Fix dynamic transforms because https://github.com/dotnet/roslyn/issues/27800 was fixed.

ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs

@@ -241,7 +241,6 @@ namespace ICSharpCode.Decompiler.Tests
 		}
 
 		[Test]
-		[Ignore("broken by Roslyn upgrade")]
 		public void DynamicTests([ValueSource(nameof(defaultOptions))] CompilerOptions cscOptions)
 		{
 			RunForLibrary(cscOptions: cscOptions);

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

@@ -2,14 +2,6 @@
 
 namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 {
-	internal static class Extension
-	{
-		public static dynamic ToDynamic(this int i, dynamic info)
-		{
-			throw null;
-		}
-	}
-
 	internal class DynamicTests
 	{
 
@@ -446,4 +438,12 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			return (int)(dynamic)o;
 		}
 	}
+
+	internal static class Extension
+	{
+		public static dynamic ToDynamic(this int i, dynamic info)
+		{
+			throw null;
+		}
+	}
 }

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -138,6 +138,7 @@ namespace ICSharpCode.Decompiler.CSharp
 							// Inlining must be first, because it doesn't trigger re-runs.
 							// Any other transform that opens up new inlining opportunities should call RequestRerun().
 							new ExpressionTransforms(),
+							new DynamicIsEventAssignmentTransform(),
 							new TransformAssignment(), // inline and compound assignments
 							new NullCoalescingTransform(),
 							new NullableLiftingStatementTransform(),

ICSharpCode.Decompiler/ICSharpCode.Decompiler.csproj

@@ -269,6 +269,7 @@
     <Compile Include="Disassembler\ILParser.cs" />
     <Compile Include="IL\ILInstructionExtensions.cs" />
     <Compile Include="IL\Transforms\CombineExitsTransform.cs" />
+    <Compile Include="IL\Transforms\DynamicIsEventAssignmentTransform.cs" />
     <Compile Include="IL\Transforms\ReduceNestingTransform.cs" />
     <Compile Include="IL\Transforms\LocalFunctionDecompiler.cs" />
     <Compile Include="IL\Transforms\UserDefinedLogicTransform.cs" />

