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8266615: C2 incorrectly folds subtype checks involving an interface array #4060

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@@ -4058,16 +4058,22 @@ int Compile::static_subtype_check(ciKlass* superk, ciKlass* subk) {
}

ciType* superelem = superk;
if (superelem->is_array_klass())
ciType* subelem = subk;
if (superelem->is_array_klass()) {
superelem = superelem->as_array_klass()->base_element_type();
}
if (subelem->is_array_klass()) {
subelem = subelem->as_array_klass()->base_element_type();
}

if (!subk->is_interface()) { // cannot trust static interface types yet
if (subk->is_subtype_of(superk)) {
return SSC_always_true; // (1) false path dead; no dynamic test needed
}
if (!(superelem->is_klass() && superelem->as_klass()->is_interface()) &&
!(subelem->is_klass() && subelem->as_klass()->is_interface()) &&
!superk->is_subtype_of(subk)) {
return SSC_always_false;
return SSC_always_false; // (2) true path dead; no dynamic test needed
}
}

@@ -0,0 +1,79 @@
/*
* 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
* @bug 8266615
* @summary C2 incorrectly folds subtype checks involving an interface array.
* @run main/othervm -Xbatch
* compiler.types.TestInterfaceArraySubtypeCheck
*/

package compiler.types;

public class TestInterfaceArraySubtypeCheck {

static interface MyInterface { }

static class MyClassA { }

static class MyClassB extends MyClassA implements MyInterface { }

static MyInterface[] getMyInterfaceArray() {
return new MyClassB[0];
}

static MyInterface getMyInterface() {
return new MyClassB();
}

static MyClassA[] test1() {
return (MyClassA[])getMyInterfaceArray();
}

static void test2() {
if (!(getMyInterfaceArray() instanceof MyClassA[])) {
throw new RuntimeException("test2 failed");
}
}

static MyClassA test3() {
return (MyClassA)getMyInterface();
}

static void test4() {
if (!(getMyInterface() instanceof MyClassA)) {
throw new RuntimeException("test4 failed");
}
}

public static void main(String[] args) {
for (int i = 0; i < 50_000; ++i) {
test1();
test2();
test3();
test4();
}
}
}