Ensure we don't reuse temps when calling fgMorphArgs on LIR nodes

src/coreclr/jit/rationalize.cpp

@@ -69,8 +69,9 @@ void Rationalizer::RewriteNodeAsCall(GenTree**             use,
         }
     }
 
-    CORINFO_ARG_LIST_HANDLE sigArg   = sig->args;
-    size_t                  firstArg = 0;
+    CORINFO_ARG_LIST_HANDLE sigArg       = sig->args;
+    size_t                  firstArg     = 0;
+    bool                    hasStructArg = false;
 
     if (sig->hasThis())
     {
@@ -117,7 +118,8 @@ void Rationalizer::RewriteNodeAsCall(GenTree**             use,
                 unreached();
 #endif // FEATURE_HW_INTRINSICS
             }
-            arg = NewCallArg::Struct(operand, sigTyp, clsHnd);
+            arg          = NewCallArg::Struct(operand, sigTyp, clsHnd);
+            hasStructArg = true;
         }
         else
         {
@@ -150,6 +152,12 @@ void Rationalizer::RewriteNodeAsCall(GenTree**             use,
         call->gtType = TYP_VOID;
     }
 
+    // We need to ensure we don't use any of the available outgoing arg temps
+    // as those were valid from a different scope. We do want to restore them
+    // back to what they were after we're done here. This is expected to be
+    // a rare scenario in the first place, so the allocation/copy isn't a big
+    // concern, but we still don't want to do it unnecessarily
+
     call = comp->fgMorphArgs(call);
 
     GenTree* result = call;

src/tests/JIT/Regression/JitBlue/Runtime_105468/Runtime_105468.cs

@@ -0,0 +1,45 @@
+// Generated by Fuzzlyn v1.7 on 2024-07-25 11:40:55
+// Run on X64 Windows
+// Seed: 418121815423725559-vectort,vector128,vector256,x86aes,x86avx,x86avx2,x86bmi1,x86bmi1x64,x86bmi2,x86bmi2x64,x86fma,x86lzcnt,x86lzcntx64,x86pclmulqdq,x86popcnt,x86popcntx64,x86sse,x86ssex64,x86sse2,x86sse2x64,x86sse3,x86sse41,x86sse41x64,x86sse42,x86sse42x64,x86ssse3,x86x86base
+// Reduced from 72.7 KiB to 1.0 KiB in 00:01:55
+// Debug: Outputs <0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0>
+// Release: Outputs <1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1>
+using System;
+using System.Runtime.CompilerServices;
+using System.Runtime.Intrinsics;
+using System.Runtime.Intrinsics.X86;
+using Xunit;
+
+[module: SkipLocalsInit]
+
+public struct S3
+{
+    public byte F0;
+}
+
+public class Runtime_105468
+{
+    public static S3 s_3;
+
+    [Fact]
+    public static void TestEntryPoint()
+    {
+        if (Avx2.IsSupported)
+        {
+            var vr15 = (ushort)0;
+            var vr16 = Vector256.CreateScalar(vr15);
+            var vr17 = Vector256.Create<ushort>(1);
+            var vr18 = (ushort)0;
+            var vr19 = Vector256.CreateScalar(vr18);
+            var vr20 = s_3.F0;
+            var vr21 = Avx2.AlignRight(vr17, vr19, vr20);
+            M6(vr16, vr21);
+        }
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static void M6(Vector256<ushort> arg1, Vector256<ushort> arg3)
+    {
+        Assert.Equal(Vector256<ushort>.Zero, arg1);
+    }
+}

src/tests/JIT/Regression/JitBlue/Runtime_105468/Runtime_105468.csproj

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