Validate store-coalescing constants before modifying IR

src/coreclr/jit/lower.cpp

@@ -11434,6 +11434,28 @@ void Lowering::LowerStoreCoalescing(GenTree* node)
 
         assert(newType != TYP_UNDEF);
 
+        // Validate the constants before removing the previous store or widening the current one.
+        uint64_t lowerCns = 0;
+        uint64_t upperCns = 0;
+#if defined(TARGET_AMD64) && defined(FEATURE_HW_INTRINSICS)
+        // Only on x64 since ARM64 has no options above SIMD16.
+        if (varTypeIsSIMD(oldType))
+        {
+            if (!prevData.value->OperIs(GT_CNS_VEC) || !currData.value->OperIs(GT_CNS_VEC))
+            {
+                return;
+            }
+        }
+        else
+#endif // TARGET_AMD64 && FEATURE_HW_INTRINSICS
+        {
+            if (!TryGetStoreCoalescingConstantBits(prevData.value, &lowerCns) ||
+                !TryGetStoreCoalescingConstantBits(currData.value, &upperCns))
+            {
+                return;
+            }
+        }
+
         if (node->OperIs(GT_STOREIND, GT_STORE_BLK))
         {
             auto* ind     = node->AsStoreInd();
@@ -11487,11 +11509,6 @@ void Lowering::LowerStoreCoalescing(GenTree* node)
         // Only on x64 since ARM64 has no options above SIMD16.
         if (varTypeIsSIMD(oldType))
         {
-            if (!prevData.value->OperIs(GT_CNS_VEC) || !currData.value->OperIs(GT_CNS_VEC))
-            {
-                return;
-            }
-
             int8_t* lowerCns = prevData.value->AsVecCon()->gtSimdVal.i8;
             int8_t* upperCns = currData.value->AsVecCon()->gtSimdVal.i8;
 
@@ -11512,14 +11529,6 @@ void Lowering::LowerStoreCoalescing(GenTree* node)
 
         // The integer path below places each constant according to its byte offset, so it doesn't need to swap the
         // values first. Only the SIMD packing paths above need to normalize lower/upper order explicitly.
-        uint64_t lowerCns = 0;
-        uint64_t upperCns = 0;
-        if (!TryGetStoreCoalescingConstantBits(prevData.value, &lowerCns) ||
-            !TryGetStoreCoalescingConstantBits(currData.value, &upperCns))
-        {
-            return;
-        }
-
 #if defined(TARGET_64BIT) && defined(FEATURE_HW_INTRINSICS)
         if (varTypeIsSIMD(newType))
         {

src/tests/JIT/Regression_2/Runtime_133746/Runtime_133746.cs

@@ -0,0 +1,49 @@
+// 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.CompilerServices;
+using System.Runtime.Intrinsics;
+using Xunit;
+
+public class Runtime_133746
+{
+    [Fact]
+    [SkipLocalsInit]
+    public static void TestEntryPoint()
+    {
+        Vector2 pair = new Vector2(1.0f, -2.0f);
+        Unsafe.As<Vector2, sbyte>(ref pair) = -1;
+        ValidatePair(in pair);
+
+        Validate(Vector64.CreateScalar((sbyte)-1), (sbyte)-1);
+        Validate(Vector64.CreateScalar(sbyte.MinValue), sbyte.MinValue);
+        Validate(Vector64.CreateScalar(sbyte.MaxValue), sbyte.MaxValue);
+        Validate(Vector64.CreateScalar((short)-1), (short)-1);
+        Validate(Vector64.CreateScalar(short.MinValue), short.MinValue);
+        Validate(Vector64.CreateScalar(short.MaxValue), short.MaxValue);
+        Validate(Vector64.CreateScalar(-1), -1);
+        Validate(Vector64.CreateScalar(int.MinValue), int.MinValue);
+        Validate(Vector64.CreateScalar(int.MaxValue), int.MaxValue);
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static void ValidatePair(in Vector2 value)
+    {
+        int expected = BitConverter.IsLittleEndian ? 0x3F8000FF : unchecked((int)0xFF800000);
+        Assert.Equal(expected, BitConverter.SingleToInt32Bits(value.X));
+        Assert.Equal(-2.0f, value.Y);
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static void Validate<T>(in Vector64<T> value, T expected) where T : struct
+    {
+        Assert.Equal(expected, value.GetElement(0));
+
+        for (int i = 1; i < Vector64<T>.Count; i++)
+        {
+            Assert.Equal(default(T), value.GetElement(i));
+        }
+    }
+}

src/tests/JIT/Regression_2/Runtime_133746/Runtime_133746.csproj

@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <Optimize>True</Optimize>
+    <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
+    <CLRTestPriority>1</CLRTestPriority>
+    <RequiresProcessIsolation>true</RequiresProcessIsolation>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="Runtime_133746.cs" />
+    <CLRTestEnvironmentVariable Include="DOTNET_TieredCompilation" Value="0" />
+  </ItemGroup>
+</Project>

src/tests/JIT/Regression_2/Runtime_133746/Runtime_133746_nohw.csproj

@@ -0,0 +1,6 @@
+<Project>
+  <Import Project="Runtime_133746.csproj" />
+  <ItemGroup>
+    <CLRTestEnvironmentVariable Include="DOTNET_EnableHWIntrinsic" Value="0" />
+  </ItemGroup>
+</Project>