same rule and the same bottom type will produce 347 // identical effects into a register. This seems like it must be 348 // objectively true unless there are hidden inputs to the nodes 349 // but if that were to change this code would need to updated. 350 // Since they are equivalent the second one if redundant and can 351 // be removed. 352 // 353 // n will be replaced with the old value but n might have 354 // kills projections associated with it so remove them now so that 355 // yank_if_dead will be able to eliminate the copy once the uses 356 // have been transferred to the old[value]. 357 for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax; i++) { 358 Node* use = n->fast_out(i); 359 if (use->is_Proj() && use->outcnt() == 0) { 360 // Kill projections have no users and one input 361 use->set_req(0, C->top()); 362 yank_if_dead(use, current_block, &value, ®nd); 363 --i; --imax; 364 } 365 } 366 _post_alloc++; 367 return true; 368 } 369 return false; 370 } 371 372 // The algorithms works as follows: 373 // We traverse the block top to bottom. possibly_merge_multidef() is invoked for every input edge k 374 // of the instruction n. We check to see if the input is a multidef lrg. If it is, we record the fact that we've 375 // seen a definition (coming as an input) and add that fact to the reg2defuse array. The array maps registers to their 376 // current reaching definitions (we track only multidefs though). With each definition we also associate the first 377 // instruction we saw use it. If we encounter the situation when we observe an def (an input) that is a part of the 378 // same lrg but is different from the previous seen def we merge the two with a MachMerge node and substitute 379 // all the uses that we've seen so far to use the merge. After that we keep replacing the new defs in the same lrg 380 // as they get encountered with the merge node and keep adding these defs to the merge inputs. 381 void PhaseChaitin::merge_multidefs() { 382 Compile::TracePhase tp("mergeMultidefs", &timers[_t_mergeMultidefs]); 383 ResourceMark rm; 384 // Keep track of the defs seen in registers and collect their uses in the block. 385 RegToDefUseMap reg2defuse(_max_reg, _max_reg, RegDefUse()); 386 for (uint i = 0; i < _cfg.number_of_blocks(); i++) { 387 Block* block = _cfg.get_block(i); 388 for (uint j = 1; j < block->number_of_nodes(); j++) { 389 Node* n = block->get_node(j); 390 if (n->is_Phi()) continue; 391 for (uint k = 1; k < n->req(); k++) { 392 j += possibly_merge_multidef(n, k, block, reg2defuse); 393 } 394 // Null out the value produced by the instruction itself, since we're only interested in defs 395 // implicitly defined by the uses. We are actually interested in tracking only redefinitions 396 // of the multidef lrgs in the same register. For that matter it's enough to track changes in 397 // the base register only and ignore other effects of multi-register lrgs and fat projections. 398 // It is also ok to ignore defs coming from singledefs. After an implicit overwrite by one of 399 // those our register is guaranteed to be used by another lrg and we won't attempt to merge it. 400 uint lrg = _lrg_map.live_range_id(n); 401 if (lrg > 0 && lrgs(lrg).is_multidef()) { 402 OptoReg::Name reg = lrgs(lrg).reg(); 403 reg2defuse.at(reg).clear(); 404 } 405 } 406 // Clear reg->def->use tracking for the next block 407 for (int j = 0; j < reg2defuse.length(); j++) { 408 reg2defuse.at(j).clear(); 409 } 410 } 411 } 412 413 int PhaseChaitin::possibly_merge_multidef(Node *n, uint k, Block *block, RegToDefUseMap& reg2defuse) { 414 int blk_adjust = 0; 415 416 uint lrg = _lrg_map.live_range_id(n->in(k)); 417 if (lrg > 0 && lrgs(lrg).is_multidef()) { 418 OptoReg::Name reg = lrgs(lrg).reg(); 419 420 Node* def = reg2defuse.at(reg).def(); 421 if (def != NULL && lrg == _lrg_map.live_range_id(def) && def != n->in(k)) { 422 // Same lrg but different node, we have to merge. 