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/*
* Copyright (c) 2006, 2012, 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 "memory/allocation.inline.hpp"
#include "opto/connode.hpp"
#include "opto/loopnode.hpp"
#include "opto/rootnode.hpp"
//================= Loop Unswitching =====================
//
// orig: transformed:
// if (invariant-test) then
// predicate predicate
// loop loop
// stmt1 stmt1
// if (invariant-test) then stmt2
// stmt2 stmt4
// else endloop
// stmt3 else
// endif predicate [clone]
// stmt4 loop [clone]
// endloop stmt1 [clone]
// stmt3
// stmt4 [clone]
// endloop
// endif
//
// Note: the "else" clause may be empty
//------------------------------policy_unswitching-----------------------------
// Return TRUE or FALSE if the loop should be unswitched
// (ie. clone loop with an invariant test that does not exit the loop)
bool IdealLoopTree::policy_unswitching( PhaseIdealLoop *phase ) const {
if( !LoopUnswitching ) {
return false;
}
if (!_head->is_Loop()) {
return false;
}
uint nodes_left = MaxNodeLimit - phase->C->live_nodes();
if (2 * _body.size() > nodes_left) {
return false; // Too speculative if running low on nodes.
}
LoopNode* head = _head->as_Loop();
if (head->unswitch_count() + 1 > head->unswitch_max()) {
return false;
}
return phase->find_unswitching_candidate(this) != NULL;
}
//------------------------------find_unswitching_candidate-----------------------------
// Find candidate "if" for unswitching
IfNode* PhaseIdealLoop::find_unswitching_candidate(const IdealLoopTree *loop) const {
// Find first invariant test that doesn't exit the loop
LoopNode *head = loop->_head->as_Loop();
IfNode* unswitch_iff = NULL;
Node* n = head->in(LoopNode::LoopBackControl);
while (n != head) {
Node* n_dom = idom(n);
if (n->is_Region()) {
if (n_dom->is_If()) {
IfNode* iff = n_dom->as_If();
if (iff->in(1)->is_Bool()) {
BoolNode* bol = iff->in(1)->as_Bool();
if (bol->in(1)->is_Cmp()) {
// If condition is invariant and not a loop exit,
// then found reason to unswitch.
if (loop->is_invariant(bol) && !loop->is_loop_exit(iff)) {
unswitch_iff = iff;
}
}
}
}
}
n = n_dom;
}
return unswitch_iff;
}
//------------------------------do_unswitching-----------------------------
// Clone loop with an invariant test (that does not exit) and
// insert a clone of the test that selects which version to
// execute.
void PhaseIdealLoop::do_unswitching (IdealLoopTree *loop, Node_List &old_new) {
// Find first invariant test that doesn't exit the loop
LoopNode *head = loop->_head->as_Loop();
IfNode* unswitch_iff = find_unswitching_candidate((const IdealLoopTree *)loop);
assert(unswitch_iff != NULL, "should be at least one");
#ifndef PRODUCT
if (TraceLoopOpts) {
tty->print("Unswitch %d ", head->unswitch_count()+1);
loop->dump_head();
}
#endif
// Need to revert back to normal loop
if (head->is_CountedLoop() && !head->as_CountedLoop()->is_normal_loop()) {
head->as_CountedLoop()->set_normal_loop();
}
ProjNode* proj_true = create_slow_version_of_loop(loop, old_new);
#ifdef ASSERT
Node* uniqc = proj_true->unique_ctrl_out();
Node* entry = head->in(LoopNode::EntryControl);
Node* predicate = find_predicate(entry);
if (predicate != NULL && LoopLimitCheck && UseLoopPredicate) {
// We may have two predicates, find first.
entry = find_predicate(entry->in(0)->in(0));
if (entry != NULL) predicate = entry;
}
if (predicate != NULL) predicate = predicate->in(0);
assert(proj_true->is_IfTrue() &&
(predicate == NULL && uniqc == head ||
predicate != NULL && uniqc == predicate), "by construction");
#endif
// Increment unswitch count
LoopNode* head_clone = old_new[head->_idx]->as_Loop();
int nct = head->unswitch_count() + 1;
head->set_unswitch_count(nct);
head_clone->set_unswitch_count(nct);
// Add test to new "if" outside of loop
IfNode* invar_iff = proj_true->in(0)->as_If();
Node* invar_iff_c = invar_iff->in(0);
BoolNode* bol = unswitch_iff->in(1)->as_Bool();
invar_iff->set_req(1, bol);
invar_iff->_prob = unswitch_iff->_prob;
ProjNode* proj_false = invar_iff->proj_out(0)->as_Proj();
// Hoist invariant casts out of each loop to the appropriate
// control projection.
