1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/src/share/vm/opto/split_if.cpp Wed Apr 27 01:25:04 2016 +0800
1.3 @@ -0,0 +1,542 @@
1.4 +/*
1.5 + * Copyright (c) 1999, 2012, Oracle and/or its affiliates. All rights reserved.
1.6 + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
1.7 + *
1.8 + * This code is free software; you can redistribute it and/or modify it
1.9 + * under the terms of the GNU General Public License version 2 only, as
1.10 + * published by the Free Software Foundation.
1.11 + *
1.12 + * This code is distributed in the hope that it will be useful, but WITHOUT
1.13 + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
1.14 + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
1.15 + * version 2 for more details (a copy is included in the LICENSE file that
1.16 + * accompanied this code).
1.17 + *
1.18 + * You should have received a copy of the GNU General Public License version
1.19 + * 2 along with this work; if not, write to the Free Software Foundation,
1.20 + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
1.21 + *
1.22 + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
1.23 + * or visit www.oracle.com if you need additional information or have any
1.24 + * questions.
1.25 + *
1.26 + */
1.27 +
1.28 +#include "precompiled.hpp"
1.29 +#include "memory/allocation.inline.hpp"
1.30 +#include "opto/callnode.hpp"
1.31 +#include "opto/connode.hpp"
1.32 +#include "opto/loopnode.hpp"
1.33 +
1.34 +
1.35 +//------------------------------split_thru_region------------------------------
1.36 +// Split Node 'n' through merge point.
1.37 +Node *PhaseIdealLoop::split_thru_region( Node *n, Node *region ) {
1.38 + uint wins = 0;
1.39 + assert( n->is_CFG(), "" );
1.40 + assert( region->is_Region(), "" );
1.41 + Node *r = new (C) RegionNode( region->req() );
1.42 + IdealLoopTree *loop = get_loop( n );
1.43 + for( uint i = 1; i < region->req(); i++ ) {
1.44 + Node *x = n->clone();
1.45 + Node *in0 = n->in(0);
1.46 + if( in0->in(0) == region ) x->set_req( 0, in0->in(i) );
1.47 + for( uint j = 1; j < n->req(); j++ ) {
1.48 + Node *in = n->in(j);
1.49 + if( get_ctrl(in) == region )
1.50 + x->set_req( j, in->in(i) );
1.51 + }
1.52 + _igvn.register_new_node_with_optimizer(x);
1.53 + set_loop(x, loop);
1.54 + set_idom(x, x->in(0), dom_depth(x->in(0))+1);
1.55 + r->init_req(i, x);
1.56 + }
1.57 +
1.58 + // Record region
1.59 + r->set_req(0,region); // Not a TRUE RegionNode
1.60 + _igvn.register_new_node_with_optimizer(r);
1.61 + set_loop(r, loop);
1.62 + if( !loop->_child )
1.63 + loop->_body.push(r);
1.64 + return r;
1.65 +}
1.66 +
1.67 +//------------------------------split_up---------------------------------------
1.68 +// Split block-local op up through the phis to empty the current block
1.69 +bool PhaseIdealLoop::split_up( Node *n, Node *blk1, Node *blk2 ) {
1.70 + if( n->is_CFG() ) {
1.71 + assert( n->in(0) != blk1, "Lousy candidate for split-if" );
1.72 + return false;
1.73 + }
1.74 + if( get_ctrl(n) != blk1 && get_ctrl(n) != blk2 )
1.75 + return false; // Not block local
1.76 + if( n->is_Phi() ) return false; // Local PHIs are expected
1.77 +
1.78 + // Recursively split-up inputs
1.79 + for (uint i = 1; i < n->req(); i++) {
1.80 + if( split_up( n->in(i), blk1, blk2 ) ) {
1.81 + // Got split recursively and self went dead?
