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 "compiler/oopMap.hpp"
  27 #include "opto/addnode.hpp"
  28 #include "opto/callnode.hpp"
  29 #include "opto/compile.hpp"
  30 #include "opto/machnode.hpp"
  31 #include "opto/matcher.hpp"
  32 #include "opto/phase.hpp"
  33 #include "opto/regalloc.hpp"
  34 #include "opto/rootnode.hpp"
  35 #ifdef TARGET_ARCH_x86
  36 # include "vmreg_x86.inline.hpp"
  37 #endif
  38 #ifdef TARGET_ARCH_sparc
  39 # include "vmreg_sparc.inline.hpp"
  40 #endif
  41 #ifdef TARGET_ARCH_zero
  42 # include "vmreg_zero.inline.hpp"
  43 #endif
  44 #ifdef TARGET_ARCH_arm
  45 # include "vmreg_arm.inline.hpp"
  46 #endif
  47 #ifdef TARGET_ARCH_ppc
  48 # include "vmreg_ppc.inline.hpp"
  49 #endif
  50 #ifdef TARGET_ARCH_aarch32
  51 # include "vmreg_aarch32.inline.hpp"
  52 #endif
  53 
  54 // The functions in this file builds OopMaps after all scheduling is done.
  55 //
  56 // OopMaps contain a list of all registers and stack-slots containing oops (so
  57 // they can be updated by GC).  OopMaps also contain a list of derived-pointer
  58 // base-pointer pairs.  When the base is moved, the derived pointer moves to
  59 // follow it.  Finally, any registers holding callee-save values are also
  60 // recorded.  These might contain oops, but only the caller knows.
  61 //
  62 // BuildOopMaps implements a simple forward reaching-defs solution.  At each
  63 // GC point we'll have the reaching-def Nodes.  If the reaching Nodes are
  64 // typed as pointers (no offset), then they are oops.  Pointers+offsets are
  65 // derived pointers, and bases can be found from them.  Finally, we'll also
  66 // track reaching callee-save values.  Note that a copy of a callee-save value
  67 // "kills" it's source, so that only 1 copy of a callee-save value is alive at
  68 // a time.
  69 //
  70 // We run a simple bitvector liveness pass to help trim out dead oops.  Due to
  71 // irreducible loops, we can have a reaching def of an oop that only reaches
  72 // along one path and no way to know if it's valid or not on the other path.
  73 // The bitvectors are quite dense and the liveness pass is fast.
  74 //
  75 // At GC points, we consult this information to build OopMaps.  All reaching
  76 // defs typed as oops are added to the OopMap.  Only 1 instance of a
  77 // callee-save register can be recorded.  For derived pointers, we'll have to
  78 // find and record the register holding the base.
  79 //
  80 // The reaching def's is a simple 1-pass worklist approach.  I tried a clever
  81 // breadth-first approach but it was worse (showed O(n^2) in the
  82 // pick-next-block code).
  83 //
  84 // The relevant data is kept in a struct of arrays (it could just as well be
  85 // an array of structs, but the struct-of-arrays is generally a little more
  86 // efficient).  The arrays are indexed by register number (including
  87 // stack-slots as registers) and so is bounded by 200 to 300 elements in
  88 // practice.  One array will map to a reaching def Node (or NULL for
  89 // conflict/dead).  The other array will map to a callee-saved register or
  90 // OptoReg::Bad for not-callee-saved.
  91 
  92 
  93 // Structure to pass around
  94 struct OopFlow : public ResourceObj {
  95   short *_callees;              // Array mapping register to callee-saved
  96   Node **_defs;                 // array mapping register to reaching def
  97                                 // or NULL if dead/conflict
  98   // OopFlow structs, when not being actively modified, describe the _end_ of
  99   // this block.
