Fix #1767: Fix detection switch-on-string that uses leave instead of branch instructions.

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

@@ -47,6 +47,8 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			Null
 		}
 
+		private static char ch1767;
+
 #if !ROSLYN
 		public static State SwitchOverNullableBool(bool? value)
 		{
@@ -465,7 +467,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			}
 			Console.WriteLine("End of method");
 		}
-		
+
 		public static void SwitchWithGotoComplex(string s)
 		{
 			Console.WriteLine("SwitchWithGotoComplex: " + s);
@@ -640,7 +642,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 				Console.WriteLine();
 			}
 		}
-		
+
 		// while condition, return and break cases
 		public static void SwitchWithContinue2(int i, bool b)
 		{
@@ -681,7 +683,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 				i++;
 			}
 		}
-		
+
 		// for loop version
 		public static void SwitchWithContinue3(bool b)
 		{
@@ -721,7 +723,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 				Console.WriteLine("loop-tail");
 			}
 		}
-		
+
 		// foreach version
 		public static void SwitchWithContinue4(bool b)
 		{
@@ -843,7 +845,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 						continue;
 				}
 				Console.WriteLine("loop-tail");
-			 } while (++i < 10);
+			} while (++i < 10);
 		}
 
 		// double break from switch to loop exit requires additional pattern matching in HighLevelLoopTransform
@@ -918,7 +920,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 		}
 
 		// These decompile poorly into switch statements and should be left as is
-#region Overagressive Switch Use
+		#region Overagressive Switch Use
 
 #if ROSLYN || OPT
 		public static void SingleIf1(int i, bool a)
@@ -929,7 +931,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			Console.WriteLine(2);
 		}
 #endif
-		
+
 		public static void SingleIf2(int i, bool a, bool b)
 		{
 			if (i == 1 || (i == 2 && a) || (i == 3 && b)) {
@@ -937,7 +939,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			}
 			Console.WriteLine(2);
 		}
-		
+
 		public static void SingleIf3(int i, bool a, bool b)
 		{
 			if (a || i == 1 || (i == 2 && b)) {
@@ -945,7 +947,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			}
 			Console.WriteLine(2);
 		}
-		
+
 		public static void SingleIf4(int i, bool a)
 		{
 			if (i == 1 || i == 2 || (i != 3 && a) || i != 4) {
@@ -964,7 +966,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			}
 			Console.WriteLine();
 		}
-		
+
 		public static void IfChainWithCondition(int i)
 		{
 			if (i == 0) {
@@ -985,7 +987,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 
 			Console.WriteLine();
 		}
-		
+
 		public static bool SwitchlikeIf(int i, int j)
 		{
 			if (i != 0 && j != 0) {
@@ -1023,7 +1025,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 				}
 				return false;
 			}
-			
+
 			return true;
 		}
 
@@ -1052,7 +1054,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			}
 			Console.WriteLine("end");
 		}
-		
+
 		public static bool Loop8(char c, bool b, Func<char> getChar)
 		{
 			if (b) {
@@ -1071,8 +1073,8 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 				c = getChar();
 			} while (c != -1 && c != '\n' && c != '\u2028' && c != '\u2029');
 		}
-#endregion
-		
+		#endregion
+
 		// Ensure correctness of SwitchDetection.UseCSharpSwitch control flow heuristics
 		public static void SwitchWithBreakCase(int i, bool b)
 		{
@@ -1108,7 +1110,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			}
 			Console.WriteLine();
 		}
-		
+
 		public static int SwitchWithReturnAndBreak2(int i, bool b)
 		{
 			switch (i) {
@@ -1130,7 +1132,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			Console.WriteLine();
 			return 0;
 		}
-		
+
 		public static void SwitchWithReturnAndBreak3(int i)
 		{
 			switch (i) {
@@ -1229,5 +1231,29 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			}
 			return key != (ConsoleKey)0;
 		}
+
+		public static void Issue1767(string s)
+		{
+			switch (s) {
+				case "a":
+					ch1767 = s[0];
+					break;
+				case "b":
+					ch1767 = s[0];
+					break;
+				case "c":
+					ch1767 = s[0];
+					break;
+				case "d":
+					ch1767 = s[0];
+					break;
+				case "e":
+					ch1767 = s[0];
+					break;
+				case "f":
+					ch1767 = s[0];
+					break;
+			}
+		}
 	}
 }

ICSharpCode.Decompiler/IL/Transforms/SwitchOnStringTransform.cs

@@ -154,26 +154,33 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 
 		bool SimplifyCascadingIfStatements(InstructionCollection<ILInstruction> instructions, ref int i)
 		{
-			if (i < 1) return false;
 			// match first block: checking switch-value for null or first value (Roslyn)
 			// if (call op_Equality(ldloc switchValueVar, ldstr value)) br firstBlock
 			// -or-
 			// if (comp(ldloc switchValueVar == ldnull)) br defaultBlock
-			if (!(instructions[i].MatchIfInstruction(out var condition, out var firstBlockJump)))
+			if (!instructions[i].MatchIfInstruction(out var condition, out var firstBlockOrDefaultJump))
 				return false;
-			if (!firstBlockJump.MatchBranch(out var firstBlock))
+
+			if (firstBlockOrDefaultJump.MatchBranch(out var firstBlock)) {
+				// success
+			} else if (firstBlockOrDefaultJump.MatchLeave(out _)) {
+				firstBlock = null;
+				// success
+			} else {
 				return false;
-			List<(string, Block)> values = new List<(string, Block)>();
+			}
+
+			List<(string, ILInstruction)> values = new List<(string, ILInstruction)>();
 			ILInstruction switchValue = null;
 
