7079317: Incorrect branch's destination block in PrintoOptoAssembly output
Summary: save/restore label and block in scratch_emit_size()
Reviewed-by: never
/*
* Copyright (c) 1997, 2010, 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
* or visit www.oracle.com if you need additional information or have any
* questions.
*
*/
#include "precompiled.hpp"
#include "libadt/vectset.hpp"
#include "memory/allocation.inline.hpp"
#include "opto/block.hpp"
#include "opto/cfgnode.hpp"
#include "opto/chaitin.hpp"
#include "opto/loopnode.hpp"
#include "opto/machnode.hpp"
#include "opto/matcher.hpp"
#include "opto/opcodes.hpp"
#include "opto/rootnode.hpp"
#include "utilities/copy.hpp"
// Optimization - Graph Style
//-----------------------------------------------------------------------------
void Block_Array::grow( uint i ) {
assert(i >= Max(), "must be an overflow");
debug_only(_limit = i+1);
if( i < _size ) return;
if( !_size ) {
_size = 1;
_blocks = (Block**)_arena->Amalloc( _size * sizeof(Block*) );
_blocks[0] = NULL;
}
uint old = _size;
while( i >= _size ) _size <<= 1; // Double to fit
_blocks = (Block**)_arena->Arealloc( _blocks, old*sizeof(Block*),_size*sizeof(Block*));
Copy::zero_to_bytes( &_blocks[old], (_size-old)*sizeof(Block*) );
}
//=============================================================================
void Block_List::remove(uint i) {
assert(i < _cnt, "index out of bounds");
Copy::conjoint_words_to_lower((HeapWord*)&_blocks[i+1], (HeapWord*)&_blocks[i], ((_cnt-i-1)*sizeof(Block*)));
pop(); // shrink list by one block
}
void Block_List::insert(uint i, Block *b) {
push(b); // grow list by one block
Copy::conjoint_words_to_higher((HeapWord*)&_blocks[i], (HeapWord*)&_blocks[i+1], ((_cnt-i-1)*sizeof(Block*)));
_blocks[i] = b;
}
#ifndef PRODUCT
void Block_List::print() {
for (uint i=0; i < size(); i++) {
tty->print("B%d ", _blocks[i]->_pre_order);
}
tty->print("size = %d\n", size());
}
#endif
//=============================================================================
uint Block::code_alignment() {
// Check for Root block
if (_pre_order == 0) return CodeEntryAlignment;
// Check for Start block
if (_pre_order == 1) return InteriorEntryAlignment;
// Check for loop alignment
if (has_loop_alignment()) return loop_alignment();
return relocInfo::addr_unit(); // no particular alignment
}
uint Block::compute_loop_alignment() {
Node *h = head();
int unit_sz = relocInfo::addr_unit();
if (h->is_Loop() && h->as_Loop()->is_inner_loop()) {
// Pre- and post-loops have low trip count so do not bother with
// NOPs for align loop head. The constants are hidden from tuning
// but only because my "divide by 4" heuristic surely gets nearly
// all possible gain (a "do not align at all" heuristic has a
// chance of getting a really tiny gain).
if (h->is_CountedLoop() && (h->as_CountedLoop()->is_pre_loop() ||
h->as_CountedLoop()->is_post_loop())) {
return (OptoLoopAlignment > 4*unit_sz) ? (OptoLoopAlignment>>2) : unit_sz;
}
// Loops with low backedge frequency should not be aligned.
Node *n = h->in(LoopNode::LoopBackControl)->in(0);
if (n->is_MachIf() && n->as_MachIf()->_prob < 0.01) {
return unit_sz; // Loop does not loop, more often than not!
}
return OptoLoopAlignment; // Otherwise align loop head
}
return unit_sz; // no particular alignment
}
//-----------------------------------------------------------------------------
// Compute the size of first 'inst_cnt' instructions in this block.
// Return the number of instructions left to compute if the block has
// less then 'inst_cnt' instructions. Stop, and return 0 if sum_size
// exceeds OptoLoopAlignment.
uint Block::compute_first_inst_size(uint& sum_size, uint inst_cnt,
PhaseRegAlloc* ra) {
uint last_inst = _nodes.size();
for( uint j = 0; j < last_inst && inst_cnt > 0; j++ ) {
uint inst_size = _nodes[j]->size(ra);
if( inst_size > 0 ) {
inst_cnt--;
uint sz = sum_size + inst_size;
if( sz <= (uint)OptoLoopAlignment ) {
// Compute size of instructions which fit into fetch buffer only
// since all inst_cnt instructions will not fit even if we align them.
sum_size = sz;
} else {
return 0;
}
}
}
return inst_cnt;
}
//-----------------------------------------------------------------------------
uint Block::find_node( const Node *n ) const {
for( uint i = 0; i < _nodes.size(); i++ ) {
if( _nodes[i] == n )
return i;
}
ShouldNotReachHere();
return 0;
}
// Find and remove n from block list
void Block::find_remove( const Node *n ) {
_nodes.remove(find_node(n));
}
//------------------------------is_Empty---------------------------------------
// Return empty status of a block. Empty blocks contain only the head, other
// ideal nodes, and an optional trailing goto.
int Block::is_Empty() const {
// Root or start block is not considered empty
if (head()->is_Root() || head()->is_Start()) {
return not_empty;
}
int success_result = completely_empty;
int end_idx = _nodes.size()-1;
// Check for ending goto
if ((end_idx > 0) && (_nodes[end_idx]->is_MachGoto())) {
success_result = empty_with_goto;
end_idx--;
}
// Unreachable blocks are considered empty
if (num_preds() <= 1) {
return success_result;
}
// Ideal nodes are allowable in empty blocks: skip them Only MachNodes
// turn directly into code, because only MachNodes have non-trivial
// emit() functions.
while ((end_idx > 0) && !_nodes[end_idx]->is_Mach()) {
end_idx--;
}
// No room for any interesting instructions?
if (end_idx == 0) {
return success_result;
}
return not_empty;
}
//------------------------------has_uncommon_code------------------------------
// Return true if the block's code implies that it is likely to be
// executed infrequently. Check to see if the block ends in a Halt or
// a low probability call.
bool Block::has_uncommon_code() const {
Node* en = end();
if (en->is_MachGoto())
en = en->in(0);
if (en->is_Catch())
en = en->in(0);
if (en->is_MachProj() && en->in(0)->is_MachCall()) {
MachCallNode* call = en->in(0)->as_MachCall();
if (call->cnt() != COUNT_UNKNOWN && call->cnt() <= PROB_UNLIKELY_MAG(4)) {
// This is true for slow-path stubs like new_{instance,array},
// slow_arraycopy, complete_monitor_locking, uncommon_trap.