ICSharpCode.Decompiler/IL/Transforms/DynamicIsEventAssignmentTransform.cs

@@ -0,0 +1,127 @@
+// Copyright (c) 2019 Siegfried Pammer
+// 
+// Permission is hereby granted, free of charge, to any person obtaining a copy of this
+// software and associated documentation files (the "Software"), to deal in the Software
+// without restriction, including without limitation the rights to use, copy, modify, merge,
+// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
+// to whom the Software is furnished to do so, subject to the following conditions:
+// 
+// The above copyright notice and this permission notice shall be included in all copies or
+// substantial portions of the Software.
+// 
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
+// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+namespace ICSharpCode.Decompiler.IL.Transforms
+{
+	public class DynamicIsEventAssignmentTransform : IStatementTransform
+	{
+		/// stloc V_1(dynamic.isevent (target))
+		/// if (logic.not(ldloc V_1)) Block IL_004a {
+		/// 	stloc V_2(dynamic.getmember B(target))
+		/// }
+		/// if (logic.not(ldloc V_1)) Block IL_0149 {
+		/// 	dynamic.setmember.compound B(target, dynamic.binary.operator AddAssign(ldloc V_2,  value))
+		/// } else Block IL_0151 {
+		/// 	dynamic.invokemember.invokespecial.discard add_B(target, value)
+		/// }
+		/// =>
+		/// if (logic.not(dynamic.isevent (target))) Block IL_0149 {
+		/// 	dynamic.setmember.compound B(target, dynamic.binary.operator AddAssign(dynamic.getmember B(target),  value))
+		/// } else Block IL_0151 {
+		/// 	dynamic.invokemember.invokespecial.discard add_B(target, value)
+		/// }
+		public void Run(Block block, int pos, StatementTransformContext context)
+		{
+			if (!(pos + 3 < block.Instructions.Count && block.Instructions[pos].MatchStLoc(out var flagVar, out var inst) && inst is DynamicIsEventInstruction isEvent))
+				return;
+			if (!(flagVar.IsSingleDefinition && flagVar.LoadCount == 2))
+				return;
+			if (!(MatchLhsCacheIfInstruction(block.Instructions[pos + 1], flagVar, out var dynamicGetMemberStore)))
+				return;
+			if (!(dynamicGetMemberStore.MatchStLoc(out var getMemberVar, out inst) && inst is DynamicGetMemberInstruction getMemberInst))
+				return;
+			foreach (var descendant in block.Instructions[pos + 2].Descendants) {
+				if (!MatchIsEventAssignmentIfInstruction(descendant, isEvent, flagVar, getMemberVar, out var setMemberInst, out var getMemberVarUse, out var isEventConditionUse))
+					continue;
+				context.Step("DynamicIsEventAssignmentTransform", block.Instructions[pos]);
+				// Collapse duplicate condition
+				getMemberVarUse.ReplaceWith(getMemberInst);
+				isEventConditionUse.ReplaceWith(isEvent);
+				block.Instructions.RemoveRange(pos, 2);
+				// Reuse ExpressionTransforms
+				ExpressionTransforms.TransformDynamicSetMemberInstruction(setMemberInst, context);
+				context.RequestRerun();
+				break;
+			}
+		}
+
+		/// <summary>
+		/// if (logic.not(ldloc V_1)) Block IL_0149 {
+		/// 	dynamic.setmember.compound B(target, dynamic.binary.operator AddAssign(ldloc V_2,  value))
+		/// } else Block IL_0151 {
+		/// 	dynamic.invokemember.invokespecial.discard add_B(target, value)
+		/// }
+		/// </summary>
+		static bool MatchIsEventAssignmentIfInstruction(ILInstruction ifInst, DynamicIsEventInstruction isEvent, ILVariable flagVar, ILVariable getMemberVar,
+			out DynamicSetMemberInstruction setMemberInst, out ILInstruction getMemberVarUse, out ILInstruction isEventConditionUse)
+		{
+			setMemberInst = null;
+			getMemberVarUse = null;
+			isEventConditionUse = null;
+			if (!ifInst.MatchIfInstruction(out var condition, out var trueInst, out var falseInst))
+				return false;
+			if (MatchFlagEqualsZero(condition, flagVar)) {
+				if (!condition.MatchCompEquals(out var left, out _))
+					return false;
+				isEventConditionUse = left;
+			} else if (condition.MatchLdLoc(flagVar)) {
+				var tmp = trueInst;
+				trueInst = falseInst;
+				falseInst = tmp;
+				isEventConditionUse = condition;
+			} else
+				return false;
+			setMemberInst = Block.Unwrap(trueInst) as DynamicSetMemberInstruction;
+			if (!(setMemberInst != null))
+				return false;
+			if (!isEvent.Argument.Match(setMemberInst.Target).Success)
+				return false;
+			if (!(Block.Unwrap(falseInst) is DynamicInvokeMemberInstruction invokeMemberInst && invokeMemberInst.Arguments.Count == 2))
+				return false;
+			if (!isEvent.Argument.Match(invokeMemberInst.Arguments[0]).Success)
+				return false;
+			if (!(setMemberInst.Value is DynamicBinaryOperatorInstruction binOp && binOp.Left.MatchLdLoc(getMemberVar)))
+				return false;
+			getMemberVarUse = binOp.Left;
+			return true;
+		}
+
+		/// <summary>
+		/// if (logic.not(ldloc V_1)) Block IL_004a {
+		/// 	stloc V_2(dynamic.getmember B(target))
+		/// }
+		/// </summary>
+		static bool MatchLhsCacheIfInstruction(ILInstruction ifInst, ILVariable flagVar, out StLoc cacheStore)
+		{
+			cacheStore = null;
+			if (!ifInst.MatchIfInstruction(out var condition, out var trueInst))
+				return false;
+			if (!MatchFlagEqualsZero(condition, flagVar))
+				return false;
+			cacheStore = Block.Unwrap(trueInst) as StLoc;
+			return cacheStore != null;
+		}
+
+		static bool MatchFlagEqualsZero(ILInstruction condition, ILVariable flagVar)
+		{
+			return condition.MatchCompEquals(out var left, out var right)
+				&& left.MatchLdLoc(flagVar)
+				&& right.MatchLdcI4(0);
+		}
+	}
+}

ICSharpCode.Decompiler/IL/Transforms/ExpressionTransforms.cs

@@ -499,7 +499,11 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		protected internal override void VisitDynamicSetMemberInstruction(DynamicSetMemberInstruction inst)
 		{
 			base.VisitDynamicSetMemberInstruction(inst);
+			TransformDynamicSetMemberInstruction(inst, context);
+		}
 
+		internal static void TransformDynamicSetMemberInstruction(DynamicSetMemberInstruction inst, StatementTransformContext context)
+		{
 			if (!inst.BinderFlags.HasFlag(CSharpBinderFlags.ValueFromCompoundAssignment))
 				return;
 			if (!(inst.Value is DynamicBinaryOperatorInstruction binaryOp))