/*
* Copyright (c) 2002, 2018, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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*/
#include "precompiled.hpp"
#include "code/vmreg.inline.hpp"
#include "compiler/oopMap.hpp"
#include "memory/resourceArea.hpp"
#include "opto/addnode.hpp"
#include "opto/callnode.hpp"
#include "opto/compile.hpp"
#include "opto/machnode.hpp"
#include "opto/matcher.hpp"
#include "opto/phase.hpp"
#include "opto/regalloc.hpp"
#include "opto/rootnode.hpp"
#include "utilities/align.hpp"
// 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.
// 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
// or NULL if dead/conflict
Compile* C;
OopFlow( short *callees, Node **defs, Compile* c ) : _callees(callees), _defs(defs),
_b(NULL), _next(NULL), C(c) { }
// 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, Compile* C );
// Build an oopmap from the current flow info
OopMap *build_oop_map( Node *n, int max_reg, PhaseRegAlloc *regalloc, int* live );
};
// 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->number_of_nodes(); i++ ) {
Node *n = _b->get_node(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 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;
}
}
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);
}
OopFlow *OopFlow::make( Arena *A, int max_size, Compile* C ) {
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, C);
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;
}
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 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
#ifdef ASSERT
if( t->isa_rawptr() && C->cfg()->_raw_oops.member(def) ) {
def->dump();
n->dump();
assert(false, "there should be a oop in OopMap instead of a live raw oop at safepoint");
}
#endif
}
}
#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
#ifdef ASSERT
for( OopMapStream oms1(omap); !oms1.is_done(); oms1.next()) {
OopMapValue omv1 = oms1.current();
if (omv1.type() != OopMapValue::derived_oop_value) {
continue;
}
bool found = false;
for( OopMapStream oms2(omap); !oms2.is_done(); oms2.next()) {
OopMapValue omv2 = oms2.current();
if (omv2.type() != OopMapValue::oop_value) {
continue;
}
if( omv1.content_reg() == omv2.reg() ) {
found = true;
break;
}
}
assert( found, "derived with no base in oopmap" );
}
#endif
return omap;
}
// 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->number_of_blocks() + 1) * max_reg_ints);
int* tmp_live = &live[cfg->number_of_blocks() * max_reg_ints];
Node* root = cfg->get_root_node();
// 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->number_of_blocks() * (max_reg_ints << LogBytesPerInt));
// Push preds onto worklist
for (uint i = 1; i < root->req(); i++) {
Block* block = cfg->get_block_for_node(root->in(i));
worklist->push(block);
}
// 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->number_of_nodes()-1; k>=0; k-- ) {
Node *n = b->get_node(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++) {
Block* block = cfg->get_block_for_node(b->pred(l));
worklist->push(block);
}
}
}
// Scan for any missing safepoints. Happens to infinite loops
// ala ZKM.jar
uint i;
for (i = 1; i < cfg->number_of_blocks(); i++) {
Block* block = cfg->get_block(i);
uint j;
for (j = 1; j < block->number_of_nodes(); j++) {
if (block->get_node(j)->jvms() && (*safehash)[block->get_node(j)] == NULL) {
break;
}
}
if (j < block->number_of_nodes()) {
break;
}
}
if (i == cfg->number_of_blocks()) {
break; // Got 'em all
}
if (PrintOpto && Verbose) {
tty->print_cr("retripping live calc");
}
// Force the issue (expensively): recheck everybody
for (i = 1; i < cfg->number_of_blocks(); i++) {
worklist->push(cfg->get_block(i));
}
}
}
// Collect GC mask info - where are all the OOPs?
void Compile::BuildOopMaps() {
TracePhase tp("bldOopMaps", &timers[_t_buildOopMaps]);
// 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 = align_up(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->number_of_blocks());
memset( flows, 0, _cfg->number_of_blocks() * sizeof(OopFlow*) );
// Do the first block 'by hand' to prime the worklist
Block *entry = _cfg->get_block(1);
OopFlow *rootflow = OopFlow::make(A,max_reg,this);
// 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->get_root_block()) {
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*)((intptr_t)0xdeadbeef);
// Scan this block's preds to find a done predecessor
for (uint j = 1; j < b->num_preds(); j++) {
Block* p = _cfg->get_block_for_node(b->pred(j));
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,C);
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]);
}
}