Unity IL2CPP Bug:正则表达式导致 IL2CPP 崩溃的解决办法

Unity4.7版本在 IL2CPP 打包 IOS的时候出现错误：

IL2CPP error for method 'System.Void <PrivateImplementationDetails>::.ctor()' in assembly 'C:\Users\DELL\Documents\New Unity Project 4\Temp\StagingArea\Data\Managed\UnityEngine.UI.dll'  
Additional information: Build a development build for more information. Reentrant Fallback method invocation occured. It might be because either this FallbackBuffer is incorrectly shared by multiple threads, invoked inside Encoding recursively, or Reset invocation is forgotten.  

stdout;  
IL2CPP error for method 'System.Void <PrivateImplementationDetails>::.ctor()' in assembly 'C:\Users\DELL\Documents\New Unity Project 4\Temp\StagingArea\Data\Managed\UnityEngine.UI.dll'  
Additional information: Build a development build for more information. Reentrant Fallback method invocation occured. It might be because either this FallbackBuffer is incorrectly shared by multiple threads, invoked inside Encoding recursively, or Reset invocation is forgotten.  
il2cpp.exe didn't catch exception: System.ArgumentException: Reentrant Fallback method invocation occured. It might be because either this FallbackBuffer is incorrectly shared by multiple threads, invoked inside Encoding recursively, or Reset invocation is forgotten.  
  at System.Text.EncoderReplacementFallbackBuffer.Fallback (Int32 index) [0x00000] in <filename unknown>:0   
  at System.Text.EncoderReplacementFallbackBuffer.Fallback (Char charUnknown, Int32 index) [0x00000] in <filename unknown>:0   
  at System.Text.UTF8Encoding.GetFallbackChars (System.Char* chars, System.Char* start, System.Text.EncoderFallback fallback, System.Text.EncoderFallbackBuffer& buffer) [0x00000] in <filename unknown>:0   
  at System.Text.UTF8Encoding.InternalGetByteCount (System.Char* chars, Int32 count, System.Text.EncoderFallback fallback, System.Char& leftOver, Boolean flush) [0x00000] in <filename unknown>:0   
  at System.Text.UTF8Encoding.GetByteCount (System.Char* chars, Int32 count) [0x00000] in <filename unknown>:0   
  at System.Text.Encoding.GetByteCount (System.String s) [0x00000] in <filename unknown>:0   
  at System.Text.UTF8Encoding.GetByteCount (System.String chars) [0x00000] in <filename unknown>:0   
  at System.Text.Encoding.GetBytes (System.String s) [0x00000] in <filename unknown>:0   
  at Unity.IL2CPP.StringLiterals.StringLiteralWriter.Write (System.IO.Stream stringLiteralStream, System.IO.Stream stringLiteralDataStream) [0x00000] in <filename unknown>:0   
  at Unity.IL2CPP.MetadataCacheWriter.WriteMetadata (NiceIO.NPath outputDir, Unity.IL2CPP.GenericsCollection.InflatedCollection generics, Mono.Cecil.TypeDefinition[] allTypeDefinitions, ICollection`1 usedAssemblies, Unity.IL2CPP.MethodTables methodTables, Unity.IL2CPP.Metadata.MetadataCollector metadataCollector, Unity.IL2CPP.AttributeCollection attributeCollection, Unity.IL2CPP.Metadata.VTableBuilder vTableBuilder, Unity.IL2CPP.MethodCollector methodCollector) [0x00000] in <filename unknown>:0   
  at Unity.IL2CPP.SourceWriter.WriteCollectedMetadata (Unity.IL2CPP.GenericsCollection.InflatedCollection genericsCollection, ICollection`1 usedAssemblies, NiceIO.NPath outputDir, Unity.IL2CPP.Metadata.MetadataCollector metadataCollector, Unity.IL2CPP.AttributeCollection attributeCollection, Unity.IL2CPP.Metadata.VTableBuilder vTableBuilder, Unity.IL2CPP.MethodCollector methodCollector) [0x00000] in <filename unknown>:0   
  at Unity.IL2CPP.AssemblyConverter.Apply () [0x00000] in <filename unknown>:0   
  at Unity.IL2CPP.AssemblyConverter.ConvertAssemblies (System.String[] assemblies, NiceIO.NPath outputDir) [0x00000] in <filename unknown>:0   
