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8271056: C2: "assert(no_dead_loop) failed: dead loop detected" due to…
… cmoving identity

Reviewed-by: kvn, thartmann
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chhagedorn committed Nov 8, 2021
1 parent 0395e4e commit 54481394a3b7d36b2326e22e4aa910a3e8041b5c
Showing 2 changed files with 87 additions and 2 deletions.
@@ -1366,9 +1366,12 @@ Node* PhiNode::Identity(PhaseGVN* phase) {
}

int true_path = is_diamond_phi();
if (true_path != 0) {
// Delay CMove'ing identity if Ideal has not had the chance to handle unsafe cases, yet.
if (true_path != 0 && !(phase->is_IterGVN() && wait_for_region_igvn(phase))) {
Node* id = is_cmove_id(phase, true_path);
if (id != NULL) return id;
if (id != NULL) {
return id;
}
}

// Looking for phis with identical inputs. If we find one that has
@@ -0,0 +1,82 @@
/*
* Copyright (c) 2021, 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
* @key stress randomness
* @bug 8271056
* @summary A dead data loop is created when applying an unsafe case of Cmov'ing identity.
* @run main/othervm -Xcomp -XX:-TieredCompilation -XX:CompileCommand=compileonly,compiler.c2.TestDeadDataLoopCmoveIdentity::*
* -XX:+UnlockDiagnosticVMOptions -XX:+StressIGVN -XX:StressSeed=359948366 compiler.c2.TestDeadDataLoopCmoveIdentity
* @run main/othervm -Xcomp -XX:-TieredCompilation -XX:CompileCommand=compileonly,compiler.c2.TestDeadDataLoopCmoveIdentity::*
* -XX:+UnlockDiagnosticVMOptions -XX:+StressIGVN compiler.c2.TestDeadDataLoopCmoveIdentity
*/

package compiler.c2;

public class TestDeadDataLoopCmoveIdentity {
static boolean bFld;

public static void main(String[] strArr) {
test();
test2();
}

static void test() {
int i33 = 51925, iArr3[] = new int[10];
if (bFld) {
;
} else if (bFld) {
for (int i = 0; i < 100; i++) { }
do {
if (i33 != 0) {
}
int i34 = 1;
do {
switch (0) {
case 122: { }
}
} while (i34 < 1);
i33 += i33 + 3;
} while (i33 < 5);
}
}

static void test2() {
int i33 = 51925, iArr3[] = new int[10];
if (bFld) {
;
} else if (bFld) {
do {
if (i33 != 0) {
}
int i34 = 1;
do {
switch (0) {
case 122: {}
}
} while (i34 < 1);
} while (++i33 < 5);
}
}
}

3 comments on commit 5448139

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@openjdk-notifier openjdk-notifier bot commented on 5448139 Nov 8, 2021

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@GoeLin
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@GoeLin GoeLin commented on 5448139 Jan 31, 2022

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/backport jdk17u-dev

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@openjdk openjdk bot commented on 5448139 Jan 31, 2022

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@GoeLin the backport was successfully created on the branch GoeLin-backport-54481394 in my personal fork of openjdk/jdk17u-dev. To create a pull request with this backport targeting openjdk/jdk17u-dev:master, just click the following link:

➡️ Create pull request

The title of the pull request is automatically filled in correctly and below you find a suggestion for the pull request body:

Hi all,

This pull request contains a backport of commit 54481394 from the openjdk/jdk repository.

The commit being backported was authored by Christian Hagedorn on 8 Nov 2021 and was reviewed by Vladimir Kozlov and Tobias Hartmann.

Thanks!

If you need to update the source branch of the pull then run the following commands in a local clone of your personal fork of openjdk/jdk17u-dev:

$ git fetch https://github.com/openjdk-bots/jdk17u-dev GoeLin-backport-54481394:GoeLin-backport-54481394
$ git checkout GoeLin-backport-54481394
# make changes
$ git add paths/to/changed/files
$ git commit --message 'Describe additional changes made'
$ git push https://github.com/openjdk-bots/jdk17u-dev GoeLin-backport-54481394

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