 100   Block *_b;                    // Block for this struct
 101   OopFlow *_next;               // Next free OopFlow
 102                                 // or NULL if dead/conflict
 103   Compile* C;
 104 
 105   OopFlow( short *callees, Node **defs, Compile* c ) : _callees(callees), _defs(defs),
 106     _b(NULL), _next(NULL), C(c) { }
 107 
 108   // Given reaching-defs for this block start, compute it for this block end
 109   void compute_reach( PhaseRegAlloc *regalloc, int max_reg, Dict *safehash );
 110 
 111   // Merge these two OopFlows into the 'this' pointer.
 112   void merge( OopFlow *flow, int max_reg );
 113 
 114   // Copy a 'flow' over an existing flow
 115   void clone( OopFlow *flow, int max_size);
 116 
 117   // Make a new OopFlow from scratch
 118   static OopFlow *make( Arena *A, int max_size, Compile* C );
 119 
 120   // Build an oopmap from the current flow info
 121   OopMap *build_oop_map( Node *n, int max_reg, PhaseRegAlloc *regalloc, int* live );
 122 };
 123 
 124 // Given reaching-defs for this block start, compute it for this block end
 125 void OopFlow::compute_reach( PhaseRegAlloc *regalloc, int max_reg, Dict *safehash ) {
 126 
 127   for( uint i=0; i<_b->number_of_nodes(); i++ ) {
 128     Node *n = _b->get_node(i);
 129 
 130     if( n->jvms() ) {           // Build an OopMap here?
 131       JVMState *jvms = n->jvms();
 132       // no map needed for leaf calls
 133       if( n->is_MachSafePoint() && !n->is_MachCallLeaf() ) {
 134         int *live = (int*) (*safehash)[n];
 135         assert( live, "must find live" );
 136         n->as_MachSafePoint()->set_oop_map( build_oop_map(n,max_reg,regalloc, live) );
 137       }
 138     }
 139 
 140     // Assign new reaching def's.
 141     // Note that I padded the _defs and _callees arrays so it's legal
 142     // to index at _defs[OptoReg::Bad].
 143     OptoReg::Name first = regalloc->get_reg_first(n);
 144     OptoReg::Name second = regalloc->get_reg_second(n);
 145     _defs[first] = n;
 146     _defs[second] = n;
 147 
 148     // Pass callee-save info around copies
 149     int idx = n->is_Copy();
 150     if( idx ) {                 // Copies move callee-save info
 151       OptoReg::Name old_first = regalloc->get_reg_first(n->in(idx));
 152       OptoReg::Name old_second = regalloc->get_reg_second(n->in(idx));
 153       int tmp_first = _callees[old_first];
 154       int tmp_second = _callees[old_second];
 155       _callees[old_first] = OptoReg::Bad; // callee-save is moved, dead in old location
 156       _callees[old_second] = OptoReg::Bad;
 157       _callees[first] = tmp_first;
 158       _callees[second] = tmp_second;
 159     } else if( n->is_Phi() ) {  // Phis do not mod callee-saves
 160       assert( _callees[first] == _callees[regalloc->get_reg_first(n->in(1))], "" );
 161       assert( _callees[second] == _callees[regalloc->get_reg_second(n->in(1))], "" );
 162       assert( _callees[first] == _callees[regalloc->get_reg_first(n->in(n->req()-1))], "" );
 163       assert( _callees[second] == _callees[regalloc->get_reg_second(n->in(n->req()-1))], "" );
 164     } else {
 165       _callees[first] = OptoReg::Bad; // No longer holding a callee-save value
 166       _callees[second] = OptoReg::Bad;
 167 
 168       // Find base case for callee saves
 169       if( n->is_Proj() && n->in(0)->is_Start() ) {
 170         if( OptoReg::is_reg(first) &&
 171             regalloc->_matcher.is_save_on_entry(first) )
 172           _callees[first] = first;
 173         if( OptoReg::is_reg(second) &&
 174             regalloc->_matcher.is_save_on_entry(second) )
 175           _callees[second] = second;
 176       }
 177     }
 178   }
 179 }
 180 
 181 // Merge the given flow into the 'this' flow
 182 void OopFlow::merge( OopFlow *flow, int max_reg ) {
 183   assert( _b == NULL, "merging into a happy flow" );
 184   assert( flow->_b, "this flow is still alive" );
 185   assert( flow != this, "no self flow" );
 186 
 187   // Do the merge.  If there are any differences, drop to 'bottom' which
 188   // is OptoReg::Bad or NULL depending.
