1 /*
   2  * Copyright (c) 2002, 2018, 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 "code/vmreg.inline.hpp"
  27 #include "compiler/oopMap.hpp"
  28 #include "memory/resourceArea.hpp"
  29 #include "opto/addnode.hpp"
  30 #include "opto/callnode.hpp"
  31 #include "opto/compile.hpp"
  32 #include "opto/machnode.hpp"
  33 #include "opto/matcher.hpp"
  34 #include "opto/phase.hpp"
  35 #include "opto/regalloc.hpp"
  36 #include "opto/rootnode.hpp"
  37 #include "utilities/align.hpp"
  38 
  39 // The functions in this file builds OopMaps after all scheduling is done.
  40 //
  41 // OopMaps contain a list of all registers and stack-slots containing oops (so
  42 // they can be updated by GC).  OopMaps also contain a list of derived-pointer
  43 // base-pointer pairs.  When the base is moved, the derived pointer moves to
  44 // follow it.  Finally, any registers holding callee-save values are also
  45 // recorded.  These might contain oops, but only the caller knows.
  46 //
  47 // BuildOopMaps implements a simple forward reaching-defs solution.  At each
  48 // GC point we'll have the reaching-def Nodes.  If the reaching Nodes are
  49 // typed as pointers (no offset), then they are oops.  Pointers+offsets are
  50 // derived pointers, and bases can be found from them.  Finally, we'll also
  51 // track reaching callee-save values.  Note that a copy of a callee-save value
  52 // "kills" it's source, so that only 1 copy of a callee-save value is alive at
  53 // a time.
  54 //
  55 // We run a simple bitvector liveness pass to help trim out dead oops.  Due to
  56 // irreducible loops, we can have a reaching def of an oop that only reaches
  57 // along one path and no way to know if it's valid or not on the other path.
  58 // The bitvectors are quite dense and the liveness pass is fast.
  59 //
  60 // At GC points, we consult this information to build OopMaps.  All reaching
  61 // defs typed as oops are added to the OopMap.  Only 1 instance of a
  62 // callee-save register can be recorded.  For derived pointers, we'll have to
  63 // find and record the register holding the base.
  64 //
  65 // The reaching def's is a simple 1-pass worklist approach.  I tried a clever
  66 // breadth-first approach but it was worse (showed O(n^2) in the
  67 // pick-next-block code).
  68 //
  69 // The relevant data is kept in a struct of arrays (it could just as well be
  70 // an array of structs, but the struct-of-arrays is generally a little more
  71 // efficient).  The arrays are indexed by register number (including
  72 // stack-slots as registers) and so is bounded by 200 to 300 elements in
  73 // practice.  One array will map to a reaching def Node (or NULL for
  74 // conflict/dead).  The other array will map to a callee-saved register or
  75 // OptoReg::Bad for not-callee-saved.
  76 
  77 
  78 // Structure to pass around
  79 struct OopFlow : public ResourceObj {
  80   short *_callees;              // Array mapping register to callee-saved
  81   Node **_defs;                 // array mapping register to reaching def
  82                                 // or NULL if dead/conflict
  83   // OopFlow structs, when not being actively modified, describe the _end_ of
  84   // this block.
  85   Block *_b;                    // Block for this struct
  86   OopFlow *_next;               // Next free OopFlow
  87                                 // or NULL if dead/conflict
  88   Compile* C;
  89 
  90   OopFlow( short *callees, Node **defs, Compile* c ) : _callees(callees), _defs(defs),
  91     _b(NULL), _next(NULL), C(c) { }
  92 
  93   // Given reaching-defs for this block start, compute it for this block end
  94   void compute_reach( PhaseRegAlloc *regalloc, int max_reg, Dict *safehash );
  95 
  96   // Merge these two OopFlows into the 'this' pointer.
