Merge pull request #4132 from icsharpcode/fix/3320-legacy-dynamic-await

Fix #3320: detect dynamic await in pre-Roslyn state machines

ICSharpCode.Decompiler.Tests/ILPrettyTestRunner.cs

@@ -51,6 +51,12 @@ namespace ICSharpCode.Decompiler.Tests
 			}
 		}
 
+		[Test]
+		public async Task Issue3320()
+		{
+			await Run();
+		}
+
 		[Test]
 		public async Task ConditionalChain()
 		{

ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs

@@ -525,7 +525,7 @@ namespace ICSharpCode.Decompiler.Tests
 		}
 
 		[Test]
-		public async Task DynamicAwait([ValueSource(nameof(roslynOnlyOptions))] CompilerOptions cscOptions)
+		public async Task DynamicAwait([ValueSource(nameof(defaultOptions))] CompilerOptions cscOptions)
 		{
 			await RunForLibrary(cscOptions: cscOptions);
 		}

ICSharpCode.Decompiler.Tests/TestCases/ILPretty/Issue3320.cs

@@ -0,0 +1,22 @@
+using System.Threading.Tasks;
+
+public interface IDapperAsyncImplementor
+{
+	Task<T> GetAsync<T>(IDbConnection connection, object id, IDbTransaction transaction, int? commandTimeout) where T : class;
+}
+public interface IDbConnection
+{
+}
+public interface IDbTransaction
+{
+}
+public static class Issue3320
+{
+	public static IDapperAsyncImplementor Instance => null;
+
+	public static async Task<T> GetAsync<T>(this IDbConnection connection, dynamic id, IDbTransaction transaction = null, int? commandTimeout = null) where T : class
+	{
+		dynamic async = Instance.GetAsync<T>(connection, id, transaction, commandTimeout);
+		return await async;
+	}
+}