1.82 + if (n->outcnt() == 0)
1.83 + _igvn.remove_dead_node(n);
1.84 + return true;
1.85 + }
1.86 + }
1.87 +
1.88 + // Check for needing to clone-up a compare. Can't do that, it forces
1.89 + // another (nested) split-if transform. Instead, clone it "down".
1.90 + if( n->is_Cmp() ) {
1.91 + assert(get_ctrl(n) == blk2 || get_ctrl(n) == blk1, "must be in block with IF");
1.92 + // Check for simple Cmp/Bool/CMove which we can clone-up. Cmp/Bool/CMove
1.93 + // sequence can have no other users and it must all reside in the split-if
1.94 + // block. Non-simple Cmp/Bool/CMove sequences are 'cloned-down' below -
1.95 + // private, per-use versions of the Cmp and Bool are made. These sink to
1.96 + // the CMove block. If the CMove is in the split-if block, then in the
1.97 + // next iteration this will become a simple Cmp/Bool/CMove set to clone-up.
1.98 + Node *bol, *cmov;
1.99 + if( !(n->outcnt() == 1 && n->unique_out()->is_Bool() &&
1.100 + (bol = n->unique_out()->as_Bool()) &&
1.101 + (get_ctrl(bol) == blk1 ||
1.102 + get_ctrl(bol) == blk2) &&
1.103 + bol->outcnt() == 1 &&
1.104 + bol->unique_out()->is_CMove() &&
1.105 + (cmov = bol->unique_out()->as_CMove()) &&
1.106 + (get_ctrl(cmov) == blk1 ||
1.107 + get_ctrl(cmov) == blk2) ) ) {
1.108 +
1.109 + // Must clone down
1.110 +#ifndef PRODUCT
1.111 + if( PrintOpto && VerifyLoopOptimizations ) {
1.112 + tty->print("Cloning down: ");
1.113 + n->dump();
1.114 + }
1.115 +#endif
1.116 + // Clone down any block-local BoolNode uses of this CmpNode
1.117 + for (DUIterator i = n->outs(); n->has_out(i); i++) {
1.118 + Node* bol = n->out(i);
1.119 + assert( bol->is_Bool(), "" );
1.120 + if (bol->outcnt() == 1) {
1.121 + Node* use = bol->unique_out();
1.122 + Node *use_c = use->is_If() ? use->in(0) : get_ctrl(use);
1.123 + if (use_c == blk1 || use_c == blk2) {
1.124 + continue;
1.125 + }
1.126 + }
1.127 + if (get_ctrl(bol) == blk1 || get_ctrl(bol) == blk2) {
1.128 + // Recursively sink any BoolNode
1.129 +#ifndef PRODUCT
1.130 + if( PrintOpto && VerifyLoopOptimizations ) {
1.131 + tty->print("Cloning down: ");
1.132 + bol->dump();
1.133 + }
1.134 +#endif
1.135 + for (DUIterator_Last jmin, j = bol->last_outs(jmin); j >= jmin; --j) {
1.136 + // Uses are either IfNodes or CMoves
1.137 + Node* iff = bol->last_out(j);
1.138 + assert( iff->in(1) == bol, "" );
1.139 + // Get control block of either the CMove or the If input
1.140 + Node *iff_ctrl = iff->is_If() ? iff->in(0) : get_ctrl(iff);
1.141 + Node *x = bol->clone();
1.142 + register_new_node(x, iff_ctrl);
1.143 + _igvn.replace_input_of(iff, 1, x);
1.144 + }
1.145 + _igvn.remove_dead_node( bol );
1.146 + --i;
1.147 + }
1.148 + }
1.149 + // Clone down this CmpNode
1.150 + for (DUIterator_Last jmin, j = n->last_outs(jmin); j >= jmin; --j) {
1.151 + Node* bol = n->last_out(j);
1.152 + assert( bol->in(1) == n, "" );
1.153 + Node *x = n->clone();
1.154 + register_new_node(x, get_ctrl(bol));
1.155 + _igvn.replace_input_of(bol, 1, x);
1.156 + }
1.157 + _igvn.remove_dead_node( n );
1.158 +
1.159 + return true;
1.160 + }
1.161 + }
1.162 +
1.163 + // See if splitting-up a Store. Any anti-dep loads must go up as
1.164 + // well. An anti-dep load might be in the wrong block, because in
1.165 + // this particular layout/schedule we ignored anti-deps and allow
1.166 + // memory to be alive twice. This only works if we do the same
1.167 + // operations on anti-dep loads as we do their killing stores.
