8262721: Add Tests to verify single iteration loops are properly optimized

Reviewed-by: neliasso, chagedorn, kvn

Author: rwestrel

test/hotspot/jtreg/compiler/c2/irTests/TestFewIterationsCountedLoop.java

@@ -0,0 +1,139 @@
+/*
+ * 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.
+ */
+
+package compiler.c2.irTests;
+
+import compiler.lib.ir_framework.*;
+
+/*
+ * @test
+ * @bug 8262721
+ * @summary Add Tests to verify single iteration loops are properly optimized
+ * @library /test/lib /
+ * @run driver compiler.c2.irTests.TestFewIterationsCountedLoop
+ */
+
+public class TestFewIterationsCountedLoop {
+
+    public static void main(String[] args) {
+        TestFramework.runWithFlags("-XX:LoopUnrollLimit=0");
+        TestFramework.run();
+    }
+
+    static volatile int barrier;
+    static final Object object = new Object();
+
+    @Test
+    @IR(failOn = { IRNode.COUNTEDLOOP, IRNode.LOOP })
+    public static void singleIterationFor() {
+        for (int i = 0; i < 1; i++) {
+            barrier = 0x42; // something that can't be optimized out
+        }
+    }
+
+    @Test
+    @IR(failOn = { IRNode.COUNTEDLOOP, IRNode.LOOP })
+    public static void singleIterationWhile() {
+        int i = 0;
+        while (i < 1) {
+            barrier = 0x42;
+            i++;
+        }
+    }
+
+    @Test
+    @IR(failOn = { IRNode.COUNTEDLOOP, IRNode.LOOP })
+    @Warmup(1) // So C2 can't rely on profile data
+    public static void singleIterationDoWhile() {
+        int i = 0;
+        do {
+            synchronized(object) {} // so loop head is not cloned by ciTypeFlow
+            barrier = 0x42;
+            i++;
+        } while (i < 1);
+    }
+
+    @Test
+    @IR(applyIf = { "LoopUnrollLimit", "0" }, counts = { IRNode.COUNTEDLOOP, "1" })
+    @IR(applyIf = { "LoopUnrollLimit", "> 0" }, failOn = { IRNode.COUNTEDLOOP, IRNode.LOOP })
+    public static void twoIterationsFor() {
+        for (int i = 0; i < 2; i++) {
+            barrier = 0x42; // something that can't be optimized out
+        }
+    }
+
+    @Test
+    @IR(applyIf = { "LoopUnrollLimit", "0" }, counts = { IRNode.COUNTEDLOOP, "1" })
+    @IR(applyIf = { "LoopUnrollLimit", "> 0" }, failOn = { IRNode.COUNTEDLOOP, IRNode.LOOP })
+    public static void twoIterationsWhile() {
+        int i = 0;
+        while (i < 2) {
+            barrier = 0x42;
+            i++;
+        }
+    }
+
+    @Test
+    @IR(applyIf = { "LoopUnrollLimit", "0" }, counts = { IRNode.COUNTEDLOOP, "1" })
+    @IR(applyIf = { "LoopUnrollLimit", "> 0" }, failOn = { IRNode.COUNTEDLOOP, IRNode.LOOP })
+    public static void twoIterationsDoWhile() {
+        int i = 0;
+        do {
+            synchronized(object) {} // so loop head is not cloned by ciTypeFlow
+            barrier = 0x42;
+            i++;
+        } while (i < 2);
+    }
+
+    @Test
+    @IR(applyIf = { "LoopUnrollLimit", "0" }, counts = { IRNode.COUNTEDLOOP, "1" })
+    @IR(applyIf = { "LoopUnrollLimit", "> 0" }, failOn = { IRNode.COUNTEDLOOP, IRNode.LOOP })
+    public static void threadIterationsFor() {
+        for (int i = 0; i < 2; i++) {
+            barrier = 0x42; // something that can't be optimized out
+        }
+    }
+
+    @Test
+    @IR(applyIf = { "LoopUnrollLimit", "0" }, counts = { IRNode.COUNTEDLOOP, "1" })
+    @IR(applyIf = { "LoopUnrollLimit", "> 0" }, failOn = { IRNode.COUNTEDLOOP, IRNode.LOOP })
+    public static void threeIterationsWhile() {
+        int i = 0;
+        while (i < 2) {
+            barrier = 0x42;
+            i++;
+        }
+    }
+
+    @Test
+    @IR(applyIf = { "LoopUnrollLimit", "0" }, counts = { IRNode.COUNTEDLOOP, "1" })
+    @IR(applyIf = { "LoopUnrollLimit", "> 0" }, failOn = { IRNode.COUNTEDLOOP, IRNode.LOOP })
+    public static void threeIterationsDoWhile() {
+        int i = 0;
+        do {
+            synchronized(object) {} // so loop head is not cloned by ciTypeFlow
+            barrier = 0x42;
+            i++;
+        } while (i < 2);
+    }
+}