jdk8-mips64-public/hotspot: src/share/vm/opto/buildOopMap.cpp@98cb887364d3 (annotated)

src/share/vm/opto/buildOopMap.cpp@98cb887364d3 (annotated)

src/share/vm/opto/buildOopMap.cpp

Fri, 27 Feb 2009 13:27:09 -0800

author: twisti
date: Fri, 27 Feb 2009 13:27:09 -0800
changeset 1040: 98cb887364d3
parent 631: d1605aabd0a1
child 1164: 04fa5affa478
permissions: -rw-r--r--

6810672: Comment typos
Summary: I have collected some typos I have found while looking at the code.
Reviewed-by: kvn, never

 /*
  * Copyright 2002-2008 Sun Microsystems, Inc.  All Rights Reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.
  *
  * This code is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  * version 2 for more details (a copy is included in the LICENSE file that
  * accompanied this code).
  *
  * You should have received a copy of the GNU General Public License version
  * 2 along with this work; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  *
  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
  * CA 95054 USA or visit www.sun.com if you need additional information or
  * have any questions.
  *
  */
 #include "incls/_precompiled.incl"
 #include "incls/_buildOopMap.cpp.incl"
 // The functions in this file builds OopMaps after all scheduling is done.
 //
 // OopMaps contain a list of all registers and stack-slots containing oops (so
 // they can be updated by GC).  OopMaps also contain a list of derived-pointer
 // base-pointer pairs.  When the base is moved, the derived pointer moves to
 // follow it.  Finally, any registers holding callee-save values are also
 // recorded.  These might contain oops, but only the caller knows.
 //
 // BuildOopMaps implements a simple forward reaching-defs solution.  At each
 // GC point we'll have the reaching-def Nodes.  If the reaching Nodes are
 // typed as pointers (no offset), then they are oops.  Pointers+offsets are
 // derived pointers, and bases can be found from them.  Finally, we'll also
 // track reaching callee-save values.  Note that a copy of a callee-save value
 // "kills" it's source, so that only 1 copy of a callee-save value is alive at
 // a time.
 //
 // We run a simple bitvector liveness pass to help trim out dead oops.  Due to
 // irreducible loops, we can have a reaching def of an oop that only reaches
 // along one path and no way to know if it's valid or not on the other path.
 // The bitvectors are quite dense and the liveness pass is fast.
 //
 // At GC points, we consult this information to build OopMaps.  All reaching
 // defs typed as oops are added to the OopMap.  Only 1 instance of a
 // callee-save register can be recorded.  For derived pointers, we'll have to
 // find and record the register holding the base.
 //
 // The reaching def's is a simple 1-pass worklist approach.  I tried a clever
 // breadth-first approach but it was worse (showed O(n^2) in the
 // pick-next-block code).
 //
 // The relevant data is kept in a struct of arrays (it could just as well be
 // an array of structs, but the struct-of-arrays is generally a little more
 // efficient).  The arrays are indexed by register number (including
 // stack-slots as registers) and so is bounded by 200 to 300 elements in
 // practice.  One array will map to a reaching def Node (or NULL for
 // conflict/dead).  The other array will map to a callee-saved register or
 // OptoReg::Bad for not-callee-saved.
 //------------------------------OopFlow----------------------------------------
 // Structure to pass around
 struct OopFlow : public ResourceObj {
   short *_callees;              // Array mapping register to callee-saved
   Node **_defs;                 // array mapping register to reaching def
                                 // or NULL if dead/conflict
   // OopFlow structs, when not being actively modified, describe the _end_ of
   // this block.
