Ensure Vector.Sum uses SSE3, rather than SSSE3, for floating-point

src/coreclr/jit/simdashwintrinsic.cpp

@@ -479,6 +479,27 @@ GenTree* Compiler::impSimdAsHWIntrinsicSpecial(NamedIntrinsic       intrinsic,
             }
             break;
         }
+
+        case NI_VectorT128_Sum:
+        {
+            // TODO-XArch-CQ: We could support this all the way down to SSE2 and that might be
+            // worthwhile so we can accelerate cases like byte/sbyte and long/ulong
+
+            if (varTypeIsFloating(simdBaseType))
+            {
+                if (!compOpportunisticallyDependsOn(InstructionSet_SSE3))
+                {
+                    // Floating-point types require SSE3.HorizontalAdd
+                    return nullptr;
+                }
+            }
+            else if (!compOpportunisticallyDependsOn(InstructionSet_SSSE3))
+            {
+                // Integral types require SSSE3.HorizontalAdd
+                return nullptr;
+            }
+            break;
+        }
 #endif // TARGET_XARCH
 
         default:
@@ -721,25 +742,22 @@ GenTree* Compiler::impSimdAsHWIntrinsicSpecial(NamedIntrinsic       intrinsic,
                 }
                 case NI_VectorT128_Sum:
                 {
-                    if (compOpportunisticallyDependsOn(InstructionSet_SSSE3))
-                    {
-                        GenTree* tmp;
-                        unsigned vectorLength = getSIMDVectorLength(simdSize, simdBaseType);
-                        int      haddCount    = genLog2(vectorLength);
 
-                        for (int i = 0; i < haddCount; i++)
-                        {
-                            op1 = impCloneExpr(op1, &tmp, clsHnd, (unsigned)CHECK_SPILL_ALL,
-                                               nullptr DEBUGARG("Clone op1 for Vector<T>.Sum"));
-                            op1 = gtNewSimdAsHWIntrinsicNode(simdType, op1, tmp, NI_SSSE3_HorizontalAdd,
-                                                             simdBaseJitType, simdSize);
-                        }
+                    GenTree* tmp;
+                    unsigned vectorLength = getSIMDVectorLength(simdSize, simdBaseType);
+                    int      haddCount    = genLog2(vectorLength);
 
-                        return gtNewSimdAsHWIntrinsicNode(retType, op1, NI_Vector128_ToScalar, simdBaseJitType,
-                                                          simdSize);
+                    NamedIntrinsic horizontalAdd =
+                        varTypeIsFloating(simdBaseType) ? NI_SSE3_HorizontalAdd : NI_SSSE3_HorizontalAdd;
+
+                    for (int i = 0; i < haddCount; i++)
+                    {
+                        op1 = impCloneExpr(op1, &tmp, clsHnd, (unsigned)CHECK_SPILL_ALL,
+                                           nullptr DEBUGARG("Clone op1 for Vector<T>.Sum"));
+                        op1 = gtNewSimdAsHWIntrinsicNode(simdType, op1, tmp, horizontalAdd, simdBaseJitType, simdSize);
                     }
 
-                    return nullptr;
+                    return gtNewSimdAsHWIntrinsicNode(retType, op1, NI_Vector128_ToScalar, simdBaseJitType, simdSize);
                 }
                 case NI_VectorT256_Sum:
                 {

