buildOopMap.cpp revision 0:a61af66fc99e
1/* 2 * Copyright 2002-2007 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, 20 * CA 95054 USA or visit www.sun.com if you need additional information or 21 * have any questions. 22 * 23 */ 24 25#include "incls/_precompiled.incl" 26#include "incls/_buildOopMap.cpp.incl" 27 28// The functions in this file builds OopMaps after all scheduling is done. 29// 30// OopMaps contain a list of all registers and stack-slots containing oops (so 31// they can be updated by GC). OopMaps also contain a list of derived-pointer 32// base-pointer pairs. When the base is moved, the derived pointer moves to 33// follow it. Finally, any registers holding callee-save values are also 34// recorded. These might contain oops, but only the caller knows. 35// 36// BuildOopMaps implements a simple forward reaching-defs solution. At each 37// GC point we'll have the reaching-def Nodes. If the reaching Nodes are 38// typed as pointers (no offset), then they are oops. Pointers+offsets are 39// derived pointers, and bases can be found from them. Finally, we'll also 40// track reaching callee-save values. Note that a copy of a callee-save value 41// "kills" it's source, so that only 1 copy of a callee-save value is alive at 42// a time. 43// 44// We run a simple bitvector liveness pass to help trim out dead oops. Due to 45// irreducible loops, we can have a reaching def of an oop that only reaches 46// along one path and no way to know if it's valid or not on the other path. 47// The bitvectors are quite dense and the liveness pass is fast. 48// 49// At GC points, we consult this information to build OopMaps. All reaching 50// defs typed as oops are added to the OopMap. Only 1 instance of a 51// callee-save register can be recorded. For derived pointers, we'll have to 52// find and record the register holding the base. 53// 54// The reaching def's is a simple 1-pass worklist approach. I tried a clever 55// breadth-first approach but it was worse (showed O(n^2) in the 56// pick-next-block code). 57// 58// The relevent data is kept in a struct of arrays (it could just as well be 59// an array of structs, but the struct-of-arrays is generally a little more 60// efficient). The arrays are indexed by register number (including 61// stack-slots as registers) and so is bounded by 200 to 300 elements in 62// practice. One array will map to a reaching def Node (or NULL for 63// conflict/dead). The other array will map to a callee-saved register or 64// OptoReg::Bad for not-callee-saved. 65 66 67//------------------------------OopFlow---------------------------------------- 68// Structure to pass around 69struct OopFlow : public ResourceObj { 70 short *_callees; // Array mapping register to callee-saved 71 Node **_defs; // array mapping register to reaching def 72 // or NULL if dead/conflict 73 // OopFlow structs, when not being actively modified, describe the _end_ of 74 // this block. 75 Block *_b; // Block for this struct 76 OopFlow *_next; // Next free OopFlow 77 78 OopFlow( short *callees, Node **defs ) : _callees(callees), _defs(defs), 79 _b(NULL), _next(NULL) { } 80 81 // Given reaching-defs for this block start, compute it for this block end 82 void compute_reach( PhaseRegAlloc *regalloc, int max_reg, Dict *safehash ); 83 84 // Merge these two OopFlows into the 'this' pointer. 