ICSharpCode.Decompiler.Tests/TestCases/ILPretty/Issue3320.il

@@ -0,0 +1,508 @@
+.assembly extern mscorlib
+{
+  .publickeytoken = (B7 7A 5C 56 19 34 E0 89 )
+  .ver 4:0:0:0
+}
+.assembly extern System.Core
+{
+  .publickeytoken = (B7 7A 5C 56 19 34 E0 89 )
+  .ver 4:0:0:0
+}
+.assembly extern Microsoft.CSharp
+{
+  .publickeytoken = (B0 3F 5F 7F 11 D5 0A 3A )
+  .ver 4:0:0:0
+}
+.assembly Issue3320
+{
+  .hash algorithm 0x00008004
+  .ver 1:0:0:0
+}
+.module Issue3320.dll
+.imagebase 0x00400000
+.file alignment 0x00000200
+.stackreserve 0x00100000
+.subsystem 0x0003       // WINDOWS_CUI
+.corflags 0x00000001    //  ILONLY
+
+.class interface public abstract auto ansi IDbConnection
+{
+}
+
+.class interface public abstract auto ansi IDbTransaction
+{
+}
+
+.class interface public abstract auto ansi IDapperAsyncImplementor
+{
+	.method public hidebysig newslot abstract virtual
+		instance class [mscorlib]System.Threading.Tasks.Task`1<!!T> GetAsync<class T> (
+			class IDbConnection connection,
+			object id,
+			class IDbTransaction transaction,
+			valuetype [mscorlib]System.Nullable`1<int32> commandTimeout
+		) cil managed
+	{
+	}
+}
+
+.class public abstract auto ansi sealed beforefieldinit Issue3320
+	extends [mscorlib]System.Object
+{
+	.method public hidebysig specialname static
+		class IDapperAsyncImplementor get_Instance () cil managed
+	{
+		.maxstack 8
+
+		IL_0000: ldnull
+		IL_0001: ret
+	}
+
+	.property class IDapperAsyncImplementor Instance()
+	{
+		.get class IDapperAsyncImplementor Issue3320::get_Instance()
+	}
+
+	.class nested private auto ansi abstract sealed beforefieldinit '<GetAsync>o__SiteContainer6`1'<T>
+		extends [mscorlib]System.Object
+	{
+		.custom instance void [mscorlib]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = (
+			01 00 00 00
+		)
+		// Fields
+		.field public static class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, !T>> '<>p__Site7'
+		.field public static class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`7<class [System.Core]System.Runtime.CompilerServices.CallSite, class IDapperAsyncImplementor, class IDbConnection, object, class IDbTransaction, valuetype [mscorlib]System.Nullable`1<int32>, object>> '<>p__Site8'
+		.field public static class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>> '<>p__Site9'
+		.field public static class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, bool>> '<>p__Sitea'
+		.field public static class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>> '<>p__Siteb'
+		.field public static class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>> '<>p__Sitec'
+
+	} // end of class <GetAsync>o__SiteContainer6`1
+
+	.class nested private auto ansi sealed beforefieldinit '<GetAsync>d__d`1'<class T>
+		extends [mscorlib]System.ValueType
+		implements [mscorlib]System.Runtime.CompilerServices.IAsyncStateMachine
+	{
+		.custom instance void [mscorlib]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = (
+			01 00 00 00
+		)
+		// Fields
+		.field public int32 '<>1__state'
+		.field public valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<!T> '<>t__builder'
+		.field public class IDbConnection connection
+		.field public object id
+		.field public class IDbTransaction transaction
+		.field public valuetype [mscorlib]System.Nullable`1<int32> commandTimeout
+		.field private object '<>u__$awaitere'
+		.field private object '<>t__stack'
+
+		// Methods
+		.method private final hidebysig newslot virtual 
+			instance void MoveNext () cil managed 
+		{
+			.override method instance void [mscorlib]System.Runtime.CompilerServices.IAsyncStateMachine::MoveNext()
+			// Method begins at RVA 0x7188
+			// Header size: 12
+			// Code size: 788 (0x314)
+			.maxstack 11
+			.locals init (
+				[0] bool,
+				[1] !T,
+				[2] class [mscorlib]System.Exception,
+				[3] int32,
+				[4] class [mscorlib]System.Type[],
+				[5] class [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo[],
+				[6] object,
+				[7] class [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo[],
+				[8] object,
+				[9] object,
+				[10] class [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo[],
+				[11] class [mscorlib]System.Tuple`2<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, !T>, class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, !T>>>,
+				[12] object,
+				[13] class [mscorlib]System.Runtime.CompilerServices.ICriticalNotifyCompletion,
+				[14] object,
+				[15] class [mscorlib]System.Runtime.CompilerServices.INotifyCompletion,
+				[16] class [mscorlib]System.Tuple`2<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, !T>, class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, !T>>>,
+				[17] object,
+				[18] class [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo[]
+			)
+
+			.try
+			{
+				IL_0000: ldc.i4.1
+				IL_0001: stloc.0
+				IL_0002: ldarg.0
+				IL_0003: ldfld int32 valuetype Issue3320/'<GetAsync>d__d`1'<!T>::'<>1__state'
+				IL_0008: stloc.3
+				IL_0009: ldloc.3
+				IL_000a: ldc.i4.0
+				IL_000b: beq IL_024a
+
+				IL_0010: ldsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, !0>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Site7'
+				IL_0015: brtrue.s IL_003b
+
+				IL_0017: ldc.i4.0
+				IL_0018: ldtoken !T
+				IL_001d: call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
+				IL_0022: ldtoken Issue3320
+				IL_0027: call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
+				IL_002c: call class [System.Core]System.Runtime.CompilerServices.CallSiteBinder [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.Binder::Convert(valuetype [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpBinderFlags, class [mscorlib]System.Type, class [mscorlib]System.Type)