  97   void merge( OopFlow *flow, int max_reg );
  98 
  99   // Copy a 'flow' over an existing flow
 100   void clone( OopFlow *flow, int max_size);
 101 
 102   // Make a new OopFlow from scratch
 103   static OopFlow *make( Arena *A, int max_size, Compile* C );
 104 
 105   // Build an oopmap from the current flow info
 106   OopMap *build_oop_map( Node *n, int max_reg, PhaseRegAlloc *regalloc, int* live );
 107 };
 108 
 109 // Given reaching-defs for this block start, compute it for this block end
 110 void OopFlow::compute_reach( PhaseRegAlloc *regalloc, int max_reg, Dict *safehash ) {
 111 
 112   for( uint i=0; i<_b->number_of_nodes(); i++ ) {
 113     Node *n = _b->get_node(i);
 114 
 115     if( n->jvms() ) {           // Build an OopMap here?
 116       JVMState *jvms = n->jvms();
 117       // no map needed for leaf calls
 118       if( n->is_MachSafePoint() && !n->is_MachCallLeaf() ) {
 119         int *live = (int*) (*safehash)[n];
 120         assert( live, "must find live" );
 121         n->as_MachSafePoint()->set_oop_map( build_oop_map(n,max_reg,regalloc, live) );
 122       }
 123     }
 124 
 125     // Assign new reaching def's.
 126     // Note that I padded the _defs and _callees arrays so it's legal
 127     // to index at _defs[OptoReg::Bad].
 128     OptoReg::Name first = regalloc->get_reg_first(n);
 129     OptoReg::Name second = regalloc->get_reg_second(n);
 130     _defs[first] = n;
 131     _defs[second] = n;
 132 
 133     // Pass callee-save info around copies
 134     int idx = n->is_Copy();
 135     if( idx ) {                 // Copies move callee-save info
 136       OptoReg::Name old_first = regalloc->get_reg_first(n->in(idx));
 137       OptoReg::Name old_second = regalloc->get_reg_second(n->in(idx));
 138       int tmp_first = _callees[old_first];
 139       int tmp_second = _callees[old_second];
 140       _callees[old_first] = OptoReg::Bad; // callee-save is moved, dead in old location
 141       _callees[old_second] = OptoReg::Bad;
 142       _callees[first] = tmp_first;
 143       _callees[second] = tmp_second;
 144     } else if( n->is_Phi() ) {  // Phis do not mod callee-saves
 145       assert( _callees[first] == _callees[regalloc->get_reg_first(n->in(1))], "" );
 146       assert( _callees[second] == _callees[regalloc->get_reg_second(n->in(1))], "" );
 147       assert( _callees[first] == _callees[regalloc->get_reg_first(n->in(n->req()-1))], "" );
 148       assert( _callees[second] == _callees[regalloc->get_reg_second(n->in(n->req()-1))], "" );
 149     } else {
 150       _callees[first] = OptoReg::Bad; // No longer holding a callee-save value
 151       _callees[second] = OptoReg::Bad;
 152 
 153       // Find base case for callee saves
 154       if( n->is_Proj() && n->in(0)->is_Start() ) {
 155         if( OptoReg::is_reg(first) &&
 156             regalloc->_matcher.is_save_on_entry(first) )
 157           _callees[first] = first;
 158         if( OptoReg::is_reg(second) &&
 159             regalloc->_matcher.is_save_on_entry(second) )
 160           _callees[second] = second;
 161       }
 162     }
 163   }
 164 }
 165 
 166 // Merge the given flow into the 'this' flow
 167 void OopFlow::merge( OopFlow *flow, int max_reg ) {
 168   assert( _b == NULL, "merging into a happy flow" );
 169   assert( flow->_b, "this flow is still alive" );
 170   assert( flow != this, "no self flow" );
 171 
 172   // Do the merge.  If there are any differences, drop to 'bottom' which
 173   // is OptoReg::Bad or NULL depending.