423 MachMergeNode* merge; 424 if (def->is_MachMerge()) { // is it already a merge? 425 merge = def->as_MachMerge(); 426 } else { 427 merge = new MachMergeNode(def); 428 429 // Insert the merge node into the block before the first use. 430 uint use_index = block->find_node(reg2defuse.at(reg).first_use()); 431 block->insert_node(merge, use_index++); 432 _cfg.map_node_to_block(merge, block); 433 434 // Let the allocator know about the new node, use the same lrg 435 _lrg_map.extend(merge->_idx, lrg); 436 blk_adjust++; 437 438 // Fixup all the uses (there is at least one) that happened between the first 439 // use and before the current one. 440 for (; use_index < block->number_of_nodes(); use_index++) { 441 Node* use = block->get_node(use_index); 442 if (use == n) { 443 break; 444 } 445 use->replace_edge(def, merge); 446 } 447 } 448 if (merge->find_edge(n->in(k)) == -1) { 449 merge->add_req(n->in(k)); 450 } 451 n->set_req(k, merge); 452 } 453 454 // update the uses 455 reg2defuse.at(reg).update(n->in(k), n); 456 } 457 458 return blk_adjust; 459 } 460 461 462 //------------------------------post_allocate_copy_removal--------------------- 463 // Post-Allocation peephole copy removal. We do this in 1 pass over the 464 // basic blocks. We maintain a mapping of registers to Nodes (an array of 465 // Nodes indexed by machine register or stack slot number). NULL means that a 466 // register is not mapped to any Node. We can (want to have!) have several 467 // registers map to the same Node. We walk forward over the instructions 468 // updating the mapping as we go. At merge points we force a NULL if we have 469 // to merge 2 different Nodes into the same register. Phi functions will give 470 // us a new Node if there is a proper value merging. Since the blocks are 471 // arranged in some RPO, we will visit all parent blocks before visiting any 472 // successor blocks (except at loops). 473 // 474 // If we find a Copy we look to see if the Copy's source register is a stack 475 // slot and that value has already been loaded into some machine register; if 476 // so we use machine register directly. This turns a Load into a reg-reg 477 // Move. We also look for reloads of identical constants. 478 // 479 // When we see a use from a reg-reg Copy, we will attempt to use the copy's 480 // source directly and make the copy go dead. 481 void PhaseChaitin::post_allocate_copy_removal() { 482 Compile::TracePhase tp("postAllocCopyRemoval", &timers[_t_postAllocCopyRemoval]); 483 ResourceMark rm; 484 485 // Need a mapping from basic block Node_Lists. We need a Node_List to 486 // map from register number to value-producing Node. 487 Node_List **blk2value = NEW_RESOURCE_ARRAY( Node_List *, _cfg.number_of_blocks() + 1); 488 memset(blk2value, 0, sizeof(Node_List*) * (_cfg.number_of_blocks() + 1)); 489 // Need a mapping from basic block Node_Lists. We need a Node_List to 490 // map from register number to register-defining Node. 491 Node_List **blk2regnd = NEW_RESOURCE_ARRAY( Node_List *, _cfg.number_of_blocks() + 1); 492 memset(blk2regnd, 0, sizeof(Node_List*) * (_cfg.number_of_blocks() + 1)); 493 494 // We keep unused Node_Lists on a free_list to avoid wasting 495 // memory. 