1.168 + if( n->is_Store() && n->in(MemNode::Memory)->in(0) == n->in(0) ) {
1.169 + // Get store's memory slice
1.170 + int alias_idx = C->get_alias_index(_igvn.type(n->in(MemNode::Address))->is_ptr());
1.171 +
1.172 + // Get memory-phi anti-dep loads will be using
1.173 + Node *memphi = n->in(MemNode::Memory);
1.174 + assert( memphi->is_Phi(), "" );
1.175 + // Hoist any anti-dep load to the splitting block;
1.176 + // it will then "split-up".
1.177 + for (DUIterator_Fast imax,i = memphi->fast_outs(imax); i < imax; i++) {
1.178 + Node *load = memphi->fast_out(i);
1.179 + if( load->is_Load() && alias_idx == C->get_alias_index(_igvn.type(load->in(MemNode::Address))->is_ptr()) )
1.180 + set_ctrl(load,blk1);
1.181 + }
1.182 + }
1.183 +
1.184 + // Found some other Node; must clone it up
1.185 +#ifndef PRODUCT
1.186 + if( PrintOpto && VerifyLoopOptimizations ) {
1.187 + tty->print("Cloning up: ");
1.188 + n->dump();
1.189 + }
1.190 +#endif
1.191 +
1.192 + // ConvI2L may have type information on it which becomes invalid if
1.193 + // it moves up in the graph so change any clones so widen the type
1.194 + // to TypeLong::INT when pushing it up.
1.195 + const Type* rtype = NULL;
1.196 + if (n->Opcode() == Op_ConvI2L && n->bottom_type() != TypeLong::INT) {
1.197 + rtype = TypeLong::INT;
1.198 + }
1.199 +
1.200 + // Now actually split-up this guy. One copy per control path merging.
1.201 + Node *phi = PhiNode::make_blank(blk1, n);
1.202 + for( uint j = 1; j < blk1->req(); j++ ) {
1.203 + Node *x = n->clone();
1.204 + // Widen the type of the ConvI2L when pushing up.
1.205 + if (rtype != NULL) x->as_Type()->set_type(rtype);
1.206 + if( n->in(0) && n->in(0) == blk1 )
1.207 + x->set_req( 0, blk1->in(j) );
1.208 + for( uint i = 1; i < n->req(); i++ ) {
1.209 + Node *m = n->in(i);
1.210 + if( get_ctrl(m) == blk1 ) {
1.211 + assert( m->in(0) == blk1, "" );
1.212 + x->set_req( i, m->in(j) );
1.213 + }
1.214 + }
1.215 + register_new_node( x, blk1->in(j) );
1.216 + phi->init_req( j, x );
1.217 + }
1.218 + // Announce phi to optimizer
1.219 + register_new_node(phi, blk1);
1.220 +
1.221 + // Remove cloned-up value from optimizer; use phi instead
1.222 + _igvn.replace_node( n, phi );
1.223 +
1.224 + // (There used to be a self-recursive call to split_up() here,
1.225 + // but it is not needed. All necessary forward walking is done
1.226 + // by do_split_if() below.)