   Block *_b;                    // Block for this struct
   OopFlow *_next;               // Next free OopFlow
   OopFlow( short *callees, Node **defs ) : _callees(callees), _defs(defs),
     _b(NULL), _next(NULL) { }
   // Given reaching-defs for this block start, compute it for this block end
   void compute_reach( PhaseRegAlloc *regalloc, int max_reg, Dict *safehash );
   // Merge these two OopFlows into the 'this' pointer.
   void merge( OopFlow *flow, int max_reg );
   // Copy a 'flow' over an existing flow
   void clone( OopFlow *flow, int max_size);
   // Make a new OopFlow from scratch
   static OopFlow *make( Arena *A, int max_size );
   // Build an oopmap from the current flow info
   OopMap *build_oop_map( Node *n, int max_reg, PhaseRegAlloc *regalloc, int* live );
 };
 //------------------------------compute_reach----------------------------------
 // Given reaching-defs for this block start, compute it for this block end
 void OopFlow::compute_reach( PhaseRegAlloc *regalloc, int max_reg, Dict *safehash ) {
   for( uint i=0; i<_b->_nodes.size(); i++ ) {
     Node *n = _b->_nodes[i];
     if( n->jvms() ) {           // Build an OopMap here?
       JVMState *jvms = n->jvms();
       // no map needed for leaf calls
       if( n->is_MachSafePoint() && !n->is_MachCallLeaf() ) {
         int *live = (int*) (*safehash)[n];
         assert( live, "must find live" );
         n->as_MachSafePoint()->set_oop_map( build_oop_map(n,max_reg,regalloc, live) );
       }
     }
     // Assign new reaching def's.
     // Note that I padded the _defs and _callees arrays so it's legal
     // to index at _defs[OptoReg::Bad].
     OptoReg::Name first = regalloc->get_reg_first(n);
     OptoReg::Name second = regalloc->get_reg_second(n);
     _defs[first] = n;
     _defs[second] = n;
     // Pass callee-save info around copies
     int idx = n->is_Copy();
     if( idx ) {                 // Copies move callee-save info
       OptoReg::Name old_first = regalloc->get_reg_first(n->in(idx));
       OptoReg::Name old_second = regalloc->get_reg_second(n->in(idx));
       int tmp_first = _callees[old_first];
       int tmp_second = _callees[old_second];
       _callees[old_first] = OptoReg::Bad; // callee-save is moved, dead in old location
       _callees[old_second] = OptoReg::Bad;
       _callees[first] = tmp_first;
       _callees[second] = tmp_second;
     } else if( n->is_Phi() ) {  // Phis do not mod callee-saves
       assert( _callees[first] == _callees[regalloc->get_reg_first(n->in(1))], "" );
       assert( _callees[second] == _callees[regalloc->get_reg_second(n->in(1))], "" );
       assert( _callees[first] == _callees[regalloc->get_reg_first(n->in(n->req()-1))], "" );
       assert( _callees[second] == _callees[regalloc->get_reg_second(n->in(n->req()-1))], "" );
     } else {
       _callees[first] = OptoReg::Bad; // No longer holding a callee-save value
       _callees[second] = OptoReg::Bad;
       // Find base case for callee saves
       if( n->is_Proj() && n->in(0)->is_Start() ) {
         if( OptoReg::is_reg(first) &&
             regalloc->_matcher.is_save_on_entry(first) )
           _callees[first] = first;
         if( OptoReg::is_reg(second) &&
             regalloc->_matcher.is_save_on_entry(second) )
           _callees[second] = second;
       }
     }
   }
 }
 //------------------------------merge------------------------------------------
 // Merge the given flow into the 'this' flow
 void OopFlow::merge( OopFlow *flow, int max_reg ) {
   assert( _b == NULL, "merging into a happy flow" );
   assert( flow->_b, "this flow is still alive" );
   assert( flow != this, "no self flow" );
   // Do the merge.  If there are any differences, drop to 'bottom' which
   // is OptoReg::Bad or NULL depending.
