Fix SIMD12 spills

src/coreclr/jit/codegenlinear.cpp

@@ -937,9 +937,20 @@ void CodeGen::genSpillVar(GenTree* tree)
         // but we will kill the var in the reg (below).
         if (!varDsc->IsAlwaysAliveInMemory())
         {
-            instruction storeIns = ins_Store(lclType, compiler->isSIMDTypeLocalAligned(varNum));
             assert(varDsc->GetRegNum() == tree->GetRegNum());
-            inst_TT_RV(storeIns, size, tree, tree->GetRegNum());
+#if defined(FEATURE_SIMD)
+            if ((lclType == TYP_SIMD12) && !compiler->lvaMapSimd12ToSimd16(varDsc))
+            {
+                // Store SIMD12 to stack as 12 bytes
+                GetEmitter()->emitStoreSimd12ToLclOffset(varNum, tree->AsLclVarCommon()->GetLclOffs(),
+                                                         tree->GetRegNum(), nullptr);
+            }
+            else
+#endif
+            {
+                instruction storeIns = ins_Store(lclType, compiler->isSIMDTypeLocalAligned(varNum));
+                inst_TT_RV(storeIns, size, tree, tree->GetRegNum());
+            }
         }
 
         // We should only have both GTF_SPILL (i.e. the flag causing this method to be called) and

src/coreclr/jit/emitxarch.cpp

@@ -5620,7 +5620,7 @@ void emitter::emitIns_R(instruction ins, emitAttr attr, regNumber reg)
 //     varNum         - the variable on the stack to use as a base;
 //     offset         - the offset from the varNum;
 //     dataReg        - the src reg with SIMD12 value;
-//     tmpRegProvider - a tree to grab a tmp reg from if needed.
+//     tmpRegProvider - a tree to grab a tmp reg from if needed (can be null).
 //
 void emitter::emitStoreSimd12ToLclOffset(unsigned varNum, unsigned offset, regNumber dataReg, GenTree* tmpRegProvider)
 {
@@ -5635,7 +5635,7 @@ void emitter::emitStoreSimd12ToLclOffset(unsigned varNum, unsigned offset, regNu
         // Extract and store upper 4 bytes
         emitIns_S_R_I(INS_extractps, EA_16BYTE, varNum, offset + 8, dataReg, 2);
     }
-    else
+    else if (tmpRegProvider != nullptr)
     {
         regNumber tmpReg = codeGen->internalRegisters.GetSingle(tmpRegProvider);
         assert(isFloatReg(tmpReg));
@@ -5646,6 +5646,19 @@ void emitter::emitStoreSimd12ToLclOffset(unsigned varNum, unsigned offset, regNu
         // Store upper 4 bytes
         emitIns_S_R(INS_movss, EA_4BYTE, tmpReg, varNum, offset + 8);
     }
+    else
+    {
+        // We don't have temp regs - let's do two shuffles then
+
+        // [0,1,2,3] -> [2,3,0,1]
+        emitIns_R_R_I(INS_pshufd, EA_16BYTE, dataReg, dataReg, 78);
+
+        //  Store upper 4 bytes
+        emitIns_S_R(INS_movss, EA_4BYTE, dataReg, varNum, offset + 8);
+
+        // Restore dataReg to its previous state: [2,3,0,1] -> [0,1,2,3]
+        emitIns_R_R_I(INS_pshufd, EA_16BYTE, dataReg, dataReg, 78);
+    }
 }
 #endif // FEATURE_SIMD
 

src/tests/JIT/Regression/JitBlue/Runtime_95043/Runtime_95043.cs

@@ -0,0 +1,37 @@
+// 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 Xunit;
+
+public unsafe class Runtime_95043
+{
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public static void Sweep(int ecx, int* edx, Vector3 stack12)
+    {
+        for (int i = 0; i < 5; i++)
+        {
+            Console.WriteLine(ecx);
+            if (ecx == -1)
+            {
+                ecx = edx[0];
+            }
+            else if (!float.IsNaN(stack12.X))
+            {
+                edx[0] = -1;
+                ecx = -1;
+            }
+        }
+    }
+
+    [Fact]
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public static void Test()
+    {
+        int x = 42;
+        Sweep(1, &x, Vector3.Zero);
+        Assert.Equal(-1, x);
+    }
+}

src/tests/JIT/Regression/JitBlue/Runtime_95043/Runtime_95043.csproj

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <Optimize>True</Optimize>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>