Replace nested signature indices by TypeSignature type

src/coreclr/System.Private.CoreLib/System.Private.CoreLib.csproj

@@ -190,7 +190,6 @@
     <Compile Include="$(BclSourcesRoot)\System\Reflection\Metadata\MetadataUpdater.cs" />
     <Compile Include="$(BclSourcesRoot)\System\Reflection\MethodBase.CoreCLR.cs" />
     <Compile Include="$(BclSourcesRoot)\System\Reflection\MethodInvoker.CoreCLR.cs" />
-    <Compile Include="$(BclSourcesRoot)\System\Reflection\ModifiedFunctionPointerType.CoreCLR.cs" />
     <Compile Include="$(BclSourcesRoot)\System\Reflection\ModifiedType.CoreCLR.cs" />
     <Compile Include="$(BclSourcesRoot)\System\Reflection\RtFieldInfo.cs" />
     <Compile Include="$(BclSourcesRoot)\System\Reflection\RuntimeAssembly.cs" />

src/coreclr/System.Private.CoreLib/src/System/Reflection/ModifiedType.CoreCLR.cs

@@ -5,47 +5,31 @@ namespace System.Reflection
 {
     internal partial class ModifiedType
     {
-        /// <summary>
-        /// Called from FieldInfo, PropertyInfo and ParameterInfo to create a modified type tree.
-        /// </summary>
-        public static ModifiedType CreateRoot(
-            Type unmodifiedType,
-            object? signatureProvider,
-            int rootSignatureParameterIndex)
+        internal struct TypeSignature
         {
-            int nestedSignatureIndex = -1;
-            return Create(
-                unmodifiedType,
-                signatureProvider,
-                rootSignatureParameterIndex,
-                ref nestedSignatureIndex,
-                nestedSignatureParameterIndex: -1,
-                isRoot: true);
+            internal Signature? _signature;
+            internal int _offset;
         }
 
-        private Type[] GetCustomModifiers(bool required)
-        {
-            Type[] modifiers = EmptyTypes;
-            Signature? signature = GetSignature();
-            if (signature is not null)
+        internal Type GetTypeParameter(Type unmodifiedType, int index) =>
+            Create(unmodifiedType, new TypeSignature()
             {
-                if (IsRoot)
-                {
-                    // For a root node, which is the original field\parameter\property Type, get the root-level modifiers.
-                    modifiers = signature.GetCustomModifiers(RootSignatureParameterIndex, required);
-                }
-                else if (NestedSignatureParameterIndex >= 0)
-                {
-                    modifiers = signature.GetCustomModifiers(RootSignatureParameterIndex, required, NestedSignatureIndex, NestedSignatureParameterIndex);
-                }
-            }
+                _signature = _typeSignature._signature,
+                _offset = _typeSignature._signature?.GetTypeParameterFromOffset(_typeSignature._offset, index) ?? 0
+            });
 
-            return modifiers;
-        }
+        internal SignatureCallingConvention GetCallingConventionFromFunctionPointer() =>
+            _typeSignature._signature?.GetCallingConventionFromFunctionPointerAtOffset(_typeSignature._offset) ?? default;
 
-        internal Signature? GetSignature()
-        {
-            return (Signature?)SignatureProvider; // Signature is a CoreClr-specific class.
-        }
+        internal static Type Create(Type unmodifiedType, Signature? signature, int parameterIndex = 0) =>
+            Create(unmodifiedType, new TypeSignature()
+            {
+                _signature = signature,
+                _offset = signature?.GetParameterOffset(parameterIndex) ?? 0
+            });
+
+        private Type[] GetCustomModifiers(bool required) =>
+             (_typeSignature._signature != null) ?
+                _typeSignature._signature.GetCustomModifiersAtOffset(_typeSignature._offset, required) : Type.EmptyTypes;
     }
 }

src/coreclr/System.Private.CoreLib/src/System/Reflection/RtFieldInfo.cs

@@ -268,7 +268,7 @@ public override Type[] GetOptionalCustomModifiers()
         internal Signature GetSignature() => new Signature(this, m_declaringType);
 
         public override Type GetModifiedFieldType() =>
-            ModifiedType.CreateRoot(FieldType, GetSignature(), rootSignatureParameterIndex: 1);
+            ModifiedType.Create(FieldType, GetSignature());
         #endregion
     }
 }

src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeParameterInfo.cs

@@ -441,10 +441,7 @@ public override Type[] GetOptionalCustomModifiers()
         }
 
         public override Type GetModifiedParameterType() =>
-            ModifiedType.CreateRoot(
-                unmodifiedType: ParameterType,
-                m_signature,
-                rootSignatureParameterIndex: PositionImpl + 1);
+            ModifiedType.Create(unmodifiedType: ParameterType, m_signature, parameterIndex: PositionImpl + 1);
 
         #endregion
 

src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimePropertyInfo.cs

@@ -205,10 +205,7 @@ public override Type[] GetOptionalCustomModifiers()
             return Signature.GetCustomModifiers(0, false);
         }
 