   for( int i=0; i<max_reg; i++ ) {
     // Merge the callee-save's
     if( _callees[i] != flow->_callees[i] )
       _callees[i] = OptoReg::Bad;
     // Merge the reaching defs
     if( _defs[i] != flow->_defs[i] )
       _defs[i] = NULL;
   }
 }
 //------------------------------clone------------------------------------------
 void OopFlow::clone( OopFlow *flow, int max_size ) {
   _b = flow->_b;
   memcpy( _callees, flow->_callees, sizeof(short)*max_size);
   memcpy( _defs   , flow->_defs   , sizeof(Node*)*max_size);
 }
 //------------------------------make-------------------------------------------
 OopFlow *OopFlow::make( Arena *A, int max_size ) {
   short *callees = NEW_ARENA_ARRAY(A,short,max_size+1);
   Node **defs    = NEW_ARENA_ARRAY(A,Node*,max_size+1);
   debug_only( memset(defs,0,(max_size+1)*sizeof(Node*)) );
   OopFlow *flow = new (A) OopFlow(callees+1, defs+1);
   assert( &flow->_callees[OptoReg::Bad] == callees, "Ok to index at OptoReg::Bad" );
   assert( &flow->_defs   [OptoReg::Bad] == defs   , "Ok to index at OptoReg::Bad" );
   return flow;
 }
 //------------------------------bit twiddlers----------------------------------
 static int get_live_bit( int *live, int reg ) {
   return live[reg>>LogBitsPerInt] &   (1<<(reg&(BitsPerInt-1))); }
 static void set_live_bit( int *live, int reg ) {
          live[reg>>LogBitsPerInt] |=  (1<<(reg&(BitsPerInt-1))); }
 static void clr_live_bit( int *live, int reg ) {
          live[reg>>LogBitsPerInt] &= ~(1<<(reg&(BitsPerInt-1))); }
 //------------------------------build_oop_map----------------------------------
 // Build an oopmap from the current flow info
 OopMap *OopFlow::build_oop_map( Node *n, int max_reg, PhaseRegAlloc *regalloc, int* live ) {
   int framesize = regalloc->_framesize;
   int max_inarg_slot = OptoReg::reg2stack(regalloc->_matcher._new_SP);
   debug_only( char *dup_check = NEW_RESOURCE_ARRAY(char,OptoReg::stack0());
               memset(dup_check,0,OptoReg::stack0()) );
   OopMap *omap = new OopMap( framesize,  max_inarg_slot );
   MachCallNode *mcall = n->is_MachCall() ? n->as_MachCall() : NULL;
   JVMState* jvms = n->jvms();
   // For all registers do...
   for( int reg=0; reg<max_reg; reg++ ) {
     if( get_live_bit(live,reg) == 0 )
       continue;                 // Ignore if not live
     // %%% C2 can use 2 OptoRegs when the physical register is only one 64bit
     // register in that case we'll get an non-concrete register for the second
     // half. We only need to tell the map the register once!
     //
     // However for the moment we disable this change and leave things as they
     // were.
     VMReg r = OptoReg::as_VMReg(OptoReg::Name(reg), framesize, max_inarg_slot);
     if (false && r->is_reg() && !r->is_concrete()) {
       continue;
     }
     // See if dead (no reaching def).
     Node *def = _defs[reg];     // Get reaching def
     assert( def, "since live better have reaching def" );
     // Classify the reaching def as oop, derived, callee-save, dead, or other
     const Type *t = def->bottom_type();
     if( t->isa_oop_ptr() ) {    // Oop or derived?
       assert( !OptoReg::is_valid(_callees[reg]), "oop can't be callee save" );
 #ifdef _LP64
       // 64-bit pointers record oop-ishness on 2 aligned adjacent registers.
       // Make sure both are record from the same reaching def, but do not
       // put both into the oopmap.
       if( (reg&1) == 1 ) {      // High half of oop-pair?
         assert( _defs[reg-1] == _defs[reg], "both halves from same reaching def" );
         continue;               // Do not record high parts in oopmap
       }
 #endif
       // Check for a legal reg name in the oopMap and bailout if it is not.
       if (!omap->legal_vm_reg_name(r)) {
         regalloc->C->record_method_not_compilable("illegal oopMap register name");
         continue;
       }
       if( t->is_ptr()->_offset == 0 ) { // Not derived?
         if( mcall ) {
           // Outgoing argument GC mask responsibility belongs to the callee,
           // not the caller.  Inspect the inputs to the call, to see if
           // this live-range is one of them.
           uint cnt = mcall->tf()->domain()->cnt();
           uint j;
           for( j = TypeFunc::Parms; j < cnt; j++)
             if( mcall->in(j) == def )
               break;            // reaching def is an argument oop
           if( j < cnt )         // arg oops dont go in GC map
             continue;           // Continue on to the next register
         }
         omap->set_oop(r);
       } else {                  // Else it's derived.