 174   for( int i=0; i<max_reg; i++ ) {
 175     // Merge the callee-save's
 176     if( _callees[i] != flow->_callees[i] )
 177       _callees[i] = OptoReg::Bad;
 178     // Merge the reaching defs
 179     if( _defs[i] != flow->_defs[i] )
 180       _defs[i] = NULL;
 181   }
 182 
 183 }
 184 
 185 void OopFlow::clone( OopFlow *flow, int max_size ) {
 186   _b = flow->_b;
 187   memcpy( _callees, flow->_callees, sizeof(short)*max_size);
 188   memcpy( _defs   , flow->_defs   , sizeof(Node*)*max_size);
 189 }
 190 
 191 OopFlow *OopFlow::make( Arena *A, int max_size, Compile* C ) {
 192   short *callees = NEW_ARENA_ARRAY(A,short,max_size+1);
 193   Node **defs    = NEW_ARENA_ARRAY(A,Node*,max_size+1);
 194   debug_only( memset(defs,0,(max_size+1)*sizeof(Node*)) );
 195   OopFlow *flow = new (A) OopFlow(callees+1, defs+1, C);
 196   assert( &flow->_callees[OptoReg::Bad] == callees, "Ok to index at OptoReg::Bad" );
 197   assert( &flow->_defs   [OptoReg::Bad] == defs   , "Ok to index at OptoReg::Bad" );
 198   return flow;
 199 }
 200 
 201 static int get_live_bit( int *live, int reg ) {
 202   return live[reg>>LogBitsPerInt] &   (1<<(reg&(BitsPerInt-1))); }
 203 static void set_live_bit( int *live, int reg ) {
 204          live[reg>>LogBitsPerInt] |=  (1<<(reg&(BitsPerInt-1))); }
 205 static void clr_live_bit( int *live, int reg ) {
 206          live[reg>>LogBitsPerInt] &= ~(1<<(reg&(BitsPerInt-1))); }
 207 
 208 // Build an oopmap from the current flow info
 209 OopMap *OopFlow::build_oop_map( Node *n, int max_reg, PhaseRegAlloc *regalloc, int* live ) {
 210   int framesize = regalloc->_framesize;
 211   int max_inarg_slot = OptoReg::reg2stack(regalloc->_matcher._new_SP);
 212   debug_only( char *dup_check = NEW_RESOURCE_ARRAY(char,OptoReg::stack0());
 213               memset(dup_check,0,OptoReg::stack0()) );
 214 
 215   OopMap *omap = new OopMap( framesize,  max_inarg_slot );
 216   MachCallNode *mcall = n->is_MachCall() ? n->as_MachCall() : NULL;
 217   JVMState* jvms = n->jvms();
 218 
 219   // For all registers do...
 220   for( int reg=0; reg<max_reg; reg++ ) {
 221     if( get_live_bit(live,reg) == 0 )
 222       continue;                 // Ignore if not live
 223 
 224     // %%% C2 can use 2 OptoRegs when the physical register is only one 64bit
 225     // register in that case we'll get an non-concrete register for the second
 226     // half. We only need to tell the map the register once!
 227     //
 228     // However for the moment we disable this change and leave things as they
 229     // were.
 230 
 231     VMReg r = OptoReg::as_VMReg(OptoReg::Name(reg), framesize, max_inarg_slot);
 232 
 233     if (false && r->is_reg() && !r->is_concrete()) {
 234       continue;
 235     }
 236 
 237     // See if dead (no reaching def).
 238     Node *def = _defs[reg];     // Get reaching def
 239     assert( def, "since live better have reaching def" );
 240 
 241     // Classify the reaching def as oop, derived, callee-save, dead, or other
 242     const Type *t = def->bottom_type();
 243     if( t->isa_oop_ptr() ) {    // Oop or derived?
 244       assert( !OptoReg::is_valid(_callees[reg]), "oop can't be callee save" );
 245 #ifdef _LP64
 246       // 64-bit pointers record oop-ishness on 2 aligned adjacent registers.
 247       // Make sure both are record from the same reaching def, but do not
 248       // put both into the oopmap.
 249       if( (reg&1) == 1 ) {      // High half of oop-pair?
