CIL trivia: Mono implements an extra opcode from the ECMA-355 standard that CoreCLR does not have

[AustinWise]

I noticed an unfamiliar opcode on page 356 of the fifth edition ECMA-355 standard: the "no. prefix". It's description is:

The specified fault check(s) normally performed as part of the execution of the subsequent instruction can/shall be skipped.

The types of checks that can be disabled include type checks, range checks on array access, and null checking.

Mono implements this opcode, using it internally in few places in generated marshaling code. In CoreClr it is CEE_UNUSED69 and does not appear to be implemented.

That's all, I just thought this was mildly interesting.

[EgorBo]

Related: #10112