85 void merge( OopFlow *flow, int max_reg ); 86 87 // Copy a 'flow' over an existing flow 88 void clone( OopFlow *flow, int max_size); 89 90 // Make a new OopFlow from scratch 91 static OopFlow *make( Arena *A, int max_size ); 92 93 // Build an oopmap from the current flow info 94 OopMap *build_oop_map( Node *n, int max_reg, PhaseRegAlloc *regalloc, int* live ); 95}; 96 97//------------------------------compute_reach---------------------------------- 98// Given reaching-defs for this block start, compute it for this block end 99void OopFlow::compute_reach( PhaseRegAlloc *regalloc, int max_reg, Dict *safehash ) { 100 101 for( uint i=0; i<_b->_nodes.size(); i++ ) { 102 Node *n = _b->_nodes[i]; 103 104 if( n->jvms() ) { // Build an OopMap here? 105 JVMState *jvms = n->jvms(); 106 // no map needed for leaf calls 107 if( n->is_MachSafePoint() && !n->is_MachCallLeaf() ) { 108 int *live = (int*) (*safehash)[n]; 109 assert( live, "must find live" ); 110 n->as_MachSafePoint()->set_oop_map( build_oop_map(n,max_reg,regalloc, live) ); 111 } 112 } 113 114 // Assign new reaching def's. 115 // Note that I padded the _defs and _callees arrays so it's legal 116 // to index at _defs[OptoReg::Bad]. 117 OptoReg::Name first = regalloc->get_reg_first(n); 118 OptoReg::Name second = regalloc->get_reg_second(n); 119 _defs[first] = n; 120 _defs[second] = n; 121 122 // Pass callee-save info around copies 123 int idx = n->is_Copy(); 124 if( idx ) { // Copies move callee-save info 125 OptoReg::Name old_first = regalloc->get_reg_first(n->in(idx)); 126 OptoReg::Name old_second = regalloc->get_reg_second(n->in(idx)); 127 int tmp_first = _callees[old_first]; 128 int tmp_second = _callees[old_second]; 129 _callees[old_first] = OptoReg::Bad; // callee-save is moved, dead in old location 130 _callees[old_second] = OptoReg::Bad; 131 _callees[first] = tmp_first; 132 _callees[second] = tmp_second; 133 } else if( n->is_Phi() ) { // Phis do not mod callee-saves 134 assert( _callees[first] == _callees[regalloc->get_reg_first(n->in(1))], "" ); 135 assert( _callees[second] == _callees[regalloc->get_reg_second(n->in(1))], "" ); 136 assert( _callees[first] == _callees[regalloc->get_reg_first(n->in(n->req()-1))], "" ); 137 assert( _callees[second] == _callees[regalloc->get_reg_second(n->in(n->req()-1))], "" ); 138 } else { 139 _callees[first] = OptoReg::Bad; // No longer holding a callee-save value 140 _callees[second] = OptoReg::Bad; 141 142 // Find base case for callee saves 143 if( n->is_Proj() && n->in(0)->is_Start() ) { 144 if( OptoReg::is_reg(first) && 145 regalloc->_matcher.is_save_on_entry(first) ) 146 _callees[first] = first; 147 if( OptoReg::is_reg(second) && 148 regalloc->_matcher.is_save_on_entry(second) ) 149 _callees[second] = second; 150 } 151 } 152 } 153} 154 155//------------------------------merge------------------------------------------ 156// Merge the given flow into the 'this' flow 157void OopFlow::merge( OopFlow *flow, int max_reg ) { 158 assert( _b == NULL, "merging into a happy flow" ); 159 assert( flow->_b, "this flow is still alive" ); 160 assert( flow != this, "no self flow" ); 161 162 // Do the merge. If there are any differences, drop to 'bottom' which 163 // is OptoReg::Bad or NULL depending. 