// The magic number corresponds to the probability of an uncommon_trap,
// even though it is a count not a probability.
return true;
}
}
int op = en->is_Mach() ? en->as_Mach()->ideal_Opcode() : en->Opcode();
return op == Op_Halt;
}
//------------------------------is_uncommon------------------------------------
// True if block is low enough frequency or guarded by a test which
// mostly does not go here.
bool Block::is_uncommon( Block_Array &bbs ) const {
// Initial blocks must never be moved, so are never uncommon.
if (head()->is_Root() || head()->is_Start()) return false;
// Check for way-low freq
if( _freq < BLOCK_FREQUENCY(0.00001f) ) return true;
// Look for code shape indicating uncommon_trap or slow path
if (has_uncommon_code()) return true;
const float epsilon = 0.05f;
const float guard_factor = PROB_UNLIKELY_MAG(4) / (1.f - epsilon);
uint uncommon_preds = 0;
uint freq_preds = 0;
uint uncommon_for_freq_preds = 0;
for( uint i=1; i<num_preds(); i++ ) {
Block* guard = bbs[pred(i)->_idx];
// Check to see if this block follows its guard 1 time out of 10000
// or less.
//
// See list of magnitude-4 unlikely probabilities in cfgnode.hpp which
// we intend to be "uncommon", such as slow-path TLE allocation,
// predicted call failure, and uncommon trap triggers.
//
// Use an epsilon value of 5% to allow for variability in frequency
// predictions and floating point calculations. The net effect is
// that guard_factor is set to 9500.
//
// Ignore low-frequency blocks.
// The next check is (guard->_freq < 1.e-5 * 9500.).
if(guard->_freq*BLOCK_FREQUENCY(guard_factor) < BLOCK_FREQUENCY(0.00001f)) {
uncommon_preds++;
} else {
freq_preds++;
if( _freq < guard->_freq * guard_factor ) {
uncommon_for_freq_preds++;
}
}
}
if( num_preds() > 1 &&
// The block is uncommon if all preds are uncommon or
(uncommon_preds == (num_preds()-1) ||
// it is uncommon for all frequent preds.
uncommon_for_freq_preds == freq_preds) ) {
return true;
}
return false;
}
//------------------------------dump-------------------------------------------
#ifndef PRODUCT
void Block::dump_bidx(const Block* orig, outputStream* st) const {
if (_pre_order) st->print("B%d",_pre_order);
else st->print("N%d", head()->_idx);
if (Verbose && orig != this) {
// Dump the original block's idx
st->print(" (");
orig->dump_bidx(orig, st);
st->print(")");
}
}
void Block::dump_pred(const Block_Array *bbs, Block* orig, outputStream* st) const {
if (is_connector()) {
for (uint i=1; i<num_preds(); i++) {
Block *p = ((*bbs)[pred(i)->_idx]);
p->dump_pred(bbs, orig, st);
}
} else {
dump_bidx(orig, st);
st->print(" ");
}
}
void Block::dump_head( const Block_Array *bbs, outputStream* st ) const {
// Print the basic block
dump_bidx(this, st);
st->print(": #\t");
// Print the incoming CFG edges and the outgoing CFG edges
for( uint i=0; i<_num_succs; i++ ) {
non_connector_successor(i)->dump_bidx(_succs[i], st);
st->print(" ");
}
st->print("<- ");
if( head()->is_block_start() ) {
for (uint i=1; i<num_preds(); i++) {
Node *s = pred(i);
if (bbs) {
Block *p = (*bbs)[s->_idx];
p->dump_pred(bbs, p, st);
} else {
while (!s->is_block_start())
s = s->in(0);
st->print("N%d ", s->_idx );
}
}
} else
st->print("BLOCK HEAD IS JUNK ");
// Print loop, if any
const Block *bhead = this; // Head of self-loop
Node *bh = bhead->head();
if( bbs && bh->is_Loop() && !head()->is_Root() ) {
LoopNode *loop = bh->as_Loop();
const Block *bx = (*bbs)[loop->in(LoopNode::LoopBackControl)->_idx];
while (bx->is_connector()) {
bx = (*bbs)[bx->pred(1)->_idx];
}
st->print("\tLoop: B%d-B%d ", bhead->_pre_order, bx->_pre_order);
// Dump any loop-specific bits, especially for CountedLoops.
loop->dump_spec(st);
} else if (has_loop_alignment()) {
st->print(" top-of-loop");
}
st->print(" Freq: %g",_freq);
if( Verbose || WizardMode ) {
st->print(" IDom: %d/#%d", _idom ? _idom->_pre_order : 0, _dom_depth);
st->print(" RegPressure: %d",_reg_pressure);
st->print(" IHRP Index: %d",_ihrp_index);
st->print(" FRegPressure: %d",_freg_pressure);
st->print(" FHRP Index: %d",_fhrp_index);
}
st->print_cr("");
}
void Block::dump() const { dump(NULL); }
void Block::dump( const Block_Array *bbs ) const {
dump_head(bbs);
uint cnt = _nodes.size();
for( uint i=0; i<cnt; i++ )
_nodes[i]->dump();
tty->print("\n");
}
#endif
//=============================================================================
//------------------------------PhaseCFG---------------------------------------
PhaseCFG::PhaseCFG( Arena *a, RootNode *r, Matcher &m ) :
Phase(CFG),
_bbs(a),
_root(r),
_node_latency(NULL)
#ifndef PRODUCT
, _trace_opto_pipelining(TraceOptoPipelining || C->method_has_option("TraceOptoPipelining"))
#endif
#ifdef ASSERT
, _raw_oops(a)
#endif
{
ResourceMark rm;
// I'll need a few machine-specific GotoNodes. Make an Ideal GotoNode,
// then Match it into a machine-specific Node. Then clone the machine
// Node on demand.
Node *x = new (C, 1) GotoNode(NULL);
x->init_req(0, x);
_goto = m.match_tree(x);
assert(_goto != NULL, "");
_goto->set_req(0,_goto);
// Build the CFG in Reverse Post Order
_num_blocks = build_cfg();
_broot = _bbs[_root->_idx];
}
//------------------------------build_cfg--------------------------------------
// Build a proper looking CFG. Make every block begin with either a StartNode
// or a RegionNode. Make every block end with either a Goto, If or Return.