+				IL_0031: call class [System.Core]System.Runtime.CompilerServices.CallSite`1<!0> class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, !T>>::Create(class [System.Core]System.Runtime.CompilerServices.CallSiteBinder)
+				IL_0036: stsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, !0>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Site7'
+
+				IL_003b: ldsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, !0>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Site7'
+				IL_0040: ldfld !0 class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, !T>>::Target
+				IL_0045: ldsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, !0>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Site7'
+				IL_004a: ldsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`7<class [System.Core]System.Runtime.CompilerServices.CallSite, class IDapperAsyncImplementor, class IDbConnection, object, class IDbTransaction, valuetype [mscorlib]System.Nullable`1<int32>, object>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Site8'
+				IL_004f: brtrue.s IL_00c9
+
+				IL_0051: ldc.i4.0
+				IL_0052: ldstr "GetAsync"
+				IL_0057: ldc.i4.1
+				IL_0058: newarr [mscorlib]System.Type
+				IL_005d: stloc.s 4
+				IL_005f: ldloc.s 4
+				IL_0061: ldc.i4.0
+				IL_0062: ldtoken !T
+				IL_0067: call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
+				IL_006c: stelem.ref
+				IL_006d: ldloc.s 4
+				IL_006f: ldtoken Issue3320
+				IL_0074: call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
+				IL_0079: ldc.i4.5
+				IL_007a: newarr [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo
+				IL_007f: stloc.s 5
+				IL_0081: ldloc.s 5
+				IL_0083: ldc.i4.0
+				IL_0084: ldc.i4.1
+				IL_0085: ldnull
+				IL_0086: call class [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo::Create(valuetype [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfoFlags, string)
+				IL_008b: stelem.ref
+				IL_008c: ldloc.s 5
+				IL_008e: ldc.i4.1
+				IL_008f: ldc.i4.1
+				IL_0090: ldnull
+				IL_0091: call class [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo::Create(valuetype [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfoFlags, string)
+				IL_0096: stelem.ref
+				IL_0097: ldloc.s 5
+				IL_0099: ldc.i4.2
+				IL_009a: ldc.i4.0
+				IL_009b: ldnull
+				IL_009c: call class [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo::Create(valuetype [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfoFlags, string)
+				IL_00a1: stelem.ref
+				IL_00a2: ldloc.s 5
+				IL_00a4: ldc.i4.3
+				IL_00a5: ldc.i4.1
+				IL_00a6: ldnull
+				IL_00a7: call class [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo::Create(valuetype [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfoFlags, string)
+				IL_00ac: stelem.ref
+				IL_00ad: ldloc.s 5
+				IL_00af: ldc.i4.4
+				IL_00b0: ldc.i4.1
+				IL_00b1: ldnull
+				IL_00b2: call class [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo::Create(valuetype [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfoFlags, string)
+				IL_00b7: stelem.ref
+				IL_00b8: ldloc.s 5
+				IL_00ba: call class [System.Core]System.Runtime.CompilerServices.CallSiteBinder [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.Binder::InvokeMember(valuetype [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpBinderFlags, string, class [mscorlib]System.Collections.Generic.IEnumerable`1<class [mscorlib]System.Type>, class [mscorlib]System.Type, class [mscorlib]System.Collections.Generic.IEnumerable`1<class [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo>)
+				IL_00bf: call class [System.Core]System.Runtime.CompilerServices.CallSite`1<!0> class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`7<class [System.Core]System.Runtime.CompilerServices.CallSite, class IDapperAsyncImplementor, class IDbConnection, object, class IDbTransaction, valuetype [mscorlib]System.Nullable`1<int32>, object>>::Create(class [System.Core]System.Runtime.CompilerServices.CallSiteBinder)
+				IL_00c4: stsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`7<class [System.Core]System.Runtime.CompilerServices.CallSite, class IDapperAsyncImplementor, class IDbConnection, object, class IDbTransaction, valuetype [mscorlib]System.Nullable`1<int32>, object>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Site8'
+
+				IL_00c9: ldsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`7<class [System.Core]System.Runtime.CompilerServices.CallSite, class IDapperAsyncImplementor, class IDbConnection, object, class IDbTransaction, valuetype [mscorlib]System.Nullable`1<int32>, object>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Site8'
+				IL_00ce: ldfld !0 class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`7<class [System.Core]System.Runtime.CompilerServices.CallSite, class IDapperAsyncImplementor, class IDbConnection, object, class IDbTransaction, valuetype [mscorlib]System.Nullable`1<int32>, object>>::Target
+				IL_00d3: ldsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`7<class [System.Core]System.Runtime.CompilerServices.CallSite, class IDapperAsyncImplementor, class IDbConnection, object, class IDbTransaction, valuetype [mscorlib]System.Nullable`1<int32>, object>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Site8'
+				IL_00d8: call class IDapperAsyncImplementor Issue3320::get_Instance()
+				IL_00dd: ldarg.0
+				IL_00de: ldfld class IDbConnection valuetype Issue3320/'<GetAsync>d__d`1'<!T>::connection
+				IL_00e3: ldarg.0
+				IL_00e4: ldfld object valuetype Issue3320/'<GetAsync>d__d`1'<!T>::id