Node_List worklist;
for (DUIterator_Fast imax, i = unswitch_iff->fast_outs(imax); i < imax; i++) {
ProjNode* proj= unswitch_iff->fast_out(i)->as_Proj();
// Copy to a worklist for easier manipulation
for (DUIterator_Fast jmax, j = proj->fast_outs(jmax); j < jmax; j++) {
Node* use = proj->fast_out(j);
if (use->Opcode() == Op_CheckCastPP && loop->is_invariant(use->in(1))) {
worklist.push(use);
}
}
ProjNode* invar_proj = invar_iff->proj_out(proj->_con)->as_Proj();
while (worklist.size() > 0) {
Node* use = worklist.pop();
Node* nuse = use->clone();
nuse->set_req(0, invar_proj);
_igvn.replace_input_of(use, 1, nuse);
register_new_node(nuse, invar_proj);
// Same for the clone
Node* use_clone = old_new[use->_idx];
_igvn.replace_input_of(use_clone, 1, nuse);
}
}
// Hardwire the control paths in the loops into if(true) and if(false)
_igvn.rehash_node_delayed(unswitch_iff);
short_circuit_if(unswitch_iff, proj_true);
IfNode* unswitch_iff_clone = old_new[unswitch_iff->_idx]->as_If();
_igvn.rehash_node_delayed(unswitch_iff_clone);
short_circuit_if(unswitch_iff_clone, proj_false);
// Reoptimize loops
loop->record_for_igvn();
for(int i = loop->_body.size() - 1; i >= 0 ; i--) {
Node *n = loop->_body[i];
Node *n_clone = old_new[n->_idx];
_igvn._worklist.push(n_clone);
}
#ifndef PRODUCT
if (TraceLoopUnswitching) {
tty->print_cr("Loop unswitching orig: %d @ %d new: %d @ %d",
head->_idx, unswitch_iff->_idx,
old_new[head->_idx]->_idx, unswitch_iff_clone->_idx);
}
#endif
C->set_major_progress();
}
//-------------------------create_slow_version_of_loop------------------------
// Create a slow version of the loop by cloning the loop
// and inserting an if to select fast-slow versions.
// Return control projection of the entry to the fast version.
ProjNode* PhaseIdealLoop::create_slow_version_of_loop(IdealLoopTree *loop,
Node_List &old_new) {
LoopNode* head = loop->_head->as_Loop();
bool counted_loop = head->is_CountedLoop();
Node* entry = head->in(LoopNode::EntryControl);
_igvn.rehash_node_delayed(entry);
IdealLoopTree* outer_loop = loop->_parent;
Node *cont = _igvn.intcon(1);
set_ctrl(cont, C->root());
Node* opq = new (C) Opaque1Node(C, cont);
register_node(opq, outer_loop, entry, dom_depth(entry));
Node *bol = new (C) Conv2BNode(opq);
register_node(bol, outer_loop, entry, dom_depth(entry));
IfNode* iff = new (C) IfNode(entry, bol, PROB_MAX, COUNT_UNKNOWN);
register_node(iff, outer_loop, entry, dom_depth(entry));
ProjNode* iffast = new (C) IfTrueNode(iff);
register_node(iffast, outer_loop, iff, dom_depth(iff));
ProjNode* ifslow = new (C) IfFalseNode(iff);
register_node(ifslow, outer_loop, iff, dom_depth(iff));
// Clone the loop body. The clone becomes the fast loop. The
// original pre-header will (illegally) have 3 control users
// (old & new loops & new if).
clone_loop(loop, old_new, dom_depth(head), iff);
assert(old_new[head->_idx]->is_Loop(), "" );
// Fast (true) control
Node* iffast_pred = clone_loop_predicates(entry, iffast, !counted_loop);
_igvn.replace_input_of(head, LoopNode::EntryControl, iffast_pred);
set_idom(head, iffast_pred, dom_depth(head));
// Slow (false) control
Node* ifslow_pred = clone_loop_predicates(entry, ifslow, !counted_loop);
LoopNode* slow_head = old_new[head->_idx]->as_Loop();
_igvn.replace_input_of(slow_head, LoopNode::EntryControl, ifslow_pred);
set_idom(slow_head, ifslow_pred, dom_depth(slow_head));
recompute_dom_depth();
return iffast;
}
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