[mono][arm64] Fixed passing/receiving hfa structures with fixed buffers. (#90502)

Fixes https://github.com/dotnet/runtime/issues/90423.

src/mono/mono/mini/mini-arm64.c

@@ -28,6 +28,7 @@
 #include <mono/utils/mono-hwcap.h>
 #include <mono/metadata/abi-details.h>
 #include <mono/metadata/tokentype.h>
+#include <mono/metadata/marshal-shared.h>
 #include "llvm-intrinsics-types.h"
 
 #include "interp/interp.h"
@@ -1483,7 +1484,7 @@ is_hfa (MonoType *t, int *out_nfields, int *out_esize, int *field_offsets)
 	gpointer iter;
 	MonoClassField *field;
 	MonoType *ftype, *prev_ftype = NULL;
-	int i, nfields = 0;
+	int nfields = 0;
 
 	klass = mono_class_from_mono_type_internal (t);
 	iter = NULL;
@@ -1497,8 +1498,22 @@ is_hfa (MonoType *t, int *out_nfields, int *out_esize, int *field_offsets)
 			int nested_nfields, nested_esize;
 			int nested_field_offsets [16];
 
-			if (!is_hfa (ftype, &nested_nfields, &nested_esize, nested_field_offsets))
-				return FALSE;
+			MonoType *fixed_etype;
+			int fixed_len;
+			if (mono_marshal_shared_get_fixed_buffer_attr (field, &fixed_etype, &fixed_len)) {
+				if (fixed_etype->type != MONO_TYPE_R4 && fixed_etype->type != MONO_TYPE_R8)
+					return FALSE;
+				if (fixed_len > 16)
+					return FALSE;
+				nested_nfields = fixed_len;
+				nested_esize = fixed_etype->type == MONO_TYPE_R4 ? 4 : 8;
+				for (int i = 0; i < nested_nfields; ++i)
+					nested_field_offsets [i] = i * nested_esize;
+			} else {
+				if (!is_hfa (ftype, &nested_nfields, &nested_esize, nested_field_offsets))
+					return FALSE;
+			}
+
 			if (nested_esize == 4)
 				ftype = m_class_get_byval_arg (mono_defaults.single_class);
 			else
@@ -1506,7 +1521,7 @@ is_hfa (MonoType *t, int *out_nfields, int *out_esize, int *field_offsets)
 			if (prev_ftype && prev_ftype->type != ftype->type)
 				return FALSE;
 			prev_ftype = ftype;
-			for (i = 0; i < nested_nfields; ++i) {
+			for (int i = 0; i < nested_nfields; ++i) {
 				if (nfields + i < 4)
 					field_offsets [nfields + i] = field->offset - MONO_ABI_SIZEOF (MonoObject) + nested_field_offsets [i];
 			}

src/tests/JIT/Regression/JitBlue/Runtime_90423/Runtime_90423.cs

+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Runtime.CompilerServices;
+using System.Runtime.Intrinsics;
+using System.Runtime.Intrinsics.X86;
+using Xunit;
+
+using System;
+
+public class Runtime_90423
+{
+    public static BaconClass.BaconStruct foo;
+
+    [Fact]
+    public unsafe static int EntryPoint()
+    {
+        foo = BaconClass.GetBacon();
+            
+        for (int i = 0; i < BaconClass.BaconStruct.RESOLUTION; i++)
+        {
+            if (Math.Abs(foo.table[i] - BaconClass.foo.table[i]) > float.Epsilon)
+                return 101;
+        }
+        return 100;
+    }
+        
+    public class BaconClass
+    {
+        public unsafe struct BaconStruct
+        {
+            public float length;
+            public const int RESOLUTION = 5;
+            public fixed float table[RESOLUTION];
+        }
+        
+        public static BaconStruct foo;
+        
+        public unsafe static BaconStruct GetBacon()
+        {
+            const int resolution = BaconStruct.RESOLUTION;
+            var length = 1;
+            BaconStruct lut = new BaconStruct()
+            {
+                length = length
+            };
+            foo = new BaconStruct(){length = length};
+		
+            float[] bacon = new float[] { 1.1f, 1.2f, 1.3f, 1.4f, 1.5f };
+            for (int x = 0; x < BaconStruct.RESOLUTION; x++)
+            {
+                lut.table[x] = bacon[x];
+                foo.table[x] = bacon[x];
+            }
+            return lut;
+        }
+    }
+}

src/tests/JIT/Regression/JitBlue/Runtime_90423/Runtime_90423.csproj

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