 			// match call to operator ==(string, string)
 			if (!MatchStringEqualityComparison(condition, out var switchValueVar, out string firstBlockValue))
 				return false;
-			values.Add((firstBlockValue, firstBlock));
+			values.Add((firstBlockValue, firstBlock ?? firstBlockOrDefaultJump));
 
 			bool extraLoad = false;
 			bool keepAssignmentBefore = false;
-			if (instructions[i - 1].MatchStLoc(switchValueVar, out switchValue)) {
+			if (i >= 1 && instructions[i - 1].MatchStLoc(switchValueVar, out switchValue)) {
 				// stloc switchValueVar(switchValue)
 				// if (call op_Equality(ldloc switchValueVar, ldstr value)) br firstBlock
 
@@ -183,7 +190,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					switchValue = newSwitchValue;
 					extraLoad = true;
 				}
-			} else if (instructions[i - 1] is StLoc stloc) {
+			} else if (i >= 1 && instructions[i - 1] is StLoc stloc) {
 				if (stloc.Value.MatchLdLoc(switchValueVar)) {
 					// in case of optimized legacy code there are two stlocs:
 					// stloc otherSwitchValueVar(ldloc switchValue)
@@ -212,10 +219,12 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				return false;
 			// extract all cases and add them to the values list.
 			Block currentCaseBlock = nextCaseJump.TargetBlock;
-			Block nextCaseBlock;
+			ILInstruction nextCaseBlock;
 			while ((nextCaseBlock = MatchCaseBlock(currentCaseBlock, switchValueVar, out string value, out Block block)) != null) {
 				values.Add((value, block));
-				currentCaseBlock = nextCaseBlock;
+				currentCaseBlock = nextCaseBlock as Block;
+				if (currentCaseBlock == null)
+					break;
 			}
 			// We didn't find enough cases, exit
 			if (values.Count < 3)
@@ -225,9 +234,10 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				keepAssignmentBefore = true;
 				switchValue = new LdLoc(switchValueVar);
 			}
-			var sections = new List<SwitchSection>(values.SelectWithIndex((index, b) => new SwitchSection { Labels = new LongSet(index), Body = new Branch(b.Item2) }));
-			sections.Add(new SwitchSection { Labels = new LongSet(new LongInterval(0, sections.Count)).Invert(), Body = new Branch(currentCaseBlock) });
-			var stringToInt = new StringToInt(switchValue, values.SelectArray(item => item.Item1));
+			int offset = firstBlock == null ? 1 : 0;
+			var sections = new List<SwitchSection>(values.Skip(offset).SelectWithIndex((index, b) => new SwitchSection { Labels = new LongSet(index), Body = new Branch((Block)b.Item2) }));
+			sections.Add(new SwitchSection { Labels = new LongSet(new LongInterval(0, sections.Count)).Invert(), Body = currentCaseBlock != null ? (ILInstruction)new Branch(currentCaseBlock) : new Leave((BlockContainer)nextCaseBlock) });
+			var stringToInt = new StringToInt(switchValue, values.Skip(offset).Select(item => item.Item1).ToArray());
 			var inst = new SwitchInstruction(stringToInt);
 			inst.Sections.AddRange(sections);
 			if (extraLoad) {
@@ -357,7 +367,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// The <paramref name="switchVariable"/> is updated if the value gets copied to a different variable.
 		/// See comments below for more info.
 		/// </summary>
-		Block MatchCaseBlock(Block currentBlock, ILVariable switchVariable, out string value, out Block caseBlock)
+		ILInstruction MatchCaseBlock(Block currentBlock, ILVariable switchVariable, out string value, out Block caseBlock)
 		{
 			value = null;
 			caseBlock = null;
@@ -369,19 +379,25 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			if (!caseBlockBranch.MatchBranch(out caseBlock))
 				return null;
 			Block nextBlock;
+			BlockContainer blockContainer = null;
 			if (condition.MatchLogicNot(out var inner)) {
 				condition = inner;
 				nextBlock = caseBlock;
 				if (!currentBlock.Instructions[1].MatchBranch(out caseBlock))
 					return null;
 			} else {
-				if (!currentBlock.Instructions[1].MatchBranch(out nextBlock))
+				if (currentBlock.Instructions[1].MatchBranch(out nextBlock)) {
+					// success
+				} else if (currentBlock.Instructions[1].MatchLeave(out blockContainer)) {
+					// success
+				} else {
 					return null;
+				}
 			}
 			if (!MatchStringEqualityComparison(condition, switchVariable, out value)) {
 				return null;
 			}
-			return nextBlock;
+			return nextBlock ?? (ILInstruction)blockContainer;
 		}
 
 		/// <summary>