8273454: C2: Transform (-a)*(-b) into a*b

Reviewed-by: thartmann, eliu, chagedorn

src/hotspot/share/opto/mulnode.cpp

@@ -63,9 +63,24 @@ Node *MulNode::Ideal(PhaseGVN *phase, bool can_reshape) {
   const Type *t2 = phase->type( in(2) );
   Node *progress = NULL;        // Progress flag
 
-  // convert "max(a,b) * min(a,b)" into "a*b".
+  // convert "(-a)*(-b)" into "a*b"
   Node *in1 = in(1);
   Node *in2 = in(2);
+  if (in1->is_Sub() && in2->is_Sub()) {
+    if (phase->type(in1->in(1))->is_zero_type() &&
+        phase->type(in2->in(1))->is_zero_type()) {
+      set_req(1, in1->in(2));
+      set_req(2, in2->in(2));
+      PhaseIterGVN* igvn = phase->is_IterGVN();
+      if (igvn) {
+        igvn->_worklist.push(in1);
+        igvn->_worklist.push(in2);
+      }
+      progress = this;
+    }
+  }
+
+  // convert "max(a,b) * min(a,b)" into "a*b".
   if ((in(1)->Opcode() == max_opcode() && in(2)->Opcode() == min_opcode())
       || (in(1)->Opcode() == min_opcode() && in(2)->Opcode() == max_opcode())) {
     Node *in11 = in(1)->in(1);

test/hotspot/jtreg/compiler/integerArithmetic/TestNegMultiply.java

@@ -0,0 +1,104 @@
+/*
+ * Copyright (c) 2021, 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
+ * @key randomness
+ * @bug 8273454
+ * @summary Test transformation (-a)*(-b) = a*b
+ *
+ * @library /test/lib
+ *
+ * @run main/othervm -XX:-TieredCompilation -XX:-BackgroundCompilation -XX:-UseOnStackReplacement -XX:CompileCommand="dontinline,TestNegMultiply::test*" TestNegMultiply
+ *
+ */
+
+import java.util.Random;
+import jdk.test.lib.Utils;
+import jdk.test.lib.Asserts;
+
+public class TestNegMultiply {
+    private static final Random random = Utils.getRandomInstance();
+    // Enough cycles to ensure test methods are JIT-ed
+    private static final int TEST_COUNT = 20_000;
+
+    private static int testInt(int a, int b) {
+        return (-a) * (-b);
+    }
+    private static long testLong(long a, long b) {
+        return (-a) * (-b);
+    }
+    private static float testFloat(float a, float b) {
+        return (-a) * (-b);
+    }
+    private static double testDouble(double a, double b) {
+        return (-a) * (-b);
+    }
+
+    private static void runIntTests() {
+        for (int index = 0; index < TEST_COUNT; index ++) {
+            int a = random.nextInt();
+            int b = random.nextInt();
+            int expected = (-a) * (-b);
+            int res = testInt(a, b);
+            Asserts.assertEQ(res, expected);
+        }
+    }
+
+    private static void runLongTests() {
+        for (int index = 0; index < TEST_COUNT; index ++) {
+            long a = random.nextLong();
+            long b = random.nextLong();
+            long expected = (-a) * (-b);
+            long res = testLong(a, b);
+            Asserts.assertEQ(res, expected);
+        }
+    }
+
+    private static void runFloatTests() {
+        for (int index = 0; index < TEST_COUNT; index ++) {
+            float a = random.nextFloat();
+            float b = random.nextFloat();
+            float expected = (-a) * (-b);
+            float res = testFloat(a, b);
+            Asserts.assertEQ(res, expected);
+        }
+    }
+
+    private static void runDoubleTests() {
+        for (int index = 0; index < TEST_COUNT; index ++) {
+            double a = random.nextDouble();
+            double b = random.nextDouble();
+            double expected = (-a) * (-b);
+            double res = testDouble(a, b);
+            Asserts.assertEQ(res, expected);
+        }
+    }
+
+    public static void main(String[] args) {
+        runIntTests();
+        runLongTests();
+        runFloatTests();
+        runDoubleTests();
+    }
+}