164 for( int i=0; i<max_reg; i++ ) { 165 // Merge the callee-save's 166 if( _callees[i] != flow->_callees[i] ) 167 _callees[i] = OptoReg::Bad; 168 // Merge the reaching defs 169 if( _defs[i] != flow->_defs[i] ) 170 _defs[i] = NULL; 171 } 172 173} 174 175//------------------------------clone------------------------------------------ 176void OopFlow::clone( OopFlow *flow, int max_size ) { 177 _b = flow->_b; 178 memcpy( _callees, flow->_callees, sizeof(short)*max_size); 179 memcpy( _defs , flow->_defs , sizeof(Node*)*max_size); 180} 181 182//------------------------------make------------------------------------------- 183OopFlow *OopFlow::make( Arena *A, int max_size ) { 184 short *callees = NEW_ARENA_ARRAY(A,short,max_size+1); 185 Node **defs = NEW_ARENA_ARRAY(A,Node*,max_size+1); 186 debug_only( memset(defs,0,(max_size+1)*sizeof(Node*)) ); 187 OopFlow *flow = new (A) OopFlow(callees+1, defs+1); 188 assert( &flow->_callees[OptoReg::Bad] == callees, "Ok to index at OptoReg::Bad" ); 189 assert( &flow->_defs [OptoReg::Bad] == defs , "Ok to index at OptoReg::Bad" ); 190 return flow; 191} 192 193//------------------------------bit twiddlers---------------------------------- 194static int get_live_bit( int *live, int reg ) { 195 return live[reg>>LogBitsPerInt] & (1<<(reg&(BitsPerInt-1))); } 196static void set_live_bit( int *live, int reg ) { 197 live[reg>>LogBitsPerInt] |= (1<<(reg&(BitsPerInt-1))); } 198static void clr_live_bit( int *live, int reg ) { 199 live[reg>>LogBitsPerInt] &= ~(1<<(reg&(BitsPerInt-1))); } 200 201//------------------------------build_oop_map---------------------------------- 202// Build an oopmap from the current flow info 203OopMap *OopFlow::build_oop_map( Node *n, int max_reg, PhaseRegAlloc *regalloc, int* live ) { 204 int framesize = regalloc->_framesize; 205 int max_inarg_slot = OptoReg::reg2stack(regalloc->_matcher._new_SP); 206 debug_only( char *dup_check = NEW_RESOURCE_ARRAY(char,OptoReg::stack0()); 207 memset(dup_check,0,OptoReg::stack0()) ); 208 209 OopMap *omap = new OopMap( framesize, max_inarg_slot ); 210 MachCallNode *mcall = n->is_MachCall() ? n->as_MachCall() : NULL; 211 JVMState* jvms = n->jvms(); 212 213 // For all registers do... 214 for( int reg=0; reg<max_reg; reg++ ) { 215 if( get_live_bit(live,reg) == 0 ) 216 continue; // Ignore if not live 217 218 // %%% C2 can use 2 OptoRegs when the physical register is only one 64bit 219 // register in that case we'll get an non-concrete register for the second 220 // half. We only need to tell the map the register once! 221 // 222 // However for the moment we disable this change and leave things as they 223 // were. 224 225 VMReg r = OptoReg::as_VMReg(OptoReg::Name(reg), framesize, max_inarg_slot); 226 227 if (false && r->is_reg() && !r->is_concrete()) { 228 continue; 229 } 230 231 // See if dead (no reaching def). 232 Node *def = _defs[reg]; // Get reaching def 233 assert( def, "since live better have reaching def" ); 234 235 // Classify the reaching def as oop, derived, callee-save, dead, or other 236 const Type *t = def->bottom_type(); 237 if( t->isa_oop_ptr() ) { // Oop or derived? 238 assert( !OptoReg::is_valid(_callees[reg]), "oop can't be callee save" ); 239#ifdef _LP64 240 // 64-bit pointers record oop-ishness on 2 aligned adjacent registers. 241 // Make sure both are record from the same reaching def, but do not 242 // put both into the oopmap. 243 if( (reg&1) == 1 ) { // High half of oop-pair? 244 assert( _defs[reg-1] == _defs[reg], "both halves from same reaching def" ); 245 continue; // Do not record high parts in oopmap 246 } 247#endif 248 249 // Check for a legal reg name in the oopMap and bailout if it is not. 250 if (!omap->legal_vm_reg_name(r)) { 251 regalloc->C->record_method_not_compilable("illegal oopMap register name"); 252 continue; 253 } 254 if( t->is_ptr()->_offset == 0 ) { // Not derived? 