+				IL_00e9: ldarg.0
+				IL_00ea: ldfld class IDbTransaction valuetype Issue3320/'<GetAsync>d__d`1'<!T>::transaction
+				IL_00ef: ldarg.0
+				IL_00f0: ldfld valuetype [mscorlib]System.Nullable`1<int32> valuetype Issue3320/'<GetAsync>d__d`1'<!T>::commandTimeout
+				IL_00f5: callvirt instance !6 class [mscorlib]System.Func`7<class [System.Core]System.Runtime.CompilerServices.CallSite, class IDapperAsyncImplementor, class IDbConnection, object, class IDbTransaction, valuetype [mscorlib]System.Nullable`1<int32>, object>::Invoke(!0, !1, !2, !3, !4, !5)
+				IL_00fa: stloc.s 6
+				IL_00fc: ldsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Site9'
+				IL_0101: brtrue.s IL_0138
+
+				IL_0103: ldc.i4.0
+				IL_0104: ldstr "GetAwaiter"
+				IL_0109: ldnull
+				IL_010a: ldtoken Issue3320
+				IL_010f: call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
+				IL_0114: ldc.i4.1
+				IL_0115: newarr [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo
+				IL_011a: stloc.s 7
+				IL_011c: ldloc.s 7
+				IL_011e: ldc.i4.0
+				IL_011f: ldc.i4.0
+				IL_0120: ldnull
+				IL_0121: call class [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo::Create(valuetype [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfoFlags, string)
+				IL_0126: stelem.ref
+				IL_0127: ldloc.s 7
+				IL_0129: call class [System.Core]System.Runtime.CompilerServices.CallSiteBinder [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.Binder::InvokeMember(valuetype [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpBinderFlags, string, class [mscorlib]System.Collections.Generic.IEnumerable`1<class [mscorlib]System.Type>, class [mscorlib]System.Type, class [mscorlib]System.Collections.Generic.IEnumerable`1<class [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo>)
+				IL_012e: call class [System.Core]System.Runtime.CompilerServices.CallSite`1<!0> class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>>::Create(class [System.Core]System.Runtime.CompilerServices.CallSiteBinder)
+				IL_0133: stsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Site9'
+
+				IL_0138: ldsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Site9'
+				IL_013d: ldfld !0 class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>>::Target
+				IL_0142: ldsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Site9'
+				IL_0147: ldloc.s 6
+				IL_0149: callvirt instance !2 class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>::Invoke(!0, !1)
+				IL_014e: stloc.s 8
+				IL_0150: ldloc.s 8
+				IL_0152: stloc.s 9
+				IL_0154: ldsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, bool>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Sitea'
+				IL_0159: brtrue.s IL_017f
+
+				IL_015b: ldc.i4.0
+				IL_015c: ldtoken [mscorlib]System.Boolean
+				IL_0161: call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
+				IL_0166: ldtoken Issue3320
+				IL_016b: call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
+				IL_0170: call class [System.Core]System.Runtime.CompilerServices.CallSiteBinder [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.Binder::Convert(valuetype [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpBinderFlags, class [mscorlib]System.Type, class [mscorlib]System.Type)
+				IL_0175: call class [System.Core]System.Runtime.CompilerServices.CallSite`1<!0> class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, bool>>::Create(class [System.Core]System.Runtime.CompilerServices.CallSiteBinder)
+				IL_017a: stsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, bool>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Sitea'
+
+				IL_017f: ldsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, bool>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Sitea'
+				IL_0184: ldfld !0 class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, bool>>::Target
+				IL_0189: ldsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, bool>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Sitea'
+				IL_018e: ldsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Siteb'
+				IL_0193: brtrue.s IL_01c9
+
+				IL_0195: ldc.i4.0
+				IL_0196: ldstr "IsCompleted"
+				IL_019b: ldtoken Issue3320
+				IL_01a0: call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
+				IL_01a5: ldc.i4.1
+				IL_01a6: newarr [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo
+				IL_01ab: stloc.s 10
+				IL_01ad: ldloc.s 10
+				IL_01af: ldc.i4.0
+				IL_01b0: ldc.i4.0
+				IL_01b1: ldnull
+				IL_01b2: call class [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo::Create(valuetype [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfoFlags, string)
+				IL_01b7: stelem.ref
+				IL_01b8: ldloc.s 10
+				IL_01ba: call class [System.Core]System.Runtime.CompilerServices.CallSiteBinder [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.Binder::GetMember(valuetype [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpBinderFlags, string, class [mscorlib]System.Type, class [mscorlib]System.Collections.Generic.IEnumerable`1<class [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo>)
+				IL_01bf: call class [System.Core]System.Runtime.CompilerServices.CallSite`1<!0> class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>>::Create(class [System.Core]System.Runtime.CompilerServices.CallSiteBinder)
+				IL_01c4: stsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Siteb'
+
+				IL_01c9: ldsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Siteb'
+				IL_01ce: ldfld !0 class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>>::Target
+				IL_01d3: ldsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Siteb'