 250         assert( _defs[reg-1] == _defs[reg], "both halves from same reaching def" );
 251         continue;               // Do not record high parts in oopmap
 252       }
 253 #endif
 254 
 255       // Check for a legal reg name in the oopMap and bailout if it is not.
 256       if (!omap->legal_vm_reg_name(r)) {
 257         regalloc->C->record_method_not_compilable("illegal oopMap register name");
 258         continue;
 259       }
 260       if( t->is_ptr()->_offset == 0 ) { // Not derived?
 261         if( mcall ) {
 262           // Outgoing argument GC mask responsibility belongs to the callee,
 263           // not the caller.  Inspect the inputs to the call, to see if
 264           // this live-range is one of them.
 265           uint cnt = mcall->tf()->domain()->cnt();
 266           uint j;
 267           for( j = TypeFunc::Parms; j < cnt; j++)
 268             if( mcall->in(j) == def )
 269               break;            // reaching def is an argument oop
 270           if( j < cnt )         // arg oops dont go in GC map
 271             continue;           // Continue on to the next register
 272         }
 273         omap->set_oop(r);
 274       } else {                  // Else it's derived.
 275         // Find the base of the derived value.
 276         uint i;
 277         // Fast, common case, scan
 278         for( i = jvms->oopoff(); i < n->req(); i+=2 )
 279           if( n->in(i) == def ) break; // Common case
 280         if( i == n->req() ) {   // Missed, try a more generous scan
 281           // Scan again, but this time peek through copies
 282           for( i = jvms->oopoff(); i < n->req(); i+=2 ) {
 283             Node *m = n->in(i); // Get initial derived value
 284             while( 1 ) {
 285               Node *d = def;    // Get initial reaching def
 286               while( 1 ) {      // Follow copies of reaching def to end
 287                 if( m == d ) goto found; // breaks 3 loops
 288                 int idx = d->is_Copy();
 289                 if( !idx ) break;
 290                 d = d->in(idx);     // Link through copy
 291               }
 292               int idx = m->is_Copy();
 293               if( !idx ) break;
 294               m = m->in(idx);
 295             }
 296           }
 297           guarantee( 0, "must find derived/base pair" );
 298         }
 299       found: ;
 300         Node *base = n->in(i+1); // Base is other half of pair
 301         int breg = regalloc->get_reg_first(base);
 302         VMReg b = OptoReg::as_VMReg(OptoReg::Name(breg), framesize, max_inarg_slot);
 303 
 304         // I record liveness at safepoints BEFORE I make the inputs
 305         // live.  This is because argument oops are NOT live at a
 306         // safepoint (or at least they cannot appear in the oopmap).
 307         // Thus bases of base/derived pairs might not be in the
 308         // liveness data but they need to appear in the oopmap.
 309         if( get_live_bit(live,breg) == 0 ) {// Not live?
 310           // Flag it, so next derived pointer won't re-insert into oopmap
 311           set_live_bit(live,breg);
 312           // Already missed our turn?
 313           if( breg < reg ) {
 314             if (b->is_stack() || b->is_concrete() || true ) {
 315               omap->set_oop( b);
 316             }
 317           }
 318         }
 319         if (b->is_stack() || b->is_concrete() || true ) {
 320           omap->set_derived_oop( r, b);
 321         }
 322       }
 323 
 324     } else if( t->isa_narrowoop() ) {
 325       assert( !OptoReg::is_valid(_callees[reg]), "oop can't be callee save" );
 326       // Check for a legal reg name in the oopMap and bailout if it is not.
 327       if (!omap->legal_vm_reg_name(r)) {
 328         regalloc->C->record_method_not_compilable("illegal oopMap register name");
 329         continue;
 330       }
 331       if( mcall ) {
 332           // Outgoing argument GC mask responsibility belongs to the callee,
 333           // not the caller.  Inspect the inputs to the call, to see if
 334           // this live-range is one of them.