         // Find the base of the derived value.
         uint i;
         // Fast, common case, scan
         for( i = jvms->oopoff(); i < n->req(); i+=2 )
           if( n->in(i) == def ) break; // Common case
         if( i == n->req() ) {   // Missed, try a more generous scan
           // Scan again, but this time peek through copies
           for( i = jvms->oopoff(); i < n->req(); i+=2 ) {
             Node *m = n->in(i); // Get initial derived value
             while( 1 ) {
               Node *d = def;    // Get initial reaching def
               while( 1 ) {      // Follow copies of reaching def to end
                 if( m == d ) goto found; // breaks 3 loops
                 int idx = d->is_Copy();
                 if( !idx ) break;
                 d = d->in(idx);     // Link through copy
               }
               int idx = m->is_Copy();
               if( !idx ) break;
               m = m->in(idx);
             }
           }
          guarantee( 0, "must find derived/base pair" );
         }
       found: ;
         Node *base = n->in(i+1); // Base is other half of pair
         int breg = regalloc->get_reg_first(base);
         VMReg b = OptoReg::as_VMReg(OptoReg::Name(breg), framesize, max_inarg_slot);
         // I record liveness at safepoints BEFORE I make the inputs
         // live.  This is because argument oops are NOT live at a
         // safepoint (or at least they cannot appear in the oopmap).
         // Thus bases of base/derived pairs might not be in the
         // liveness data but they need to appear in the oopmap.
         if( get_live_bit(live,breg) == 0 ) {// Not live?
           // Flag it, so next derived pointer won't re-insert into oopmap
           set_live_bit(live,breg);
           // Already missed our turn?
           if( breg < reg ) {
             if (b->is_stack() || b->is_concrete() || true ) {
               omap->set_oop( b);
             }
           }
         }
         if (b->is_stack() || b->is_concrete() || true ) {
           omap->set_derived_oop( r, b);
         }
       }
     } else if( t->isa_narrowoop() ) {
       assert( !OptoReg::is_valid(_callees[reg]), "oop can't be callee save" );
       // Check for a legal reg name in the oopMap and bailout if it is not.
       if (!omap->legal_vm_reg_name(r)) {
         regalloc->C->record_method_not_compilable("illegal oopMap register name");
         continue;
       }
       if( mcall ) {
           // Outgoing argument GC mask responsibility belongs to the callee,
           // not the caller.  Inspect the inputs to the call, to see if
           // this live-range is one of them.
         uint cnt = mcall->tf()->domain()->cnt();
         uint j;
         for( j = TypeFunc::Parms; j < cnt; j++)
           if( mcall->in(j) == def )
             break;            // reaching def is an argument oop
         if( j < cnt )         // arg oops dont go in GC map
           continue;           // Continue on to the next register
       }
       omap->set_narrowoop(r);
     } else if( OptoReg::is_valid(_callees[reg])) { // callee-save?
