Combine switch sections that branch to same label.

ICSharpCode.Decompiler/IL/ControlFlow/ControlFlowSimplification.cs

@@ -41,29 +41,76 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			foreach (var block in function.Descendants.OfType<Block>()) {
 				// Remove 'nop' instructions
 				block.Instructions.RemoveAll(inst => inst.OpCode == OpCode.Nop);
-				// Ensure return blocks are inlined:
-				if (block.Instructions.Count == 2 && block.Instructions[1].OpCode == OpCode.Return) {
-					Return ret = (Return)block.Instructions[1];
-					ILVariable v;
-					ILInstruction inst;
-					if (ret.ReturnValue != null && ret.ReturnValue.MatchLdLoc(out v)
-					    && v.IsSingleDefinition && v.LoadCount == 1 && block.Instructions[0].MatchStLoc(v, out inst))
-					{
-						inst.AddILRange(ret.ReturnValue.ILRange);
-						inst.AddILRange(block.Instructions[0].ILRange);
-						ret.ReturnValue = inst;
-						block.Instructions.RemoveAt(0);
-					}
+				
+				InlineReturnBlock(block);
+				// due to our of of basic blocks at this point,
+				// switch instructions can only appear as second-to-last insturction
+				SimplifySwitchInstruction(block.Instructions.ElementAtOrDefault(block.Instructions.Count - 2) as SwitchInstruction);
+			}
+			SimplifyBranchChains(function);
+			CleanUpEmptyBlocks(function);
+		}
+		
+		void InlineReturnBlock(Block block)
+		{
+			// In debug mode, the C#-compiler generates 'return blocks' that
+			// unnecessarily store the return value to a local and then load it again:
+			//   v = <inst>
+			//   ret(v)
+			// (where 'v' has no other uses)
+			// Simplify these to a simple `ret(<inst>)` so that they match the release build version.
+			// 
+			if (block.Instructions.Count == 2 && block.Instructions[1].OpCode == OpCode.Return) {
+				Return ret = (Return)block.Instructions[1];
+				ILVariable v;
+				ILInstruction inst;
+				if (ret.ReturnValue != null && ret.ReturnValue.MatchLdLoc(out v)
+				    && v.IsSingleDefinition && v.LoadCount == 1 && block.Instructions[0].MatchStLoc(v, out inst))
+				{
+					inst.AddILRange(ret.ReturnValue.ILRange);
+					inst.AddILRange(block.Instructions[0].ILRange);
+					ret.ReturnValue = inst;
+					block.Instructions.RemoveAt(0);
 				}
 			}
+		}
+		
+		void SimplifySwitchInstruction(SwitchInstruction sw)
+		{
+			if (sw == null)
+				return;
+			
+			// ControlFlowSimplification runs early (before any other control flow transforms).
+			// Any switch instructions will only have branch instructions in the sections.
+			
+			// dict from branch target to switch section
+			var dict = new Dictionary<Block, SwitchSection>();
+			sw.Sections.RemoveAll(
+				section => {
+					Block target;
+					if (section.Body.MatchBranch(out target)) {
+						SwitchSection primarySection;
+						if (dict.TryGetValue(target, out primarySection)) {
+							primarySection.Labels = primarySection.Labels.UnionWith(section.Labels);
+							return true; // remove this section
+						} else {
+							dict.Add(target, section);
+						}
+					}
+					return false;
+				});
+		}
+		
+		void SimplifyBranchChains(ILFunction function)
+		{
 			HashSet<Block> visitedBlocks = new HashSet<Block>();
 			foreach (var branch in function.Descendants.OfType<Branch>()) {
-				// Resolve indirect branches
+				// Resolve chained branches to the final target:
 				var targetBlock = branch.TargetBlock;
 				visitedBlocks.Clear();
 				while (targetBlock.Instructions.Count == 1 && targetBlock.Instructions[0].OpCode == OpCode.Branch) {
 					if (!visitedBlocks.Add(targetBlock)) {
-						// prevent infinite loop when indirect branches point in infinite loop
+						// prevent infinite loop when branch chain is cyclic
 						break;
 					}
 					var nextBranch = (Branch)targetBlock.Instructions[0];
@@ -75,14 +122,18 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				if (IsReturnBlock(targetBlock)) {
 					// Replace branches to 'return blocks' with the return instruction
 					branch.ReplaceWith(targetBlock.Instructions[0].Clone());
-				} else if (branch.TargetBlock.Instructions.Count == 1 && branch.TargetBlock.Instructions[0].OpCode == OpCode.Leave) {
+				} else if (targetBlock.Instructions.Count == 1 && targetBlock.Instructions[0].OpCode == OpCode.Leave) {
 					// Replace branches to 'leave' instruction with the leave instruction
-					Leave leave = (Leave)branch.TargetBlock.Instructions[0];
+					Leave leave = (Leave)targetBlock.Instructions[0];
 					branch.ReplaceWith(new Leave(leave.TargetContainer) { ILRange = branch.ILRange });
 				}
 				if (targetBlock.IncomingEdgeCount == 0)
 					targetBlock.Instructions.Clear(); // mark the block for deletion
 			}
+		}
+		
+		void CleanUpEmptyBlocks(ILFunction function)
+		{
 			foreach (var container in function.Descendants.OfType<BlockContainer>()) {
 				foreach (var block in container.Blocks) {
 					if (block.Instructions.Count == 0)
@@ -123,5 +174,6 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			targetBlock.Instructions.Clear(); // mark targetBlock for deletion
 			return true;
 		}
+		
 	}
 }