+				IL_01d8: ldloc.s 9
+				IL_01da: callvirt instance !2 class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>::Invoke(!0, !1)
+				IL_01df: callvirt instance !2 class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, bool>::Invoke(!0, !1)
+				IL_01e4: brtrue IL_0287
+
+				IL_01e9: newobj instance void class [mscorlib]System.Tuple`2<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, !T>, class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, !T>>>::.ctor(!0, !1)
+				IL_01ee: stloc.s 11
+				IL_01f0: ldarg.0
+				IL_01f1: ldloc.s 11
+				IL_01f3: stfld object valuetype Issue3320/'<GetAsync>d__d`1'<!T>::'<>t__stack'
+				IL_01f8: ldarg.0
+				IL_01f9: ldc.i4.0
+				IL_01fa: stfld int32 valuetype Issue3320/'<GetAsync>d__d`1'<!T>::'<>1__state'
+				IL_01ff: ldarg.0
+				IL_0200: ldloc.s 8
+				IL_0202: stfld object valuetype Issue3320/'<GetAsync>d__d`1'<!T>::'<>u__$awaitere'
+				IL_0207: ldloc.s 8
+				IL_0209: stloc.s 12
+				IL_020b: ldloc.s 12
+				IL_020d: isinst [mscorlib]System.Runtime.CompilerServices.ICriticalNotifyCompletion
+				IL_0212: stloc.s 13
+				IL_0214: ldloc.s 13
+				IL_0216: brtrue.s IL_0235
+
+				IL_0218: ldloc.s 8
+				IL_021a: stloc.s 14
+				IL_021c: ldloc.s 14
+				IL_021e: castclass [mscorlib]System.Runtime.CompilerServices.INotifyCompletion
+				IL_0223: stloc.s 15
+				IL_0225: ldarg.0
+				IL_0226: ldflda valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<!0> valuetype Issue3320/'<GetAsync>d__d`1'<!T>::'<>t__builder'
+				IL_022b: ldloca.s 15
+				IL_022d: ldarg.0
+				IL_022e: call instance void valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<!T>::AwaitOnCompleted<class [mscorlib]System.Runtime.CompilerServices.INotifyCompletion, valuetype Issue3320/'<GetAsync>d__d`1'<!T>>(!!0&, !!1&)
+				IL_0233: br.s IL_0243
+
+				IL_0235: ldarg.0
+				IL_0236: ldflda valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<!0> valuetype Issue3320/'<GetAsync>d__d`1'<!T>::'<>t__builder'
+				IL_023b: ldloca.s 13
+				IL_023d: ldarg.0
+				IL_023e: call instance void valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<!T>::AwaitUnsafeOnCompleted<class [mscorlib]System.Runtime.CompilerServices.ICriticalNotifyCompletion, valuetype Issue3320/'<GetAsync>d__d`1'<!T>>(!!0&, !!1&)
+
+				IL_0243: ldc.i4.0
+				IL_0244: stloc.0
+				IL_0245: leave IL_0313
+
+				IL_024a: ldarg.0
+				IL_024b: ldfld object valuetype Issue3320/'<GetAsync>d__d`1'<!T>::'<>t__stack'
+				IL_0250: unbox.any class [mscorlib]System.Tuple`2<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, !T>, class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, !T>>>
+				IL_0255: stloc.s 16
+				IL_0257: ldloc.s 16
+				IL_0259: callvirt instance !0 class [mscorlib]System.Tuple`2<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, !T>, class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, !T>>>::get_Item1()
+				IL_025e: ldloc.s 16
+				IL_0260: callvirt instance !1 class [mscorlib]System.Tuple`2<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, !T>, class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, !T>>>::get_Item2()
+				IL_0265: ldarg.0
+				IL_0266: ldnull
+				IL_0267: stfld object valuetype Issue3320/'<GetAsync>d__d`1'<!T>::'<>t__stack'
+				IL_026c: ldarg.0
+				IL_026d: ldfld object valuetype Issue3320/'<GetAsync>d__d`1'<!T>::'<>u__$awaitere'
+				IL_0272: unbox.any [mscorlib]System.Object
+				IL_0277: stloc.s 8
+				IL_0279: ldarg.0
+				IL_027a: ldnull
+				IL_027b: stfld object valuetype Issue3320/'<GetAsync>d__d`1'<!T>::'<>u__$awaitere'
+				IL_0280: ldarg.0
+				IL_0281: ldc.i4.m1
+				IL_0282: stfld int32 valuetype Issue3320/'<GetAsync>d__d`1'<!T>::'<>1__state'
+
+				IL_0287: ldloc.s 8
+				IL_0289: stloc.s 17
+				IL_028b: ldsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Sitec'
+				IL_0290: brtrue.s IL_02c7
+
+				IL_0292: ldc.i4.0
+				IL_0293: ldstr "GetResult"
+				IL_0298: ldnull
+				IL_0299: ldtoken Issue3320
+				IL_029e: call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
+				IL_02a3: ldc.i4.1
+				IL_02a4: newarr [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo
+				IL_02a9: stloc.s 18
+				IL_02ab: ldloc.s 18
+				IL_02ad: ldc.i4.0
+				IL_02ae: ldc.i4.0
+				IL_02af: ldnull
+				IL_02b0: call class [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo::Create(valuetype [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfoFlags, string)
+				IL_02b5: stelem.ref
+				IL_02b6: ldloc.s 18
+				IL_02b8: call class [System.Core]System.Runtime.CompilerServices.CallSiteBinder [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.Binder::InvokeMember(valuetype [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpBinderFlags, string, class [mscorlib]System.Collections.Generic.IEnumerable`1<class [mscorlib]System.Type>, class [mscorlib]System.Type, class [mscorlib]System.Collections.Generic.IEnumerable`1<class [Microsoft.CSharp]Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo>)
+				IL_02bd: call class [System.Core]System.Runtime.CompilerServices.CallSite`1<!0> class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>>::Create(class [System.Core]System.Runtime.CompilerServices.CallSiteBinder)
+				IL_02c2: stsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Sitec'
+
+				IL_02c7: ldsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Sitec'
+				IL_02cc: ldfld !0 class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>>::Target
+				IL_02d1: ldsfld class [System.Core]System.Runtime.CompilerServices.CallSite`1<class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>> class Issue3320/'<GetAsync>o__SiteContainer6`1'<!T>::'<>p__Sitec'
