8288303: C1: Miscompilation due to broken Class.getModifiers intrinsic

Backport-of: 8cd87e731bcaff2d7838995c68056742d577ad3b

src/hotspot/share/c1/c1_LIRGenerator.cpp

@@ -1311,20 +1311,27 @@ void LIRGenerator::do_getModifiers(Intrinsic* x) {
     info = state_for(x);
   }
 
-  LabelObj* L_not_prim = new LabelObj();
-  LabelObj* L_done = new LabelObj();
+  // While reading off the universal constant mirror is less efficient than doing
+  // another branch and returning the constant answer, this branchless code runs into
+  // much less risk of confusion for C1 register allocator. The choice of the universe
+  // object here is correct as long as it returns the same modifiers we would expect
+  // from the primitive class itself. See spec for Class.getModifiers that provides
+  // the typed array klasses with similar modifiers as their component types.
+
+  Klass* univ_klass_obj = Universe::byteArrayKlassObj();
+  assert(univ_klass_obj->modifier_flags() == (JVM_ACC_ABSTRACT | JVM_ACC_FINAL | JVM_ACC_PUBLIC), "Sanity");
+  LIR_Opr prim_klass = LIR_OprFact::metadataConst(univ_klass_obj);
+
+  LIR_Opr recv_klass = new_register(T_METADATA);
+  __ move(new LIR_Address(receiver.result(), java_lang_Class::klass_offset(), T_ADDRESS), recv_klass, info);
 
+  // Check if this is a Java mirror of primitive type, and select the appropriate klass.
   LIR_Opr klass = new_register(T_METADATA);
-  // Checking if it's a java mirror of primitive type
-  __ move(new LIR_Address(receiver.result(), java_lang_Class::klass_offset(), T_ADDRESS), klass, info);
-  __ cmp(lir_cond_notEqual, klass, LIR_OprFact::metadataConst(0));
-  __ branch(lir_cond_notEqual, L_not_prim->label());
-  __ move(LIR_OprFact::intConst(JVM_ACC_ABSTRACT | JVM_ACC_FINAL | JVM_ACC_PUBLIC), result);
-  __ branch(lir_cond_always, L_done->label());
+  __ cmp(lir_cond_equal, recv_klass, LIR_OprFact::metadataConst(0));
+  __ cmove(lir_cond_equal, prim_klass, recv_klass, klass, T_ADDRESS);
 
-  __ branch_destination(L_not_prim->label());
+  // Get the answer.
   __ move(new LIR_Address(klass, in_bytes(Klass::modifier_flags_offset()), T_INT), result);
-  __ branch_destination(L_done->label());
 }
 
 // Example: Thread.currentThread()

test/hotspot/jtreg/compiler/intrinsics/klass/TestGetModifiers.java

@@ -0,0 +1,118 @@
+/*
+ * Copyright (c) 2022, Red Hat, Inc. 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
+ * @library /test/lib
+ * @run main/othervm -Xint
+ *                   -XX:CompileCommand=dontinline,*TestGetModifiers.test
+ *                   compiler.intrinsics.klass.TestGetModifiers
+ */
+
+/*
+ * @test
+ * @requires vm.compiler1.enabled
+ * @library /test/lib
+ * @run main/othervm -XX:TieredStopAtLevel=1 -XX:+TieredCompilation
+ *                   -XX:CompileCommand=dontinline,*TestGetModifiers.test
+ *                   compiler.intrinsics.klass.TestGetModifiers
+ */
+
+/*
+ * @test
+ * @requires vm.compiler2.enabled
+ * @library /test/lib
+ * @run main/othervm -XX:-TieredCompilation
+ *                   -XX:CompileCommand=dontinline,*TestGetModifiers.test
+ *                   compiler.intrinsics.klass.TestGetModifiers
+ */
+
+package compiler.intrinsics.klass;
+
+import java.lang.reflect.Modifier;
+import static java.lang.reflect.Modifier.*;
+
+import jdk.test.lib.Asserts;
+
+public class TestGetModifiers {
+    public static class T1 {
+    }
+
+    public static final class T2 {
+    }
+
+    private static class T3 {
+    }
+
+    protected static class T4 {
+    }
+
+    class T5 {
+    }
+
+    interface T6 {
+    }
+
+    static void test(Class cl, int expectedMods) {
+        for (int i = 0; i < 100_000; i++) {
+            int actualMods = cl.getModifiers();
+            if (actualMods != expectedMods) {
+                throw new IllegalStateException("Error with: " + cl);
+            }
+        }
+    }
+
+    public static void main(String... args) {
+        test(T1.class,                                      PUBLIC | STATIC);
+        test(T2.class,                                      PUBLIC | FINAL | STATIC);
+        test(T3.class,                                      PRIVATE | STATIC);
+        test(T4.class,                                      PROTECTED | STATIC);
+        test(new TestGetModifiers().new T5().getClass(),    0);
+        test(T6.class,                                      ABSTRACT | STATIC | INTERFACE);
+
+        test(int.class,                                     PUBLIC | ABSTRACT | FINAL);
+        test(long.class,                                    PUBLIC | ABSTRACT | FINAL);
+        test(double.class,                                  PUBLIC | ABSTRACT | FINAL);
+        test(float.class,                                   PUBLIC | ABSTRACT | FINAL);
+        test(char.class,                                    PUBLIC | ABSTRACT | FINAL);
+        test(byte.class,                                    PUBLIC | ABSTRACT | FINAL);
+        test(short.class,                                   PUBLIC | ABSTRACT | FINAL);
+        test(void.class,                                    PUBLIC | ABSTRACT | FINAL);
+        test(int[].class,                                   PUBLIC | ABSTRACT | FINAL);
+        test(long[].class,                                  PUBLIC | ABSTRACT | FINAL);
+        test(double[].class,                                PUBLIC | ABSTRACT | FINAL);
+        test(float[].class,                                 PUBLIC | ABSTRACT | FINAL);
+        test(char[].class,                                  PUBLIC | ABSTRACT | FINAL);
+        test(byte[].class,                                  PUBLIC | ABSTRACT | FINAL);
+        test(short[].class,                                 PUBLIC | ABSTRACT | FINAL);
+        test(Object[].class,                                PUBLIC | ABSTRACT | FINAL);
+        test(TestGetModifiers[].class,                      PUBLIC | ABSTRACT | FINAL);
+
+        test(new TestGetModifiers().getClass(),             PUBLIC);
+        test(new T1().getClass(),                           PUBLIC | STATIC);
+        test(new T2().getClass(),                           PUBLIC | FINAL | STATIC);
+        test(new T3().getClass(),                           PRIVATE | STATIC);
+        test(new T4().getClass(),                           PROTECTED | STATIC);
+    }
+}