1.227 +
1.228 + return true;
1.229 +}
1.230 +
1.231 +//------------------------------register_new_node------------------------------
1.232 +void PhaseIdealLoop::register_new_node( Node *n, Node *blk ) {
1.233 + assert(!n->is_CFG(), "must be data node");
1.234 + _igvn.register_new_node_with_optimizer(n);
1.235 + set_ctrl(n, blk);
1.236 + IdealLoopTree *loop = get_loop(blk);
1.237 + if( !loop->_child )
1.238 + loop->_body.push(n);
1.239 +}
1.240 +
1.241 +//------------------------------small_cache------------------------------------
1.242 +struct small_cache : public Dict {
1.243 +
1.244 + small_cache() : Dict( cmpkey, hashptr ) {}
1.245 + Node *probe( Node *use_blk ) { return (Node*)((*this)[use_blk]); }
1.246 + void lru_insert( Node *use_blk, Node *new_def ) { Insert(use_blk,new_def); }
1.247 +};
1.248 +
1.249 +//------------------------------spinup-----------------------------------------
1.250 +// "Spin up" the dominator tree, starting at the use site and stopping when we
1.251 +// find the post-dominating point.
1.252 +
1.253 +// We must be at the merge point which post-dominates 'new_false' and
1.254 +// 'new_true'. Figure out which edges into the RegionNode eventually lead up
1.255 +// to false and which to true. Put in a PhiNode to merge values; plug in
1.256 +// the appropriate false-arm or true-arm values. If some path leads to the
1.257 +// original IF, then insert a Phi recursively.
1.258 +Node *PhaseIdealLoop::spinup( Node *iff_dom, Node *new_false, Node *new_true, Node *use_blk, Node *def, small_cache *cache ) {
1.259 + if (use_blk->is_top()) // Handle dead uses
1.260 + return use_blk;
1.261 + Node *prior_n = (Node*)0xdeadbeef;
1.262 + Node *n = use_blk; // Get path input
1.263 + assert( use_blk != iff_dom, "" );
1.264 + // Here's the "spinup" the dominator tree loop. Do a cache-check
1.265 + // along the way, in case we've come this way before.
1.266 + while( n != iff_dom ) { // Found post-dominating point?
1.267 + prior_n = n;
1.268 + n = idom(n); // Search higher
1.269 + Node *s = cache->probe( prior_n ); // Check cache
1.270 + if( s ) return s; // Cache hit!
1.271 + }
1.272 +
1.273 + Node *phi_post;
1.274 + if( prior_n == new_false || prior_n == new_true ) {
1.275 + phi_post = def->clone();
1.276 + phi_post->set_req(0, prior_n );
1.277 + register_new_node(phi_post, prior_n);
1.278 + } else {
1.279 + // This method handles both control uses (looking for Regions) or data
1.280 + // uses (looking for Phis). If looking for a control use, then we need
1.281 + // to insert a Region instead of a Phi; however Regions always exist
1.282 + // previously (the hash_find_insert below would always hit) so we can
1.283 + // return the existing Region.
1.284 + if( def->is_CFG() ) {
1.285 + phi_post = prior_n; // If looking for CFG, return prior
1.286 + } else {
1.287 + assert( def->is_Phi(), "" );
1.288 + assert( prior_n->is_Region(), "must be a post-dominating merge point" );
1.289 +
1.290 + // Need a Phi here
1.291 + phi_post = PhiNode::make_blank(prior_n, def);
1.292 + // Search for both true and false on all paths till find one.
1.293 + for( uint i = 1; i < phi_post->req(); i++ ) // For all paths
1.294 + phi_post->init_req( i, spinup( iff_dom, new_false, new_true, prior_n->in(i), def, cache ) );
1.295 + Node *t = _igvn.hash_find_insert(phi_post);
1.296 + if( t ) { // See if we already have this one
1.297 + // phi_post will not be used, so kill it
1.298 + _igvn.remove_dead_node(phi_post);
1.299 + phi_post->destruct();
1.300 + phi_post = t;
1.301 + } else {
1.302 + register_new_node( phi_post, prior_n );
1.303 + }
1.304 + }
1.305 + }
1.306 +
1.307 + // Update cache everywhere
1.308 + prior_n = (Node*)0xdeadbeef; // Reset IDOM walk
1.309 + n = use_blk; // Get path input
1.310 + // Spin-up the idom tree again, basically doing path-compression.