255 if( mcall ) { 256 // Outgoing argument GC mask responsibility belongs to the callee, 257 // not the caller. Inspect the inputs to the call, to see if 258 // this live-range is one of them. 259 uint cnt = mcall->tf()->domain()->cnt(); 260 uint j; 261 for( j = TypeFunc::Parms; j < cnt; j++) 262 if( mcall->in(j) == def ) 263 break; // reaching def is an argument oop 264 if( j < cnt ) // arg oops dont go in GC map 265 continue; // Continue on to the next register 266 } 267 omap->set_oop(r); 268 } else { // Else it's derived. 269 // Find the base of the derived value. 270 uint i; 271 // Fast, common case, scan 272 for( i = jvms->oopoff(); i < n->req(); i+=2 ) 273 if( n->in(i) == def ) break; // Common case 274 if( i == n->req() ) { // Missed, try a more generous scan 275 // Scan again, but this time peek through copies 276 for( i = jvms->oopoff(); i < n->req(); i+=2 ) { 277 Node *m = n->in(i); // Get initial derived value 278 while( 1 ) { 279 Node *d = def; // Get initial reaching def 280 while( 1 ) { // Follow copies of reaching def to end 281 if( m == d ) goto found; // breaks 3 loops 282 int idx = d->is_Copy(); 283 if( !idx ) break; 284 d = d->in(idx); // Link through copy 285 } 286 int idx = m->is_Copy(); 287 if( !idx ) break; 288 m = m->in(idx); 289 } 290 } 291 guarantee( 0, "must find derived/base pair" ); 292 } 293 found: ; 294 Node *base = n->in(i+1); // Base is other half of pair 295 int breg = regalloc->get_reg_first(base); 296 VMReg b = OptoReg::as_VMReg(OptoReg::Name(breg), framesize, max_inarg_slot); 297 298 // I record liveness at safepoints BEFORE I make the inputs 299 // live. This is because argument oops are NOT live at a 300 // safepoint (or at least they cannot appear in the oopmap). 301 // Thus bases of base/derived pairs might not be in the 302 // liveness data but they need to appear in the oopmap. 303 if( get_live_bit(live,breg) == 0 ) {// Not live? 304 // Flag it, so next derived pointer won't re-insert into oopmap 305 set_live_bit(live,breg); 306 // Already missed our turn? 307 if( breg < reg ) { 308 if (b->is_stack() || b->is_concrete() || true ) { 309 omap->set_oop( b); 310 } 311 } 312 } 313 if (b->is_stack() || b->is_concrete() || true ) { 314 omap->set_derived_oop( r, b); 315 } 316 } 317 318 } else if( OptoReg::is_valid(_callees[reg])) { // callee-save? 319 // It's a callee-save value 320 assert( dup_check[_callees[reg]]==0, "trying to callee save same reg twice" ); 321 debug_only( dup_check[_callees[reg]]=1; ) 322 VMReg callee = OptoReg::as_VMReg(OptoReg::Name(_callees[reg])); 323 if ( callee->is_concrete() || true ) { 324 omap->set_callee_saved( r, callee); 325 } 326 327 } else { 328 // Other - some reaching non-oop value 329 omap->set_value( r); 330 } 331 332 } 333 334#ifdef ASSERT 335 /* Nice, Intel-only assert 336 int cnt_callee_saves=0; 337 int reg2 = 0; 338 while (OptoReg::is_reg(reg2)) { 339 if( dup_check[reg2] != 0) cnt_callee_saves++; 340 assert( cnt_callee_saves==3 || cnt_callee_saves==5, "missed some callee-save" ); 341 reg2++; 342 } 343 */ 344#endif 345 346 return omap; 347} 348 349//------------------------------do_liveness------------------------------------ 350// Compute backwards liveness on registers 351static void do_liveness( PhaseRegAlloc *regalloc, PhaseCFG *cfg, Block_List *worklist, int max_reg_ints, Arena *A, Dict *safehash ) { 352 int *live = NEW_ARENA_ARRAY(A, int, (cfg->_num_blocks+1) * max_reg_ints); 353 int *tmp_live = &live[cfg->_num_blocks * max_reg_ints]; 354 Node *root = cfg->C->root(); 355 // On CISC platforms, get the node representing the stack pointer that regalloc 356 // used for spills 357 Node *fp = NodeSentinel; 358 if (UseCISCSpill && root->req() > 1) { 359 fp = root->in(1)->in(TypeFunc::FramePtr); 360 } 361 memset( live, 0, cfg->_num_blocks * (max_reg_ints<<LogBytesPerInt) ); 362 // Push preds onto worklist 363 for( uint i=1; i<root->req(); i++ ) 364 worklist->push(cfg->_bbs[root->in(i)->_idx]); 365 366 // ZKM.jar includes tiny infinite loops which are unreached from below. 367 // If we missed any blocks, we'll retry here after pushing all missed 368 // blocks on the worklist. Normally this outer loop never trips more 369 // than once. 370 while( 1 ) { 371 372 while( worklist->size() ) { // Standard worklist algorithm 373 Block *b = worklist->rpop(); 374 375 // Copy first successor into my tmp_live space 376 int s0num = b->_succs[0]->_pre_order; 377 int *t = &live[s0num*max_reg_ints]; 378 for( int i=0; i<max_reg_ints; i++ ) 379 tmp_live[i] = t[i]; 380 381 // OR in the remaining live registers 382 for( uint j=1; j<b->_num_succs; j++ ) { 383 uint sjnum = b->_succs[j]->_pre_order; 384 int *t = &live[sjnum*max_reg_ints]; 385 for( int i=0; i<max_reg_ints; i++ ) 386 tmp_live[i] |= t[i]; 387 } 388 389 // Now walk tmp_live up the block backwards, computing live 390 for( int k=b->_nodes.size()-1; k>=0; k-- ) { 391 Node *n = b->_nodes[k]; 392 // KILL def'd bits 393 int first = regalloc->get_reg_first(n); 394 int second = regalloc->get_reg_second(n); 395 if( OptoReg::is_valid(first) ) clr_live_bit(tmp_live,first); 396 if( OptoReg::is_valid(second) ) clr_live_bit(tmp_live,second); 397 398 MachNode *m = n->is_Mach() ? n->as_Mach() : NULL; 399 400 // Check if m is potentially a CISC alternate instruction (i.e, possibly 401 // synthesized by RegAlloc from a conventional instruction and a 402 // spilled input) 403 bool is_cisc_alternate = false; 404 if (UseCISCSpill && m) { 405 is_cisc_alternate = m->is_cisc_alternate(); 406 } 407 408 // GEN use'd bits 409 for( uint l=1; l<n->req(); l++ ) { 410 Node *def = n->in(l); 411 assert(def != 0, "input edge required"); 412 int first = regalloc->get_reg_first(def); 413 int second = regalloc->get_reg_second(def); 414 if( OptoReg::is_valid(first) ) set_live_bit(tmp_live,first); 415 if( OptoReg::is_valid(second) ) set_live_bit(tmp_live,second); 416 // If we use the stack pointer in a cisc-alternative instruction, 417 // check for use as a memory operand. Then reconstruct the RegName 418 // for this stack location, and set the appropriate bit in the 419 // live vector 4987749. 420 if (is_cisc_alternate && def == fp) { 421 const TypePtr *adr_type = NULL; 422 intptr_t offset; 423 const Node* base = m->get_base_and_disp(offset, adr_type); 424 if (base == NodeSentinel) { 425 // Machnode has multiple memory inputs. We are unable to reason 426 // with these, but are presuming (with trepidation) that not any of 427 // them are oops. This can be fixed by making get_base_and_disp() 428 // look at a specific input instead of all inputs. 