Optimize Math.Pow(x, c) where c is 2, 1, -1 or 0

src/coreclr/src/jit/morph.cpp

@@ -12255,8 +12255,8 @@ GenTree* Compiler::fgMorphSmpOp(GenTree* tree, MorphAddrContext* mac)
         case GT_RUNTIMELOOKUP:
             return fgMorphTree(op1);
 
-#ifdef TARGET_ARM
         case GT_INTRINSIC:
+#ifdef TARGET_ARM
             if (tree->AsIntrinsic()->gtIntrinsicName == NI_System_Math_Round)
             {
                 switch (tree->TypeGet())
@@ -12268,9 +12268,37 @@ GenTree* Compiler::fgMorphSmpOp(GenTree* tree, MorphAddrContext* mac)
                     default:
                         unreached();
                 }
+                break;
             }
-            break;
 #endif
+            if ((tree->AsIntrinsic()->gtIntrinsicName == NI_System_Math_Pow) && op2->IsCnsFltOrDbl())
+            {
+                double power = op2->AsDblCon()->gtDconVal;
+                if (power == 1.0)
+                {
+                    // Math.Pow(x, 1) -> x
+                    return op1;
+                }
+                if (power == 2.0)
+                {
+                    // Math.Pow(x, 2) -> x*x
+                    if (op1->OperIsLeaf() || optValnumCSE_phase)
+                    {
+                        GenTree* arg0Clone = op1;
+                        if (!op1->OperIsLeaf())
+                        {
+                            // if op1 is not a leaf op we need to introduce a variable
+                            // and it should be done after LoopHoisting phase
+                            arg0Clone = fgMakeMultiUse(&op1);
+                        }
+                        tree = gtNewOperNode(GT_MUL, tree->TypeGet(), op1, gtCloneExpr(arg0Clone));
+                        INDEBUG(tree->gtDebugFlags |= GTF_DEBUG_NODE_MORPHED);
+                        return tree;
+                    }
+                }
+            }
+            break;
+
         case GT_LIST:
             // Special handling for the arg list.
             return fgMorphArgList(tree->AsArgList(), mac);