// The RootNode both starts and ends it's own block. Do this with a recursive
// backwards walk over the control edges.
uint PhaseCFG::build_cfg() {
Arena *a = Thread::current()->resource_area();
VectorSet visited(a);
// Allocate stack with enough space to avoid frequent realloc
Node_Stack nstack(a, C->unique() >> 1);
nstack.push(_root, 0);
uint sum = 0; // Counter for blocks
while (nstack.is_nonempty()) {
// node and in's index from stack's top
// 'np' is _root (see above) or RegionNode, StartNode: we push on stack
// only nodes which point to the start of basic block (see below).
Node *np = nstack.node();
// idx > 0, except for the first node (_root) pushed on stack
// at the beginning when idx == 0.
// We will use the condition (idx == 0) later to end the build.
uint idx = nstack.index();
Node *proj = np->in(idx);
const Node *x = proj->is_block_proj();
// Does the block end with a proper block-ending Node? One of Return,
// If or Goto? (This check should be done for visited nodes also).
if (x == NULL) { // Does not end right...
Node *g = _goto->clone(); // Force it to end in a Goto
g->set_req(0, proj);
np->set_req(idx, g);
x = proj = g;
}
if (!visited.test_set(x->_idx)) { // Visit this block once
// Skip any control-pinned middle'in stuff
Node *p = proj;
do {
proj = p; // Update pointer to last Control
p = p->in(0); // Move control forward
} while( !p->is_block_proj() &&
!p->is_block_start() );
// Make the block begin with one of Region or StartNode.
if( !p->is_block_start() ) {
RegionNode *r = new (C, 2) RegionNode( 2 );
r->init_req(1, p); // Insert RegionNode in the way
proj->set_req(0, r); // Insert RegionNode in the way
p = r;
}
// 'p' now points to the start of this basic block
// Put self in array of basic blocks
Block *bb = new (_bbs._arena) Block(_bbs._arena,p);
_bbs.map(p->_idx,bb);
_bbs.map(x->_idx,bb);
if( x != p ) { // Only for root is x == p
bb->_nodes.push((Node*)x);
}
// Now handle predecessors
++sum; // Count 1 for self block
uint cnt = bb->num_preds();
for (int i = (cnt - 1); i > 0; i-- ) { // For all predecessors
Node *prevproj = p->in(i); // Get prior input
assert( !prevproj->is_Con(), "dead input not removed" );
// Check to see if p->in(i) is a "control-dependent" CFG edge -
// i.e., it splits at the source (via an IF or SWITCH) and merges
// at the destination (via a many-input Region).
// This breaks critical edges. The RegionNode to start the block
// will be added when <p,i> is pulled off the node stack
if ( cnt > 2 ) { // Merging many things?
assert( prevproj== bb->pred(i),"");
if(prevproj->is_block_proj() != prevproj) { // Control-dependent edge?
// Force a block on the control-dependent edge
Node *g = _goto->clone(); // Force it to end in a Goto
g->set_req(0,prevproj);
p->set_req(i,g);
}
}
nstack.push(p, i); // 'p' is RegionNode or StartNode
}
} else { // Post-processing visited nodes
nstack.pop(); // remove node from stack
// Check if it the fist node pushed on stack at the beginning.
if (idx == 0) break; // end of the build
// Find predecessor basic block
Block *pb = _bbs[x->_idx];
// Insert into nodes array, if not already there
if( !_bbs.lookup(proj->_idx) ) {
assert( x != proj, "" );
// Map basic block of projection
_bbs.map(proj->_idx,pb);
pb->_nodes.push(proj);
}
// Insert self as a child of my predecessor block
pb->_succs.map(pb->_num_succs++, _bbs[np->_idx]);
assert( pb->_nodes[ pb->_nodes.size() - pb->_num_succs ]->is_block_proj(),
"too many control users, not a CFG?" );
}
}
// Return number of basic blocks for all children and self
return sum;
}
//------------------------------insert_goto_at---------------------------------
// Inserts a goto & corresponding basic block between
// block[block_no] and its succ_no'th successor block
void PhaseCFG::insert_goto_at(uint block_no, uint succ_no) {
// get block with block_no
assert(block_no < _num_blocks, "illegal block number");
Block* in = _blocks[block_no];
// get successor block succ_no
assert(succ_no < in->_num_succs, "illegal successor number");
Block* out = in->_succs[succ_no];
// Compute frequency of the new block. Do this before inserting
// new block in case succ_prob() needs to infer the probability from
// surrounding blocks.
float freq = in->_freq * in->succ_prob(succ_no);
// get ProjNode corresponding to the succ_no'th successor of the in block
ProjNode* proj = in->_nodes[in->_nodes.size() - in->_num_succs + succ_no]->as_Proj();
// create region for basic block
RegionNode* region = new (C, 2) RegionNode(2);
region->init_req(1, proj);
// setup corresponding basic block
Block* block = new (_bbs._arena) Block(_bbs._arena, region);
_bbs.map(region->_idx, block);
C->regalloc()->set_bad(region->_idx);
// add a goto node
Node* gto = _goto->clone(); // get a new goto node
gto->set_req(0, region);
// add it to the basic block
block->_nodes.push(gto);
_bbs.map(gto->_idx, block);
C->regalloc()->set_bad(gto->_idx);
// hook up successor block
block->_succs.map(block->_num_succs++, out);
// remap successor's predecessors if necessary
for (uint i = 1; i < out->num_preds(); i++) {
if (out->pred(i) == proj) out->head()->set_req(i, gto);
}
// remap predecessor's successor to new block
in->_succs.map(succ_no, block);
// Set the frequency of the new block
block->_freq = freq;
// add new basic block to basic block list
_blocks.insert(block_no + 1, block);
_num_blocks++;
}
//------------------------------no_flip_branch---------------------------------
// Does this block end in a multiway branch that cannot have the default case
// flipped for another case?