496 GrowableArray<Node_List*> free_list = GrowableArray<Node_List*>(16); 497 498 // For all blocks 499 for (uint i = 0; i < _cfg.number_of_blocks(); i++) { 500 uint j; 501 Block* block = _cfg.get_block(i); 502 503 // Count of Phis in block 504 uint phi_dex; 505 for (phi_dex = 1; phi_dex < block->number_of_nodes(); phi_dex++) { 506 Node* phi = block->get_node(phi_dex); 507 if (!phi->is_Phi()) { 508 break; 509 } 510 } 511 512 // If any predecessor has not been visited, we do not know the state 513 // of registers at the start. Check for this, while updating copies 514 // along Phi input edges 515 bool missing_some_inputs = false; 516 Block *freed = NULL; 517 for (j = 1; j < block->num_preds(); j++) { 518 Block* pb = _cfg.get_block_for_node(block->pred(j)); 519 // Remove copies along phi edges 520 for (uint k = 1; k < phi_dex; k++) { 521 elide_copy(block->get_node(k), j, block, *blk2value[pb->_pre_order], *blk2regnd[pb->_pre_order], false); 522 } 523 if (blk2value[pb->_pre_order]) { // Have a mapping on this edge? 524 // See if this predecessor's mappings have been used by everybody 525 // who wants them. If so, free 'em. 526 uint k; 527 for (k = 0; k < pb->_num_succs; k++) { 528 Block* pbsucc = pb->_succs[k]; 529 if (!blk2value[pbsucc->_pre_order] && pbsucc != block) { 530 break; // Found a future user 531 } 532 } 533 if (k >= pb->_num_succs) { // No more uses, free! 534 freed = pb; // Record last block freed 535 free_list.push(blk2value[pb->_pre_order]); 536 free_list.push(blk2regnd[pb->_pre_order]); 537 } 538 } else { // This block has unvisited (loopback) inputs 539 missing_some_inputs = true; 540 } 541 } 542 543 544 // Extract Node_List mappings. If 'freed' is non-zero, we just popped 545 // 'freed's blocks off the list 546 Node_List ®nd = *(free_list.is_empty() ? new Node_List() : free_list.pop()); 547 Node_List &value = *(free_list.is_empty() ? new Node_List() : free_list.pop()); 548 assert( !freed || blk2value[freed->_pre_order] == &value, "" ); 549 value.map(_max_reg,NULL); 550 regnd.map(_max_reg,NULL); 551 // Set mappings as OUR mappings 552 blk2value[block->_pre_order] = &value; 553 blk2regnd[block->_pre_order] = ®nd; 554 555 // Initialize value & regnd for this block 556 if (missing_some_inputs) { 557 // Some predecessor has not yet been visited; zap map to empty 558 for (uint k = 0; k < (uint)_max_reg; k++) { 559 value.map(k,NULL); 560 regnd.map(k,NULL); 561 } 562 } else { 563 if( !freed ) { // Didn't get a freebie prior block 564 // Must clone some data 565 freed = _cfg.get_block_for_node(block->pred(1)); 566 Node_List &f_value = *blk2value[freed->_pre_order]; 567 Node_List &f_regnd = *blk2regnd[freed->_pre_order]; 568 for( uint k = 0; k < (uint)_max_reg; k++ ) { 569 value.map(k,f_value[k]); 570 regnd.map(k,f_regnd[k]); 571 } 572 } 573 // Merge all inputs together, setting to NULL any conflicts. 574 for (j = 1; j < block->num_preds(); j++) { 575 Block* pb = _cfg.get_block_for_node(block->pred(j)); 576 if (pb == freed) { 577 continue; // Did self already via freelist 578 } 579 Node_List &p_regnd = *blk2regnd[pb->_pre_order]; 580 for( uint k = 0; k < (uint)_max_reg; k++ ) { 581 if( regnd[k] != p_regnd[k] ) { // Conflict on reaching defs? 582 value.map(k,NULL); // Then no value handy 583 regnd.map(k,NULL); 584 } 585 } 586 } 587 } 588 589 // For all Phi's 590 for (j = 1; j < phi_dex; j++) { 591 uint k; 592 Node *phi = block->get_node(j); 593 uint pidx = _lrg_map.live_range_id(phi); 594 OptoReg::Name preg = lrgs(_lrg_map.live_range_id(phi)).reg(); 595 596 // Remove copies remaining on edges. Check for junk phi. 597 Node *u = NULL; 598 for (k = 1; k < phi->req(); k++) { 599 Node *x = phi->in(k); 600 if( phi != x && u != x ) // Found a different input 601 u = u ? NodeSentinel : x; // Capture unique