stderr:  
Unhandled Exception: System.ArgumentException: Reentrant Fallback method invocation occured. It might be because either this FallbackBuffer is incorrectly shared by multiple threads, invoked inside Encoding recursively, or Reset invocation is forgotten.  
  at System.Text.EncoderReplacementFallbackBuffer.Fallback (Int32 index) [0x00000] in <filename unknown>:0   
  at System.Text.EncoderReplacementFallbackBuffer.Fallback (Char charUnknown, Int32 index) [0x00000] in <filename unknown>:0   
  at System.Text.UTF8Encoding.GetFallbackChars (System.Char* chars, System.Char* start, System.Text.EncoderFallback fallback, System.Text.EncoderFallbackBuffer& buffer) [0x00000] in <filename unknown>:0   
  at System.Text.UTF8Encoding.InternalGetByteCount (System.Char* chars, Int32 count, System.Text.EncoderFallback fallback, System.Char& leftOver, Boolean flush) [0x00000] in <filename unknown>:0   
  at System.Text.UTF8Encoding.GetByteCount (System.Char* chars, Int32 count) [0x00000] in <filename unknown>:0   
  at System.Text.Encoding.GetByteCount (System.String s) [0x00000] in <filename unknown>:0   
  at System.Text.UTF8Encoding.GetByteCount (System.String chars) [0x00000] in <filename unknown>:0   
  at System.Text.Encoding.GetBytes (System.String s) [0x00000] in <filename unknown>:0   
  at Unity.IL2CPP.StringLiterals.StringLiteralWriter.Write (System.IO.Stream stringLiteralStream, System.IO.Stream stringLiteralDataStream) [0x00000] in <filename unknown>:0   
  at Unity.IL2CPP.MetadataCacheWriter.WriteMetadata (NiceIO.NPath outputDir, Unity.IL2CPP.GenericsCollection.InflatedCollection generics, Mono.Cecil.TypeDefinition[] allTypeDefinitions, ICollection`1 usedAssemblies, Unity.IL2CPP.MethodTables methodTables, Unity.IL2CPP.Metadata.MetadataCollector metadataCollector, Unity.IL2CPP.AttributeCollection attributeCollection, Unity.IL2CPP.Metadata.VTableBuilder vTableBuilder, Unity.IL2CPP.MethodCollector methodCollector) [0x00000] in <filename unknown>:0   
  at Unity.IL2CPP.SourceWriter.WriteCollectedMetadata (Unity.IL2CPP.GenericsCollection.InflatedCollection genericsCollection, ICollection`1 usedAssemblies, NiceIO.NPath outputDir, Unity.IL2CPP.Metadata.MetadataCollector metadataCollector, Unity.IL2CPP.AttributeCollection attributeCollection, Unity.IL2CPP.Metadata.VTableBuilder vTableBuilder, Unity.IL2CPP.MethodCollector methodCollector) [0x00000] in <filename unknown>:0   
  at Unity.IL2CPP.AssemblyConverter.Apply () [0x00000] in <filename unknown>:0   
  at Unity.IL2CPP.AssemblyConverter.ConvertAssemblies (System.String[] assemblies, NiceIO.NPath outputDir) [0x00000] in <filename unknown>:0   
UnityEngine.Debug:LogError(Object)  
UnityEditorInternal.Runner:RunManagedProgram(String, String, String, CompilerOutputParserBase) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:66)  
UnityEditorInternal.IL2CPPBuilder:ConvertPlayerDlltoCpp(ICollection`1, String, String) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:424)  
UnityEditorInternal.IL2CPPBuilder:Run() (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:293)  
UnityEditorInternal.IL2CPPUtils:RunIl2Cpp(String, String, IIl2CppPlatformProvider, Action`1, RuntimeClassRegistry) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:211)  
UnityEditor.HostView:OnGUI()  

Error building Player: Exception: E:\Program Files (x86)\Unity4.7.0f1\Editor\Data\il2cpp/build/il2cpp.exe did not run properly!  

根据错误Log可以判断是 IL2CPP 在将C# 代码转成 CPP的时候解析出错 。 但是却没有具体的提示到底是哪里有问题！

还好有SVN，在经过一晚上的各种回滚之后，找到了罪魁祸首，一个复杂的正则表达式：

string regstr = "[\uD800-\uDBFF][\uDC00-\uDFFF]|[\u2600-\u26FF][\uDE00-\uDEFF]";  

就是这个正则表达式导致的 IL2CPP 崩溃。