RyuJIT: x*2 -> x+x; x*1 -> x (fp)

src/coreclr/src/jit/morph.cpp

@@ -13034,6 +13034,30 @@ GenTree* Compiler::fgMorphSmpOp(GenTree* tree, MorphAddrContext* mac)
                 op2 = tree->AsOp()->gtOp2;
             }
 
+            // See if we can fold floating point operations
+            if (varTypeIsFloating(tree->TypeGet()) && !optValnumCSE_phase)
+            {
+                if ((oper == GT_MUL) && !op1->IsCnsFltOrDbl() && op2->IsCnsFltOrDbl())
+                {
+                    if (op2->AsDblCon()->gtDconVal == 2.0)
+                    {
+                        // Fold "x*2.0" to "x+x"
+                        op2  = op1->OperIsLeaf() ? gtCloneExpr(op1) : fgMakeMultiUse(&tree->AsOp()->gtOp1);
+                        op1  = tree->AsOp()->gtOp1;
+                        oper = GT_ADD;
+                        tree = gtNewOperNode(oper, tree->TypeGet(), op1, op2);
+                        INDEBUG(tree->gtDebugFlags |= GTF_DEBUG_NODE_MORPHED);
+                    }
+                    else if (op2->AsDblCon()->gtDconVal == 1.0)
+                    {
+                        // Fold "x*1.0" to "x"
+                        DEBUG_DESTROY_NODE(op2);
+                        DEBUG_DESTROY_NODE(tree);
+                        return op1;
+                    }
+                }
+            }
+
             /* See if we can fold GT_ADD nodes. */
 
             if (oper == GT_ADD)

src/coreclr/tests/src/JIT/opt/InstructionCombining/MulToAdd.cs

@@ -0,0 +1,133 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Linq;
+using System.Runtime.CompilerServices;
+
+// Test "X * 2" to "X + X"
+
+public class Program
+{
+    private static int resultCode = 100;
+
+    public static int Main(string[] args)
+    {
+        float[] testValues =
+            {
+                0, 0.01f, 1.333f, 1/3.0f, 0.5f, 1, 2, 3, 4,
+                MathF.PI, MathF.E,
+                float.MinValue, float.MaxValue,
+                int.MaxValue, long.MaxValue,
+                int.MinValue, long.MinValue,
+                float.NegativeInfinity,
+                float.PositiveInfinity,
+                float.NaN,
+            };
+
+        testValues = testValues.Concat(testValues.Select(v => -v)).ToArray();
+
+        foreach (float testValue in testValues)
+        {
+            var tf = new TestFloats();
+
+            // Case 1: argument
+            AssertEquals(tf.TestArg(testValue), tf.TestArg_var(testValue));
+
+            // Case 2: ref argument
+            float t1 = testValue, t2 = testValue;
+            tf.TestArgRef(ref t1);
+            tf.TestArgRef_var(ref t2);
+            AssertEquals(t1, t2);
+
+            // Case 3: out argument
+            tf.TestArgOut(t1, out t1);
+            tf.TestArgOut_var(t2, out t2);
+            AssertEquals(t1, t2);
+
+            // Case 4: field
+            tf.TestField();
+            tf.TestField_var();
+            AssertEquals(tf.field1, tf.field2);
+
+            // Case 5: call
+            AssertEquals(tf.TestCall(), tf.TestCall_var());
+            AssertEquals(tf.field1, tf.field2);
+        }
+
+        return resultCode;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static void AssertEquals(float expected, float actual)
+    {
+        int expectedBits = BitConverter.SingleToInt32Bits(expected);
+        int actualBits = BitConverter.SingleToInt32Bits(actual);
+        if (expectedBits != actualBits)
+        {
+            resultCode++;
+            Console.WriteLine($"AssertEquals: {expected} != {actual}");
+        }
+    }
+}
+
+public class TestFloats
+{
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public static T Var<T>(T t) => t;
+
+
+    // Case 1: argument
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public float TestArg(float x) => x * 2;
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public float TestArg_var(float x) => x * Var(2);
+
+
+    // Case 2: ref argument
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public void TestArgRef(ref float x) => x *= 2;
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public void TestArgRef_var(ref float x) => x *= Var(2);
+
+
+    // Case 3: out argument
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public void TestArgOut(float x, out float y) => y = x * 2;
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public void TestArgOut_var(float x, out float y) => y = x * Var(2);
+
+
+    // Case 4: field
+
+    public float field1 = 3.14f;
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public void TestField() => field1 *= 2;
+
+    public float field2 = 3.14f;
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public void TestField_var() => field2 *= Var(2);
+
+
+    // Case 5: Call
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public float Call1() => field1++; // with side-effect
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public float Call2() => field2++; // with side-effect
+
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public float TestCall() => Call1() * 2;
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public float TestCall_var() => Call2() * Var(2);
+}

src/coreclr/tests/src/JIT/opt/InstructionCombining/MulToAdd.csproj

@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+  </PropertyGroup>
+  <PropertyGroup>
+    <DebugType>None</DebugType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="MulToAdd.cs" />
+  </ItemGroup>
+</Project>