1.311 + // Insert cache entries along the way, so that if we ever hit this
1.312 + // point in the IDOM tree again we'll stop immediately on a cache hit.
1.313 + while( n != iff_dom ) { // Found post-dominating point?
1.314 + prior_n = n;
1.315 + n = idom(n); // Search higher
1.316 + cache->lru_insert( prior_n, phi_post ); // Fill cache
1.317 + } // End of while not gone high enough
1.318 +
1.319 + return phi_post;
1.320 +}
1.321 +
1.322 +//------------------------------find_use_block---------------------------------
1.323 +// Find the block a USE is in. Normally USE's are in the same block as the
1.324 +// using instruction. For Phi-USE's, the USE is in the predecessor block
1.325 +// along the corresponding path.
1.326 +Node *PhaseIdealLoop::find_use_block( Node *use, Node *def, Node *old_false, Node *new_false, Node *old_true, Node *new_true ) {
1.327 + // CFG uses are their own block
1.328 + if( use->is_CFG() )
1.329 + return use;
1.330 +
1.331 + if( use->is_Phi() ) { // Phi uses in prior block
1.332 + // Grab the first Phi use; there may be many.
1.333 + // Each will be handled as a separate iteration of
1.334 + // the "while( phi->outcnt() )" loop.
1.335 + uint j;
1.336 + for( j = 1; j < use->req(); j++ )
1.337 + if( use->in(j) == def )
1.338 + break;
1.339 + assert( j < use->req(), "def should be among use's inputs" );
1.340 + return use->in(0)->in(j);
1.341 + }
1.342 + // Normal (non-phi) use
1.343 + Node *use_blk = get_ctrl(use);
1.344 + // Some uses are directly attached to the old (and going away)
1.345 + // false and true branches.
1.346 + if( use_blk == old_false ) {
1.347 + use_blk = new_false;
1.348 + set_ctrl(use, new_false);
1.349 + }
1.350 + if( use_blk == old_true ) {
1.351 + use_blk = new_true;
1.352 + set_ctrl(use, new_true);
1.353 + }
1.354 +
1.355 + if (use_blk == NULL) { // He's dead, Jim
1.356 + _igvn.replace_node(use, C->top());
1.357 + }
1.358 +
1.359 + return use_blk;
1.360 +}
1.361 +
1.362 +//------------------------------handle_use-------------------------------------
1.363 +// Handle uses of the merge point. Basically, split-if makes the merge point
1.364 +// go away so all uses of the merge point must go away as well. Most block
1.365 +// local uses have already been split-up, through the merge point. Uses from
1.366 +// far below the merge point can't always be split up (e.g., phi-uses are
1.367 +// pinned) and it makes too much stuff live. Instead we use a path-based
1.368 +// solution to move uses down.
1.369 +//
1.370 +// If the use is along the pre-split-CFG true branch, then the new use will
1.371 +// be from the post-split-CFG true merge point. Vice-versa for the false
1.372 +// path. Some uses will be along both paths; then we sink the use to the
1.373 +// post-dominating location; we may need to insert a Phi there.
1.374 +void PhaseIdealLoop::handle_use( Node *use, Node *def, small_cache *cache, Node *region_dom, Node *new_false, Node *new_true, Node *old_false, Node *old_true ) {
1.375 +
1.376 + Node *use_blk = find_use_block(use,def,old_false,new_false,old_true,new_true);
1.377 + if( !use_blk ) return; // He's dead, Jim
1.378 +
1.379 + // Walk up the dominator tree until I hit either the old IfFalse, the old
1.380 + // IfTrue or the old If. Insert Phis where needed.
1.381 + Node *new_def = spinup( region_dom, new_false, new_true, use_blk, def, cache );
1.382 +
1.383 + // Found where this USE goes. Re-point him.