input, or NodeSentinel for 2nd input 602 } 603 if (u != NodeSentinel) { // Junk Phi. Remove 604 phi->replace_by(u); 605 j -= yank_if_dead(phi, block, &value, ®nd); 606 phi_dex--; 607 continue; 608 } 609 // Note that if value[pidx] exists, then we merged no new values here 610 // and the phi is useless. This can happen even with the above phi 611 // removal for complex flows. I cannot keep the better known value here 612 // because locally the phi appears to define a new merged value. If I 613 // keep the better value then a copy of the phi, being unable to use the 614 // global flow analysis, can't "peek through" the phi to the original 615 // reaching value and so will act like it's defining a new value. This 616 // can lead to situations where some uses are from the old and some from 617 // the new values. Not illegal by itself but throws the over-strong 618 // assert in scheduling. 619 if( pidx ) { 620 value.map(preg,phi); 621 regnd.map(preg,phi); 622 int n_regs = RegMask::num_registers(phi->ideal_reg()); 623 for (int l = 1; l < n_regs; l++) { 624 OptoReg::Name preg_lo = OptoReg::add(preg,-l); 625 value.map(preg_lo,phi); 626 regnd.map(preg_lo,phi); 627 } 628 } 629 } 630 631 // For all remaining instructions 632 for (j = phi_dex; j < block->number_of_nodes(); j++) { 633 Node* n = block->get_node(j); 634 635 if(n->outcnt() == 0 && // Dead? 636 n != C->top() && // (ignore TOP, it has no du info) 637 !n->is_Proj() ) { // fat-proj kills 638 j -= yank_if_dead(n, block, &value, ®nd); 639 continue; 640 } 641 642 // Improve reaching-def info. Occasionally post-alloc's liveness gives 643 // up (at loop backedges, because we aren't doing a full flow pass). 644 // The presence of a live use essentially asserts that the use's def is 645 // alive and well at the use (or else the allocator fubar'd). Take 646 // advantage of this info to set a reaching def for the use-reg. 647 uint k; 648 for (k = 1; k < n->req(); k++) { 649 Node *def = n->in(k); // n->in(k) is a USE; def is the DEF for this USE 650 guarantee(def != NULL, "no disconnected nodes at this point"); 651 uint useidx = _lrg_map.live_range_id(def); // useidx is the live range index for this USE 652 653 if( useidx ) { 654 OptoReg::Name ureg = lrgs(useidx).reg(); 655 if( !value[ureg] ) { 656 int idx; // Skip occasional useless copy 657 while( (idx=def->is_Copy()) != 0 && 658 def->in(idx) != NULL && // NULL should not happen 659 ureg == lrgs(_lrg_map.live_range_id(def->in(idx))).reg()) 660 def = def->in(idx); 661 Node *valdef = skip_copies(def); // tighten up val through non-useless copies 662 value.map(ureg,valdef); // record improved reaching-def info 663 regnd.map(ureg, def); 664 // Record other half of doubles 665 uint def_ideal_reg = def->ideal_reg(); 666 int n_regs = RegMask::num_registers(def_ideal_reg); 667 for (int l = 1; l < n_regs; l++) { 668 OptoReg::Name ureg_lo = OptoReg::add(ureg,-l); 669 if (!value[ureg_lo] && 670 (!RegMask::can_represent(ureg_lo) || 671 lrgs(useidx).mask().Member(ureg_lo))) { // Nearly always adjacent 672 value.map(ureg_lo,valdef); // record improved reaching-def info 673 regnd.map(ureg_lo, def); 674 } 675 } 676 } 677 } 678 } 679 680 const uint two_adr = n->is_Mach() ? n->as_Mach()->two_adr() : 0; 681 682 // Remove copies along input edges 683 for (k = 1; k < n->req(); k++) { 684 j -= elide_copy(n, k, block, value, regnd, two_adr != k); 685 } 686 687 // Unallocated Nodes define no registers 688 uint lidx = _lrg_map.live_range_id(n); 689 if (!lidx) { 690 continue; 691 } 692 693 // Update the register defined by this instruction 694 OptoReg::Name nreg = lrgs(lidx).reg(); 695 // Skip through all copies to the _value_ being defined. 