 189   for( int i=0; i<max_reg; i++ ) {
 190     // Merge the callee-save's
 191     if( _callees[i] != flow->_callees[i] )
 192       _callees[i] = OptoReg::Bad;
 193     // Merge the reaching defs
 194     if( _defs[i] != flow->_defs[i] )
 195       _defs[i] = NULL;
 196   }
 197 
 198 }
 199 
 200 void OopFlow::clone( OopFlow *flow, int max_size ) {
 201   _b = flow->_b;
 202   memcpy( _callees, flow->_callees, sizeof(short)*max_size);
 203   memcpy( _defs   , flow->_defs   , sizeof(Node*)*max_size);
 204 }
 205 
 206 OopFlow *OopFlow::make( Arena *A, int max_size, Compile* C ) {
 207   short *callees = NEW_ARENA_ARRAY(A,short,max_size+1);
 208   Node **defs    = NEW_ARENA_ARRAY(A,Node*,max_size+1);
 209   debug_only( memset(defs,0,(max_size+1)*sizeof(Node*)) );
 210   OopFlow *flow = new (A) OopFlow(callees+1, defs+1, C);
 211   assert( &flow->_callees[OptoReg::Bad] == callees, "Ok to index at OptoReg::Bad" );
 212   assert( &flow->_defs   [OptoReg::Bad] == defs   , "Ok to index at OptoReg::Bad" );
 213   return flow;
 214 }
 215 
 216 static int get_live_bit( int *live, int reg ) {
 217   return live[reg>>LogBitsPerInt] &   (1<<(reg&(BitsPerInt-1))); }
 218 static void set_live_bit( int *live, int reg ) {
 219          live[reg>>LogBitsPerInt] |=  (1<<(reg&(BitsPerInt-1))); }
 220 static void clr_live_bit( int *live, int reg ) {
 221          live[reg>>LogBitsPerInt] &= ~(1<<(reg&(BitsPerInt-1))); }
 222 
 223 // Build an oopmap from the current flow info
 224 OopMap *OopFlow::build_oop_map( Node *n, int max_reg, PhaseRegAlloc *regalloc, int* live ) {
 225   int framesize = regalloc->_framesize;
 226   int max_inarg_slot = OptoReg::reg2stack(regalloc->_matcher._new_SP);
 227   debug_only( char *dup_check = NEW_RESOURCE_ARRAY(char,OptoReg::stack0());
 228               memset(dup_check,0,OptoReg::stack0()) );
 229 
 230   OopMap *omap = new OopMap( framesize,  max_inarg_slot );
 231   MachCallNode *mcall = n->is_MachCall() ? n->as_MachCall() : NULL;
 232   JVMState* jvms = n->jvms();
 233 
 234   // For all registers do...
 235   for( int reg=0; reg<max_reg; reg++ ) {
 236     if( get_live_bit(live,reg) == 0 )
 237       continue;                 // Ignore if not live
 238 
 239     // %%% C2 can use 2 OptoRegs when the physical register is only one 64bit
 240     // register in that case we'll get an non-concrete register for the second
 241     // half. We only need to tell the map the register once!
 242     //
 243     // However for the moment we disable this change and leave things as they
 244     // were.
 245 
 246     VMReg r = OptoReg::as_VMReg(OptoReg::Name(reg), framesize, max_inarg_slot);
 247 
 248     if (false && r->is_reg() && !r->is_concrete()) {
 249       continue;
 250     }
 251 
 252     // See if dead (no reaching def).
 253     Node *def = _defs[reg];     // Get reaching def
 254     assert( def, "since live better have reaching def" );
 255 
 256     // Classify the reaching def as oop, derived, callee-save, dead, or other
 257     const Type *t = def->bottom_type();
 258     if( t->isa_oop_ptr() ) {    // Oop or derived?
