Added code action from Ciprian Khlud <ciprian.mustiata@yahoo.com>:

InvertIfAndSimplify

ICSharpCode.NRefactory.CSharp/ICSharpCode.NRefactory.CSharp.csproj

@@ -520,6 +520,7 @@
     <Compile Include="Refactoring\CodeActions\SimplifyIfFlowAction.cs" />
     <Compile Include="Refactoring\CodeActions\SimplifyIfInLoopsFlowAction.cs" />
     <Compile Include="Refactoring\CodeIssues\NoDefaultConstructorIssue.cs" />
+    <Compile Include="Refactoring\CodeActions\InvertIfAndSimplify.cs" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\ICSharpCode.NRefactory\ICSharpCode.NRefactory.csproj">

ICSharpCode.NRefactory.CSharp/Refactoring/CodeActions/InvertIfAndSimplify.cs

@@ -0,0 +1,84 @@
+//
+// InvertIfAndSimplify.cs
+//
+// Author:
+//      Ciprian Khlud <ciprian.mustiata@yahoo.com>
+//
+// Copyright (c) 2013 Ciprian Khlud <ciprian.mustiata@yahoo.com>
+//
+// 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.
+
+using System.Collections.Generic;
+using System.Linq;
+
+namespace ICSharpCode.NRefactory.CSharp.Refactoring
+{
+	[ContextAction("Invert If and Simplify", Description = "Inverts if and simplify branching")]
+	public class InvertIfAndSimplify : ICodeActionProvider
+	{
+		readonly InsertParenthesesVisitor _insertParenthesesVisitor = new InsertParenthesesVisitor();
+
+		public IEnumerable<CodeAction> GetActions(RefactoringContext context)
+		{
+			// if (condition) {CodeBlock();}else { return|break|continue;} 
+			// will be reduced to:
+			//if (!condition) return|break|continue;
+			//CodeBlock();
+
+			var ifStatement = GetIfElseStatement(context);
+			if (ifStatement == null)
+				yield break;
+			yield return new CodeAction(context.TranslateString("Simplify if in loops"), script => GenerateNewScript(
+				script, ifStatement), ifStatement);
+		}
+
+		void GenerateNewScript(Script script, IfElseStatement ifStatement)
+		{
+			var mergedIfStatement = new IfElseStatement
+			{
+				Condition = CSharpUtil.InvertCondition(ifStatement.Condition)
+			};
+			var falseStatement = ifStatement.FalseStatement;
+			var blockStatement = falseStatement as BlockStatement;
+			mergedIfStatement.TrueStatement = blockStatement != null
+				? blockStatement.Statements.First().Clone()
+					: falseStatement.Clone();
+			mergedIfStatement.Condition.AcceptVisitor(_insertParenthesesVisitor);
+
+			script.Replace(ifStatement, mergedIfStatement);
+
+			SimplifyIfFlowAction.InsertBody(script, ifStatement);
+		}
+
+		static IfElseStatement GetIfElseStatement(RefactoringContext context)
+		{
+			var result = context.GetNode<IfElseStatement>();
+			if (result == null || !result.IfToken.Contains(context.Location))
+				return null;
+			var falseStatement = result.FalseStatement;
+			var isQuitingStatement = falseStatement;
+			var blockStatement = falseStatement as BlockStatement;
+			if (blockStatement != null)
+				isQuitingStatement = blockStatement.Statements.FirstOrDefault();
+			if (isQuitingStatement is ReturnStatement || isQuitingStatement is ContinueStatement || isQuitingStatement is BreakStatement)
+				return result;
+			return null;
+		}
+	}
+}

ICSharpCode.NRefactory.Tests/CSharp/CodeActions/InvertIfAndSimplifyTests.cs

@@ -0,0 +1,100 @@
+using ICSharpCode.NRefactory.CSharp.Refactoring;
+using NUnit.Framework;
+
+namespace ICSharpCode.NRefactory.CSharp.CodeActions
+{
+	[TestFixture]
+	class InvertIfAndSimplifyTests : ContextActionTestBase
+	{
+		[Test]
+		public void Test()
+		{
+			Test<InvertIfAndSimplify>(
+				@"class TestClass
+{
+	void Test ()
+	{
+		$if (true) {
+			Case1 ();
+			Case2 ();
+		}
+        else 
+        {
+            return;
+        }
+	}
+}",
+				@"class TestClass
+{
+	void Test ()
+	{
+		if (false)
+			return;
+		Case1 ();
+		Case2 ();
+	}
+}"
+				);
+		}
+
+		[Test]
+		public void TestNonVoidMoreComplexMethod()
+		{
+			Test<InvertIfAndSimplify>(
+				@"class TestClass
+{
+	int Test ()
+	{
+		$if (true) {
+			Case1 ();
+		}
+        else 
+        {
+            return 0;
+            testDummyCode();
+        }
+	}
+}",
+				@"class TestClass
+{
+	int Test ()
+	{
+		if (false)
+			return 0;
+		Case1 ();
+	}
+}"
+				);
+
+		}
+
+		[Test]
+		public void TestComplexMethod()
+		{
+			Test<InvertIfAndSimplify>(
+				@"class TestClass
+{
+	int Test ()
+	{
+		$if (true) {
+			Case1 ();
+		}
+        else 
+            continue;
+        return 0;
+	}
+}",
+				@"class TestClass
+{
+	int Test ()
+	{
+		if (false)
+			continue;
+		Case1 ();
+		return 0;
+	}
+}"
+				);
+		}
+	}
+}

ICSharpCode.NRefactory.Tests/ICSharpCode.NRefactory.Tests.csproj

@@ -399,6 +399,7 @@
     <Compile Include="CSharp\CodeActions\SimplifyIfFlowTests.cs" />
     <Compile Include="CSharp\CodeActions\SimplifyIfFlowInLoopsTests.cs" />
     <Compile Include="CSharp\CodeIssues\NoDefaultConstructorIssueTests.cs" />
+    <Compile Include="CSharp\CodeActions\InvertIfAndSimplifyTests.cs" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\..\cecil\Mono.Cecil.csproj">