# HG changeset patch # User aeriksso # Date 1449234398 -3600 # Node ID 5b34a4ae0f58ddd3099a14629c88190a58047c6b # Parent 1fcd0a08036bee2751dfdfddfeaff3de583132f3 6869327: Add new C2 flag to keep safepoints in counted loops. Reviewed-by: kvn, shade diff -r 1fcd0a08036b -r 5b34a4ae0f58 hotspot/src/share/vm/opto/c2_globals.hpp --- a/hotspot/src/share/vm/opto/c2_globals.hpp Thu Dec 03 22:30:17 2015 -0800 +++ b/hotspot/src/share/vm/opto/c2_globals.hpp Fri Dec 04 14:06:38 2015 +0100 @@ -213,6 +213,9 @@ notproduct(bool, TraceProfileTripCount, false, \ "Trace profile loop trip count information") \ \ + product(bool, UseCountedLoopSafepoints, false, \ + "Force counted loops to keep a safepoint") \ + \ product(bool, UseLoopPredicate, true, \ "Generate a predicate to select fast/slow loop versions") \ \ diff -r 1fcd0a08036b -r 5b34a4ae0f58 hotspot/src/share/vm/opto/loopnode.cpp --- a/hotspot/src/share/vm/opto/loopnode.cpp Thu Dec 03 22:30:17 2015 -0800 +++ b/hotspot/src/share/vm/opto/loopnode.cpp Fri Dec 04 14:06:38 2015 +0100 @@ -690,14 +690,16 @@ } // LoopLimitCheck - // Check for SafePoint on backedge and remove - Node *sfpt = x->in(LoopNode::LoopBackControl); - if (sfpt->Opcode() == Op_SafePoint && is_deleteable_safept(sfpt)) { - lazy_replace( sfpt, iftrue ); - if (loop->_safepts != NULL) { - loop->_safepts->yank(sfpt); + if (!UseCountedLoopSafepoints) { + // Check for SafePoint on backedge and remove + Node *sfpt = x->in(LoopNode::LoopBackControl); + if (sfpt->Opcode() == Op_SafePoint && is_deleteable_safept(sfpt)) { + lazy_replace( sfpt, iftrue ); + if (loop->_safepts != NULL) { + loop->_safepts->yank(sfpt); + } + loop->_tail = iftrue; } - loop->_tail = iftrue; } // Build a canonical trip test. @@ -786,12 +788,14 @@ lazy_replace( x, l ); set_idom(l, init_control, dom_depth(x)); - // Check for immediately preceding SafePoint and remove - Node *sfpt2 = le->in(0); - if (sfpt2->Opcode() == Op_SafePoint && is_deleteable_safept(sfpt2)) { - lazy_replace( sfpt2, sfpt2->in(TypeFunc::Control)); - if (loop->_safepts != NULL) { - loop->_safepts->yank(sfpt2); + if (!UseCountedLoopSafepoints) { + // Check for immediately preceding SafePoint and remove + Node *sfpt2 = le->in(0); + if (sfpt2->Opcode() == Op_SafePoint && is_deleteable_safept(sfpt2)) { + lazy_replace( sfpt2, sfpt2->in(TypeFunc::Control)); + if (loop->_safepts != NULL) { + loop->_safepts->yank(sfpt2); + } } } @@ -1813,6 +1817,33 @@ } } +void IdealLoopTree::remove_safepoints(PhaseIdealLoop* phase, bool keep_one) { + // Look for a safepoint on the idom-path. + Node* keep = NULL; + if (keep_one) { + // Keep one if possible + for (Node* i = tail(); i != _head; i = phase->idom(i)) { + if (i->Opcode() == Op_SafePoint && phase->get_loop(i) == this) { + keep = i; + break; // Found one + } + } + } + + // Delete other safepoints in this loop. + Node_List* sfpts = _safepts; + if (sfpts != NULL) { + assert(keep == NULL || keep->Opcode() == Op_SafePoint, "not safepoint"); + for (uint i = 0; i < sfpts->size(); i++) { + Node* n = sfpts->at(i); + assert(phase->get_loop(n) == this, ""); + if (n != keep && phase->is_deleteable_safept(n)) { + phase->lazy_replace(n, n->in(TypeFunc::Control)); + } + } + } +} + //------------------------------counted_loop----------------------------------- // Convert to counted loops where possible void IdealLoopTree::counted_loop( PhaseIdealLoop *phase ) { @@ -1824,42 +1855,23 @@ if (_head->is_CountedLoop() || phase->is_counted_loop(_head, this)) { - _has_sfpt = 1; // Indicate we do not need a safepoint here - - // Look for safepoints to remove. - Node_List* sfpts = _safepts; - if (sfpts != NULL) { - for (uint i = 0; i < sfpts->size(); i++) { - Node* n = sfpts->at(i); - assert(phase->get_loop(n) == this, ""); - if (phase->is_deleteable_safept(n)) { - phase->lazy_replace(n, n->in(TypeFunc::Control)); - } - } + + if (!UseCountedLoopSafepoints) { + // Indicate we do not need a safepoint here + _has_sfpt = 1; } + // Remove safepoints + bool keep_one_sfpt = !