 259       assert( !OptoReg::is_valid(_callees[reg]), "oop can't be callee save" );
 260 #ifdef _LP64
 261       // 64-bit pointers record oop-ishness on 2 aligned adjacent registers.
 262       // Make sure both are record from the same reaching def, but do not
 263       // put both into the oopmap.
 264       if( (reg&1) == 1 ) {      // High half of oop-pair?
 265         assert( _defs[reg-1] == _defs[reg], "both halves from same reaching def" );
 266         continue;               // Do not record high parts in oopmap
 267       }
 268 #endif
 269 
 270       // Check for a legal reg name in the oopMap and bailout if it is not.
 271       if (!omap->legal_vm_reg_name(r)) {
 272         regalloc->C->record_method_not_compilable("illegal oopMap register name");
 273         continue;
 274       }
 275       if( t->is_ptr()->_offset == 0 ) { // Not derived?
 276         if( mcall ) {
 277           // Outgoing argument GC mask responsibility belongs to the callee,
 278           // not the caller.  Inspect the inputs to the call, to see if
 279           // this live-range is one of them.
 280           uint cnt = mcall->tf()->domain()->cnt();
 281           uint j;
 282           for( j = TypeFunc::Parms; j < cnt; j++)
 283             if( mcall->in(j) == def )
 284               break;            // reaching def is an argument oop
 285           if( j < cnt )         // arg oops dont go in GC map
 286             continue;           // Continue on to the next register
 287         }
 288         omap->set_oop(r);
 289       } else {                  // Else it's derived.
 290         // Find the base of the derived value.
 291         uint i;
 292         // Fast, common case, scan
 293         for( i = jvms->oopoff(); i < n->req(); i+=2 )
 294           if( n->in(i) == def ) break; // Common case
 295         if( i == n->req() ) {   // Missed, try a more generous scan
 296           // Scan again, but this time peek through copies
 297           for( i = jvms->oopoff(); i < n->req(); i+=2 ) {
 298             Node *m = n->in(i); // Get initial derived value
 299             while( 1 ) {
 300               Node *d = def;    // Get initial reaching def
 301               while( 1 ) {      // Follow copies of reaching def to end
 302                 if( m == d ) goto found; // breaks 3 loops
 303                 int idx = d->is_Copy();
 304                 if( !idx ) break;
 305                 d = d->in(idx);     // Link through copy
 306               }
 307               int idx = m->is_Copy();
 308               if( !idx ) break;
 309               m = m->in(idx);
 310             }
 311           }
 312           guarantee( 0, "must find derived/base pair" );
 313         }
 314       found: ;
 315         Node *base = n->in(i+1); // Base is other half of pair
 316         int breg = regalloc->get_reg_first(base);
 317         VMReg b = OptoReg::as_VMReg(OptoReg::Name(breg), framesize, max_inarg_slot);
 318 
 319         // I record liveness at safepoints BEFORE I make the inputs
 320         // live.  This is because argument oops are NOT live at a
 321         // safepoint (or at least they cannot appear in the oopmap).
 322         // Thus bases of base/derived pairs might not be in the
 323         // liveness data but they need to appear in the oopmap.
 324         if( get_live_bit(live,breg) == 0 ) {// Not live?
 325           // Flag it, so next derived pointer won't re-insert into oopmap
 326           set_live_bit(live,breg);
 327           // Already missed our turn?
 328           if( breg < reg ) {
 329             if (b->is_stack() || b->is_concrete() || true ) {
 330               omap->set_oop( b);
 331             }
 332           }
 333         }
 334         if (b->is_stack() || b->is_concrete() || true ) {
 335           omap->set_derived_oop( r, b);
 336         }
 337       }
 338 
 339     } else if( t->isa_narrowoop() ) {
 340       assert( !OptoReg::is_valid(_callees[reg]), "oop can't be callee save" );
 341       // Check for a legal reg name in the oopMap and bailout if it is not.