+				IL_02d6: ldloc.s 17
+				IL_02d8: callvirt instance !2 class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, object>::Invoke(!0, !1)
+				IL_02dd: ldnull
+				IL_02de: stloc.s 8
+				IL_02e0: callvirt instance !2 class [mscorlib]System.Func`3<class [System.Core]System.Runtime.CompilerServices.CallSite, object, !T>::Invoke(!0, !1)
+				IL_02e5: stloc.1
+				IL_02e6: leave.s IL_02ff
+			} // end .try
+			catch [mscorlib]System.Exception
+			{
+				IL_02e8: stloc.2
+				IL_02e9: ldarg.0
+				IL_02ea: ldc.i4.s -2
+				IL_02ec: stfld int32 valuetype Issue3320/'<GetAsync>d__d`1'<!T>::'<>1__state'
+				IL_02f1: ldarg.0
+				IL_02f2: ldflda valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<!0> valuetype Issue3320/'<GetAsync>d__d`1'<!T>::'<>t__builder'
+				IL_02f7: ldloc.2
+				IL_02f8: call instance void valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<!T>::SetException(class [mscorlib]System.Exception)
+				IL_02fd: leave.s IL_0313
+			} // end handler
+
+			IL_02ff: ldarg.0
+			IL_0300: ldc.i4.s -2
+			IL_0302: stfld int32 valuetype Issue3320/'<GetAsync>d__d`1'<!T>::'<>1__state'
+			IL_0307: ldarg.0
+			IL_0308: ldflda valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<!0> valuetype Issue3320/'<GetAsync>d__d`1'<!T>::'<>t__builder'
+			IL_030d: ldloc.1
+			IL_030e: call instance void valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<!T>::SetResult(!0)
+
+			IL_0313: ret
+		} // end of method '<GetAsync>d__d`1'::MoveNext
+
+		.method private final hidebysig newslot virtual 
+			instance void SetStateMachine (
+				class [mscorlib]System.Runtime.CompilerServices.IAsyncStateMachine param0
+			) cil managed 
+		{
+			.custom instance void [mscorlib]System.Diagnostics.DebuggerHiddenAttribute::.ctor() = (
+				01 00 00 00
+			)
+			.override method instance void [mscorlib]System.Runtime.CompilerServices.IAsyncStateMachine::SetStateMachine(class [mscorlib]System.Runtime.CompilerServices.IAsyncStateMachine)
+			// Method begins at RVA 0x74c4
+			// Header size: 1
+			// Code size: 13 (0xd)
+			.maxstack 8
+
+			IL_0000: ldarg.0
+			IL_0001: ldflda valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<!0> valuetype Issue3320/'<GetAsync>d__d`1'<!T>::'<>t__builder'
+			IL_0006: ldarg.1
+			IL_0007: call instance void valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<!T>::SetStateMachine(class [mscorlib]System.Runtime.CompilerServices.IAsyncStateMachine)
+			IL_000c: ret
+		} // end of method '<GetAsync>d__d`1'::SetStateMachine
+
+	} // end of class <GetAsync>d__d`1
+
+
+	.method public hidebysig static 
+		class [mscorlib]System.Threading.Tasks.Task`1<!!T> GetAsync<class T> (
+			class IDbConnection connection,
+			object id,
+			[opt] class IDbTransaction transaction,
+			[opt] valuetype [mscorlib]System.Nullable`1<int32> commandTimeout
+		) cil managed 
+	{
+		.custom instance void [mscorlib]System.Diagnostics.DebuggerStepThroughAttribute::.ctor() = (
+			01 00 00 00
+		)
+		.custom instance void [mscorlib]System.Runtime.CompilerServices.AsyncStateMachineAttribute::.ctor(class [mscorlib]System.Type) = (
+			01 00 37 44 61 70 70 65 72 45 78 74 65 6e 73 69
+			6f 6e 73 2e 44 61 70 70 65 72 41 73 79 6e 63 45
+			78 74 65 6e 73 69 6f 6e 73 2b 3c 47 65 74 41 73
+			79 6e 63 3e 64 5f 5f 64 60 31 00 00
+		)
+		.custom instance void [mscorlib]System.Runtime.CompilerServices.ExtensionAttribute::.ctor() = (
+			01 00 00 00
+		)
+		.param [2]
+			.custom instance void [System.Core]System.Runtime.CompilerServices.DynamicAttribute::.ctor() = (
+				01 00 00 00
+			)
+		.param [3] = nullref
+		.param [4] = nullref
+		// Method begins at RVA 0x74d4
+		// Header size: 12
+		// Code size: 82 (0x52)
+		.maxstack 2
+		.locals init (
+			[0] valuetype Issue3320/'<GetAsync>d__d`1'<!!T>,
+			[1] valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<!!T>
+		)
+
+		IL_0000: ldloca.s 0
+		IL_0002: ldarg.0
+		IL_0003: stfld class IDbConnection valuetype Issue3320/'<GetAsync>d__d`1'<!!T>::connection
+		IL_0008: ldloca.s 0
+		IL_000a: ldarg.1
+		IL_000b: stfld object valuetype Issue3320/'<GetAsync>d__d`1'<!!T>::id
+		IL_0010: ldloca.s 0
+		IL_0012: ldarg.2
+		IL_0013: stfld class IDbTransaction valuetype Issue3320/'<GetAsync>d__d`1'<!!T>::transaction
+		IL_0018: ldloca.s 0
+		IL_001a: ldarg.3
+		IL_001b: stfld valuetype [mscorlib]System.Nullable`1<int32> valuetype Issue3320/'<GetAsync>d__d`1'<!!T>::commandTimeout
+		IL_0020: ldloca.s 0
+		IL_0022: call valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<!0> valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<!!T>::Create()
+		IL_0027: stfld valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<!0> valuetype Issue3320/'<GetAsync>d__d`1'<!!T>::'<>t__builder'
+		IL_002c: ldloca.s 0
+		IL_002e: ldc.i4.m1
+		IL_002f: stfld int32 valuetype Issue3320/'<GetAsync>d__d`1'<!!T>::'<>1__state'
+		IL_0034: ldloca.s 0
+		IL_0036: ldfld valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<!0> valuetype Issue3320/'<GetAsync>d__d`1'<!!T>::'<>t__builder'
+		IL_003b: stloc.1
+		IL_003c: ldloca.s 1
+		IL_003e: ldloca.s 0
+		IL_0040: call instance void valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<!!T>::Start<valuetype Issue3320/'<GetAsync>d__d`1'<!!T>>(!!0&)
+		IL_0045: ldloca.s 0
+		IL_0047: ldflda valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<!0> valuetype Issue3320/'<GetAsync>d__d`1'<!!T>::'<>t__builder'
+		IL_004c: call instance class [mscorlib]System.Threading.Tasks.Task`1<!0> valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<!!T>::get_Task()
+		IL_0051: ret
+	} // end of method Issue3320::GetAsync
+}

