iOS 64 bit support is implemented with the scripting backend called IL2CPP. It runs with your C#/UnityScript code.
IL2CPP 运行时将提前编译器与虚拟机相结合，将程序集转换为 C++，同时利用标准平台 C++ 编译器生成本机二进制文件。最终结果是显著改善性能、平台兼容性和可维护性。
IL2CPP is the only scripting backend to support deploying to ARM 64-bit on iOS, and is thus mandatory to deploy to the Apple app-store for releasing new apps.
Pick it in Scripting Backend dropdown in Player Settings.
By default it will build for Universal architecture (including both ARM64 and ARMv7), if needed you might switch to specific architecture in Player Settings. There is number of things that should be done before your application is up and running in 64 bits:
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