1.384 + uint i;
1.385 + for( i = 0; i < use->req(); i++ )
1.386 + if( use->in(i) == def )
1.387 + break;
1.388 + assert( i < use->req(), "def should be among use's inputs" );
1.389 + _igvn.replace_input_of(use, i, new_def);
1.390 +}
1.391 +
1.392 +//------------------------------do_split_if------------------------------------
1.393 +// Found an If getting its condition-code input from a Phi in the same block.
1.394 +// Split thru the Region.
1.395 +void PhaseIdealLoop::do_split_if( Node *iff ) {
1.396 +#ifndef PRODUCT
1.397 + if( PrintOpto && VerifyLoopOptimizations )
1.398 + tty->print_cr("Split-if");
1.399 + if (TraceLoopOpts) {
1.400 + tty->print_cr("SplitIf");
1.401 + }
1.402 +#endif
1.403 + C->set_major_progress();
1.404 + Node *region = iff->in(0);
1.405 + Node *region_dom = idom(region);
1.406 +
1.407 + // We are going to clone this test (and the control flow with it) up through
1.408 + // the incoming merge point. We need to empty the current basic block.
1.409 + // Clone any instructions which must be in this block up through the merge
1.410 + // point.
1.411 + DUIterator i, j;
1.412 + bool progress = true;
1.413 + while (progress) {
1.414 + progress = false;
1.415 + for (i = region->outs(); region->has_out(i); i++) {
1.416 + Node* n = region->out(i);
1.417 + if( n == region ) continue;
1.418 + // The IF to be split is OK.
1.419 + if( n == iff ) continue;
1.420 + if( !n->is_Phi() ) { // Found pinned memory op or such
1.421 + if (split_up(n, region, iff)) {
1.422 + i = region->refresh_out_pos(i);
1.423 + progress = true;
1.424 + }
1.425 + continue;
1.426 + }
1.427 + assert( n->in(0) == region, "" );
1.428 +
1.429 + // Recursively split up all users of a Phi
1.430 + for (j = n->outs(); n->has_out(j); j++) {
1.431 + Node* m = n->out(j);
1.432 + // If m is dead, throw it away, and declare progress
1.433 + if (_nodes[m->_idx] == NULL) {
1.434 + _igvn.remove_dead_node(m);
1.435 + // fall through
1.436 + }
1.437 + else if (m != iff && split_up(m, region, iff)) {
1.438 + // fall through
1.439 + } else {
1.440 + continue;
1.441 + }
1.442 + // Something unpredictable changed.
1.443 + // Tell the iterators to refresh themselves, and rerun the loop.
1.444 + i = region->refresh_out_pos(i);
1.445 + j = region->refresh_out_pos(j);
1.446 + progress = true;
1.447 + }
1.448 + }
1.449 + }
1.450 +
1.451 + // Now we have no instructions in the block containing the IF.
1.452 + // Split the IF.
1.453 + Node *new_iff = split_thru_region( iff, region );
1.454 +
1.455 + // Replace both uses of 'new_iff' with Regions merging True/False
1.456 + // paths. This makes 'new_iff' go dead.
1.457 + Node *old_false, *old_true;
1.458 + Node *new_false, *new_true;
1.459 + for (DUIterator_Last j2min, j2 = iff->last_outs(j2min); j2 >= j2min; --j2) {
1.460 + Node *ifp = iff->last_out(j2);
1.461 + assert( ifp->Opcode() == Op_IfFalse || ifp->Opcode() == Op_IfTrue, "" );
1.462 + ifp->set_req(0, new_iff);
1.463 + Node *ifpx = split_thru_region( ifp, region );
1.464 +
1.465 + // Replace 'If' projection of a Region with a Region of
1.466 + // 'If' projections.
