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8228772: C2 compilation fails due to unschedulable graph if DominatorSearchLimit is reached

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Ignore membar if the load is already control dependent on it.

Reviewed-by: neliasso, kvn
This commit is contained in:
Tobias Hartmann 2019-08-13 09:54:40 +02:00
parent 5225d254ee
commit f1763a5e86
2 changed files with 465 additions and 2 deletions
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17
src/hotspot/share/opto/gcm.cpp
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@ -663,6 +663,19 @@ Block* PhaseCFG::insert_anti_dependences(Block* LCA, Node* load, bool verify) {
// instead of control + memory. // instead of control + memory.
if (mstore->ideal_Opcode() == Op_SafePoint) if (mstore->ideal_Opcode() == Op_SafePoint)
continue; continue;
// Check if the store is a membar on which the load is control dependent.
// Inserting an anti-dependency between that membar and the load would
// create a cycle that causes local scheduling to fail.
if (mstore->isa_MachMemBar()) {
Node* dom = load->find_exact_control(load->in(0));
while (dom != NULL && dom != dom->in(0) && dom != mstore) {
dom = dom->in(0);
}
if (dom == mstore) {
continue;
}
}
} else { } else {
// Some raw memory, such as the load of "top" at an allocation, // Some raw memory, such as the load of "top" at an allocation,
// can be control dependent on the previous safepoint. See // can be control dependent on the previous safepoint. See
@ -747,7 +760,7 @@ Block* PhaseCFG::insert_anti_dependences(Block* LCA, Node* load, bool verify) {
// Found a possibly-interfering store in the load's 'early' block. // Found a possibly-interfering store in the load's 'early' block.
// This means 'load' cannot sink at all in the dominator tree. // This means 'load' cannot sink at all in the dominator tree.
// Add an anti-dep edge, and squeeze 'load' into the highest block. // Add an anti-dep edge, and squeeze 'load' into the highest block.
assert(store != load->in(0), "dependence cycle found"); assert(store != load->find_exact_control(load->in(0)), "dependence cycle found");
if (verify) { if (verify) {
assert(store->find_edge(load) != -1, "missing precedence edge"); assert(store->find_edge(load) != -1, "missing precedence edge");
} else { } else {
@ -787,7 +800,7 @@ Block* PhaseCFG::insert_anti_dependences(Block* LCA, Node* load, bool verify) {
Block* store_block = get_block_for_node(store); Block* store_block = get_block_for_node(store);
if (store_block == LCA) { if (store_block == LCA) {
// add anti_dependence from store to load in its own block // add anti_dependence from store to load in its own block
assert(store != load->in(0), "dependence cycle found"); assert(store != load->find_exact_control(load->in(0)), "dependence cycle found");
if (verify) { if (verify) {
assert(store->find_edge(load) != -1, "missing precedence edge"); assert(store->find_edge(load) != -1, "missing precedence edge");
} else { } else {

450
test/hotspot/jtreg/compiler/controldependency/TestAntiDependentMembar.java Normal file
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@ -0,0 +1,450 @@
/*
* Copyright (c) 2019, 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 8228772
* @summary Test correct insertion of anti-dependencies if load is already control dependent on membar.
* @run main/othervm -Xbatch -XX:-TieredCompilation
* -XX:CompileCommand=inline,compiler.controldependency.TestAntiDependentMembar::hitSearchLimit
* compiler.controldependency.TestAntiDependentMembar
* @run main/othervm -Xbatch -XX:-TieredCompilation
* -XX:CompileCommand=inline,compiler.controldependency.TestAntiDependentMembar::hitSearchLimit
* -XX:+UnlockDiagnosticVMOptions -XX:+IgnoreUnrecognizedVMOptions -XX:DominatorSearchLimit=0
* compiler.controldependency.TestAntiDependentMembar
*/
package compiler.controldependency;
public class TestAntiDependentMembar {
static volatile int step1 = 0;
static volatile int step2 = 0;
public static int test1(int count, int b1, int b2) {
int[] result = {0};
// Complex control flow to generate Region with 4 paths and therefore bail out of Node::dominates
if (b1 == 0) {
count += 1;
} else if (b1 == 1) {
if (b2 == 1) {
count += 2;
}
}
for (int i = 0; i < count; ++i) {
// Volatile field write adds a membar
step1 = i;
// Load that is dependent on the membar
result[0] += count;
}
return result[0];
}
// Same as test1 but bailing out of Node::dominates due to hitting DominatorSearchLimit
public static int test2(int count) {
int[] result = {0};
// Large method with regions to hit the DominatorSearchLimit
hitSearchLimit();
for (int i = 0; i < count; ++i) {
step1 = i;
result[0] += count;
}
return result[0];
}
// Same as test2 but with multiple membars before the load
public static int test3(int count) {
int[] result = {0};
hitSearchLimit();
for (int i = 0; i < count; ++i) {
step1 = i;
step2 = i;
step1 = i;
step2 = i;
result[0] += count;
}
return result[0];
}
public static void main(String[] args) {
for (int i = 0; i < 50_000; ++i) {
test1(10, 0, 0);
test1(10, 1, 1);
test1(10, 1, 0);
test1(10, 0, 1);
test2(10);
test3(10);
}
}
public static void hitSearchLimit() {
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}
}