8284981: Support the vectorization of some counting-down loops in SLP

Reviewed-by: roland, kvn

Author: Fei Gao

src/hotspot/share/opto/superword.cpp

@@ -3997,7 +3997,7 @@ bool SWPointer::scaled_iv_plus_offset(Node* n) {
       NOT_PRODUCT(_tracer.scaled_iv_plus_offset_5(n);)
       return true;
     }
-  } else if (opc == Op_SubI) {
+  } else if (opc == Op_SubI || opc == Op_SubL) {
     if (offset_plus_k(n->in(2), true) && scaled_iv_plus_offset(n->in(1))) {
       NOT_PRODUCT(_tracer.scaled_iv_plus_offset_6(n);)
       return true;
@@ -4316,15 +4316,15 @@ void SWPointer::Tracer::scaled_iv_plus_offset_5(Node* n) {
 
 void SWPointer::Tracer::scaled_iv_plus_offset_6(Node* n) {
   if(_slp->is_trace_alignment()) {
-    print_depth(); tty->print_cr(" %d SWPointer::scaled_iv_plus_offset: Op_SubI PASSED", n->_idx);
+    print_depth(); tty->print_cr(" %d SWPointer::scaled_iv_plus_offset: Op_%s PASSED", n->_idx, n->Name());
     print_depth(); tty->print("  \\  %d SWPointer::scaled_iv_plus_offset: in(1) is scaled_iv: ", n->in(1)->_idx); n->in(1)->dump();
     print_depth(); tty->print("  \\ %d SWPointer::scaled_iv_plus_offset: in(2) is offset_plus_k: ", n->in(2)->_idx); n->in(2)->dump();
   }
 }
 
 void SWPointer::Tracer::scaled_iv_plus_offset_7(Node* n) {
   if(_slp->is_trace_alignment()) {
-    print_depth(); tty->print_cr(" %d SWPointer::scaled_iv_plus_offset: Op_SubI PASSED", n->_idx);
+    print_depth(); tty->print_cr(" %d SWPointer::scaled_iv_plus_offset: Op_%s PASSED", n->_idx, n->Name());
     print_depth(); tty->print("  \\ %d SWPointer::scaled_iv_plus_offset: in(2) is scaled_iv: ", n->in(2)->_idx); n->in(2)->dump();
     print_depth(); tty->print("  \\ %d SWPointer::scaled_iv_plus_offset: in(1) is offset_plus_k: ", n->in(1)->_idx); n->in(1)->dump();
   }

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

@@ -0,0 +1,61 @@
+/*
+ * Copyright (c) 2022, Arm Limited. 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 8284981
+ * @summary Auto-vectorization enhancement for special counting down loops
+ * @requires os.arch=="amd64" | os.arch=="x86_64" | os.arch=="aarch64"
+ * @library /test/lib /
+ * @run driver compiler.c2.irTests.TestAutoVecCountingDownLoop
+ */
+
+public class TestAutoVecCountingDownLoop {
+    final private static int ARRLEN = 3000;
+
+    private static int[] a = new int[ARRLEN];
+    private static int[] b = new int[ARRLEN];
+
+    public static void main(String[] args) {
+        TestFramework.run();
+    }
+
+
+    @Test
+    @IR(counts = {IRNode.LOAD_VECTOR,  " >0 "})
+    @IR(counts = {IRNode.STORE_VECTOR, " >0 "})
+    private static void testCountingDown(int[] a, int[] b) {
+        for (int i = 2000; i > 0; i--) {
+            b[ARRLEN - i] = a[ARRLEN - i];
+        }
+    }
+
+    @Run(test = "testCountingDown")
+    private void testCountingDown_runner() {
+        testCountingDown(a, b);
+    }
+}

test/hotspot/jtreg/compiler/codegen/TestIntVect.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2022, 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
@@ -102,6 +102,7 @@ static int test() {
       test_andImm(a1, a2, a3);
       test_orImm(a1, a2);
       test_xorImm(a1, a2);
+      test_cp_countingdown(a1, a2);
     }
     // Initialize
     for (int i=0; i<ARRLEN; i++) {
@@ -552,6 +553,10 @@ static int test() {
       for (int i=0; i<ARRLEN; i++) {
         errn += verify("test_xorImm: a2", i, a2[i], golden);
       }
+      test_cp_countingdown(a1, a2);
+      for (int i = 500; i > 0; i--) {
+        errn += verify("test_cp_countingdown: a2", ARRLEN - i, a2[ARRLEN - i], a1[ARRLEN - i]);
+      }
 
     }
 
@@ -837,6 +842,12 @@ static int test() {
     }
     end = System.currentTimeMillis();
     System.out.println("test_xorImm: " + (end - start));
+    start = System.currentTimeMillis();
+    for (int i = 0; i < ITERS; i++) {
+      test_cp_countingdown(a1, a2);
+    }
+    end = System.currentTimeMillis();
+    System.out.println("test_cp_countingdown: " + (end - start));
 
     return errn;
   }
@@ -1095,7 +1106,11 @@ static void test_xorImm(int[] a, int[] b) {
       b[i] = a[i] ^ 2032;
     }
   }
-
+  static void test_cp_countingdown(int[] a, int[] b) {
+    for (int i = 500; i > 0; i--) {
+      b[ARRLEN - i] = a[ARRLEN - i];
+    }
+  }
 
   static int verify(String text, int i, int elem, int val) {
     if (elem != val) {