 342       if (!omap->legal_vm_reg_name(r)) {
 343         regalloc->C->record_method_not_compilable("illegal oopMap register name");
 344         continue;
 345       }
 346       if( mcall ) {
 347           // Outgoing argument GC mask responsibility belongs to the callee,
 348           // not the caller.  Inspect the inputs to the call, to see if
 349           // this live-range is one of them.
 350         uint cnt = mcall->tf()->domain()->cnt();
 351         uint j;
 352         for( j = TypeFunc::Parms; j < cnt; j++)
 353           if( mcall->in(j) == def )
 354             break;            // reaching def is an argument oop
 355         if( j < cnt )         // arg oops dont go in GC map
 356           continue;           // Continue on to the next register
 357       }
 358       omap->set_narrowoop(r);
 359     } else if( OptoReg::is_valid(_callees[reg])) { // callee-save?
 360       // It's a callee-save value
 361       assert( dup_check[_callees[reg]]==0, "trying to callee save same reg twice" );
 362       debug_only( dup_check[_callees[reg]]=1; )
 363       VMReg callee = OptoReg::as_VMReg(OptoReg::Name(_callees[reg]));
 364       if ( callee->is_concrete() || true ) {
 365         omap->set_callee_saved( r, callee);
 366       }
 367 
 368     } else {
 369       // Other - some reaching non-oop value
 370       omap->set_value( r);
 371 #ifdef ASSERT
 372       if( t->isa_rawptr() && C->cfg()->_raw_oops.member(def) ) {
 373         def->dump();
 374         n->dump();
 375         assert(false, "there should be a oop in OopMap instead of a live raw oop at safepoint");
 376       }
 377 #endif
 378     }
 379 
 380   }
 381 
 382 #ifdef ASSERT
 383   /* Nice, Intel-only assert
 384   int cnt_callee_saves=0;
 385   int reg2 = 0;
 386   while (OptoReg::is_reg(reg2)) {
 387     if( dup_check[reg2] != 0) cnt_callee_saves++;
 388     assert( cnt_callee_saves==3 || cnt_callee_saves==5, "missed some callee-save" );
 389     reg2++;
 390   }
 391   */
 392 #endif
 393 
 394 #ifdef ASSERT
 395   for( OopMapStream oms1(omap, OopMapValue::derived_oop_value); !oms1.is_done(); oms1.next()) {
 396     OopMapValue omv1 = oms1.current();
 397     bool found = false;
 398     for( OopMapStream oms2(omap,OopMapValue::oop_value); !oms2.is_done(); oms2.next()) {
 399       if( omv1.content_reg() == oms2.current().reg() ) {
 400         found = true;
 401         break;
 402       }
 403     }
 404     assert( found, "derived with no base in oopmap" );
 405   }
 406 #endif
 407 
 408   return omap;
 409 }
 410 
 411 // Compute backwards liveness on registers
 412 static void do_liveness(PhaseRegAlloc* regalloc, PhaseCFG* cfg, Block_List* worklist, int max_reg_ints, Arena* A, Dict* safehash) {
 413   int* live = NEW_ARENA_ARRAY(A, int, (cfg->number_of_blocks() + 1) * max_reg_ints);
 414   int* tmp_live = &live[cfg->number_of_blocks() * max_reg_ints];
 415   Node* root = cfg->get_root_node();
 416   // On CISC platforms, get the node representing the stack pointer  that regalloc
 417   // used for spills
 418   Node *fp = NodeSentinel;
 419   if (UseCISCSpill && root->req() > 1) {
 420     fp = root->in(1)->in(TypeFunc::FramePtr);
 421   }
 422   memset(live, 0, cfg->number_of_blocks() * (max_reg_ints << LogBytesPerInt));
 423   // Push preds onto worklist
 424   for (uint i = 1; i < root->req(); i++) {
 425     Block* block = cfg->get_block_for_node(root->in(i));
 426     worklist->push(block);
 427   }
 428 
 429   // ZKM.jar includes tiny infinite loops which are unreached from below.
 430   // If we missed any blocks, we'll retry here after pushing all missed
 431   // blocks on the worklist.  Normally this outer loop never trips more
 432   // than once.
