Assembler with possibility to create pseudo mnemonics

As I have argued in the past, these type of "fake instructions" are usually a bad idea, as they are either inefficient or could have unexpected side effects (e.g., in your example, there is either an unexpected push/pop or an unexpected modification of the DE register if you remove the push/pop). But if you still want to use these, there are two possibilities:
1) you can always define these with MACROs, most assemblers allow this, and you could just define an "ADD16" macro, for example, that does exactly what you suggest above.
2) there are assemblers that already have very long lists of these "fake instructions" defined by default like sjasmplus or sjasm (the one you state above is defined in both).

If you want to use these, my suggestion is to use macros, so that you can have some sort of indicator in the names of these new instructions (I would advise AGAINST calling them the same names as the original z80 nemonics), so that it's obvious they are composite instructions, to prevent debugging nightmares

For the sake of clean-code, I wouldn't use any of that. It might be tempting, but can be a real pain later. But hell, I'm a hardcore coder who doesn't even use cross-development shit. So, what do I know.

Here is the list of these "fake instructions" that sjasmplus supports: https://z00m128.github.io/sjasmplus/documentation.html#s_fak...

(and btw, I now see I was wrong, and the instruction you defined above is not in the list, haha, my bad!)

I don't think there is a table of T-states used by each of these though!

If you choose to use macros, let us know if you have troubles defining them. Happy to help out on creating a couple of these as examples :)

Oh, interesting, the maintainer of sjasmplus (ped7g) often reads these forums, maybe ped7g can help on that. I was able to compile it fine, but on Mac, never compiled it on Linux myself.

But another alternative is Glass (https://www.grauw.nl/projects/glass/). Glass is Java, and you can just get the .jar file, so, no need to compile it.

Some example macros inspired in your example above using the Glass syntax:

ADD_HL_CONST: MACRO ?const
    push de
    ld de, ?const
    add hl, de
    pop de
    ENDM

ADD_REG_CONST: MACRO ?reg1, ?reg2, ?const
    push ?reg2
    ld ?reg2, ?const
    add ?reg1, ?reg2
    pop ?reg2
    ENDM

And then you can call them like this:

    ADD_HL_CONST 100
    ADD_REG_CONST hl, de, 100

You can thank me later statically compiled so that it runs on any linux64 system.

Sjasmplus linux 64