       // It's a callee-save value
       assert( dup_check[_callees[reg]]==0, "trying to callee save same reg twice" );
       debug_only( dup_check[_callees[reg]]=1; )
       VMReg callee = OptoReg::as_VMReg(OptoReg::Name(_callees[reg]));
       if ( callee->is_concrete() || true ) {
         omap->set_callee_saved( r, callee);
       }
     } else {
       // Other - some reaching non-oop value
       omap->set_value( r);
     }
   }
 #ifdef ASSERT
   /* Nice, Intel-only assert
   int cnt_callee_saves=0;
   int reg2 = 0;
   while (OptoReg::is_reg(reg2)) {
     if( dup_check[reg2] != 0) cnt_callee_saves++;
     assert( cnt_callee_saves==3 || cnt_callee_saves==5, "missed some callee-save" );
     reg2++;
   }
   */
 #endif
   return omap;
 }
 //------------------------------do_liveness------------------------------------
 // Compute backwards liveness on registers
 static void do_liveness( PhaseRegAlloc *regalloc, PhaseCFG *cfg, Block_List *worklist, int max_reg_ints, Arena *A, Dict *safehash ) {
   int *live = NEW_ARENA_ARRAY(A, int, (cfg->_num_blocks+1) * max_reg_ints);
   int *tmp_live = &live[cfg->_num_blocks * max_reg_ints];
   Node *root = cfg->C->root();
   // On CISC platforms, get the node representing the stack pointer  that regalloc
   // used for spills
   Node *fp = NodeSentinel;
   if (UseCISCSpill && root->req() > 1) {
     fp = root->in(1)->in(TypeFunc::FramePtr);
   }
   memset( live, 0, cfg->_num_blocks * (max_reg_ints<<LogBytesPerInt) );
   // Push preds onto worklist
   for( uint i=1; i<root->req(); i++ )
     worklist->push(cfg->_bbs[root->in(i)->_idx]);
   // ZKM.jar includes tiny infinite loops which are unreached from below.
   // If we missed any blocks, we'll retry here after pushing all missed
   // blocks on the worklist.  Normally this outer loop never trips more
   // than once.
   while( 1 ) {
     while( worklist->size() ) { // Standard worklist algorithm
       Block *b = worklist->rpop();
       // Copy first successor into my tmp_live space
       int s0num = b->_succs[0]->_pre_order;
       int *t = &live[s0num*max_reg_ints];
       for( int i=0; i<max_reg_ints; i++ )
         tmp_live[i] = t[i];
       // OR in the remaining live registers
       for( uint j=1; j<b->_num_succs; j++ ) {
         uint sjnum = b->_succs[j]->_pre_order;
         int *t = &live[sjnum*max_reg_ints];
         for( int i=0; i<max_reg_ints; i++ )
           tmp_live[i] |= t[i];
       }
       // Now walk tmp_live up the block backwards, computing live
       for( int k=b->_nodes.size()-1; k>=0; k-- ) {
         Node *n = b->_nodes[k];
         // KILL def'd bits
         int first = regalloc->get_reg_first(n);
         int second = regalloc->get_reg_second(n);
         if( OptoReg::is_valid(first) ) clr_live_bit(tmp_live,first);
         if( OptoReg::is_valid(second) ) clr_live_bit(tmp_live,second);
         MachNode *m = n->is_Mach() ? n->as_Mach() : NULL;
         // Check if m is potentially a CISC alternate instruction (i.e, possibly
         // synthesized by RegAlloc from a conventional instruction and a
         // spilled input)
         bool is_cisc_alternate = false;
         if (UseCISCSpill && m) {
           is_cisc_alternate = m->is_cisc_alternate();
         }
         // GEN use'd bits
         for( uint l=1; l<n->req(); l++ ) {
           Node *def = n->in(l);
           assert(def != 0, "input edge required");
           int first = regalloc->get_reg_first(def);
           int second = regalloc->get_reg_second(def);
           if( OptoReg::is_valid(first) ) set_live_bit(tmp_live,first);
           if( OptoReg::is_valid(second) ) set_live_bit(tmp_live,second);
           // If we use the stack pointer in a cisc-alternative instruction,
           // check for use as a memory operand.  Then reconstruct the RegName
           // for this stack location, and set the appropriate bit in the
           // live vector 4987749.
           if (is_cisc_alternate && def == fp) {
             const TypePtr *adr_type = NULL;
             intptr_t offset;
             const Node* base = m->get_base_and_disp(offset, adr_type);
             if (base == NodeSentinel) {
               // Machnode has multiple memory inputs. We are unable to reason
               // with these, but are presuming (with trepidation) that not any of
               // them are oops. This can be fixed by making get_base_and_disp()
               // look at a specific input instead of all inputs.
               assert(!def->bottom_type()->isa_oop_ptr(), "expecting non-oop mem input");
             } else if (base != fp || offset == Type::OffsetBot) {
               // Do nothing: the fp operand is either not from a memory use
               // (base == NULL) OR the fp is used in a non-memory context
               // (base is some other register) OR the offset is not constant,
               // so it is not a stack slot.
