Is CIL an assembly language and JIT an assembler

Question

Does the Just In Time Compiler(JIT) really map each of the Common Intermediate Language(CIL) instructions in a program to underlying processor's opcodes?

And If so can we call CIL an assembly language and JIT an assembler

Note: Wikipedia doesn't list CIL as an assembly language in its list of assembly languages

Answer 1

This question is all about definitions, so let's define the terms properly. First, assembly language:

Assembly language is a low-level programming language for computers, microprocessors, microcontrollers, and other programmable devices in which each statement corresponds to a single machine language instruction. An assembly language is specific to a certain computer architecture, in contrast to most high-level programming languages, which generally are portable to multiple systems.

Now, CIL:

Common Intermediate Language is the lowest-level human-readable programming language defined by the Common Language Infrastructure (CLI) specification and is used by the .NET Framework and Mono. Languages which target a CLI-compatible runtime environment compile to CIL, which is assembled into an object code that has a bytecode-style format.

Okay, this part is technically not correct: for example C# compiler compiles directly to the bytecode, it doesn't go through CIL (the human-readable language), but theoretically, we can imagine that's what's happening.

With these two definitions, CIL is an assembly language, because each statement in it is compiled down to a single bytecode instruction. The fact that there is no physical computer that can execute that bytecode directly doesn't matter.

The definition says that each assembly language is “specific to a certain computer architecture”. In this case, the architecture is the CLR virtual machine.

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About JIT: the JIT compiler can't be considered an assembler: it doesn't do the 1:1 translation from human-readable form to bytecode, ilasm does that.

The JIT compiler is an optimizing compiler that compiles from bytecode to native machine code (for whatever ISA / CPU it's running on), while making optimizations.