429 assert(!def->bottom_type()->isa_oop_ptr(), "expecting non-oop mem input"); 430 } else if (base != fp || offset == Type::OffsetBot) { 431 // Do nothing: the fp operand is either not from a memory use 432 // (base == NULL) OR the fp is used in a non-memory context 433 // (base is some other register) OR the offset is not constant, 434 // so it is not a stack slot. 435 } else { 436 assert(offset >= 0, "unexpected negative offset"); 437 offset -= (offset % jintSize); // count the whole word 438 int stack_reg = regalloc->offset2reg(offset); 439 if (OptoReg::is_stack(stack_reg)) { 440 set_live_bit(tmp_live, stack_reg); 441 } else { 442 assert(false, "stack_reg not on stack?"); 443 } 444 } 445 } 446 } 447 448 if( n->jvms() ) { // Record liveness at safepoint 449 450 // This placement of this stanza means inputs to calls are 451 // considered live at the callsite's OopMap. Argument oops are 452 // hence live, but NOT included in the oopmap. See cutout in 453 // build_oop_map. Debug oops are live (and in OopMap). 454 int *n_live = NEW_ARENA_ARRAY(A, int, max_reg_ints); 455 for( int l=0; l<max_reg_ints; l++ ) 456 n_live[l] = tmp_live[l]; 457 safehash->Insert(n,n_live); 458 } 459 460 } 461 462 // Now at block top, see if we have any changes. If so, propagate 463 // to prior blocks. 464 int *old_live = &live[b->_pre_order*max_reg_ints]; 465 int l; 466 for( l=0; l<max_reg_ints; l++ ) 467 if( tmp_live[l] != old_live[l] ) 468 break; 469 if( l<max_reg_ints ) { // Change! 470 // Copy in new value 471 for( l=0; l<max_reg_ints; l++ ) 472 old_live[l] = tmp_live[l]; 473 // Push preds onto worklist 474 for( l=1; l<(int)b->num_preds(); l++ ) 475 worklist->push(cfg->_bbs[b->pred(l)->_idx]); 476 } 477 } 478 479 // Scan for any missing safepoints. Happens to infinite loops 480 // ala ZKM.jar 481 uint i; 482 for( i=1; i<cfg->_num_blocks; i++ ) { 483 Block *b = cfg->_blocks[i]; 484 uint j; 485 for( j=1; j<b->_nodes.size(); j++ ) 486 if( b->_nodes[j]->jvms() && 487 (*safehash)[b->_nodes[j]] == NULL ) 488 break; 489 if( j<b->_nodes.size() ) break; 490 } 491 if( i == cfg->_num_blocks ) 492 break; // Got 'em all 493#ifndef PRODUCT 494 if( PrintOpto && Verbose ) 495 tty->print_cr("retripping live calc"); 496#endif 497 // Force the issue (expensively): recheck everybody 498 for( i=1; i<cfg->_num_blocks; i++ ) 499 worklist->push(cfg->_blocks[i]); 500 } 501 502} 503 504//------------------------------BuildOopMaps----------------------------------- 505// Collect GC mask info - where are all the OOPs? 506void Compile::BuildOopMaps() { 507 NOT_PRODUCT( TracePhase t3("bldOopMaps", &_t_buildOopMaps, TimeCompiler); ) 508 // Can't resource-mark because I need to leave all those OopMaps around, 509 // or else I need to resource-mark some arena other than the default. 510 // ResourceMark rm; // Reclaim all OopFlows when done 511 int max_reg = _regalloc->_max_reg; // Current array extent 512 513 Arena *A = Thread::current()->resource_area(); 514 Block_List worklist; // Worklist of pending blocks 515 516 int max_reg_ints = round_to(max_reg, BitsPerInt)>>LogBitsPerInt; 517 Dict *safehash = NULL; // Used for assert only 518 // Compute a backwards liveness per register. Needs a bitarray of 519 // #blocks x (#registers, rounded up to ints) 520 safehash = new Dict(cmpkey,hashkey,A); 521 do_liveness( _regalloc, _cfg, &worklist, max_reg_ints, A, safehash ); 522 OopFlow *free_list = NULL; // Free, unused 523 524 // Array mapping blocks to completed oopflows 525 OopFlow **flows = NEW_ARENA_ARRAY(A, OopFlow*, _cfg->_num_blocks); 526 memset( flows, 0, _cfg->_num_blocks*sizeof(OopFlow*) ); 527 528 529 // Do the first block 'by hand' to prime the worklist 530 Block *entry = _cfg->_blocks[1]; 531 OopFlow *rootflow = OopFlow::make(A,max_reg); 