static bool no_flip_branch( Block *b ) {
int branch_idx = b->_nodes.size() - b->_num_succs-1;
if( branch_idx < 1 ) return false;
Node *bra = b->_nodes[branch_idx];
if( bra->is_Catch() )
return true;
if( bra->is_Mach() ) {
if( bra->is_MachNullCheck() )
return true;
int iop = bra->as_Mach()->ideal_Opcode();
if( iop == Op_FastLock || iop == Op_FastUnlock )
return true;
}
return false;
}
//------------------------------convert_NeverBranch_to_Goto--------------------
// Check for NeverBranch at block end. This needs to become a GOTO to the
// true target. NeverBranch are treated as a conditional branch that always
// goes the same direction for most of the optimizer and are used to give a
// fake exit path to infinite loops. At this late stage they need to turn
// into Goto's so that when you enter the infinite loop you indeed hang.
void PhaseCFG::convert_NeverBranch_to_Goto(Block *b) {
// Find true target
int end_idx = b->end_idx();
int idx = b->_nodes[end_idx+1]->as_Proj()->_con;
Block *succ = b->_succs[idx];
Node* gto = _goto->clone(); // get a new goto node
gto->set_req(0, b->head());
Node *bp = b->_nodes[end_idx];
b->_nodes.map(end_idx,gto); // Slam over NeverBranch
_bbs.map(gto->_idx, b);
C->regalloc()->set_bad(gto->_idx);
b->_nodes.pop(); // Yank projections
b->_nodes.pop(); // Yank projections
b->_succs.map(0,succ); // Map only successor
b->_num_succs = 1;
// remap successor's predecessors if necessary
uint j;
for( j = 1; j < succ->num_preds(); j++)
if( succ->pred(j)->in(0) == bp )
succ->head()->set_req(j, gto);
// Kill alternate exit path
Block *dead = b->_succs[1-idx];
for( j = 1; j < dead->num_preds(); j++)
if( dead->pred(j)->in(0) == bp )
break;
// Scan through block, yanking dead path from
// all regions and phis.
dead->head()->del_req(j);
for( int k = 1; dead->_nodes[k]->is_Phi(); k++ )
dead->_nodes[k]->del_req(j);
}
//------------------------------move_to_next-----------------------------------
// Helper function to move block bx to the slot following b_index. Return
// true if the move is successful, otherwise false
bool PhaseCFG::move_to_next(Block* bx, uint b_index) {
if (bx == NULL) return false;
// Return false if bx is already scheduled.
uint bx_index = bx->_pre_order;
if ((bx_index <= b_index) && (_blocks[bx_index] == bx)) {
return false;
}
// Find the current index of block bx on the block list
bx_index = b_index + 1;
while( bx_index < _num_blocks && _blocks[bx_index] != bx ) bx_index++;
assert(_blocks[bx_index] == bx, "block not found");
// If the previous block conditionally falls into bx, return false,
// because moving bx will create an extra jump.
for(uint k = 1; k < bx->num_preds(); k++ ) {
Block* pred = _bbs[bx->pred(k)->_idx];
if (pred == _blocks[bx_index-1]) {
if (pred->_num_succs != 1) {
return false;
}
}
}
// Reinsert bx just past block 'b'
_blocks.remove(bx_index);
_blocks.insert(b_index + 1, bx);
return true;
}
//------------------------------move_to_end------------------------------------
// Move empty and uncommon blocks to the end.
void PhaseCFG::move_to_end(Block *b, uint i) {
int e = b->is_Empty();
if (e != Block::not_empty) {
if (e == Block::empty_with_goto) {
// Remove the goto, but leave the block.
b->_nodes.pop();
}
// Mark this block as a connector block, which will cause it to be
// ignored in certain functions such as non_connector_successor().
b->set_connector();
}
// Move the empty block to the end, and don't recheck.
_blocks.remove(i);
_blocks.push(b);
}
//---------------------------set_loop_alignment--------------------------------
// Set loop alignment for every block
void PhaseCFG::set_loop_alignment() {
uint last = _num_blocks;
assert( _blocks[0] == _broot, "" );
for (uint i = 1; i < last; i++ ) {
Block *b = _blocks[i];
if (b->head()->is_Loop()) {
b->set_loop_alignment(b);
}
}
}
//-----------------------------remove_empty------------------------------------
// Make empty basic blocks to be "connector" blocks, Move uncommon blocks
// to the end.
void PhaseCFG::remove_empty() {
// Move uncommon blocks to the end
uint last = _num_blocks;
assert( _blocks[0] == _broot, "" );
for (uint i = 1; i < last; i++) {
Block *b = _blocks[i];
if (b->is_connector()) break;
// Check for NeverBranch at block end. This needs to become a GOTO to the
// true target. NeverBranch are treated as a conditional branch that
// always goes the same direction for most of the optimizer and are used
// to give a fake exit path to infinite loops. At this late stage they
// need to turn into Goto's so that when you enter the infinite loop you
// indeed hang.
if( b->_nodes[b->end_idx()]->Opcode() == Op_NeverBranch )
convert_NeverBranch_to_Goto(b);
// Look for uncommon blocks and move to end.
if (!C->do_freq_based_layout()) {
if( b->is_uncommon(_bbs) ) {
move_to_end(b, i);
last--; // No longer check for being uncommon!
if( no_flip_branch(b) ) { // Fall-thru case must follow?
b = _blocks[i]; // Find the fall-thru block
move_to_end(b, i);
last--;
}
i--; // backup block counter post-increment
}
}
}
// Move empty blocks to the end
last = _num_blocks;
for (uint i = 1; i < last; i++) {
Block *b = _blocks[i];
if (b->is_Empty() != Block::not_empty) {
move_to_end(b, i);
last--;
i--;
}
} // End of for all blocks
}
//-----------------------------fixup_flow--------------------------------------
// Fix up the final control flow for basic blocks.
void PhaseCFG::fixup_flow() {
// Fixup final control flow for the blocks. Remove jump-to-next
// block. If neither arm of a IF follows the conditional branch, we
// have to add a second jump after the conditional. We place the
// TRUE branch target in succs[0] for both GOTOs and IFs.
for (uint i=0; i < _num_blocks; i++) {
Block *b = _blocks[i];
b->_pre_order = i; // turn pre-order into block-index
// Connector blocks need no further processing.
if (b->is_connector()) {
assert((i+1) == _num_blocks || _blocks[i+1]->is_connector(),
"All connector blocks should sink to the end");
continue;
}
assert(b->is_Empty() != Block::completely_empty,
"Empty blocks should be connectors");
Block *bnext = (i < _num_blocks-1) ? _blocks[i+1] : NULL;
Block *bs0 = b->non_connector_successor(0);
// Check for multi-way branches where I cannot negate the test to
// exchange the true and false targets.