-        public override Type GetModifiedPropertyType() => ModifiedType.CreateRoot(
-            PropertyType,
-            Signature,
-            rootSignatureParameterIndex: 0);
+        public override Type GetModifiedPropertyType() => ModifiedType.Create(PropertyType, Signature);
 
         internal object GetConstantValue(bool raw)
         {

src/coreclr/System.Private.CoreLib/src/System/RuntimeHandles.cs

@@ -1634,14 +1634,20 @@ public Signature(void* pCorSig, int cCorSig, RuntimeType declaringType)
         [MethodImpl(MethodImplOptions.InternalCall)]
         internal static extern bool CompareSig(Signature sig1, Signature sig2);
 
+        internal Type[] GetCustomModifiers(int parameterIndex, bool required) =>
+            GetCustomModifiersAtOffset(GetParameterOffset(parameterIndex), required);
+
+        [MethodImpl(MethodImplOptions.InternalCall)]
+        internal extern int GetParameterOffset(int parameterIndex);
+
         [MethodImpl(MethodImplOptions.InternalCall)]
-        internal extern Type[] GetCustomModifiers(int rootSignatureParameterIndex, bool required, int nestedSignatureIndex = -1, int nestedSignatureParameterIndex = -1);
+        internal extern int GetTypeParameterFromOffset(int offset, int index);
 
         [MethodImpl(MethodImplOptions.InternalCall)]
-        internal extern byte GetCallingConventionFromFunctionPointer(int rootSignatureParameterIndex, int nestedSignatureIndex);
+        internal extern SignatureCallingConvention GetCallingConventionFromFunctionPointerAtOffset(int offset);
 
         [MethodImpl(MethodImplOptions.InternalCall)]
-        internal extern bool IsUnmanagedFunctionPointer();
+        internal extern Type[] GetCustomModifiersAtOffset(int offset, bool required);
         #endregion
     }
 

src/coreclr/System.Private.CoreLib/src/System/RuntimeType.CoreCLR.cs

@@ -3754,7 +3754,7 @@ public override Type[] GetFunctionPointerParameterTypes()
                 return EmptyTypes;
             }
 
-            return ModifiedType.CloneArray(parameters, 1);
+            return parameters.AsSpan(1).ToArray();
         }
 
         public override Type GetFunctionPointerReturnType()

src/coreclr/inc/sigparser.h

@@ -713,27 +713,16 @@ class SigParser
         // the arguments.
         //------------------------------------------------------------------------
         __checkReturn
-        HRESULT SkipMethodHeaderSignature(uint32_t *pcArgs);
+        HRESULT SkipMethodHeaderSignature(uint32_t *pcArgs, bool skipReturnType = true);
 
         //------------------------------------------------------------------------
         // Skip a sub signature (as immediately follows an ELEMENT_TYPE_FNPTR).
         //------------------------------------------------------------------------
         __checkReturn
         HRESULT SkipSignature();
 
-private:
-
-        __checkReturn
-        HRESULT MoveToSignature(uint32_t indexToFind, uint32_t* pCurrentIndex, bool* pIsFinished, CorElementType* pSignatureType);
-
 public:
 
-        //------------------------------------------------------------------------
-        // Move to the specified signature
-        //------------------------------------------------------------------------
-        __checkReturn
-        HRESULT MoveToSignature(uint32_t indexToFind, CorElementType* pSignatureType);
-
         //------------------------------------------------------------------------
         // Return pointer
         // PLEASE DON'T USE THIS.

src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <EmitCompilerGeneratedFiles>true</EmitCompilerGeneratedFiles>
   </PropertyGroup>
@@ -154,7 +154,6 @@
     <Compile Include="System\Reflection\Metadata\AssemblyExtensions.cs" />
     <Compile Include="System\Reflection\Metadata\MetadataUpdater.cs" />
     <Compile Include="System\Reflection\ModifiedType.NativeAot.cs" />
-    <Compile Include="System\Reflection\ModifiedFunctionPointerType.NativeAot.cs" />
     <Compile Include="System\Runtime\InteropServices\CriticalHandle.NativeAot.cs" />
     <Compile Include="System\Activator.NativeAot.cs" />
     <Compile Include="System\AppContext.NativeAot.cs" />

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/ModifiedType.NativeAot.cs

@@ -5,7 +5,15 @@ namespace System.Reflection
 {
     internal partial class ModifiedType
     {
+        internal struct TypeSignature
+        {
+        }
+
 #pragma warning disable IDE0060
+        internal Type GetTypeParameter(Type unmodifiedType, int index) => throw new NotSupportedException();
+
+        internal SignatureCallingConvention GetCallingConventionFromFunctionPointer() => throw new NotSupportedException();
+
         private Type[] GetCustomModifiers(bool required) => throw new NotSupportedException();
 #pragma warning restore IDE0060
     }