             } else {
               assert(offset >= 0, "unexpected negative offset");
               offset -= (offset % jintSize);  // count the whole word
               int stack_reg = regalloc->offset2reg(offset);
               if (OptoReg::is_stack(stack_reg)) {
                 set_live_bit(tmp_live, stack_reg);
               } else {
                 assert(false, "stack_reg not on stack?");
               }
             }
           }
         }
         if( n->jvms() ) {       // Record liveness at safepoint
           // This placement of this stanza means inputs to calls are
           // considered live at the callsite's OopMap.  Argument oops are
           // hence live, but NOT included in the oopmap.  See cutout in
           // build_oop_map.  Debug oops are live (and in OopMap).
           int *n_live = NEW_ARENA_ARRAY(A, int, max_reg_ints);
           for( int l=0; l<max_reg_ints; l++ )
             n_live[l] = tmp_live[l];
           safehash->Insert(n,n_live);
         }
       }
       // Now at block top, see if we have any changes.  If so, propagate
       // to prior blocks.
       int *old_live = &live[b->_pre_order*max_reg_ints];
       int l;
       for( l=0; l<max_reg_ints; l++ )
         if( tmp_live[l] != old_live[l] )
           break;
       if( l<max_reg_ints ) {     // Change!
         // Copy in new value
         for( l=0; l<max_reg_ints; l++ )
           old_live[l] = tmp_live[l];
         // Push preds onto worklist
         for( l=1; l<(int)b->num_preds(); l++ )
           worklist->push(cfg->_bbs[b->pred(l)->_idx]);
       }
     }
     // Scan for any missing safepoints.  Happens to infinite loops
     // ala ZKM.jar
     uint i;
     for( i=1; i<cfg->_num_blocks; i++ ) {
       Block *b = cfg->_blocks[i];
       uint j;
       for( j=1; j<b->_nodes.size(); j++ )
         if( b->_nodes[j]->jvms() &&
             (*safehash)[b->_nodes[j]] == NULL )
            break;
       if( j<b->_nodes.size() ) break;
     }
     if( i == cfg->_num_blocks )
       break;                    // Got 'em all
 #ifndef PRODUCT
     if( PrintOpto && Verbose )
       tty->print_cr("retripping live calc");
 #endif
     // Force the issue (expensively): recheck everybody
     for( i=1; i<cfg->_num_blocks; i++ )
       worklist->push(cfg->_blocks[i]);
   }
 }
 //------------------------------BuildOopMaps-----------------------------------
 // Collect GC mask info - where are all the OOPs?
 void Compile::BuildOopMaps() {
   NOT_PRODUCT( TracePhase t3("bldOopMaps", &_t_buildOopMaps, TimeCompiler); )
   // Can't resource-mark because I need to leave all those OopMaps around,
   // or else I need to resource-mark some arena other than the default.
   // ResourceMark rm;              // Reclaim all OopFlows when done
   int max_reg = _regalloc->_max_reg; // Current array extent
   Arena *A = Thread::current()->resource_area();
   Block_List worklist;          // Worklist of pending blocks
   int max_reg_ints = round_to(max_reg, BitsPerInt)>>LogBitsPerInt;
   Dict *safehash = NULL;        // Used for assert only
   // Compute a backwards liveness per register.  Needs a bitarray of
   // #blocks x (#registers, rounded up to ints)
   safehash = new Dict(cmpkey,hashkey,A);
   do_liveness( _regalloc, _cfg, &worklist, max_reg_ints, A, safehash );
   OopFlow *free_list = NULL;    // Free, unused
   // Array mapping blocks to completed oopflows
   OopFlow **flows = NEW_ARENA_ARRAY(A, OopFlow*, _cfg->_num_blocks);
   memset( flows, 0, _cfg->_num_blocks*sizeof(OopFlow*) );
   // Do the first block 'by hand' to prime the worklist
   Block *entry = _cfg->_blocks[1];
   OopFlow *rootflow = OopFlow::make(A,max_reg);
   // Initialize to 'bottom' (not 'top')
   memset( rootflow->_callees, OptoReg::Bad, max_reg*sizeof(short) );
   memset( rootflow->_defs   ,            0, max_reg*sizeof(Node*) );
   flows[entry->_pre_order] = rootflow;
   // Do the first block 'by hand' to prime the worklist
   rootflow->_b = entry;
   rootflow->compute_reach( _regalloc, max_reg, safehash );
   for( uint i=0; i<entry->_num_succs; i++ )
     worklist.push(entry->_succs[i]);
   // Now worklist contains blocks which have some, but perhaps not all,
   // predecessors visited.
