8330819: C2 SuperWord: bad dominance after pre-loop limit adjustment with base that has CastLL after pre-loop

Reviewed-by: chagedorn, kvn

src/hotspot/share/opto/vectorization.cpp

@@ -461,7 +461,10 @@ VPointer::VPointer(const MemNode* mem, const VLoop& vloop,
       break; // stop looking at addp's
     }
   }
-  if (is_loop_member(adr)) {
+  if (!invariant(adr)) {
+    // The address must be invariant for the current loop. But if we are in a main-loop,
+    // it must also be invariant of the pre-loop, otherwise we cannot use this address
+    // for the pre-loop limit adjustment required for main-loop alignment.
     assert(!valid(), "adr is loop variant");
     return;
   }

test/hotspot/jtreg/compiler/loopopts/superword/TestMemorySegmentMainLoopAlignment.java

@@ -0,0 +1,114 @@
+/*
+ * 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
+ * @bug 8330819
+ * @summary Case where VPointer finds an "adr" CastX2P, which contains a CastLL,
+ *          that has a ctrl after the pre-loop. This value cannot be used in the
+ *          pre-loop limit for main-loop adjustment.
+ * @modules java.base/jdk.internal.misc
+ * @modules java.base/jdk.internal.util
+ * @run main/othervm -Xbatch compiler.loopopts.superword.TestMemorySegmentMainLoopAlignment
+ */
+
+package compiler.loopopts.superword;
+
+import java.lang.foreign.*;
+import jdk.internal.misc.Unsafe;
+import jdk.internal.util.Preconditions;
+
+public class TestMemorySegmentMainLoopAlignment {
+    static final ValueLayout.OfInt ELEMENT_LAYOUT = ValueLayout.JAVA_INT.withByteAlignment(1);
+    static final Unsafe UNSAFE = Unsafe.getUnsafe();
+    static long RANGE = 6400;
+
+    // Type definition for the lambda
+    interface MSOp {
+        int apply(MemorySegment memory, long offset, int i);
+    }
+
+    // Type definition for the lambda
+    interface MemoryUnsafeOp {
+        int apply(long base, long offset, int i);
+    }
+
+    public static void main(String[] args) {
+        // Allocate some raw memory:
+        MemorySegment ms = Arena.ofAuto().allocate(6400, Integer.SIZE);
+        for (int i = 0; i < 10_000; i++) {
+            test1(ms, 0, TestMemorySegmentMainLoopAlignment::memorySegmentGet);
+        }
+        // Allocate some raw memory:
+        long base = UNSAFE.allocateMemory(6400);
+        for (int i = 0; i < 10_000; i++) {
+            test2(base, 0, TestMemorySegmentMainLoopAlignment::memoryUnsafeGet);
+        }
+    }
+
+    // Somehow, it is necessary to pass this as a lambda
+    // the checkIndex inside the "get" method produces the CastLL, which eventually pins the index
+    // between the pre and main loop.
+    static int memorySegmentGet(MemorySegment ms, long o, int i) {
+        return ms.get(ELEMENT_LAYOUT, o + i * 4L);
+    }
+
+    static int test1(MemorySegment a, long offset, MSOp f) {
+        // Constant size array size allows a known range for the array access/loop iv i.
+        int size = 16;
+        int[] res = new int[size];
+        int sum = 0;
+        for (int i = 0; i < size; i++) {
+            // With inlining, this eventually becomes:
+            // sum += LoadI(MemorySegment / unsafe) + LoadI(array)
+            // and we attempt vectorization.
+            sum += f.apply(a, offset, i) + res[i];
+        }
+        return sum;
+    }
+
+    // Somehow, it is necessary to pass this as a lambda
+    static int memoryUnsafeGet(long base, long o, int i) {
+        long index = o + i * 4L;
+        // checkIndex -> CastLL: index >= 0.
+        // Together with the info about i (known range for phi), this CastLL floats up to
+        // the offset. Then we get adr = CastX2P(base + CastLL(offset)), where the CastLL
+        // is pinned between the pre and main loop.
+        Preconditions.checkIndex(index, RANGE, null);
+        return UNSAFE.getInt(base + index);
+    }
+
+    static int test2(long base, long offset, MemoryUnsafeOp f) {
+        // Constant size array size allows a known range for the array access/loop iv i.
+        int size = 16;
+        int[] res = new int[size];
+        int sum = 0;
+        for (int i = 0; i < size; i++) {
+            // With inlining, this eventually becomes:
+            // sum += LoadI(unsafe) + LoadI(array)
+            // and we attempt vectorization.
+            sum += f.apply(base, offset, i) + res[i];
+        }
+        return sum;
+    }
+}