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

@@ -92,6 +92,14 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 
 		private static async Task DynamicAwaitInTryCatch(dynamic d)
 		{
+			// Optimized pre-Roslyn state machines keep the bookkeeping of an await inside a try
+			// block in locals that survive decompilation as dead stores; a plain await on a Task
+			// produces the same three stores.
+#if EXPECTED_OUTPUT && OPT && LEGACY_CSC
+			int num = default(int);
+			int num2 = num;
+			int num3 = 0;
+#endif
 			try
 			{
 				d.Before = 1;
@@ -151,7 +159,13 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 		// awaited dynamic stored in a dynamic local, then used (#1388)
 		private static async Task<dynamic> AwaitDynamicIntoUsedLocal()
 		{
+			// The pre-Roslyn compiler copies the awaited value into its own local first.
+#if LEGACY_CSC
+			dynamic dynamic = GetDynamic();
+			dynamic val = await dynamic;
+#else
 			dynamic val = await GetDynamic();
+#endif
 			val.UseMe();
 			return val;
 		}
@@ -159,7 +173,12 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 		// dynamic-dispatched awaited call with a dynamic-converted result (#1928)
 		private static async Task<string> AwaitDynamicConvertResult(dynamic d)
 		{
+#if LEGACY_CSC
+			dynamic val = d.RunAsync();
+			return (string)(await val);
+#else
 			return (string)(await d.RunAsync());
+#endif
 		}
 
 		// --- static-type call target spilled across an await ---
@@ -182,13 +201,19 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 
 		private static async Task AwaitDynamicMethodResult(dynamic d)
 		{
+#if LEGACY_CSC
+			dynamic val = d.RunAsync();
+			await val;
+#else
 			await d.RunAsync();
+#endif
 		}
 
 		private static async Task AwaitDynamicLocalWithStatementBefore()
 		{
-			// Optimized builds drop the local's debug name, so the decompiler regenerates one from the type.
+			// Optimized builds drop the local's debug name, so the decompiler regenerates one from
-#if OPT
+			// the type; the pre-Roslyn compiler never emits the name in the first place.
+#if OPT || LEGACY_CSC
 			dynamic dynamic = GetDynamic();
 			Console.WriteLine("before await");
 			await dynamic;

ICSharpCode.Decompiler/IL/ControlFlow/AsyncAwaitDecompiler.cs

@@ -1344,6 +1344,8 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			smallestAwaiterVarIndex = int.MaxValue;
 			foreach (var container in function.Descendants.OfType<BlockContainer>())
 			{
+				foreach (var block in container.Blocks)
+					InlineAwaiterCopies(block);
 				// Fold the runtime ICriticalNotifyCompletion type-check that the compiler emits when the
 				// awaiter's static type is not known to implement it (dynamic awaiters, some generic awaiters)
 				// into the canonical single-call form that AnalyzeAwaitBlock recognizes.
@@ -1629,7 +1631,10 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			if (!onCompletedBlock.Instructions[2].MatchBranch(out var mergeBlock2) || mergeBlock2 != mergeBlock)
 				return false;
 
-			if (mergeBlock.Instructions.Count != 1 || !(mergeBlock.Instructions[0] is Leave mergeLeave))
+			// The pre-Roslyn compiler clears doFinallyBodies right before leaving MoveNext;
+			// AnalyzeAwaitBlock expects that store directly in front of the leave.
+			int leavePos = MatchStoreDoFinallyBodies(mergeBlock.Instructions.FirstOrDefault()) ? 1 : 0;
+			if (mergeBlock.Instructions.Count != leavePos + 1 || !(mergeBlock.Instructions[leavePos] is Leave mergeLeave))
 				return false;
 