1.467 + ifpx->set_req(0, ifpx); // A TRUE RegionNode
1.468 +
1.469 + // Setup dominator info
1.470 + set_idom(ifpx, region_dom, dom_depth(region_dom) + 1);
1.471 +
1.472 + // Check for splitting loop tails
1.473 + if( get_loop(iff)->tail() == ifp )
1.474 + get_loop(iff)->_tail = ifpx;
1.475 +
1.476 + // Replace in the graph with lazy-update mechanism
1.477 + new_iff->set_req(0, new_iff); // hook self so it does not go dead
1.478 + lazy_replace_proj( ifp, ifpx );
1.479 + new_iff->set_req(0, region);
1.480 +
1.481 + // Record bits for later xforms
1.482 + if( ifp->Opcode() == Op_IfFalse ) {
1.483 + old_false = ifp;
1.484 + new_false = ifpx;
1.485 + } else {
1.486 + old_true = ifp;
1.487 + new_true = ifpx;
1.488 + }
1.489 + }
1.490 + _igvn.remove_dead_node(new_iff);
1.491 + // Lazy replace IDOM info with the region's dominator
1.492 + lazy_replace( iff, region_dom );
1.493 +
1.494 + // Now make the original merge point go dead, by handling all its uses.
1.495 + small_cache region_cache;
1.496 + // Preload some control flow in region-cache
1.497 + region_cache.lru_insert( new_false, new_false );
1.498 + region_cache.lru_insert( new_true , new_true );
1.499 + // Now handle all uses of the splitting block
1.500 + for (DUIterator k = region->outs(); region->has_out(k); k++) {
1.501 + Node* phi = region->out(k);
1.502 + if (!phi->in(0)) { // Dead phi? Remove it
1.503 + _igvn.remove_dead_node(phi);
1.504 + } else if (phi == region) { // Found the self-reference
1.505 + continue; // No roll-back of DUIterator
1.506 + } else if (phi->is_Phi()) { // Expected common case: Phi hanging off of Region
1.507 + assert(phi->in(0) == region, "Inconsistent graph");
1.508 + // Need a per-def cache. Phi represents a def, so make a cache
1.509 + small_cache phi_cache;
1.510 +
1.511 + // Inspect all Phi uses to make the Phi go dead
1.512 + for (DUIterator_Last lmin, l = phi->last_outs(lmin); l >= lmin; --l) {
1.513 + Node* use = phi->last_out(l);
1.514 + // Compute the new DEF for this USE. New DEF depends on the path
1.515 + // taken from the original DEF to the USE. The new DEF may be some
1.516 + // collection of PHI's merging values from different paths. The Phis
1.517 + // inserted depend only on the location of the USE. We use a
1.518 + // 2-element cache to handle multiple uses from the same block.
1.519 + handle_use(use, phi, &phi_cache, region_dom, new_false, new_true, old_false, old_true);
1.520 + } // End of while phi has uses
1.521 + // Remove the dead Phi
1.522 + _igvn.remove_dead_node( phi );
1.523 + } else {
1.524 + assert(phi->in(0) == region, "Inconsistent graph");
1.525 + // Random memory op guarded by Region. Compute new DEF for USE.
1.526 + handle_use(phi, region, ®ion_cache, region_dom, new_false, new_true, old_false, old_true);
1.527 + }
1.528 + // Every path above deletes a use of the region, except for the region
1.529 + // self-cycle (which is needed by handle_use calling find_use_block
1.530 + // calling get_ctrl calling get_ctrl_no_update looking for dead
1.531 + // regions). So roll back the DUIterator innards.
1.532 + --k;
1.533 + } // End of while merge point has phis
1.534 +
1.535 + assert(region->outcnt() == 1, "Only self reference should remain"); // Just Self on the Region
1.536 + region->set_req(0, NULL); // Break the self-cycle
1.537 +
1.538 + // Any leftover bits in the splitting block must not have depended on local
1.539 + // Phi inputs (these have already been split-up). Hence it's safe to hoist
1.540 + // these guys to the dominating point.
1.541 + lazy_replace( region, region_dom );
1.542 +#ifndef PRODUCT
1.543 + if( VerifyLoopOptimizations ) verify();
1.544 +#endif
1.545 +}