 433   while (1) {
 434 
 435     while( worklist->size() ) { // Standard worklist algorithm
 436       Block *b = worklist->rpop();
 437 
 438       // Copy first successor into my tmp_live space
 439       int s0num = b->_succs[0]->_pre_order;
 440       int *t = &live[s0num*max_reg_ints];
 441       for( int i=0; i<max_reg_ints; i++ )
 442         tmp_live[i] = t[i];
 443 
 444       // OR in the remaining live registers
 445       for( uint j=1; j<b->_num_succs; j++ ) {
 446         uint sjnum = b->_succs[j]->_pre_order;
 447         int *t = &live[sjnum*max_reg_ints];
 448         for( int i=0; i<max_reg_ints; i++ )
 449           tmp_live[i] |= t[i];
 450       }
 451 
 452       // Now walk tmp_live up the block backwards, computing live
 453       for( int k=b->number_of_nodes()-1; k>=0; k-- ) {
 454         Node *n = b->get_node(k);
 455         // KILL def'd bits
 456         int first = regalloc->get_reg_first(n);
 457         int second = regalloc->get_reg_second(n);
 458         if( OptoReg::is_valid(first) ) clr_live_bit(tmp_live,first);
 459         if( OptoReg::is_valid(second) ) clr_live_bit(tmp_live,second);
 460 
 461         MachNode *m = n->is_Mach() ? n->as_Mach() : NULL;
 462 
 463         // Check if m is potentially a CISC alternate instruction (i.e, possibly
 464         // synthesized by RegAlloc from a conventional instruction and a
 465         // spilled input)
 466         bool is_cisc_alternate = false;
 467         if (UseCISCSpill && m) {
 468           is_cisc_alternate = m->is_cisc_alternate();
 469         }
 470 
 471         // GEN use'd bits
 472         for( uint l=1; l<n->req(); l++ ) {
 473           Node *def = n->in(l);
 474           assert(def != 0, "input edge required");
 475           int first = regalloc->get_reg_first(def);
 476           int second = regalloc->get_reg_second(def);
 477           if( OptoReg::is_valid(first) ) set_live_bit(tmp_live,first);
 478           if( OptoReg::is_valid(second) ) set_live_bit(tmp_live,second);
 479           // If we use the stack pointer in a cisc-alternative instruction,
 480           // check for use as a memory operand.  Then reconstruct the RegName
 481           // for this stack location, and set the appropriate bit in the
 482           // live vector 4987749.
 483           if (is_cisc_alternate && def == fp) {
 484             const TypePtr *adr_type = NULL;
 485             intptr_t offset;
 486             const Node* base = m->get_base_and_disp(offset, adr_type);
 487             if (base == NodeSentinel) {
 488               // Machnode has multiple memory inputs. We are unable to reason
 489               // with these, but are presuming (with trepidation) that not any of
 490               // them are oops. This can be fixed by making get_base_and_disp()
 491               // look at a specific input instead of all inputs.
 492               assert(!def->bottom_type()->isa_oop_ptr(), "expecting non-oop mem input");
 493             } else if (base != fp || offset == Type::OffsetBot) {
 494               // Do nothing: the fp operand is either not from a memory use
 495               // (base == NULL) OR the fp is used in a non-memory context
 496               // (base is some other register) OR the offset is not constant,
 497               // so it is not a stack slot.
 498             } else {
 499               assert(offset >= 0, "unexpected negative offset");
 500               offset -= (offset % jintSize);  // count the whole word
 501               int stack_reg = regalloc->offset2reg(offset);
 502               if (OptoReg::is_stack(stack_reg)) {
 503                 set_live_bit(tmp_live, stack_reg);
 504               } else {
 505                 assert(false, "stack_reg not on stack?");
 506               }
 507             }
 508           }
 509         }
 510 
 511         if( n->jvms() ) {       // Record liveness at safepoint
 512 
 513           // This placement of this stanza means inputs to calls are
 514           // considered live at the callsite's OopMap.  Argument oops are
 515           // hence live, but NOT included in the oopmap.  See cutout in
 516           // build_oop_map.  Debug oops are live (and in OopMap).