ICSharpCode.Decompiler/IL/ILReader.cs

@@ -1042,7 +1042,7 @@ namespace ICSharpCode.Decompiler.IL
 				Debug.Assert(right.ResultType.IsIntegerType());
 				return new Comp(kind, un ? Sign.Unsigned : Sign.Signed, left, right);
 			} else {
-				// object reference or managed reference comparison
+				// integer equality, object reference or managed reference comparison
 				return new Comp(kind, Sign.None, left, right);
 			}
 		}

ICSharpCode.Decompiler/IL/Instructions/SwitchInstruction.cs

@@ -17,6 +17,8 @@
 // DEALINGS IN THE SOFTWARE.
 
 using System;
+using System.Collections.Immutable;
+using System.Diagnostics;
 using System.Linq;
 
 namespace ICSharpCode.Decompiler.IL
@@ -111,6 +113,16 @@ namespace ICSharpCode.Decompiler.IL
 			clone.Sections.AddRange(this.Sections.Select(h => (SwitchSection)h.Clone()));
 			return clone;
 		}
+		
+		internal override void CheckInvariant(ILPhase phase)
+		{
+			base.CheckInvariant(phase);
+			LongSet sets = new LongSet(ImmutableArray<LongInterval>.Empty);
+			foreach (var section in Sections) {
+				Debug.Assert(!section.Labels.Intersects(sets));
+				sets = sets.UnionWith(section.Labels);
+			}
+		}
 	}
 	
 	partial class SwitchSection

ICSharpCode.Decompiler/Util/CollectionExtensions.cs

@@ -46,5 +46,33 @@ namespace ICSharpCode.Decompiler
 			}
 			return result;
 		}
+		
+		/// <summary>
+		/// The merge step of merge sort.
+		/// </summary>
+		public static IEnumerable<T> Merge<T>(this IEnumerable<T> input1, IEnumerable<T> input2, Comparison<T> comparison)
+		{
+			var enumA = input1.GetEnumerator();
+			var enumB = input2.GetEnumerator();
+			bool moreA = enumA.MoveNext();
+			bool moreB = enumB.MoveNext();
+			while (moreA && moreB) {
+				if (comparison(enumA.Current, enumB.Current) <= 0) {
+					yield return enumA.Current;
+					moreA = enumA.MoveNext();
+				} else {
+					yield return enumB.Current;
+					moreB = enumB.MoveNext();
+				}
+			}
+			while (moreA) {
+				yield return enumA.Current;
+				moreA = enumA.MoveNext();
+			}
+			while (moreB) {
+				yield return enumB.Current;
+				moreB = enumB.MoveNext();
+			}
+		}
 	}
 }