 			// Rewrite `block` into the canonical single-call form.
@@ -1641,12 +1646,57 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			block.Instructions.RemoveRange(count - 2, 2); // if + br
 			block.Instructions.RemoveAt(isInstPos); // isinst store
 			block.Instructions.Add(awaitCall);
+			if (leavePos > 0)
+			{
+				block.Instructions.Add(mergeBlock.Instructions[0].Clone());
+			}
 			var newLeave = (Leave)mergeLeave.Clone();
 			moveNextLeaves.Add(newLeave);
 			block.Instructions.Add(newLeave);
 			return true;
 		}
 
+		/// <summary>
+		/// Matches the 'stloc doFinallyBodies(ldc.i4 0)' the pre-Roslyn compiler emits before leaving MoveNext.
+		/// </summary>
+		bool MatchStoreDoFinallyBodies(ILInstruction inst)
+		{
+			if (doFinallyBodies == null || inst == null)
+				return false;
+			return inst.MatchStLoc(out var v, out var value)
+				&& v.Kind == VariableKind.Local
+				&& v.Type.IsKnownType(KnownTypeCode.Boolean)
+				&& v.Index == doFinallyBodies.Index
+				&& value.MatchLdcI4(0);
+		}
+
+		/// <summary>
+		/// The pre-Roslyn compiler copies the awaiter into a fresh local right before each dynamic call site
+		/// and each completion-interface type test on it. The await matchers identify an await by its awaiter
+		/// variable, so inline those copies.
+		/// </summary>
+		void InlineAwaiterCopies(Block block)
+		{
+			for (int i = block.Instructions.Count - 1; i >= 0; i--)
+			{
+				if (block.Instructions[i] is StLoc { Variable: { Kind: VariableKind.Local, IsSingleDefinition: true, LoadCount: 1 } copy, Value: LdLoc } store
+					&& IsAwaiterAccess(copy.LoadInstructions[0].Parent))
+				{
+					ILInlining.InlineOne(store, InliningOptions.Aggressive, context);
+				}
+			}
+
+			static bool IsAwaiterAccess(ILInstruction inst)
+			{
+				if (inst is DynamicGetMemberInstruction { Name: "IsCompleted" } or DynamicInvokeMemberInstruction { Name: "GetResult" })
+					return true;
+				if (!inst.MatchIsInst(out _, out var type) && !inst.MatchCastClass(out _, out type))
+					return false;
+				return type.FullName is "System.Runtime.CompilerServices.ICriticalNotifyCompletion"
+					or "System.Runtime.CompilerServices.INotifyCompletion";
+			}
+		}
+
 		bool AnalyzeAwaitBlock(Block block, out ILVariable awaiter, out IField awaiterField, out int state, out int yieldOffset)
 		{
 			awaiter = null;
@@ -1654,15 +1704,9 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			state = 0;
 			yieldOffset = -1;
 			int pos = block.Instructions.Count - 2;
-			if (pos >= 0 && doFinallyBodies != null && block.Instructions[pos] is StLoc storeDoFinallyBodies)
+			if (pos >= 0 && doFinallyBodies != null && block.Instructions[pos] is StLoc)
 			{
-				if (!(storeDoFinallyBodies.Variable.Kind == VariableKind.Local
+				if (!MatchStoreDoFinallyBodies(block.Instructions[pos]))
-					  && storeDoFinallyBodies.Variable.Type.IsKnownType(KnownTypeCode.Boolean)
-					  && storeDoFinallyBodies.Variable.Index == doFinallyBodies.Index))
-				{
-					return false;
-				}
-				if (!storeDoFinallyBodies.Value.MatchLdcI4(0))
 					return false;
 				pos--;
 			}
@@ -2008,6 +2052,8 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				{
 					// keep pulling in trivial branch targets until this block can grow no further
 				}
+				// Only now is each awaiter copy in the same block as the call site that uses it.
+				InlineAwaiterCopies(block);
 			}
 		}
 
@@ -2085,11 +2131,12 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				// stloc awaiterVar(ldfld awaiterField(ldloc this))
 				if (!instr.MatchStLoc(awaiterVar, out var value))
 					return false;
-				if (value is CastClass cast && cast.Type.Equals(awaiterVar.Type))
+				// If the awaiter is a reference type, it might get stored in a field of type `object`
+				// and cast back to the awaiter type in the resume block (pre-Roslyn: with unbox.any)
+				if ((value.MatchCastClass(out var castArg, out var castType) || value.MatchUnboxAny(out castArg, out castType))
+					&& castType.Equals(awaiterVar.Type))
 				{
-					// If the awaiter is a reference type, it might get stored in a field of type `object`
+					value = castArg;
-					// and cast back to the awaiter type in the resume block
-					value = cast.Argument;
 				}
 				if (!value.MatchLdFld(out var target, out var field))
 					return false;