if( no_flip_branch( b ) ) {
// Find fall through case - if must fall into its target
int branch_idx = b->_nodes.size() - b->_num_succs;
for (uint j2 = 0; j2 < b->_num_succs; j2++) {
const ProjNode* p = b->_nodes[branch_idx + j2]->as_Proj();
if (p->_con == 0) {
// successor j2 is fall through case
if (b->non_connector_successor(j2) != bnext) {
// but it is not the next block => insert a goto
insert_goto_at(i, j2);
}
// Put taken branch in slot 0
if( j2 == 0 && b->_num_succs == 2) {
// Flip targets in succs map
Block *tbs0 = b->_succs[0];
Block *tbs1 = b->_succs[1];
b->_succs.map( 0, tbs1 );
b->_succs.map( 1, tbs0 );
}
break;
}
}
// Remove all CatchProjs
for (uint j1 = 0; j1 < b->_num_succs; j1++) b->_nodes.pop();
} else if (b->_num_succs == 1) {
// Block ends in a Goto?
if (bnext == bs0) {
// We fall into next block; remove the Goto
b->_nodes.pop();
}
} else if( b->_num_succs == 2 ) { // Block ends in a If?
// Get opcode of 1st projection (matches _succs[0])
// Note: Since this basic block has 2 exits, the last 2 nodes must
// be projections (in any order), the 3rd last node must be
// the IfNode (we have excluded other 2-way exits such as
// CatchNodes already).
MachNode *iff = b->_nodes[b->_nodes.size()-3]->as_Mach();
ProjNode *proj0 = b->_nodes[b->_nodes.size()-2]->as_Proj();
ProjNode *proj1 = b->_nodes[b->_nodes.size()-1]->as_Proj();
// Assert that proj0 and succs[0] match up. Similarly for proj1 and succs[1].
assert(proj0->raw_out(0) == b->_succs[0]->head(), "Mismatch successor 0");
assert(proj1->raw_out(0) == b->_succs[1]->head(), "Mismatch successor 1");
Block *bs1 = b->non_connector_successor(1);
// Check for neither successor block following the current
// block ending in a conditional. If so, move one of the
// successors after the current one, provided that the
// successor was previously unscheduled, but moveable
// (i.e., all paths to it involve a branch).
if( !C->do_freq_based_layout() && bnext != bs0 && bnext != bs1 ) {
// Choose the more common successor based on the probability
// of the conditional branch.
Block *bx = bs0;
Block *by = bs1;
// _prob is the probability of taking the true path. Make
// p the probability of taking successor #1.
float p = iff->as_MachIf()->_prob;
if( proj0->Opcode() == Op_IfTrue ) {
p = 1.0 - p;
}
// Prefer successor #1 if p > 0.5
if (p > PROB_FAIR) {
bx = bs1;
by = bs0;
}
// Attempt the more common successor first
if (move_to_next(bx, i)) {
bnext = bx;
} else if (move_to_next(by, i)) {
bnext = by;
}
}
// Check for conditional branching the wrong way. Negate
// conditional, if needed, so it falls into the following block
// and branches to the not-following block.
// Check for the next block being in succs[0]. We are going to branch
// to succs[0], so we want the fall-thru case as the next block in
// succs[1].
if (bnext == bs0) {
// Fall-thru case in succs[0], so flip targets in succs map
Block *tbs0 = b->_succs[0];
Block *tbs1 = b->_succs[1];
b->_succs.map( 0, tbs1 );
b->_succs.map( 1, tbs0 );
// Flip projection for each target
{ ProjNode *tmp = proj0; proj0 = proj1; proj1 = tmp; }
} else if( bnext != bs1 ) {
// Need a double-branch
// The existing conditional branch need not change.
// Add a unconditional branch to the false target.
// Alas, it must appear in its own block and adding a
// block this late in the game is complicated. Sigh.
insert_goto_at(i, 1);
}
// Make sure we TRUE branch to the target
if( proj0->Opcode() == Op_IfFalse ) {
iff->as_MachIf()->negate();
}
b->_nodes.pop(); // Remove IfFalse & IfTrue projections
b->_nodes.pop();
} else {
// Multi-exit block, e.g. a switch statement
// But we don't need to do anything here
}
} // End of for all blocks
}
//------------------------------dump-------------------------------------------
#ifndef PRODUCT
void PhaseCFG::_dump_cfg( const Node *end, VectorSet &visited ) const {
const Node *x = end->is_block_proj();
assert( x, "not a CFG" );
// Do not visit this block again
if( visited.test_set(x->_idx) ) return;
// Skip through this block
const Node *p = x;
do {
p = p->in(0); // Move control forward
assert( !p->is_block_proj() || p->is_Root(), "not a CFG" );
} while( !p->is_block_start() );
// Recursively visit
for( uint i=1; i<p->req(); i++ )
_dump_cfg(p->in(i),visited);
// Dump the block
_bbs[p->_idx]->dump(&_bbs);
}
void PhaseCFG::dump( ) const {
tty->print("\n--- CFG --- %d BBs\n",_num_blocks);
if( _blocks.size() ) { // Did we do basic-block layout?
for( uint i=0; i<_num_blocks; i++ )
_blocks[i]->dump(&_bbs);
} else { // Else do it with a DFS
VectorSet visited(_bbs._arena);
_dump_cfg(_root,visited);
}
}
void PhaseCFG::dump_headers() {
for( uint i = 0; i < _num_blocks; i++ ) {
if( _blocks[i] == NULL ) continue;
_blocks[i]->dump_head(&_bbs);
}
}
void PhaseCFG::verify( ) const {
#ifdef ASSERT
// Verify sane CFG
for( uint i = 0; i < _num_blocks; i++ ) {
Block *b = _blocks[i];
uint cnt = b->_nodes.size();
uint j;
for( j = 0; j < cnt; j++ ) {
Node *n = b->_nodes[j];
assert( _bbs[n->_idx] == b, "" );
if( j >= 1 && n->is_Mach() &&
n->as_Mach()->ideal_Opcode() == Op_CreateEx ) {
assert( j == 1 || b->_nodes[j-1]->is_Phi(),
"CreateEx must be first instruction in block" );
}
for( uint k = 0; k < n->req(); k++ ) {
Node *def = n->in(k);
if( def && def != n ) {
assert( _bbs[def->_idx] || def->is_Con(),
"must have block; constants for debug info ok" );
// Verify that instructions in the block is in correct order.
