Промежуточное представление кода в инфраструктуре CLI (CIL)

Intermediate representation defined within the CLI specification

Common Intermediate Language (CIL), formerly called Microsoft Intermediate Language (MSIL) or Intermediate Language (IL), is the intermediate language binary instruction set defined within the Common Language Infrastructure (CLI) specification. CIL instructions are executed by a CIL compatible runtime environment such as the Common Language Runtime. Languages which target the CLI compile to CIL. CIL is object oriented, stack based bytecode. Runtimes typically just in time compile CIL instructions into native code. CIL was originally known as Microsoft Intermediate Language (MSIL) during the beta releases of the NET languages. Due to standardization of C# and the CLI, the bytecode is now officially known as CIL. Windows Defender virus definitions continue to refer to binaries compiled with it as MSIL.

The Common Language Infrastructure (CLI) records information about compiled classes as metadata. Like the type library in the Component Object Model, this enables applications to support and discover the interfaces, classes, types, methods, and fields in the assembly. The process of reading such metadata is called "reflection". Metadata can be data in the form of "attributes". Attributes can be customized by extending the Attribute class. This is a powerful feature. It allows the creator of the class the ability to adorn it with extra information that consumers of the class can use in various meaningful ways, depending on the application domain.

A CIL assembly and instructions are generated by either a compiler or a utility called the IL Assembler (ILAsm) that is shipped with the execution environment. Assembled CIL can also be disassembled into code again using the IL Disassembler (ILDASM). There are other tools such as NET Reflector that can decompile CIL into a high level language (e. g. C# or Visual Basic). This makes CIL a very easy target for reverse engineering. This trait is shared with Java bytecode. However, there are tools that can obfuscate the code, and do it so that the code cannot be easily readable but still be runnable.

Just in time compilation (JIT) involves turning the byte code into code immediately executable by the CPU. The conversion is performed gradually during the program's execution. JIT compilation provides environment specific optimization, runtime type safety, and assembly verification. To accomplish this, the JIT compiler examines the assembly metadata for any illegal accesses and handles violations appropriately.

CLI compatible execution environments also come with the option to do an Ahead of time compilation (AOT) of an assembly to make it execute faster by removing the JIT process at runtime. In the NET Framework there is a special tool called the Native Image Generator (NGEN) that performs the AOT. A different approach for AOT is CoreRT that allows the compilation of Net Core code to a single executable with no dependency on a runtime. In Mono there is also an option to do an AOT.