src/tests/JIT/SIMD/VectorSum.cs

@@ -0,0 +1,77 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+//
+
+using System;
+using System.Numerics;
+using System.Runtime.Intrinsics.Arm;
+using System.Runtime.Intrinsics.X86;
+
+internal partial class VectorTest
+{
+    private const int Pass = 100;
+    private const int Fail = -1;
+
+    private class VectorSumTest<T> where T : struct, IComparable<T>, IEquatable<T>
+    {
+        public static int VectorSum(T a, T b)
+        {
+            Vector<T> A = new Vector<T>(a);
+            T B = Vector.Sum(A);
+
+            if (!(CheckValue<T>(B, b)))
+            {
+                return Fail;
+            }
+            return Pass;
+        }
+    }
+
+    private static int Main()
+    {
+        int returnVal = Pass;
+
+        if (VectorSumTest<float>.VectorSum(1, (float)Vector<float>.Count) != Pass) returnVal = Fail;
+        if (VectorSumTest<double>.VectorSum(1, (double)Vector<double>.Count) != Pass) returnVal = Fail;
+        if (VectorSumTest<int>.VectorSum(1, (int)Vector<int>.Count) != Pass) returnVal = Fail;
+        if (VectorSumTest<long>.VectorSum(1, (long)Vector<long>.Count) != Pass) returnVal = Fail;
+        if (VectorSumTest<ushort>.VectorSum(1, (ushort)Vector<ushort>.Count) != Pass) returnVal = Fail;
+        if (VectorSumTest<byte>.VectorSum(1, (byte)Vector<byte>.Count) != Pass) returnVal = Fail;
+        if (VectorSumTest<short>.VectorSum(-1, (short)(-Vector<short>.Count)) != Pass) returnVal = Fail;
+        if (VectorSumTest<sbyte>.VectorSum(-1, (sbyte)(-Vector<sbyte>.Count)) != Pass) returnVal = Fail;
+        if (VectorSumTest<uint>.VectorSum(0x41000000u, 0x41000000u * (uint)Vector<uint>.Count) != Pass) returnVal = Fail;
+        if (VectorSumTest<ulong>.VectorSum(0x4100000000000000ul, 0x4100000000000000ul * (uint)Vector<ulong>.Count) != Pass) returnVal = Fail;
+        if (VectorSumTest<nint>.VectorSum(1, (nint)Vector<nint>.Count) != Pass) returnVal = Fail;
+        if (VectorSumTest<nuint>.VectorSum(0x41000000u, 0x41000000u * (nuint)(uint)Vector<nuint>.Count) != Pass) returnVal = Fail;
+
+        JitLog jitLog = new JitLog();
+
+        if (Sse3.IsSupported || AdvSimd.IsSupported)
+        {
+            if (!jitLog.Check("Sum", "Single")) returnVal = Fail;
+            if (!jitLog.Check("Sum", "Double")) returnVal = Fail;
+        }
+
+        if (Ssse3.IsSupported || AdvSimd.IsSupported)
+        {
+            if (!jitLog.Check("Sum", "Int16")) returnVal = Fail;
+            if (!jitLog.Check("Sum", "Int32")) returnVal = Fail;
+            if (!jitLog.Check("Sum", "UInt16")) returnVal = Fail;
+            if (!jitLog.Check("Sum", "UInt32")) returnVal = Fail;
+        }
+
+        if (AdvSimd.IsSupported)
+        {
+            if (!jitLog.Check("Sum", "Byte")) returnVal = Fail;
+            if (!jitLog.Check("Sum", "Int64")) returnVal = Fail;
+            if (!jitLog.Check("Sum", "IntPtr")) returnVal = Fail;
+            if (!jitLog.Check("Sum", "SByte")) returnVal = Fail;
+            if (!jitLog.Check("Sum", "UInt64")) returnVal = Fail;
+            if (!jitLog.Check("Sum", "UIntPtr")) returnVal = Fail;
+        }
+
+        jitLog.Dispose();
+
+        return returnVal;
+    }
+}

src/tests/JIT/SIMD/VectorSum_r.csproj

@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+  </PropertyGroup>
+  <PropertyGroup>
+    <DebugType>None</DebugType>
+    <Optimize />
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="VectorSum.cs" />
+    <Compile Include="VectorUtil.cs" />
+  </ItemGroup>
+</Project>

src/tests/JIT/SIMD/VectorSum_ro.csproj

@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+  </PropertyGroup>
+  <PropertyGroup>
+    <DebugType>None</DebugType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="VectorSum.cs" />
+    <Compile Include="VectorUtil.cs" />
+  </ItemGroup>
+</Project>