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8323101: C2: assert(n->in(0) == nullptr) failed: divisions with zero …
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…check should already have bailed out earlier in split-if

Backport-of: 7e0a4ed6292586772c23292dbdd67ed1db5c12f7
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shipilev committed Jan 31, 2024
1 parent 0466741 commit 869df3b
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6 changes: 5 additions & 1 deletion src/hotspot/share/opto/loopopts.cpp
Expand Up @@ -237,7 +237,11 @@ bool PhaseIdealLoop::cannot_split_division(const Node* n, const Node* region) co
return false;
}

assert(n->in(0) == nullptr, "divisions with zero check should already have bailed out earlier in split-if");
if (n->in(0) != nullptr) {
// Cannot split through phi if Div or Mod node has a control dependency to a zero check.
return true;
}

Node* divisor = n->in(2);
return is_divisor_counted_loop_phi(divisor, region) &&
loop_phi_backedge_type_contains_zero(divisor, zero);
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@@ -0,0 +1,210 @@
/*
* Copyright (c) 2024, 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 id=normal
* @bug 8323101
* @summary Test split_thru_phi with pinned divisions/modulo that have phi as inputs.
* @run main/othervm -Xbatch
* -XX:CompileCommand=compileonly,compiler.splitif.TestSplitDivThroughPhiWithControl::*
* compiler.splitif.TestSplitDivThroughPhiWithControl
*/

/*
* @test id=fuzzer
* @bug 8323101
* @summary Test split_thru_phi with pinned divisions/modulo that have phi as inputs.
* @run main/othervm -Xbatch -XX:PerMethodTrapLimit=0
* -XX:CompileCommand=compileonly,compiler.splitif.TestSplitDivThroughPhiWithControl::*
* compiler.splitif.TestSplitDivThroughPhiWithControl
*/

package compiler.splitif;

public class TestSplitDivThroughPhiWithControl {
static int divisorInt = 34;
static int iFld;
static int x;
static int y;
static long divisorLong = 34L;
static long lFld;
static long lFld2;
static long lFld3;
static boolean flag;

static int[] iArr = new int[400];

public static void main(String[] strArr) {
iArr[0] = 52329;
for (int i = 0; i < 10000; i++) {
flag = i % 3 == 0; // Avoid unstable if trap
divisorInt = i % 2 == 0 ? 0 : 23; // Avoid div by zero trap
divisorLong = divisorInt; // Avoid div by zero trap
try {
testIntDiv();
} catch (ArithmeticException e) {
// Expected.
}

try {
testIntMod();
} catch (ArithmeticException e) {
// Expected.
}

try {
testLongDiv(); // Currently does not trigger due to JDK-8323652
} catch (ArithmeticException e) {
// Expected.
}

try {
testLongMod(); // Currently does not trigger due to JDK-8323652
} catch (ArithmeticException e) {
// Expected.
}

testFuzzer();
}
}

static void testIntDiv() {
int a;

for (int j = 0; j < 100; j++) {
y += 5;
int sub = j - 3; // AddI
int div = (sub / divisorInt); // DivI with AddI input

if (flag) {
a = y;
} else {
a = 2;
}
// Region

// Use StoreI with AddI input. Store needs to be split through Region in Split-If which is done together
// with AddI.
iFld = sub;

if (a < 3) { // If that's split in Split-If
// Use of DivI -> after Split-If, DivI gets a Phi input that merges the split AddI nodes.
// -> triggers assert that we should not find pinned div nodes in cannot_split_division().
x = div;
}
}
}

// Same as testIntDiv() but with ModI
static void testIntMod() {
int a;

for (int j = 0; j < 100; j++) {
y += 5;
int sub = j - 3;
int mod = (sub % divisorInt);

if (flag) {
a = y;
} else {
a = 2;
}

iFld = sub;

if (a < 3) {
x = mod; // Only StoreI visited first but not mod since it's an input
}
}
}

// Same as testIntDiv() but with DivL
static void testLongDiv() {
long a;

for (int j = 0; j < 100; j++) {
y += 5;
long sub = j - 3;
long div = (sub / divisorLong);

if (flag) {
a = lFld2;
} else {
a = 2;
}

lFld = sub;

if (a < 3) {
lFld3 = div;
}
}
}


// Same as testIntDiv() but with ModL
static void testLongMod() {
long a;

for (long j = 0; j < 100; j++) {
lFld2 += 5;
long sub = j - 3;
long mod = (sub % divisorLong);

if (flag) {
a = lFld2;
} else {
a = 2;
}

lFld = sub;

if (a < 3) {
lFld3 = mod; // Only StoreI visited first but not mod since it's an input
}
}
}

// Original fuzzer crash
static void testFuzzer() {
int i19, i21 = 4928, i23 = 14;
for (int i = 5; i < 100; i++) {
i19 = i23;
int j = 1;
while (true) {
try {
i21 = (iArr[0] / 34);
i23 = (j % i21);
} catch (ArithmeticException a_e) {
}
iArr = iArr;
iFld = i21;
iArr[1] += 5;
if (j == 1000) {
break;
}
j++;
}
}
}
}

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