Mercurial > hg > truffle
view src/share/vm/opto/loopUnswitch.cpp @ 452:00b023ae2d78
6722113: CMS: Incorrect overflow handling during precleaning of Reference lists
Summary: When we encounter marking stack overflow during precleaning of Reference lists, we were using the overflow list mechanism, which can cause problems on account of mutating the mark word of the header because of conflicts with mutator accesses and updates of that field. Instead we should use the usual mechanism for overflow handling in concurrent phases, namely dirtying of the card on which the overflowed object lies. Since precleaning effectively does a form of discovered list processing, albeit with discovery enabled, we needed to adjust some code to be correct in the face of interleaved processing and discovery.
Reviewed-by: apetrusenko, jcoomes
author | ysr |
---|---|
date | Thu, 20 Nov 2008 12:27:41 -0800 |
parents | 9c2ecc2ffb12 |
children | 98cb887364d3 |
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/* * Copyright 2006-2008 Sun Microsystems, Inc. All Rights Reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, * CA 95054 USA or visit www.sun.com if you need additional information or * have any questions. * */ #include "incls/_precompiled.incl" #include "incls/_loopUnswitch.cpp.incl" //================= Loop Unswitching ===================== // // orig: transformed: // if (invariant-test) then // loop loop // stmt1 stmt1 // if (invariant-test) then stmt2 // stmt2 stmt4 // else endloop // stmt3 else // endif loop [clone] // stmt4 stmt1 [clone] // endloop 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->unique(); 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"); // 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); assert(proj_true->is_IfTrue() && proj_true->unique_ctrl_out() == head, "by construction"); // 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 appropiate // 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.hash_delete(use); use->set_req(1, nuse); _igvn._worklist.push(use); register_new_node(nuse, invar_proj); // Same for the clone Node* use_clone = old_new[use->_idx]; _igvn.hash_delete(use_clone); use_clone->set_req(1, nuse); _igvn._worklist.push(use_clone); } } // Hardwire the control paths in the loops into if(true) and if(false) _igvn.hash_delete(unswitch_iff); short_circuit_if(unswitch_iff, proj_true); _igvn._worklist.push(unswitch_iff); IfNode* unswitch_iff_clone = old_new[unswitch_iff->_idx]->as_If(); _igvn.hash_delete(unswitch_iff_clone); short_circuit_if(unswitch_iff_clone, proj_false); _igvn._worklist.push(unswitch_iff_clone); // 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(); Node* entry = head->in(LoopNode::EntryControl); _igvn.hash_delete(entry); _igvn._worklist.push(entry); IdealLoopTree* outer_loop = loop->_parent; Node *cont = _igvn.intcon(1); set_ctrl(cont, C->root()); Node* opq = new (C, 2) Opaque1Node(C, cont); register_node(opq, outer_loop, entry, dom_depth(entry)); Node *bol = new (C, 2) Conv2BNode(opq); register_node(bol, outer_loop, entry, dom_depth(entry)); IfNode* iff = new (C, 2) IfNode(entry, bol, PROB_MAX, COUNT_UNKNOWN); register_node(iff, outer_loop, entry, dom_depth(entry)); ProjNode* iffast = new (C, 1) IfTrueNode(iff); register_node(iffast, outer_loop, iff, dom_depth(iff)); ProjNode* ifslow = new (C, 1) 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 2 control users (old & new loops). clone_loop(loop, old_new, dom_depth(head), iff); assert(old_new[head->_idx]->is_Loop(), "" ); // Fast (true) control _igvn.hash_delete(head); head->set_req(LoopNode::EntryControl, iffast); set_idom(head, iffast, dom_depth(head)); _igvn._worklist.push(head); // Slow (false) control LoopNode* slow_head = old_new[head->_idx]->as_Loop(); _igvn.hash_delete(slow_head); slow_head->set_req(LoopNode::EntryControl, ifslow); set_idom(slow_head, ifslow, dom_depth(slow_head)); _igvn._worklist.push(slow_head); recompute_dom_depth(); return iffast; }