   while( worklist.size() ) {
     // Scan for a block with all predecessors visited, or any randoms slob
     // otherwise.  All-preds-visited order allows me to recycle OopFlow
     // structures rapidly and cut down on the memory footprint.
     // Note: not all predecessors might be visited yet (must happen for
     // irreducible loops).  This is OK, since every live value must have the
     // SAME reaching def for the block, so any reaching def is OK.
     uint i;
     Block *b = worklist.pop();
     // Ignore root block
     if( b == _cfg->_broot ) continue;
     // Block is already done?  Happens if block has several predecessors,
     // he can get on the worklist more than once.
     if( flows[b->_pre_order] ) continue;
     // If this block has a visited predecessor AND that predecessor has this
     // last block as his only undone child, we can move the OopFlow from the
     // pred to this block.  Otherwise we have to grab a new OopFlow.
     OopFlow *flow = NULL;       // Flag for finding optimized flow
     Block *pred = (Block*)0xdeadbeef;
     uint j;
     // Scan this block's preds to find a done predecessor
     for( j=1; j<b->num_preds(); j++ ) {
       Block *p = _cfg->_bbs[b->pred(j)->_idx];
       OopFlow *p_flow = flows[p->_pre_order];
       if( p_flow ) {            // Predecessor is done
         assert( p_flow->_b == p, "cross check" );
         pred = p;               // Record some predecessor
         // If all successors of p are done except for 'b', then we can carry
         // p_flow forward to 'b' without copying, otherwise we have to draw
         // from the free_list and clone data.
         uint k;
         for( k=0; k<p->_num_succs; k++ )
           if( !flows[p->_succs[k]->_pre_order] &&
               p->_succs[k] != b )
             break;
         // Either carry-forward the now-unused OopFlow for b's use
         // or draw a new one from the free list
         if( k==p->_num_succs ) {
           flow = p_flow;
           break;                // Found an ideal pred, use him
         }
       }
     }
     if( flow ) {
       // We have an OopFlow that's the last-use of a predecessor.
       // Carry it forward.
     } else {                    // Draw a new OopFlow from the freelist
       if( !free_list )
         free_list = OopFlow::make(A,max_reg);
       flow = free_list;
       assert( flow->_b == NULL, "oopFlow is not free" );
       free_list = flow->_next;
       flow->_next = NULL;
       // Copy/clone over the data
       flow->clone(flows[pred->_pre_order], max_reg);
     }
     // Mark flow for block.  Blocks can only be flowed over once,
     // because after the first time they are guarded from entering
     // this code again.
     assert( flow->_b == pred, "have some prior flow" );
     flow->_b = NULL;
     // Now push flow forward
     flows[b->_pre_order] = flow;// Mark flow for this block
     flow->_b = b;
     flow->compute_reach( _regalloc, max_reg, safehash );
     // Now push children onto worklist
     for( i=0; i<b->_num_succs; i++ )
       worklist.push(b->_succs[i]);
   }
 }

Mercurial > jdk8-mips64-public > hotspot / annotate

src/share/vm/opto/buildOopMap.cpp@98cb887364d3 (annotated)

src/share/vm/opto/buildOopMap.cpp