// Uses must follow their definition if they are at the same block.
// Mostly done to check that MachSpillCopy nodes are placed correctly
// when CreateEx node is moved in build_ifg_physical().
if( _bbs[def->_idx] == b &&
!(b->head()->is_Loop() && n->is_Phi()) &&
// See (+++) comment in reg_split.cpp
!(n->jvms() != NULL && n->jvms()->is_monitor_use(k)) ) {
bool is_loop = false;
if (n->is_Phi()) {
for( uint l = 1; l < def->req(); l++ ) {
if (n == def->in(l)) {
is_loop = true;
break; // Some kind of loop
}
}
}
assert( is_loop || b->find_node(def) < j, "uses must follow definitions" );
}
if( def->is_SafePointScalarObject() ) {
assert(_bbs[def->_idx] == b, "SafePointScalarObject Node should be at the same block as its SafePoint node");
assert(_bbs[def->_idx] == _bbs[def->in(0)->_idx], "SafePointScalarObject Node should be at the same block as its control edge");
}
}
}
}
j = b->end_idx();
Node *bp = (Node*)b->_nodes[b->_nodes.size()-1]->is_block_proj();
assert( bp, "last instruction must be a block proj" );
assert( bp == b->_nodes[j], "wrong number of successors for this block" );
if( bp->is_Catch() ) {
while( b->_nodes[--j]->is_MachProj() ) ;
assert( b->_nodes[j]->is_MachCall(), "CatchProj must follow call" );
}
else if( bp->is_Mach() && bp->as_Mach()->ideal_Opcode() == Op_If ) {
assert( b->_num_succs == 2, "Conditional branch must have two targets");
}
}
#endif
}
#endif
//=============================================================================
//------------------------------UnionFind--------------------------------------
UnionFind::UnionFind( uint max ) : _cnt(max), _max(max), _indices(NEW_RESOURCE_ARRAY(uint,max)) {
Copy::zero_to_bytes( _indices, sizeof(uint)*max );
}
void UnionFind::extend( uint from_idx, uint to_idx ) {
_nesting.check();
if( from_idx >= _max ) {
uint size = 16;
while( size <= from_idx ) size <<=1;
_indices = REALLOC_RESOURCE_ARRAY( uint, _indices, _max, size );
_max = size;
}
while( _cnt <= from_idx ) _indices[_cnt++] = 0;
_indices[from_idx] = to_idx;
}
void UnionFind::reset( uint max ) {
assert( max <= max_uint, "Must fit within uint" );
// Force the Union-Find mapping to be at least this large
extend(max,0);
// Initialize to be the ID mapping.
for( uint i=0; i<max; i++ ) map(i,i);
}
//------------------------------Find_compress----------------------------------
// Straight out of Tarjan's union-find algorithm
uint UnionFind::Find_compress( uint idx ) {
uint cur = idx;
uint next = lookup(cur);
while( next != cur ) { // Scan chain of equivalences
assert( next < cur, "always union smaller" );
cur = next; // until find a fixed-point
next = lookup(cur);
}
// Core of union-find algorithm: update chain of
// equivalences to be equal to the root.
while( idx != next ) {
uint tmp = lookup(idx);
map(idx, next);
idx = tmp;
}
return idx;
}
//------------------------------Find_const-------------------------------------
// Like Find above, but no path compress, so bad asymptotic behavior
uint UnionFind::Find_const( uint idx ) const {
if( idx == 0 ) return idx; // Ignore the zero idx
// Off the end? This can happen during debugging dumps
// when data structures have not finished being updated.
if( idx >= _max ) return idx;
uint next = lookup(idx);
while( next != idx ) { // Scan chain of equivalences
idx = next; // until find a fixed-point
next = lookup(idx);
}
return next;
}
//------------------------------Union------------------------------------------
// union 2 sets together.
void UnionFind::Union( uint idx1, uint idx2 ) {
uint src = Find(idx1);
uint dst = Find(idx2);
assert( src, "" );
assert( dst, "" );
assert( src < _max, "oob" );
assert( dst < _max, "oob" );
assert( src < dst, "always union smaller" );
map(dst,src);
}
#ifndef PRODUCT
static void edge_dump(GrowableArray<CFGEdge *> *edges) {
tty->print_cr("---- Edges ----");
for (int i = 0; i < edges->length(); i++) {
CFGEdge *e = edges->at(i);
if (e != NULL) {
edges->at(i)->dump();
}
}
}
static void trace_dump(Trace *traces[], int count) {
tty->print_cr("---- Traces ----");
for (int i = 0; i < count; i++) {
Trace *tr = traces[i];
if (tr != NULL) {
tr->dump();
}
}
}
void Trace::dump( ) const {
tty->print_cr("Trace (freq %f)", first_block()->_freq);
for (Block *b = first_block(); b != NULL; b = next(b)) {
tty->print(" B%d", b->_pre_order);
if (b->head()->is_Loop()) {
tty->print(" (L%d)", b->compute_loop_alignment());
}
if (b->has_loop_alignment()) {
tty->print(" (T%d)", b->code_alignment());
}
}
tty->cr();
}
void CFGEdge::dump( ) const {
tty->print(" B%d --> B%d Freq: %f out:%3d%% in:%3d%% State: ",
from()->_pre_order, to()->_pre_order, freq(), _from_pct, _to_pct);
switch(state()) {
case connected:
tty->print("connected");
break;
case open:
tty->print("open");
break;
case interior:
tty->print("interior");
break;
}
if (infrequent()) {
tty->print(" infrequent");
}
tty->cr();
}
#endif
//=============================================================================
//------------------------------edge_order-------------------------------------
// Comparison function for edges
static int edge_order(CFGEdge **e0, CFGEdge **e1) {
float freq0 = (*e0)->freq();
float freq1 = (*e1)->freq();
if (freq0 != freq1) {
return freq0 > freq1 ? -1 : 1;
}
int dist0 = (*e0)->to()->_rpo - (*e0)->from()->_rpo;
int dist1 = (*e1)->to()->_rpo - (*e1)->from()->_rpo;
return dist1 - dist0;
}
//------------------------------trace_frequency_order--------------------------
// Comparison function for edges
static int trace_frequency_order(const void *p0, const void *p1) {
Trace *tr0 = *(Trace **) p0;
Trace *tr1 = *(Trace **) p1;
Block *b0 = tr0->first_block();
Block *b1 = tr1->first_block();
// The trace of connector blocks goes at the end;
// we only expect one such trace
if (b0->is_connector() != b1->is_connector()) {
return b1->is_connector() ? -1 : 1;
}
// Pull more frequently executed blocks to the beginning
float freq0 = b0->_freq;
float freq1 = b1->_freq;
if (freq0 != freq1) {
return freq0 > freq1 ? -1 : 1;
}
int diff = tr0->first_block()->_rpo - tr1->first_block()->_rpo;
return diff;
}
//------------------------------find_edges-------------------------------------
// Find edges of interest, i.e, those which can fall through. Presumes that
// edges which don't fall through are of low frequency and can be generally
// ignored. Initialize the list of traces.