 517           int *n_live = NEW_ARENA_ARRAY(A, int, max_reg_ints);
 518           for( int l=0; l<max_reg_ints; l++ )
 519             n_live[l] = tmp_live[l];
 520           safehash->Insert(n,n_live);
 521         }
 522 
 523       }
 524 
 525       // Now at block top, see if we have any changes.  If so, propagate
 526       // to prior blocks.
 527       int *old_live = &live[b->_pre_order*max_reg_ints];
 528       int l;
 529       for( l=0; l<max_reg_ints; l++ )
 530         if( tmp_live[l] != old_live[l] )
 531           break;
 532       if( l<max_reg_ints ) {     // Change!
 533         // Copy in new value
 534         for( l=0; l<max_reg_ints; l++ )
 535           old_live[l] = tmp_live[l];
 536         // Push preds onto worklist
 537         for (l = 1; l < (int)b->num_preds(); l++) {
 538           Block* block = cfg->get_block_for_node(b->pred(l));
 539           worklist->push(block);
 540         }
 541       }
 542     }
 543 
 544     // Scan for any missing safepoints.  Happens to infinite loops
 545     // ala ZKM.jar
 546     uint i;
 547     for (i = 1; i < cfg->number_of_blocks(); i++) {
 548       Block* block = cfg->get_block(i);
 549       uint j;
 550       for (j = 1; j < block->number_of_nodes(); j++) {
 551         if (block->get_node(j)->jvms() && (*safehash)[block->get_node(j)] == NULL) {
 552            break;
 553         }
 554       }
 555       if (j < block->number_of_nodes()) {
 556         break;
 557       }
 558     }
 559     if (i == cfg->number_of_blocks()) {
 560       break;                    // Got 'em all
 561     }
 562 #ifndef PRODUCT
 563     if( PrintOpto && Verbose )
 564       tty->print_cr("retripping live calc");
 565 #endif
 566     // Force the issue (expensively): recheck everybody
 567     for (i = 1; i < cfg->number_of_blocks(); i++) {
 568       worklist->push(cfg->get_block(i));
 569     }
 570   }
 571 }
 572 
 573 // Collect GC mask info - where are all the OOPs?
 574 void Compile::BuildOopMaps() {
 575   NOT_PRODUCT( TracePhase t3("bldOopMaps", &_t_buildOopMaps, TimeCompiler); )
 576   // Can't resource-mark because I need to leave all those OopMaps around,
 577   // or else I need to resource-mark some arena other than the default.
 578   // ResourceMark rm;              // Reclaim all OopFlows when done
 579   int max_reg = _regalloc->_max_reg; // Current array extent
 580 
 581   Arena *A = Thread::current()->resource_area();
 582   Block_List worklist;          // Worklist of pending blocks
 583 
 584   int max_reg_ints = round_to(max_reg, BitsPerInt)>>LogBitsPerInt;
 585   Dict *safehash = NULL;        // Used for assert only
 586   // Compute a backwards liveness per register.  Needs a bitarray of
 587   // #blocks x (#registers, rounded up to ints)
 588   safehash = new Dict(cmpkey,hashkey,A);
 589   do_liveness( _regalloc, _cfg, &worklist, max_reg_ints, A, safehash );
 590   OopFlow *free_list = NULL;    // Free, unused
 591 
 592   // Array mapping blocks to completed oopflows
 593   OopFlow **flows = NEW_ARENA_ARRAY(A, OopFlow*, _cfg->number_of_blocks());
 594   memset( flows, 0, _cfg->number_of_blocks() * sizeof(OopFlow*) );
 595 
 596 
 597   // Do the first block 'by hand' to prime the worklist
 598   Block *entry = _cfg->get_block(1);
 599   OopFlow *rootflow = OopFlow::make(A,max_reg,this);
 600   // Initialize to 'bottom' (not 'top')
 601   memset( rootflow->_callees, OptoReg::Bad, max_reg*sizeof(short) );
 602   memset( rootflow->_defs   ,            0, max_reg*sizeof(Node*) );
 603   flows[entry->_pre_order] = rootflow;
 604 
 605   // Do the first block 'by hand' to prime the worklist
 606   rootflow->_b = entry;
 607   rootflow->compute_reach( _regalloc, max_reg, safehash );
 608   for( uint i=0; i<entry->_num_succs; i++ )
 609     worklist.push(entry->_succs[i]);
 610 
 611   // Now worklist contains blocks which have some, but perhaps not all,
 612   // predecessors visited.