(_has_call || _has_sfpt); + remove_safepoints(phase, keep_one_sfpt); + // Look for induction variables phase->replace_parallel_iv(this); } else if (_parent != NULL && !_irreducible) { - // Not a counted loop. - // Look for a safepoint on the idom-path. - Node* sfpt = tail(); - for (; sfpt != _head; sfpt = phase->idom(sfpt)) { - if (sfpt->Opcode() == Op_SafePoint && phase->get_loop(sfpt) == this) - break; // Found one - } - // Delete other safepoints in this loop. - Node_List* sfpts = _safepts; - if (sfpts != NULL && sfpt != _head && sfpt->Opcode() == Op_SafePoint) { - for (uint i = 0; i < sfpts->size(); i++) { - Node* n = sfpts->at(i); - assert(phase->get_loop(n) == this, ""); - if (n != sfpt && phase->is_deleteable_safept(n)) { - phase->lazy_replace(n, n->in(TypeFunc::Control)); - } - } - } + // Not a counted loop. Keep one safepoint. + bool keep_one_sfpt = true; + remove_safepoints(phase, keep_one_sfpt); } // Recursively diff -r 1fcd0a08036b -r 5b34a4ae0f58 hotspot/src/share/vm/opto/loopnode.hpp --- a/hotspot/src/share/vm/opto/loopnode.hpp Thu Dec 03 22:30:17 2015 -0800 +++ b/hotspot/src/share/vm/opto/loopnode.hpp Fri Dec 04 14:06:38 2015 +0100 @@ -1,5 +1,5 @@ /* - * Copyright (c) 1998, 2013, Oracle and/or its affiliates. All rights reserved. + * Copyright (c) 1998, 2015, 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 @@ -429,6 +429,9 @@ // encountered. void allpaths_check_safepts(VectorSet &visited, Node_List &stack); + // Remove safepoints from loop. Optionally keeping one. + void remove_safepoints(PhaseIdealLoop* phase, bool keep_one); + // Convert to counted loops where possible void counted_loop( PhaseIdealLoop *phase ); diff -r 1fcd0a08036b -r 5b34a4ae0f58 hotspot/test/compiler/loopopts/UseCountedLoopSafepoints.java --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/hotspot/test/compiler/loopopts/UseCountedLoopSafepoints.java Fri Dec 04 14:06:38 2015 +0100 @@ -0,0 +1,68 @@ +/* + * Copyright (c) 2015, 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. + * + */ + +/** + * @test + * @bug 6869327 + * @summary Test that C2 flag UseCountedLoopSafepoints ensures a safepoint is kept in a CountedLoop + * @library /testlibrary + * @modules java.base + * @run main UseCountedLoopSafepoints + */ + +import java.util.concurrent.atomic.AtomicLong; +import jdk.test.lib.ProcessTools; +import jdk.test.lib.OutputAnalyzer; + +public class UseCountedLoopSafepoints { + private static final AtomicLong _num = new AtomicLong(0); + + // Uses the fact that an EnableBiasedLocking vmop will be started + // after 500ms, while we are still in the loop. If there is a + // safepoint in the counted loop, then we will reach safepoint + // very quickly. Otherwise SafepointTimeout will be hit. + public static void main (String args[]) throws Exception { + if (args.length == 1) { + final int loops = Integer.parseInt(args[0]); + for (int i = 0; i < loops; i++) { + _num.addAndGet(1); + } + } else { + ProcessBuilder pb = ProcessTools.createJavaProcessBuilder( + "-XX:+IgnoreUnrecognizedVMOptions", + "-XX:-TieredCompilation", + "-XX:+UseBiasedLocking", + "-XX:BiasedLockingStartupDelay=500", + "-XX:+SafepointTimeout", + "-XX:SafepointTimeoutDelay=2000", + "-XX:+UseCountedLoopSafepoints", + "UseCountedLoopSafepoints", + "2000000000" + ); + OutputAnalyzer output = new OutputAnalyzer(pb.start()); + output.shouldNotContain("Timeout detected"); + output.shouldHaveExitValue(0); + } + } +}