 335         uint cnt = mcall->tf()->domain()->cnt();
 336         uint j;
 337         for( j = TypeFunc::Parms; j < cnt; j++)
 338           if( mcall->in(j) == def )
 339             break;            // reaching def is an argument oop
 340         if( j < cnt )         // arg oops dont go in GC map
 341           continue;           // Continue on to the next register
 342       }
 343       omap->set_narrowoop(r);
 344     } else if( OptoReg::is_valid(_callees[reg])) { // callee-save?
 345       // It's a callee-save value
 346       assert( dup_check[_callees[reg]]==0, "trying to callee save same reg twice" );
 347       debug_only( dup_check[_callees[reg]]=1; )
 348       VMReg callee = OptoReg::as_VMReg(OptoReg::Name(_callees[reg]));
 349       if ( callee->is_concrete() || true ) {
 350         omap->set_callee_saved( r, callee);
 351       }
 352 
 353     } else {
 354       // Other - some reaching non-oop value
 355       omap->set_value( r);
 356 #ifdef ASSERT
 357       if( t->isa_rawptr() && C->cfg()->_raw_oops.member(def) ) {
 358         def->dump();
 359         n->dump();
 360         assert(false, "there should be a oop in OopMap instead of a live raw oop at safepoint");
 361       }
 362 #endif
 363     }
 364 
 365   }
 366 
 367 #ifdef ASSERT
 368   /* Nice, Intel-only assert
 369   int cnt_callee_saves=0;
 370   int reg2 = 0;
 371   while (OptoReg::is_reg(reg2)) {
 372     if( dup_check[reg2] != 0) cnt_callee_saves++;
 373     assert( cnt_callee_saves==3 || cnt_callee_saves==5, "missed some callee-save" );
 374     reg2++;
 375   }
 376   */
 377 #endif
 378 
 379 #ifdef ASSERT
 380   for( OopMapStream oms1(omap, OopMapValue::derived_oop_value); !oms1.is_done(); oms1.next()) {
 381     OopMapValue omv1 = oms1.current();
 382     bool found = false;
 383     for( OopMapStream oms2(omap,OopMapValue::oop_value); !oms2.is_done(); oms2.next()) {
 384       if( omv1.content_reg() == oms2.current().reg() ) {
 385         found = true;
 386         break;
 387       }
 388     }
 389     assert( found, "derived with no base in oopmap" );
 390   }
 391 
 392   int num_oops = 0;
 393   for (OopMapStream oms2(omap, OopMapValue::oop_value | OopMapValue::narrowoop_value); !oms2.is_done(); oms2.next())
 394     num_oops++;
 395   assert (num_oops == omap->num_oops(), "num_oops: %d omap->num_oops(): %d", num_oops, omap->num_oops());
 396 #endif
 397 
 398   return omap;
 399 }
 400 
 401 // Compute backwards liveness on registers
 402 static void do_liveness(PhaseRegAlloc* regalloc, PhaseCFG* cfg, Block_List* worklist, int max_reg_ints, Arena* A, Dict* safehash) {
 403   int* live = NEW_ARENA_ARRAY(A, int, (cfg->number_of_blocks() + 1) * max_reg_ints);
 404   int* tmp_live = &live[cfg->number_of_blocks() * max_reg_ints];
 405   Node* root = cfg->get_root_node();
 406   // On CISC platforms, get the node representing the stack pointer  that regalloc
 407   // used for spills
 408   Node *fp = NodeSentinel;
 409   if (UseCISCSpill && root->req() > 1) {
 410     fp = root->in(1)->in(TypeFunc::FramePtr);
 411   }
 412   memset(live, 0, cfg->number_of_blocks() * (max_reg_ints << LogBytesPerInt));
 413   // Push preds onto worklist
 414   for (uint i = 1; i < root->req(); i++) {
 415     Block* block = cfg->get_block_for_node(root->in(i));
 416     worklist->push(block);
 417   }
 418 
 419   // ZKM.jar includes tiny infinite loops which are unreached from below.
 420   // If we missed any blocks, we'll retry here after pushing all missed
 421   // blocks on the worklist.  Normally this outer loop never trips more
 422   // than once.
