8291336: Add ideal rule to convert floating point multiply by 2 into addition

Reviewed-by: qamai, thartmann, chagedorn

src/hotspot/share/opto/mulnode.cpp

@@ -423,6 +423,20 @@ const Type *MulFNode::mul_ring(const Type *t0, const Type *t1) const {
   return TypeF::make( t0->getf() * t1->getf() );
 }
 
+//------------------------------Ideal---------------------------------------
+// Check to see if we are multiplying by a constant 2 and convert to add, then try the regular MulNode::Ideal
+Node* MulFNode::Ideal(PhaseGVN* phase, bool can_reshape) {
+  const TypeF *t2 = phase->type(in(2))->isa_float_constant();
+
+  // x * 2 -> x + x
+  if (t2 != NULL && t2->getf() == 2) {
+    Node* base = in(1);
+    return new AddFNode(base, base);
+  }
+
+  return MulNode::Ideal(phase, can_reshape);
+}
+
 //=============================================================================
 //------------------------------mul_ring---------------------------------------
 // Compute the product type of two double ranges into this node.
@@ -432,6 +446,20 @@ const Type *MulDNode::mul_ring(const Type *t0, const Type *t1) const {
   return TypeD::make( t0->getd() * t1->getd() );
 }
 
+//------------------------------Ideal---------------------------------------
+// Check to see if we are multiplying by a constant 2 and convert to add, then try the regular MulNode::Ideal
+Node* MulDNode::Ideal(PhaseGVN* phase, bool can_reshape) {
+  const TypeD *t2 = phase->type(in(2))->isa_double_constant();
+
+  // x * 2 -> x + x
+  if (t2 != NULL && t2->getd() == 2) {
+    Node* base = in(1);
+    return new AddDNode(base, base);
+  }
+
+  return MulNode::Ideal(phase, can_reshape);
+}
+
 //=============================================================================
 //------------------------------Value------------------------------------------
 const Type* MulHiLNode::Value(PhaseGVN* phase) const {

src/hotspot/share/opto/mulnode.hpp

@@ -130,6 +130,7 @@ class MulFNode : public MulNode {
 public:
   MulFNode( Node *in1, Node *in2 ) : MulNode(in1,in2) {}
   virtual int Opcode() const;
+  virtual Node *Ideal(PhaseGVN *phase, bool can_reshape);
   virtual const Type *mul_ring( const Type *, const Type * ) const;
   const Type *mul_id() const { return TypeF::ONE; }
   const Type *add_id() const { return TypeF::ZERO; }
@@ -147,6 +148,7 @@ class MulDNode : public MulNode {
 public:
   MulDNode( Node *in1, Node *in2 ) : MulNode(in1,in2) {}
   virtual int Opcode() const;
+  virtual Node *Ideal(PhaseGVN *phase, bool can_reshape);
   virtual const Type *mul_ring( const Type *, const Type * ) const;
   const Type *mul_id() const { return TypeD::ONE; }
   const Type *add_id() const { return TypeD::ZERO; }

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

@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) 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
+ * 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 jdk.test.lib.Asserts;
+import compiler.lib.ir_framework.*;
+import java.util.Random;
+import jdk.test.lib.Utils;
+
+/*
+ * @test
+ * @bug 8291336
+ * @summary Test that transformation of multiply-by-2 is appropriately turned into additions.
+ * @library /test/lib /
+ * @requires vm.compiler2.enabled
+ * @run driver compiler.c2.irTests.TestMulNodeIdealization
+ */
+public class TestMulNodeIdealization {
+    private static final Random RANDOM = Utils.getRandomInstance();
+
+    public static void main(String[] args) {
+        TestFramework.run();
+    }
+
+    @Test
+    @IR(failOn = {IRNode.MUL})
+    // Checks x * 2 -> x + x
+    public float testFloat(float x) {
+        return x * 2;
+    }
+
+    @Test
+    @IR(failOn = {IRNode.MUL})
+    // Checks x * 2 -> x + x
+    public double testDouble(double x) {
+        return x * 2;
+    }
+
+    @Run(test = "testFloat")
+    public void runTestFloat() {
+        float value = RANDOM.nextFloat();
+        float interpreterResult = value * 2;
+        Asserts.assertEQ(testFloat(value), interpreterResult);
+    }
+
+    @Run(test = "testDouble")
+    public void runTestDouble() {
+        double value = RANDOM.nextDouble();
+        double interpreterResult = value * 2;
+        Asserts.assertEQ(testDouble(value), interpreterResult);
+    }
+}

test/micro/org/openjdk/bench/vm/compiler/MulNodeIdealize.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright (c) 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
+ * 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 org.openjdk.bench.vm.compiler;
+
+import org.openjdk.jmh.annotations.*;
+import org.openjdk.jmh.infra.Blackhole;
+
+import java.util.concurrent.TimeUnit;
+
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@Measurement(iterations = 5, time = 1000, timeUnit = TimeUnit.MILLISECONDS)
+@Warmup(iterations = 5, time = 1000, timeUnit = TimeUnit.MILLISECONDS)
+@Fork(3)
+public class MulNodeIdealize {
+    private static final int SIZE = 50;
+
+    @Benchmark
+    public void testMul2Float(Blackhole blackhole) {
+        for (float i = 0; i < SIZE; i++) {
+            blackhole.consume(i * 2);
+        }
+    }
+
+    @Benchmark
+    public void testMul2Double(Blackhole blackhole) {
+        for (double i = 0; i < SIZE; i++) {
+            blackhole.consume(i * 2);
+        }
+    }
+}