void PhaseBlockLayout::find_edges()
{
// Walk the blocks, creating edges and Traces
uint i;
Trace *tr = NULL;
for (i = 0; i < _cfg._num_blocks; i++) {
Block *b = _cfg._blocks[i];
tr = new Trace(b, next, prev);
traces[tr->id()] = tr;
// All connector blocks should be at the end of the list
if (b->is_connector()) break;
// If this block and the next one have a one-to-one successor
// predecessor relationship, simply append the next block
int nfallthru = b->num_fall_throughs();
while (nfallthru == 1 &&
b->succ_fall_through(0)) {
Block *n = b->_succs[0];
// Skip over single-entry connector blocks, we don't want to
// add them to the trace.
while (n->is_connector() && n->num_preds() == 1) {
n = n->_succs[0];
}
// We see a merge point, so stop search for the next block
if (n->num_preds() != 1) break;
i++;
assert(n = _cfg._blocks[i], "expecting next block");
tr->append(n);
uf->map(n->_pre_order, tr->id());
traces[n->_pre_order] = NULL;
nfallthru = b->num_fall_throughs();
b = n;
}
if (nfallthru > 0) {
// Create a CFGEdge for each outgoing
// edge that could be a fall-through.
for (uint j = 0; j < b->_num_succs; j++ ) {
if (b->succ_fall_through(j)) {
Block *target = b->non_connector_successor(j);
float freq = b->_freq * b->succ_prob(j);
int from_pct = (int) ((100 * freq) / b->_freq);
int to_pct = (int) ((100 * freq) / target->_freq);
edges->append(new CFGEdge(b, target, freq, from_pct, to_pct));
}
}
}
}
// Group connector blocks into one trace
for (i++; i < _cfg._num_blocks; i++) {
Block *b = _cfg._blocks[i];
assert(b->is_connector(), "connector blocks at the end");
tr->append(b);
uf->map(b->_pre_order, tr->id());
traces[b->_pre_order] = NULL;
}
}
//------------------------------union_traces----------------------------------
// Union two traces together in uf, and null out the trace in the list
void PhaseBlockLayout::union_traces(Trace* updated_trace, Trace* old_trace)
{
uint old_id = old_trace->id();
uint updated_id = updated_trace->id();
uint lo_id = updated_id;
uint hi_id = old_id;
// If from is greater than to, swap values to meet
// UnionFind guarantee.
if (updated_id > old_id) {
lo_id = old_id;
hi_id = updated_id;
// Fix up the trace ids
traces[lo_id] = traces[updated_id];
updated_trace->set_id(lo_id);
}
// Union the lower with the higher and remove the pointer
// to the higher.
uf->Union(lo_id, hi_id);
traces[hi_id] = NULL;
}
//------------------------------grow_traces-------------------------------------
// Append traces together via the most frequently executed edges
void PhaseBlockLayout::grow_traces()
{
// Order the edges, and drive the growth of Traces via the most
// frequently executed edges.
edges->sort(edge_order);
for (int i = 0; i < edges->length(); i++) {
CFGEdge *e = edges->at(i);
if (e->state() != CFGEdge::open) continue;
Block *src_block = e->from();
Block *targ_block = e->to();
// Don't grow traces along backedges?
if (!BlockLayoutRotateLoops) {
if (targ_block->_rpo <= src_block->_rpo) {
targ_block->set_loop_alignment(targ_block);
continue;
}
}
Trace *src_trace = trace(src_block);
Trace *targ_trace = trace(targ_block);
// If the edge in question can join two traces at their ends,
// append one trace to the other.
if (src_trace->last_block() == src_block) {
if (src_trace == targ_trace) {
e->set_state(CFGEdge::interior);
if (targ_trace->backedge(e)) {
// Reset i to catch any newly eligible edge
// (Or we could remember the first "open" edge, and reset there)
i = 0;
}
} else if (targ_trace->first_block() == targ_block) {
e->set_state(CFGEdge::connected);
src_trace->append(targ_trace);
union_traces(src_trace, targ_trace);
}
}
}
}
//------------------------------merge_traces-----------------------------------
// Embed one trace into another, if the fork or join points are sufficiently
// balanced.
void PhaseBlockLayout::merge_traces(bool fall_thru_only)
{
// Walk the edge list a another time, looking at unprocessed edges.
// Fold in diamonds
for (int i = 0; i < edges->length(); i++) {
CFGEdge *e = edges->at(i);
if (e->state() != CFGEdge::open) continue;
if (fall_thru_only) {
if (e->infrequent()) continue;
}
Block *src_block = e->from();
Trace *src_trace = trace(src_block);
bool src_at_tail = src_trace->last_block() == src_block;
Block *targ_block = e->to();
Trace *targ_trace = trace(targ_block);
bool targ_at_start = targ_trace->first_block() == targ_block;
if (src_trace == targ_trace) {
// This may be a loop, but we can't do much about it.
e->set_state(CFGEdge::interior);
continue;
}
if (fall_thru_only) {
// If the edge links the middle of two traces, we can't do anything.
// Mark the edge and continue.
if (!src_at_tail & !targ_at_start) {
continue;
}
// Don't grow traces along backedges?
if (!BlockLayoutRotateLoops && (targ_block->_rpo <= src_block->_rpo)) {
continue;
}
// If both ends of the edge are available, why didn't we handle it earlier?
assert(src_at_tail ^ targ_at_start, "Should have caught this edge earlier.");
if (targ_at_start) {
// Insert the "targ" trace in the "src" trace if the insertion point
// is a two way branch.