 423   while (1) {
 424 
 425     while( worklist->size() ) { // Standard worklist algorithm
 426       Block *b = worklist->rpop();
 427 
 428       // Copy first successor into my tmp_live space
 429       int s0num = b->_succs[0]->_pre_order;
 430       int *t = &live[s0num*max_reg_ints];
 431       for( int i=0; i<max_reg_ints; i++ )
 432         tmp_live[i] = t[i];
 433 
 434       // OR in the remaining live registers
 435       for( uint j=1; j<b->_num_succs; j++ ) {
 436         uint sjnum = b->_succs[j]->_pre_order;
 437         int *t = &live[sjnum*max_reg_ints];
 438         for( int i=0; i<max_reg_ints; i++ )
 439           tmp_live[i] |= t[i];
 440       }
 441 
 442       // Now walk tmp_live up the block backwards, computing live
 443       for( int k=b->number_of_nodes()-1; k>=0; k-- ) {
 444         Node *n = b->get_node(k);
 445         // KILL def'd bits
 446         int first = regalloc->get_reg_first(n);
 447         int second = regalloc->get_reg_second(n);
 448         if( OptoReg::is_valid(first) ) clr_live_bit(tmp_live,first);
 449         if( OptoReg::is_valid(second) ) clr_live_bit(tmp_live,second);
 450 
 451         MachNode *m = n->is_Mach() ? n->as_Mach() : NULL;
 452 
 453         // Check if m is potentially a CISC alternate instruction (i.e, possibly
 454         // synthesized by RegAlloc from a conventional instruction and a
 455         // spilled input)
 456         bool is_cisc_alternate = false;
 457         if (UseCISCSpill && m) {
 458           is_cisc_alternate = m->is_cisc_alternate();
 459         }
 460 
 461         // GEN use'd bits
 462         for( uint l=1; l<n->req(); l++ ) {
 463           Node *def = n->in(l);
 464           assert(def != 0, "input edge required");
 465           int first = regalloc->get_reg_first(def);
 466           int second = regalloc->get_reg_second(def);
 467           if( OptoReg::is_valid(first) ) set_live_bit(tmp_live,first);
 468           if( OptoReg::is_valid(second) ) set_live_bit(tmp_live,second);
 469           // If we use the stack pointer in a cisc-alternative instruction,
 470           // check for use as a memory operand.  Then reconstruct the RegName
 471           // for this stack location, and set the appropriate bit in the
 472           // live vector 4987749.
 473           if (is_cisc_alternate && def == fp) {
 474             const TypePtr *adr_type = NULL;
 475             intptr_t offset;
 476             const Node* base = m->get_base_and_disp(offset, adr_type);
 477             if (base == NodeSentinel) {
 478               // Machnode has multiple memory inputs. We are unable to reason
 479               // with these, but are presuming (with trepidation) that not any of
 480               // them are oops. This can be fixed by making get_base_and_disp()
 481               // look at a specific input instead of all inputs.
 482               assert(!def->bottom_type()->isa_oop_ptr(), "expecting non-oop mem input");
 483             } else if (base != fp || offset == Type::OffsetBot) {
 484               // Do nothing: the fp operand is either not from a memory use
 485               // (base == NULL) OR the fp is used in a non-memory context
 486               // (base is some other register) OR the offset is not constant,
 487               // so it is not a stack slot.
 488             } else {
 489               assert(offset >= 0, "unexpected negative offset");
 490               offset -= (offset % jintSize);  // count the whole word
 491               int stack_reg = regalloc->offset2reg(offset);
 492               if (OptoReg::is_stack(stack_reg)) {
 493                 set_live_bit(tmp_live, stack_reg);
 494               } else {
 495                 assert(false, "stack_reg not on stack?");
 496               }
 497             }
 498           }
 499         }
 500 
 501         if( n->jvms() ) {       // Record liveness at safepoint
 502 
 503           // This placement of this stanza means inputs to calls are
 504           // considered live at the callsite's OopMap.  Argument oops are
 505           // hence live, but NOT included in the oopmap.  See cutout in
 506           // build_oop_map.  Debug oops are live (and in OopMap).
