8228772: C2 compilation fails due to unschedulable graph if DominatorSearchLimit is reached
Summary: Ignore membar if the load is already control dependent on it.
Reviewed-by: neliasso, kvn
--- a/src/hotspot/share/opto/gcm.cpp Tue Aug 13 08:25:29 2019 +0200
+++ b/src/hotspot/share/opto/gcm.cpp Tue Aug 13 09:54:40 2019 +0200
@@ -663,6 +663,19 @@
// instead of control + memory.
if (mstore->ideal_Opcode() == Op_SafePoint)
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 {
// Some raw memory, such as the load of "top" at an allocation,
// can be control dependent on the previous safepoint. See
@@ -747,7 +760,7 @@
// Found a possibly-interfering store in the load's 'early' block.
// This means 'load' cannot sink at all in the dominator tree.
// 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) {
assert(store->find_edge(load) != -1, "missing precedence edge");
} else {
@@ -787,7 +800,7 @@
Block* store_block = get_block_for_node(store);
if (store_block == LCA) {
// 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) {
assert(store->find_edge(load) != -1, "missing precedence edge");
} else {
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/test/hotspot/jtreg/compiler/controldependency/TestAntiDependentMembar.java Tue Aug 13 09:54:40 2019 +0200
@@ -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() {
+ step1++;
+ step2++;
+ step1++;
+ step2++;
+ step1++;
+ step2++;
+ step1++;
+ step2++;
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+ }
+}