8262739: String inflation C2 intrinsic prevents insertion of anti-dependencies

Reviewed-by: neliasso, chagedorn

src/hotspot/share/adlc/formssel.cpp

@@ -781,6 +781,7 @@ bool InstructForm::captures_bottom_type(FormDict &globals) const {
        !strcmp(_matrule->_rChild->_opType,"ShenandoahCompareAndExchangeP") ||
        !strcmp(_matrule->_rChild->_opType,"ShenandoahCompareAndExchangeN") ||
 #endif
+       !strcmp(_matrule->_rChild->_opType,"StrInflatedCopy") ||
        !strcmp(_matrule->_rChild->_opType,"VectorMaskGen")||
        !strcmp(_matrule->_rChild->_opType,"CompareAndExchangeP") ||
        !strcmp(_matrule->_rChild->_opType,"CompareAndExchangeN"))) return true;

test/hotspot/jtreg/compiler/controldependency/TestAntiDependencyAfterStringInflation.java

@@ -0,0 +1,64 @@
+/*
+ * 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 8262739
+ * @summary Test correct insertion of anti-dependencies after String inflation.
+ * @run main/othervm -Xbatch
+ *                   compiler.controldependency.TestAntiDependencyAfterStringInflation
+ */
+
+package compiler.controldependency;
+
+public class TestAntiDependencyAfterStringInflation {
+
+    static String reverseString(String str) {
+        int size = str.length();
+        char[] buffer = new char[size];
+        reverse(str, buffer, size);
+        return new String(buffer, 0, size);
+    }
+
+    static void reverse(String str, char[] buffer, int size) {
+        // Inflate String.value byte[] to char[]
+        str.getChars(0, size, buffer, 0);
+        // Reverse String by copying buffer elements. This will fail
+        // if C2 does not insert anti-dependencies between loads/stores.
+        int half = size / 2;
+        for (int l = 0, r = size - 1; l < half; l++, r--) {
+            char tmp = buffer[l];
+            buffer[l] = buffer[r];
+            buffer[r] = tmp;
+        }
+    }
+
+    public static void main(String[] args) throws Exception {
+        for (int i = 0; i < 50_000; i++) {
+            String res = reverseString("0123456789");
+            if (!res.equals("9876543210")) {
+                throw new RuntimeException("Unexpected result: " + res);
+            }
+        }
+    }
+}