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c#.netassemblycil

Is CIL an assembly language and JIT an assembler

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

Solution

  • Assembly is made up of mnemonics for the machine code instructions of a particular processor. A direct representation of the 1s and 0s that make the core execute code, but written in text to make it easy on a human. Which is very unlike CIL:

    • you can't buy a processor that executes CIL
    • CIL doesn't target a specific processor, the jitter does
    • CIL assumes a stack-based execution model, processors are primarily register based
    • CIL code is optimized from its original form
    • there is no one-to-one translation of a CIL instruction to a processor instruction

    That last bullet is a key one, a design decision that makes CIL strongly different from bytecode is that CIL instructions are type-less. There is only one ADD instruction but processors have many versions of it. Specific ones that take byte, short, int, long, float and double operands. Required because different parts of the processor core are used to execute the add. The jitter picks the right one, based on the type of the operands it infers from previous CIL instructions.

    Just like the + operator in the C# language, it also can work with different operand types. Which really make the L in CIL significant, it is a Language. A simple one, but it is only simple to help make it easy to write a jitter for it.