Generate only one variable for 'dup' if possible

ICSharpCode.Decompiler/ILAst/ILAstBuilder.cs

@@ -409,6 +409,31 @@ namespace ICSharpCode.Decompiler.ILAst
 				}
 			}
 			
+			// Try to use single temporary variable insted of several if possilbe (especially useful for dup)
+			foreach(ByteCode byteCode in body) {
+				if (byteCode.StoreTo != null && byteCode.StoreTo.Count > 1) {
+					var locVars = byteCode.StoreTo;
+					// For each of the variables, find the location where it is loaded - there should be preciesly one
+					var loadedBy = locVars.Select(argVar => body.SelectMany(bc => bc.StackBefore).Where(s => s.LoadFrom == argVar).Single()).ToList();
+					// We now know that all the variables have a single load,
+					// Let's make sure that they have also a single store - us
+					if (loadedBy.All(slot => slot.PushedBy.Length == 1 && slot.PushedBy[0] == byteCode)) {
+						// Great - we can reduce everything into single variable
+						ILVariable tmpVar = new ILVariable() { Name = string.Format("expr_{0:X2}", byteCode.Offset), IsGenerated = true };
+						byteCode.StoreTo = new List<ILVariable>() { tmpVar };
+						foreach(ByteCode bc in body) {
+							for (int i = 0; i < bc.StackBefore.Count; i++) {
+								// Is it one of the variable to be merged?
+								if (locVars.Contains(bc.StackBefore[i].LoadFrom)) {
+									// Replace with the new temp variable
+									bc.StackBefore[i] = new StackSlot(bc.StackBefore[i].PushedBy, tmpVar);
+								}
+							}
+						}
+					}
+				}
+			}
+			
 			// Split and convert the normal local variables
 			ConvertLocalVariables(body);