ICSharpCode.Decompiler/Util/Interval.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Diagnostics;
@@ -94,7 +95,7 @@ namespace ICSharpCode.Decompiler
 			if (End == int.MinValue)
 				return string.Format("[{0}..int.MaxValue]", Start);
 			else
-			return string.Format("[{0}..{1})", Start, End);
+				return string.Format("[{0}..{1})", Start, End);
 		}
 		
 		#region Equals and GetHashCode implementation
@@ -111,7 +112,7 @@ namespace ICSharpCode.Decompiler
 		public override int GetHashCode()
 		{
 			return Start ^ End ^ (End << 7);
-			}
+		}
 
 		public static bool operator ==(Interval lhs, Interval rhs)
 		{
@@ -230,7 +231,7 @@ namespace ICSharpCode.Decompiler
 			if (End == long.MinValue)
 				return string.Format("[{0}..long.MaxValue]", Start);
 			else
-			return string.Format("[{0}..{1})", Start, End);
+				return string.Format("[{0}..{1})", Start, End);
 		}
 		
 		#region Equals and GetHashCode implementation
@@ -283,6 +284,81 @@ namespace ICSharpCode.Decompiler
 			get { return Intervals.IsDefaultOrEmpty; }
 		}
 
+		IEnumerable<LongInterval> DoIntersectWith(LongSet other)
+		{
+			var enumA = this.Intervals.GetEnumerator();
+			var enumB = other.Intervals.GetEnumerator();
+			bool moreA = enumA.MoveNext();
+			bool moreB = enumB.MoveNext();
+			while (moreA && moreB) {
+				LongInterval a = enumA.Current;
+				LongInterval b = enumB.Current;
+				LongInterval intersection = a.Intersect(b);
+				if (!intersection.IsEmpty) {
+					yield return intersection;
+				}
+				if (a.InclusiveEnd < b.InclusiveEnd) {
+					moreA = enumA.MoveNext();
+				} else {
+					moreB = enumB.MoveNext();
+				}
+			}
+		}
+		
+		public bool Intersects(LongSet other)
+		{
+			return DoIntersectWith(other).Any();
+		}
+		
+		public LongSet IntersectWith(LongSet other)
+		{
+			return new LongSet(DoIntersectWith(other).ToImmutableArray());
+		}
+		
+		IEnumerable<LongInterval> DoUnionWith(LongSet other)
+		{
+			long start = long.MinValue;
+			long end = long.MinValue;
+			bool empty = true;
+			foreach (var element in this.Intervals.Merge(other.Intervals, (a, b) => a.Start.CompareTo(b.Start))) {
+				Debug.Assert(start <= element.Start);
+				
+				if (!empty && element.Start < end - 1) {
+					// element overlaps or touches [start, end), so combine the intervals:
+					if (element.End == long.MinValue) {
+						// special case: element goes all the way up to long.MaxValue inclusive
+						yield return new LongInterval(start, element.End);
+						break;
+					} else {
+						end = Math.Max(end, element.End);
+					}
+				} else {
+					// flush existing interval:
+					if (!empty) {
+						yield return new LongInterval(start, end);
+					} else {
+						empty = false;
+					}
+					start = element.Start;
+					end = element.End;
+				}
+				if (end == long.MinValue) {
+					// special case: element goes all the way up to long.MaxValue inclusive
+					// all further intervals in the input must be contained in [start, end),
+					// so ignore them (and avoid trouble due to the overflow in `end`).
+					break;
+				}
+			}
+			if (!empty) {
+				yield return new LongInterval(start, end);
+			}
+		}
+		
+		public LongSet UnionWith(LongSet other)
+		{
+			return new LongSet(DoUnionWith(other).ToImmutableArray());
+		}
+		
 		public bool Contains(long val)
 		{
 			int index = upper_bound(val);