Fix typing of BlendVariableMask condition when optimizing TernaryLogic (#114837)

* Fix typing of BlendVariableMask condition when optimizing TernaryLogic

TernaryLogic nodes normalize small types to large types. When optimizing
a TernaryLogic node to a BlendVariableMask, if we leave the normalized
type, then the Blend uses the wrong instruction.

To fix this, change the Blend node to use the mask simd base type.
We only do this for mask base types that are small, which is
unsatisfying: there exists codegen today for double->int casts,
for example, that uses a 'double' type mask but an 'int' sized
TernaryLogic node. This works because we end up only using lane '0', as
the vector is converted to scalar. I didn't find any other case like
this, so hopefully if the mask type is small we can safely use it.

Fixes #114572

* Unconditionally set the base element type to the condition base element type

But only if the condition is a HW intrinsic.

Author: BruceForstall

src/coreclr/jit/lowerxarch.cpp

@@ -3875,6 +3875,20 @@ GenTree* Lowering::LowerHWIntrinsicTernaryLogic(GenTreeHWIntrinsic* node)
                 }
 
                 assert(varTypeIsMask(condition));
+
+                // The TernaryLogic node normalizes small SIMD base types on import. To optimize
+                // to BlendVariableMask, we need to "un-normalize". We no longer have the original
+                // base type, so we use the mask base type instead.
+                NamedIntrinsic intrinsicId = node->GetHWIntrinsicId();
+                assert(HWIntrinsicInfo::NeedsNormalizeSmallTypeToInt(intrinsicId));
+
+                if (!condition->OperIsHWIntrinsic())
+                {
+                    break;
+                }
+
+                node->SetSimdBaseJitType(condition->AsHWIntrinsic()->GetSimdBaseJitType());
+
                 node->ResetHWIntrinsicId(NI_EVEX_BlendVariableMask, comp, selectFalse, selectTrue, condition);
                 BlockRange().Remove(op4);
                 break;

src/tests/JIT/Regression/JitBlue/Runtime_114572/Runtime_114572.cs

@@ -0,0 +1,72 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+//
+// Generated by Fuzzlyn v2.5 on 2025-04-11 19:29:41
+// Run on X64 Windows
+// Seed: 557319528607462789-vectort,vector128,vector256,x86aes,x86avx,x86avx2,x86avx512bw,x86avx512bwvl,x86avx512cd,x86avx512cdvl,x86avx512dq,x86avx512dqvl,x86avx512f,x86avx512fvl,x86avx512fx64,x86bmi1,x86bmi1x64,x86bmi2,x86bmi2x64,x86fma,x86lzcnt,x86lzcntx64,x86pclmulqdq,x86popcnt,x86popcntx64,x86sse,x86ssex64,x86sse2,x86sse2x64,x86sse3,x86sse41,x86sse41x64,x86sse42,x86sse42x64,x86ssse3,x86x86base
+// Reduced from 41.1 KiB to 0.7 KiB in 00:01:23
+// Debug: Outputs <0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1>
+// Release: Outputs <0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1>
+
+using System;
+using System.Numerics;
+using System.Runtime.Intrinsics;
+using System.Runtime.Intrinsics.X86;
+using Xunit;
+
+public class Runtime_114572
+{
+    public static Vector256<ushort> s_2;
+    public static ushort s_4;
+    public static byte s_ub = 1;
+    public static ushort s_us = 1;
+
+    [Fact]
+    public static void Problem()
+    {
+        if (Avx512F.VL.IsSupported)
+        {
+            var vr11 = Vector256.Create<ushort>(0);
+            var vr12 = Vector256.Create<ushort>(1);
+            var vr13 = (ushort)0;
+            var vr14 = Vector256.CreateScalar(vr13);
+            var vr15 = (ushort)1;
+            var vr16 = Vector256.CreateScalar(vr15);
+            var vr17 = Vector256.Create<ushort>(s_4);
+            var vr18 = Avx2.Max(vr16, vr17);
+            s_2 = Avx512F.VL.TernaryLogic(vr11, vr12, Avx512BW.VL.CompareGreaterThanOrEqual(vr14, vr18), 216);
+            System.Console.WriteLine(s_2);
+            Assert.Equal(Vector256.Create((ushort)0, (ushort)1, (ushort)1, (ushort)1, (ushort)1, (ushort)1, (ushort)1, (ushort)1, (ushort)1, (ushort)1, (ushort)1, (ushort)1, (ushort)1, (ushort)1, (ushort)1, (ushort)1), s_2);
+        }
+    }
+
+    [Fact]
+    public static void Problem2()
+    {
+        if (Avx512F.VL.IsSupported)
+        {
+            var v0 = Vector128<ushort>.Zero;
+            var v1 = Vector128<ushort>.One;
+            var vs = Vector128.CreateScalar(s_us);
+
+            var vr = Avx512F.VL.TernaryLogic(v0, v1, Avx512BW.VL.CompareGreaterThanOrEqual(v0, vs), 0xE4);
+            Console.WriteLine(vr);
+            Assert.Equal(Vector128.Create((ushort)1, (ushort)0, (ushort)0, (ushort)0, (ushort)0, (ushort)0, (ushort)0, (ushort)0), vr);
+        }
+    }
+
+    [Fact]
+    public static void Problem3()
+    {
+        if (Avx512F.VL.IsSupported)
+        {
+            var v0 = Vector128<byte>.Zero;
+            var v1 = Vector128<byte>.One;
+            var vs = Vector128.CreateScalar(s_ub);
+
+            var vr = Avx512F.VL.TernaryLogic(v0, v1, Avx512BW.VL.CompareGreaterThanOrEqual(v0, vs), 0xE4);
+            Console.WriteLine(vr);
+            Assert.Equal(Vector128.Create((byte)1, (byte)0, (byte)0, (byte)0, (byte)0, (byte)0, (byte)0, (byte)0, (byte)0, (byte)0, (byte)0, (byte)0, (byte)0, (byte)0, (byte)0, (byte)0), vr);
+        }
+    }
+}

src/tests/JIT/Regression/JitBlue/Runtime_114572/Runtime_114572.csproj

@@ -0,0 +1,8 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>