 507           int *n_live = NEW_ARENA_ARRAY(A, int, max_reg_ints);
 508           for( int l=0; l<max_reg_ints; l++ )
 509             n_live[l] = tmp_live[l];
 510           safehash->Insert(n,n_live);
 511         }
 512 
 513       }
 514 
 515       // Now at block top, see if we have any changes.  If so, propagate
 516       // to prior blocks.
 517       int *old_live = &live[b->_pre_order*max_reg_ints];
 518       int l;
 519       for( l=0; l<max_reg_ints; l++ )
 520         if( tmp_live[l] != old_live[l] )
 521           break;
 522       if( l<max_reg_ints ) {     // Change!
 523         // Copy in new value
 524         for( l=0; l<max_reg_ints; l++ )
 525           old_live[l] = tmp_live[l];
 526         // Push preds onto worklist
 527         for (l = 1; l < (int)b->num_preds(); l++) {
 528           Block* block = cfg->get_block_for_node(b->pred(l));
 529           worklist->push(block);
 530         }
 531       }
 532     }
 533 
 534     // Scan for any missing safepoints.  Happens to infinite loops
 535     // ala ZKM.jar
 536     uint i;
 537     for (i = 1; i < cfg->number_of_blocks(); i++) {
 538       Block* block = cfg->get_block(i);
 539       uint j;
 540       for (j = 1; j < block->number_of_nodes(); j++) {
 541         if (block->get_node(j)->jvms() && (*safehash)[block->get_node(j)] == NULL) {
 542            break;
 543         }
 544       }
 545       if (j < block->number_of_nodes()) {
 546         break;
 547       }
 548     }
 549     if (i == cfg->number_of_blocks()) {
 550       break;                    // Got 'em all
 551     }
 552 
 553     if (PrintOpto && Verbose) {
 554       tty->print_cr("retripping live calc");
 555     }
 556 
 557     // Force the issue (expensively): recheck everybody
 558     for (i = 1; i < cfg->number_of_blocks(); i++) {
 559       worklist->push(cfg->get_block(i));
 560     }
 561   }
 562 }
 563 
 564 // Collect GC mask info - where are all the OOPs?
 565 void Compile::BuildOopMaps() {
 566   TracePhase tp("bldOopMaps", &timers[_t_buildOopMaps]);
 567   // Can't resource-mark because I need to leave all those OopMaps around,
 568   // or else I need to resource-mark some arena other than the default.
 569   // ResourceMark rm;              // Reclaim all OopFlows when done
 570   int max_reg = _regalloc->_max_reg; // Current array extent
 571 
 572   Arena *A = Thread::current()->resource_area();
 573   Block_List worklist;          // Worklist of pending blocks
 574 
 575   int max_reg_ints = align_up(max_reg, BitsPerInt)>>LogBitsPerInt;
 576   Dict *safehash = NULL;        // Used for assert only
 577   // Compute a backwards liveness per register.  Needs a bitarray of
 578   // #blocks x (#registers, rounded up to ints)
 579   safehash = new Dict(cmpkey,hashkey,A);
 580   do_liveness( _regalloc, _cfg, &worklist, max_reg_ints, A, safehash );
 581   OopFlow *free_list = NULL;    // Free, unused
 582 
 583   // Array mapping blocks to completed oopflows
 584   OopFlow **flows = NEW_ARENA_ARRAY(A, OopFlow*, _cfg->number_of_blocks());
 585   memset( flows, 0, _cfg->number_of_blocks() * sizeof(OopFlow*) );
 586 
 587 
 588   // Do the first block 'by hand' to prime the worklist
 589   Block *entry = _cfg->get_block(1);
 590   OopFlow *rootflow = OopFlow::make(A,max_reg,this);
 591   // Initialize to 'bottom' (not 'top')
 592   memset( rootflow->_callees, OptoReg::Bad, max_reg*sizeof(short) );
 593   memset( rootflow->_defs   ,            0, max_reg*sizeof(Node*) );
 594   flows[entry->_pre_order] = rootflow;
 595 
 596   // Do the first block 'by hand' to prime the worklist
 597   rootflow->_b = entry;
 598   rootflow->compute_reach( _regalloc, max_reg, safehash );
 599   for( uint i=0; i<entry->_num_succs; i++ )
 600     worklist.push(entry->_succs[i]);
 601 
 602   // Now worklist contains blocks which have some, but perhaps not all,
 603   // predecessors visited.