 613   while( worklist.size() ) {
 614     // Scan for a block with all predecessors visited, or any randoms slob
 615     // otherwise.  All-preds-visited order allows me to recycle OopFlow
 616     // structures rapidly and cut down on the memory footprint.
 617     // Note: not all predecessors might be visited yet (must happen for
 618     // irreducible loops).  This is OK, since every live value must have the
 619     // SAME reaching def for the block, so any reaching def is OK.
 620     uint i;
 621 
 622     Block *b = worklist.pop();
 623     // Ignore root block
 624     if (b == _cfg->get_root_block()) {
 625       continue;
 626     }
 627     // Block is already done?  Happens if block has several predecessors,
 628     // he can get on the worklist more than once.
 629     if( flows[b->_pre_order] ) continue;
 630 
 631     // If this block has a visited predecessor AND that predecessor has this
 632     // last block as his only undone child, we can move the OopFlow from the
 633     // pred to this block.  Otherwise we have to grab a new OopFlow.
 634     OopFlow *flow = NULL;       // Flag for finding optimized flow
 635     Block *pred = (Block*)((intptr_t)0xdeadbeef);
 636     // Scan this block's preds to find a done predecessor
 637     for (uint j = 1; j < b->num_preds(); j++) {
 638       Block* p = _cfg->get_block_for_node(b->pred(j));
 639       OopFlow *p_flow = flows[p->_pre_order];
 640       if( p_flow ) {            // Predecessor is done
 641         assert( p_flow->_b == p, "cross check" );
 642         pred = p;               // Record some predecessor
 643         // If all successors of p are done except for 'b', then we can carry
 644         // p_flow forward to 'b' without copying, otherwise we have to draw
 645         // from the free_list and clone data.
 646         uint k;
 647         for( k=0; k<p->_num_succs; k++ )
 648           if( !flows[p->_succs[k]->_pre_order] &&
 649               p->_succs[k] != b )
 650             break;
 651 
 652         // Either carry-forward the now-unused OopFlow for b's use
 653         // or draw a new one from the free list
 654         if( k==p->_num_succs ) {
 655           flow = p_flow;
 656           break;                // Found an ideal pred, use him
 657         }
 658       }
 659     }
 660 
 661     if( flow ) {
 662       // We have an OopFlow that's the last-use of a predecessor.
 663       // Carry it forward.
 664     } else {                    // Draw a new OopFlow from the freelist
 665       if( !free_list )
 666         free_list = OopFlow::make(A,max_reg,C);
 667       flow = free_list;
 668       assert( flow->_b == NULL, "oopFlow is not free" );
 669       free_list = flow->_next;
 670       flow->_next = NULL;
 671 
 672       // Copy/clone over the data
 673       flow->clone(flows[pred->_pre_order], max_reg);
 674     }
 675 
 676     // Mark flow for block.  Blocks can only be flowed over once,
 677     // because after the first time they are guarded from entering
 678     // this code again.
 679     assert( flow->_b == pred, "have some prior flow" );
 680     flow->_b = NULL;
 681 
 682     // Now push flow forward
 683     flows[b->_pre_order] = flow;// Mark flow for this block
 684     flow->_b = b;
 685     flow->compute_reach( _regalloc, max_reg, safehash );
 686 
 687     // Now push children onto worklist
 688     for( i=0; i<b->_num_succs; i++ )
 689       worklist.push(b->_succs[i]);
 690 
 691   }
 692 }