src/coreclr/tests/src/JIT/Directed/intrinsic/pow/pow_cns.cs

@@ -0,0 +1,209 @@
+using System;
+using System.Runtime.CompilerServices;
+
+class MathPowTests
+{
+    static int returnCode = 100;
+
+    static int Main(string[] args)
+    {
+        var tests = new MathPowTests();
+        tests.TestCorrectnessDouble();
+        tests.TestCorrectnessFloat();
+        tests.TestFieldArg();
+        tests.TestCallArg1();
+        tests.TestCallArgN1();
+        tests.TestCallArg2();
+        tests.TestWithInlining();
+
+        float x = 0, y = 0;
+        tests.TestRefArgs(ref x, ref y);
+        return returnCode;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public static T ToVar<T>(T arg) => arg;
+
+    public static void AssertEquals(double arg, double a, double b, [CallerLineNumber] int line = 0)
+    {
+        if (BitConverter.DoubleToInt64Bits(a) !=
+            BitConverter.DoubleToInt64Bits(b))
+        {
+            returnCode++;
+            Console.WriteLine($"Failed: {a} != {b}, ({BitConverter.DoubleToInt64Bits(a):X} != {BitConverter.DoubleToInt64Bits(b):X}), arg={arg} ({BitConverter.DoubleToInt64Bits(arg):X}) line:{line}");
+        }
+    }
+
+    public static void AssertEquals(float arg, float a, float b, [CallerLineNumber] int line = 0)
+    {
+        if (BitConverter.SingleToInt32Bits(a) !=
+            BitConverter.SingleToInt32Bits(b))
+        {
+            returnCode++;
+            Console.WriteLine($"Failed: {a} != {b}, ({BitConverter.SingleToInt32Bits(a):X} != {BitConverter.SingleToInt32Bits(b):X}), arg={arg} ({BitConverter.SingleToInt32Bits(arg):X}) line:{line}");
+        }
+    }
+
+    private double[] testDblValues =
+        {
+            -1000, -2, -1, -0.0, 0, 1, 2, 1000,
+            Math.PI, Math.E,
+            double.MinValue, double.MaxValue,
+            double.PositiveInfinity, double.NegativeInfinity
+        };
+
+    public void TestCorrectnessDouble()
+    {
+        foreach (double testValue in testDblValues)
+        {
+            AssertEquals(testValue, Math.Pow(testValue, 0.0), Math.Pow(testValue, ToVar(0.0)));
+            AssertEquals(testValue, Math.Pow(testValue, -0.0), Math.Pow(testValue, ToVar(-0.0)));
+            AssertEquals(testValue, Math.Pow(testValue, 1.0), Math.Pow(testValue, ToVar(1.0)));
+            AssertEquals(testValue, Math.Pow(testValue, -1.0), Math.Pow(testValue, ToVar(-1.0)));
+            AssertEquals(testValue, Math.Pow(testValue, 2.0), Math.Pow(testValue, ToVar(2.0)));
+            AssertEquals(testValue, Math.Pow(testValue, 3.0), Math.Pow(testValue, ToVar(3.0)));
+            AssertEquals(testValue, Math.Pow(testValue, 4.0), Math.Pow(testValue, ToVar(4.0)));
+        }
+    }
+
+    private float[] testFltValues =
+        {
+            -1000, -2, -1, -0.0f, 0, 1, 2, 1000,
+            MathF.PI, MathF.E,
+            float.MinValue, float.MaxValue,
+            float.PositiveInfinity, float.NegativeInfinity
+        };
+
+    public void TestCorrectnessFloat()
+    {
+        foreach (float testValue in testFltValues)
+        {
+            AssertEquals(testValue, MathF.Pow(testValue, 0.0f), MathF.Pow(testValue, ToVar(0.0f)));
+            AssertEquals(testValue, MathF.Pow(testValue, -0.0f), MathF.Pow(testValue, ToVar(-0.0f)));
+            AssertEquals(testValue, MathF.Pow(testValue, 1.0f), MathF.Pow(testValue, ToVar(1.0f)));
+            AssertEquals(testValue, MathF.Pow(testValue, -1.0f), MathF.Pow(testValue, ToVar(-1.0f)));
+            AssertEquals(testValue, MathF.Pow(testValue, 2.0f), MathF.Pow(testValue, ToVar(2.0f)));
+            AssertEquals(testValue, MathF.Pow(testValue, 3.0f), MathF.Pow(testValue, ToVar(3.0f)));
+            AssertEquals(testValue, MathF.Pow(testValue, 4.0f), MathF.Pow(testValue, ToVar(4.0f)));
+        }
+    }
+
+
+    private float testField1 = MathF.PI;
+    private float testField2 = MathF.PI;
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public void TestFieldArg()
+    {
+        AssertEquals(testField1, MathF.Pow(testField1, 2.0f), MathF.Pow(testField2, ToVar(2.0f)));
+    }
+
+
+    private int sideeffects = 0;
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private double TestCall1()
+    {
+        sideeffects++;
+        return Math.PI;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private double TestCall2() => Math.PI;
+
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public void TestCallArg1()
+    {
+        sideeffects = 0;
+        AssertEquals(Math.PI, Math.Pow(TestCall1(), 1.0), Math.Pow(TestCall2(), ToVar(1.0)));
+        if (sideeffects != 1)
+            returnCode++;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public void TestCallArgN1()
+    {
+        sideeffects = 0;
+        AssertEquals(Math.PI, Math.Pow(TestCall1(), -1.0), Math.Pow(TestCall2(), ToVar(-1.0)));
+        if (sideeffects != 1)
+            returnCode++;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public void TestCallArg2()
+    {
+        sideeffects = 0;
+        AssertEquals(Math.PI, Math.Pow(TestCall1(), 2.0), Math.Pow(TestCall2(), ToVar(2.0)));
+        // make sure it's not optimized into
+        // `TestCall1() * TestCall1()`:
+        if (sideeffects != 1)
+            returnCode++;
+    }
+
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public void TestRefArgs(ref float x, ref float y)
+    {
+        AssertEquals(x, Math.Pow(x, 2.0), Math.Pow(y, ToVar(2.0)));
+    }
+
+
+    // inlining tests
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public float InlineablePow0(float x, float y) => MathF.Pow(x, y);
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public float InlineablePow1(float x, float y) => MathF.Pow(x, y + 1.0f);
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public float InlineablePow2(float x, float y) => MathF.Pow(x, y + 2.0f);
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public float NonInlineablePow0(float x, float y) => MathF.Pow(x, y);
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public float NonInlineablePow1(float x, float y) => MathF.Pow(x, y + 1.0f);
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public float NonInlineablePow2(float x, float y) => MathF.Pow(x, y + 2.0f);
+
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public bool Test0(float x) =>
+        BitConverter.SingleToInt32Bits(InlineablePow0(x, 2.0f)) ==
+        BitConverter.SingleToInt32Bits(NonInlineablePow0(x, 2.0f));
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public bool Test0_1(float x) =>
+        BitConverter.SingleToInt32Bits(InlineablePow0(x, 1.0f)) ==
+        BitConverter.SingleToInt32Bits(NonInlineablePow0(x, 1.0f));
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public bool Test1(float x) =>
+        BitConverter.SingleToInt32Bits(InlineablePow1(x, 1.0f)) ==
+        BitConverter.SingleToInt32Bits(NonInlineablePow1(x, 1.0f));
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public bool Test1_1(float x) =>
+        BitConverter.SingleToInt32Bits(InlineablePow1(x, 2.0f)) ==
+        BitConverter.SingleToInt32Bits(NonInlineablePow1(x, 2.0f));
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public bool Test2(float x) =>
+        BitConverter.SingleToInt32Bits(InlineablePow2(x, -0.0f)) ==
+        BitConverter.SingleToInt32Bits(NonInlineablePow2(x, -0.0f));
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public bool Test2_1(float x) =>
+        BitConverter.SingleToInt32Bits(InlineablePow2(x, 0.0f)) ==
+        BitConverter.SingleToInt32Bits(NonInlineablePow2(x, 0.0f));
+
+    public void TestWithInlining()
+    {
+        foreach (float value in testFltValues)
+        {
+            if (!Test0(value) || !Test0_1(value) || !Test1(value) ||
+                !Test1_1(value) || !Test2(value) || !Test2_1(value))
+            {
+                returnCode++;
+            }
+        }
+    }
+}

src/coreclr/tests/src/JIT/Directed/intrinsic/pow/pow_cns_r.csproj

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

src/coreclr/tests/src/JIT/Directed/intrinsic/pow/pow_cns_ro.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="pow_cns.cs" />
+  </ItemGroup>
+</Project>