Handle SIMD8/LONG recasts for LCL_FLD

Lowering needs to insert a `BITCAST` in the case of a `STORE_LCL_FLD` with mismatched `TYP_SIMD8`/`TYP_LONG` operands, just as for `STORE_LCL_VAR`.

src/jit/lower.cpp

@@ -276,8 +276,12 @@ GenTree* Lowering::LowerNode(GenTree* node)
             break;
 
         case GT_STORE_LCL_VAR:
-#if defined(_TARGET_AMD64_) && defined(FEATURE_SIMD)
+            WidenSIMD12IfNecessary(node->AsLclVarCommon());
+            __fallthrough;
+
+        case GT_STORE_LCL_FLD:
         {
+#if defined(_TARGET_AMD64_) && defined(FEATURE_SIMD)
             GenTreeLclVarCommon* const store = node->AsLclVarCommon();
             if ((store->TypeGet() == TYP_SIMD8) != (store->gtOp1->TypeGet() == TYP_SIMD8))
             {
@@ -286,12 +290,7 @@ GenTree* Lowering::LowerNode(GenTree* node)
                 store->gtOp1 = bitcast;
                 BlockRange().InsertBefore(store, bitcast);
             }
-        }
 #endif // _TARGET_AMD64_
-            WidenSIMD12IfNecessary(node->AsLclVarCommon());
-            __fallthrough;
-
-        case GT_STORE_LCL_FLD:
             // TODO-1stClassStructs: Once we remove the requirement that all struct stores
             // are block stores (GT_STORE_BLK or GT_STORE_OBJ), here is where we would put the local
             // store under a block store if codegen will require it.
@@ -306,6 +305,7 @@ GenTree* Lowering::LowerNode(GenTree* node)
             }
             LowerStoreLoc(node->AsLclVarCommon());
             break;
+        }
 
 #ifdef _TARGET_ARM64_
         case GT_CMPXCHG:

tests/src/JIT/Regression/JitBlue/DevDiv_590358/DevDiv_590358.cs

@@ -0,0 +1,49 @@
+using System;
+using System.Numerics;
+
+// In this test case, we have a struct S that contains a single Vector2 field (Vector),
+// with an implicit conversion from an array of float to S.
+// We inline a call to this op_Implicit, and then the constructor that it invokes.
+// The op_Implicit RET_EXPR is TYP_LONG, since that's how the value is returned from the method.
+// It is then stored to the Vector field which is TYP_SIMD8.
+//
+// Bug: The JIT had code to deal with this kind of retyping (which must be made explicit by
+//      Lowering, as the two types require different register types), when it involves locals
+//      (GT_LCL_VAR) but not fields of locals (GT_LCL_FLD).
+//
+// Perf Issue: What we wind up with is this: (V05 & V07 are both TYP_SIMD8, V01 is the struct type S
+//          V05 = *(TYP_SIMD8)numbers
+//          V07 = V05
+//          LCL_FLD(V01) = LCL_FLD(V07)  // Both re-typed as TYP_LONG
+// This generates:
+//          vmovsd   xmm0, qword ptr [rax+16]
+//          vmovsd   qword ptr[rsp + 28H], xmm0
+//          vmovsd   xmm0, qword ptr[rsp + 28H]
+//          vmovsd   qword ptr[rsp + 20H], xmm0
+//          vmovsd   xmm0, qword ptr[rsp + 20H]
+//          vmovsd   qword ptr[rsp + 30H], xmm0
+//
+// We should be able to elide these excessive copies and unnecessary retyping, producing close to this:
+//          vmovsd   xmm0, qword ptr [rax+16]
+//          vmovsd   qword ptr[rsp + 30H], xmm0
+
+namespace Repro
+{
+    class Program
+    {
+	    struct S
+	    {
+	        public Vector2 Vector;
+	        public S(float[] numbers)
+	        {
+		        Vector = new Vector2(numbers[0], numbers[1]);
+	        }
+	        public static implicit operator S(float[] numbers) => new S(numbers);
+	    }
+	    static void Main(string[] args)
+	    {
+	        S s = new float[] { 1.0f, 2.0f };
+	        Console.WriteLine(s.Vector);
+	    }
+    }
+}

tests/src/JIT/Regression/JitBlue/DevDiv_590358/DevDiv_590358.csproj

@@ -0,0 +1,37 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="12.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.props))\dir.props" />
+  <PropertyGroup>
+    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
+    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
+    <AssemblyName>$(MSBuildProjectName)</AssemblyName>
+    <SchemaVersion>2.0</SchemaVersion>
+    <ProjectGuid>{95DFC527-4DC1-495E-97D7-E94EE1F7140D}</ProjectGuid>
+    <OutputType>Exe</OutputType>
+    <ProjectTypeGuids>{786C830F-07A1-408B-BD7F-6EE04809D6DB};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
+    <SolutionDir Condition="$(SolutionDir) == '' Or $(SolutionDir) == '*Undefined*'">..\..\</SolutionDir>
+  </PropertyGroup>
+  <!-- Default configurations to help VS understand the configurations -->
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
+  </PropertyGroup>
+  <ItemGroup>
+    <CodeAnalysisDependentAssemblyPaths Condition=" '$(VS100COMNTOOLS)' != '' " Include="$(VS100COMNTOOLS)..\IDE\PrivateAssemblies">
+      <Visible>False</Visible>
+    </CodeAnalysisDependentAssemblyPaths>
+  </ItemGroup>
+  <PropertyGroup>
+    <DebugType></DebugType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />
+  </ItemGroup>
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.targets))\dir.targets" />
+  <PropertyGroup Condition=" '$(MsBuildProjectDirOverride)' != '' ">
+  </PropertyGroup> 
+</Project>