// Better profitability check possible, but may not be worth it.
// Someday, see if the this "fork" has an associated "join";
// then make a policy on merging this trace at the fork or join.
// For example, other things being equal, it may be better to place this
// trace at the join point if the "src" trace ends in a two-way, but
// the insertion point is one-way.
assert(src_block->num_fall_throughs() == 2, "unexpected diamond");
e->set_state(CFGEdge::connected);
src_trace->insert_after(src_block, targ_trace);
union_traces(src_trace, targ_trace);
} else if (src_at_tail) {
if (src_trace != trace(_cfg._broot)) {
e->set_state(CFGEdge::connected);
targ_trace->insert_before(targ_block, src_trace);
union_traces(targ_trace, src_trace);
}
}
} else if (e->state() == CFGEdge::open) {
// Append traces, even without a fall-thru connection.
// But leave root entry at the beginning of the block list.
if (targ_trace != trace(_cfg._broot)) {
e->set_state(CFGEdge::connected);
src_trace->append(targ_trace);
union_traces(src_trace, targ_trace);
}
}
}
}
//----------------------------reorder_traces-----------------------------------
// Order the sequence of the traces in some desirable way, and fixup the
// jumps at the end of each block.
void PhaseBlockLayout::reorder_traces(int count)
{
ResourceArea *area = Thread::current()->resource_area();
Trace ** new_traces = NEW_ARENA_ARRAY(area, Trace *, count);
Block_List worklist;
int new_count = 0;
// Compact the traces.
for (int i = 0; i < count; i++) {
Trace *tr = traces[i];
if (tr != NULL) {
new_traces[new_count++] = tr;
}
}
// The entry block should be first on the new trace list.
Trace *tr = trace(_cfg._broot);
assert(tr == new_traces[0], "entry trace misplaced");
// Sort the new trace list by frequency
qsort(new_traces + 1, new_count - 1, sizeof(new_traces[0]), trace_frequency_order);
// Patch up the successor blocks
_cfg._blocks.reset();
_cfg._num_blocks = 0;
for (int i = 0; i < new_count; i++) {
Trace *tr = new_traces[i];
if (tr != NULL) {
tr->fixup_blocks(_cfg);
}
}
}
//------------------------------PhaseBlockLayout-------------------------------
// Order basic blocks based on frequency
PhaseBlockLayout::PhaseBlockLayout(PhaseCFG &cfg) :
Phase(BlockLayout),
_cfg(cfg)
{
ResourceMark rm;
ResourceArea *area = Thread::current()->resource_area();
// List of traces
int size = _cfg._num_blocks + 1;
traces = NEW_ARENA_ARRAY(area, Trace *, size);
memset(traces, 0, size*sizeof(Trace*));
next = NEW_ARENA_ARRAY(area, Block *, size);
memset(next, 0, size*sizeof(Block *));
prev = NEW_ARENA_ARRAY(area, Block *, size);
memset(prev , 0, size*sizeof(Block *));
// List of edges
edges = new GrowableArray<CFGEdge*>;
// Mapping block index --> block_trace
uf = new UnionFind(size);
uf->reset(size);
// Find edges and create traces.
find_edges();
// Grow traces at their ends via most frequent edges.
grow_traces();
// Merge one trace into another, but only at fall-through points.
// This may make diamonds and other related shapes in a trace.
merge_traces(true);
// Run merge again, allowing two traces to be catenated, even if
// one does not fall through into the other. This appends loosely
// related traces to be near each other.
merge_traces(false);
// Re-order all the remaining traces by frequency
reorder_traces(size);
assert(_cfg._num_blocks >= (uint) (size - 1), "number of blocks can not shrink");
}
//------------------------------backedge---------------------------------------
// Edge e completes a loop in a trace. If the target block is head of the
// loop, rotate the loop block so that the loop ends in a conditional branch.
bool Trace::backedge(CFGEdge *e) {
bool loop_rotated = false;
Block *src_block = e->from();
Block *targ_block = e->to();
assert(last_block() == src_block, "loop discovery at back branch");
if (first_block() == targ_block) {
if (BlockLayoutRotateLoops && last_block()->num_fall_throughs() < 2) {
// Find the last block in the trace that has a conditional
// branch.
Block *b;
for (b = last_block(); b != NULL; b = prev(b)) {
if (b->num_fall_throughs() == 2) {
break;
}
}
if (b != last_block() && b != NULL) {
loop_rotated = true;
// Rotate the loop by doing two-part linked-list surgery.
append(first_block());
break_loop_after(b);
}
}
// Backbranch to the top of a trace
// Scroll forward through the trace from the targ_block. If we find
// a loop head before another loop top, use the the loop head alignment.
for (Block *b = targ_block; b != NULL; b = next(b)) {
if (b->has_loop_alignment()) {
break;
}
if (b->head()->is_Loop()) {
targ_block = b;
break;
}
}
first_block()->set_loop_alignment(targ_block);
} else {
// Backbranch into the middle of a trace
targ_block->set_loop_alignment(targ_block);
}
return loop_rotated;
}
//------------------------------fixup_blocks-----------------------------------
// push blocks onto the CFG list
// ensure that blocks have the correct two-way branch sense
void Trace::fixup_blocks(PhaseCFG &cfg) {
Block *last = last_block();
for (Block *b = first_block(); b != NULL; b = next(b)) {
cfg._blocks.push(b);
cfg._num_blocks++;
if (!b->is_connector()) {
int nfallthru = b->num_fall_throughs();
if (b != last) {
if (nfallthru == 2) {
// Ensure that the sense of the branch is correct
Block *bnext = next(b);
Block *bs0 = b->non_connector_successor(0);
MachNode *iff = b->_nodes[b->_nodes.size()-3]->as_Mach();
ProjNode *proj0 = b->_nodes[b->_nodes.size()-2]->as_Proj();
ProjNode *proj1 = b->_nodes[b->_nodes.size()-1]->as_Proj();
if (bnext == bs0) {
// Fall-thru case in succs[0], should be in succs[1]
// Flip targets in _succs map
Block *tbs0 = b->_succs[0];
Block *tbs1 = b->_succs[1];
b->_succs.map( 0, tbs1 );
b->_succs.map( 1, tbs0 );
// Flip projections to match targets
b->_nodes.map(b->_nodes.size()-2, proj1);
b->_nodes.map(b->_nodes.size()-1, proj0);
}
}
}
}
}
}