532 // Initialize to 'bottom' (not 'top') 533 memset( rootflow->_callees, OptoReg::Bad, max_reg*sizeof(short) ); 534 memset( rootflow->_defs , 0, max_reg*sizeof(Node*) ); 535 flows[entry->_pre_order] = rootflow; 536 537 // Do the first block 'by hand' to prime the worklist 538 rootflow->_b = entry; 539 rootflow->compute_reach( _regalloc, max_reg, safehash ); 540 for( uint i=0; i<entry->_num_succs; i++ ) 541 worklist.push(entry->_succs[i]); 542 543 // Now worklist contains blocks which have some, but perhaps not all, 544 // predecessors visited. 545 while( worklist.size() ) { 546 // Scan for a block with all predecessors visited, or any randoms slob 547 // otherwise. All-preds-visited order allows me to recycle OopFlow 548 // structures rapidly and cut down on the memory footprint. 549 // Note: not all predecessors might be visited yet (must happen for 550 // irreducible loops). This is OK, since every live value must have the 551 // SAME reaching def for the block, so any reaching def is OK. 552 uint i; 553 554 Block *b = worklist.pop(); 555 // Ignore root block 556 if( b == _cfg->_broot ) continue; 557 // Block is already done? Happens if block has several predecessors, 558 // he can get on the worklist more than once. 559 if( flows[b->_pre_order] ) continue; 560 561 // If this block has a visited predecessor AND that predecessor has this 562 // last block as his only undone child, we can move the OopFlow from the 563 // pred to this block. Otherwise we have to grab a new OopFlow. 564 OopFlow *flow = NULL; // Flag for finding optimized flow 565 Block *pred = (Block*)0xdeadbeef; 566 uint j; 567 // Scan this block's preds to find a done predecessor 568 for( j=1; j<b->num_preds(); j++ ) { 569 Block *p = _cfg->_bbs[b->pred(j)->_idx]; 570 OopFlow *p_flow = flows[p->_pre_order]; 571 if( p_flow ) { // Predecessor is done 572 assert( p_flow->_b == p, "cross check" ); 573 pred = p; // Record some predecessor 574 // If all successors of p are done except for 'b', then we can carry 575 // p_flow forward to 'b' without copying, otherwise we have to draw 576 // from the free_list and clone data. 577 uint k; 578 for( k=0; k<p->_num_succs; k++ ) 579 if( !flows[p->_succs[k]->_pre_order] && 580 p->_succs[k] != b ) 581 break; 582 583 // Either carry-forward the now-unused OopFlow for b's use 584 // or draw a new one from the free list 585 if( k==p->_num_succs ) { 586 flow = p_flow; 587 break; // Found an ideal pred, use him 588 } 589 } 590 } 591 592 if( flow ) { 593 // We have an OopFlow that's the last-use of a predecessor. 594 // Carry it forward. 595 } else { // Draw a new OopFlow from the freelist 596 if( !free_list ) 597 free_list = OopFlow::make(A,max_reg); 598 flow = free_list; 599 assert( flow->_b == NULL, "oopFlow is not free" ); 600 free_list = flow->_next; 601 flow->_next = NULL; 602 603 // Copy/clone over the data 604 flow->clone(flows[pred->_pre_order], max_reg); 605 } 606 607 // Mark flow for block. Blocks can only be flowed over once, 608 // because after the first time they are guarded from entering 609 // this code again. 610 assert( flow->_b == pred, "have some prior flow" ); 611 flow->_b = NULL; 612 613 // Now push flow forward 614 flows[b->_pre_order] = flow;// Mark flow for this block 615 flow->_b = b; 616 flow->compute_reach( _regalloc, max_reg, safehash ); 617 618 // Now push children onto worklist 619 for( i=0; i<b->_num_succs; i++ ) 620 worklist.push(b->_succs[i]); 621 622 } 623} 624