696 // Do not change from int to pointer 697 Node *val = skip_copies(n); 698 699 // Clear out a dead definition before starting so that the 700 // elimination code doesn't have to guard against it. The 701 // definition could in fact be a kill projection with a count of 702 // 0 which is safe but since those are uninteresting for copy 703 // elimination just delete them as well. 704 if (regnd[nreg] != NULL && regnd[nreg]->outcnt() == 0) { 705 regnd.map(nreg, NULL); 706 value.map(nreg, NULL); 707 } 708 709 uint n_ideal_reg = n->ideal_reg(); 710 int n_regs = RegMask::num_registers(n_ideal_reg); 711 if (n_regs == 1) { 712 // If Node 'n' does not change the value mapped by the register, 713 // then 'n' is a useless copy. Do not update the register->node 714 // mapping so 'n' will go dead. 715 if( value[nreg] != val ) { 716 if (eliminate_copy_of_constant(val, n, block, value, regnd, nreg, OptoReg::Bad)) { 717 j -= replace_and_yank_if_dead(n, nreg, block, value, regnd); 718 } else { 719 // Update the mapping: record new Node defined by the register 720 regnd.map(nreg,n); 721 // Update mapping for defined *value*, which is the defined 722 // Node after skipping all copies. 723 value.map(nreg,val); 724 } 725 } else if( !may_be_copy_of_callee(n) ) { 726 assert(n->is_Copy(), ""); 727 j -= replace_and_yank_if_dead(n, nreg, block, value, regnd); 728 } 729 } else if (RegMask::is_vector(n_ideal_reg)) { 730 // If Node 'n' does not change the value mapped by the register, 731 // then 'n' is a useless copy. Do not update the register->node 732 // mapping so 'n' will go dead. 733 if (!register_contains_value(val, nreg, n_regs, value)) { 734 // Update the mapping: record new Node defined by the register 735 regnd.map(nreg,n); 736 // Update mapping for defined *value*, which is the defined 737 // Node after skipping all copies. 738 value.map(nreg,val); 739 for (int l = 1; l < n_regs; l++) { 740 OptoReg::Name nreg_lo = OptoReg::add(nreg,-l); 741 regnd.map(nreg_lo, n ); 742 value.map(nreg_lo,val); 743 } 744 } else if (n->is_Copy()) { 745 // Note: vector can't be constant and can't be copy of calee. 746 j -= replace_and_yank_if_dead(n, nreg, block, value, regnd); 747 } 748 } else { 749 // If the value occupies a register pair, record same info 750 // in both registers. 751 OptoReg::Name nreg_lo = OptoReg::add(nreg,-1); 752 if( RegMask::can_represent(nreg_lo) && // Either a spill slot, or 753 !lrgs(lidx).mask().Member(nreg_lo) ) { // Nearly always adjacent 754 // Sparc occasionally has non-adjacent pairs. 755 // Find the actual other value 756 RegMask tmp = lrgs(lidx).mask(); 757 tmp.Remove(nreg); 758 nreg_lo = tmp.find_first_elem(); 759 } 760 if (value[nreg] != val || value[nreg_lo] != val) { 761 if (eliminate_copy_of_constant(val, n, block, value, regnd, nreg, nreg_lo)) { 762 j -= replace_and_yank_if_dead(n, nreg, block, value, regnd); 763 } else { 764 regnd.map(nreg , n ); 765 regnd.map(nreg_lo, n ); 766 value.map(nreg ,val); 767 value.map(nreg_lo,val); 768 } 769 } else if (!may_be_copy_of_callee(n)) { 770 assert(n->is_Copy(), ""); 771 j -= replace_and_yank_if_dead(n, nreg, block, value, regnd); 772 } 773 } 774 775 // Fat projections kill many registers 776 if( n_ideal_reg == MachProjNode::fat_proj ) { 777 RegMask rm = n->out_RegMask(); 778 // wow, what an expensive iterator... 779 nreg = rm.find_first_elem(); 780 while( OptoReg::is_valid(nreg)) { 781 rm.Remove(nreg); 782 value.map(nreg,n); 783 regnd.map(nreg,n); 784 nreg = rm.find_first_elem(); 785 } 786 } 787 788 } // End of for all instructions in the block 789 790 } // End for all blocks 791 }