Handle multiple calling conventions at once

Author: ds5678

ICSharpCode.Decompiler.Tests/TestCases/Pretty/FunctionPointers.cs

@@ -129,6 +129,32 @@ static void LocalFunction()
 			}
 		}
 
+		public unsafe delegate* unmanaged[Cdecl, Fastcall]<void> AddressOfLocalFunction_CDeclAndFastcall()
+		{
+			return &LocalFunction;
+
+			[UnmanagedCallersOnly(CallConvs = new Type[] {
+				typeof(CallConvCdecl),
+				typeof(CallConvFastcall)
+			})]
+			static void LocalFunction()
+			{
+			}
+		}
+
+		public unsafe delegate* unmanaged[Fastcall, Cdecl]<void> AddressOfLocalFunction_FastcallAndCDecl()
+		{
+			return &LocalFunction;
+
+			[UnmanagedCallersOnly(CallConvs = new Type[] {
+				typeof(CallConvFastcall),
+				typeof(CallConvCdecl)
+			})]
+			static void LocalFunction()
+			{
+			}
+		}
+
 #if NET60
 		public unsafe delegate* unmanaged[Cdecl, SuppressGCTransition]<void> AddressOfLocalFunction_CDeclAndSuppressGCTransition()
 		{

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -4611,7 +4611,7 @@ protected internal override TranslatedExpression VisitLdFtn(LdFtn inst, Translat
 					var builder = ImmutableArray.CreateBuilder<IType>(array.Length);
 					foreach (var type in array.Select(a => a.Value).OfType<IType>())
 					{
-						SignatureCallingConvention? foundCallingConvention = type.Namespace is not "System.Runtime.CompilerServices" ? null : type.Name switch {
+						SignatureCallingConvention? foundCallingConvention = type.Namespace is not "System.Runtime.CompilerServices" || callingConvention != SignatureCallingConvention.Unmanaged ? null : type.Name switch {
 							"CallConvCdecl" => SignatureCallingConvention.CDecl,
 							"CallConvFastcall" => SignatureCallingConvention.FastCall,
 							"CallConvStdcall" => SignatureCallingConvention.StdCall,

ICSharpCode.Decompiler/TypeSystem/FunctionPointerType.cs

@@ -46,23 +46,30 @@ public static FunctionPointerType FromSignature(MethodSignature<IType> signature
 					&& modReturn.Modifier.Namespace == "System.Runtime.CompilerServices")
 				{
 					returnType = modReturn.ElementType;
-					switch (modReturn.Modifier.Name)
+					if (callingConvention == SignatureCallingConvention.Unmanaged)
 					{
-						case "CallConvCdecl":
-							callingConvention = SignatureCallingConvention.CDecl;
-							break;
-						case "CallConvFastcall":
-							callingConvention = SignatureCallingConvention.FastCall;
-							break;
-						case "CallConvStdcall":
-							callingConvention = SignatureCallingConvention.StdCall;
-							break;
-						case "CallConvThiscall":
-							callingConvention = SignatureCallingConvention.ThisCall;
-							break;
-						default:
-							customCallConvs.Add(modReturn.Modifier);
-							break;
+						switch (modReturn.Modifier.Name)
+						{
+							case "CallConvCdecl":
+								callingConvention = SignatureCallingConvention.CDecl;
+								break;
+							case "CallConvFastcall":
+								callingConvention = SignatureCallingConvention.FastCall;
+								break;
+							case "CallConvStdcall":
+								callingConvention = SignatureCallingConvention.StdCall;
+								break;
+							case "CallConvThiscall":
+								callingConvention = SignatureCallingConvention.ThisCall;
+								break;
+							default:
+								customCallConvs.Add(modReturn.Modifier);
+								break;
+						}
+					}
+					else
+					{
+						customCallConvs.Add(modReturn.Modifier);
 					}
 				}
 				else