 604   while( worklist.size() ) {
 605     // Scan for a block with all predecessors visited, or any randoms slob
 606     // otherwise.  All-preds-visited order allows me to recycle OopFlow
 607     // structures rapidly and cut down on the memory footprint.
 608     // Note: not all predecessors might be visited yet (must happen for
 609     // irreducible loops).  This is OK, since every live value must have the
 610     // SAME reaching def for the block, so any reaching def is OK.
 611     uint i;
 612 
 613     Block *b = worklist.pop();
 614     // Ignore root block
 615     if (b == _cfg->get_root_block()) {
 616       continue;
 617     }
 618     // Block is already done?  Happens if block has several predecessors,
 619     // he can get on the worklist more than once.
 620     if( flows[b->_pre_order] ) continue;
 621 
 622     // If this block has a visited predecessor AND that predecessor has this
 623     // last block as his only undone child, we can move the OopFlow from the
 624     // pred to this block.  Otherwise we have to grab a new OopFlow.
 625     OopFlow *flow = NULL;       // Flag for finding optimized flow
 626     Block *pred = (Block*)((intptr_t)0xdeadbeef);
 627     // Scan this block's preds to find a done predecessor
 628     for (uint j = 1; j < b->num_preds(); j++) {
 629       Block* p = _cfg->get_block_for_node(b->pred(j));
 630       OopFlow *p_flow = flows[p->_pre_order];
 631       if( p_flow ) {            // Predecessor is done
 632         assert( p_flow->_b == p, "cross check" );
 633         pred = p;               // Record some predecessor
 634         // If all successors of p are done except for 'b', then we can carry
 635         // p_flow forward to 'b' without copying, otherwise we have to draw
 636         // from the free_list and clone data.
 637         uint k;
 638         for( k=0; k<p->_num_succs; k++ )
 639           if( !flows[p->_succs[k]->_pre_order] &&
 640               p->_succs[k] != b )
 641             break;
 642 
 643         // Either carry-forward the now-unused OopFlow for b's use
 644         // or draw a new one from the free list
 645         if( k==p->_num_succs ) {
 646           flow = p_flow;
 647           break;                // Found an ideal pred, use him
 648         }
 649       }
 650     }
 651 
 652     if( flow ) {
 653       // We have an OopFlow that's the last-use of a predecessor.
 654       // Carry it forward.
 655     } else {                    // Draw a new OopFlow from the freelist
 656       if( !free_list )
 657         free_list = OopFlow::make(A,max_reg,C);
 658       flow = free_list;
 659       assert( flow->_b == NULL, "oopFlow is not free" );
 660       free_list = flow->_next;
 661       flow->_next = NULL;
 662 
 663       // Copy/clone over the data
 664       flow->clone(flows[pred->_pre_order], max_reg);
 665     }
 666 
 667     // Mark flow for block.  Blocks can only be flowed over once,
 668     // because after the first time they are guarded from entering
 669     // this code again.
 670     assert( flow->_b == pred, "have some prior flow" );
 671     flow->_b = NULL;
 672 
 673     // Now push flow forward
 674     flows[b->_pre_order] = flow;// Mark flow for this block
 675     flow->_b = b;
 676     flow->compute_reach( _regalloc, max_reg, safehash );
 677 
 678     // Now push children onto worklist
 679     for( i=0; i<b->_num_succs; i++ )
 680       worklist.push(b->_succs[i]);
 681 
 682   }
 683 }