YJIT: Refactor into gen_push_frame

[jhawthorn]

One of my hopes with the introduction of the new backend IR is the ability to refactor some of our more complex methods into smaller and (hopefully) reusable methods.

This refactors the "push frame" operation common to both gen_send_iseq and gen_send_cfunc into its own method. This allows that logic to live in one place.

A few things motivated this extraction in particular:

• @matthewd and have been pairing on improving "blockarg" support, which required making an identical change to both gen_send_iseq and gen_send_cfunc
• I have a wip branch which implements "bmethods", which required performing this same push frame operation in a 3rd place 😅
• I'd like to experiment with pushing an extra frame for some optimizations (specifically to combine new/initialize)

I like how this turned out. It is slightly more code, but much of that is comments. I used a struct to pass the arguments describing how the frame is to be constructed, which I think makes the calls easier to read and less error-prone. I used an enum for PushFrameBlockHandler in anticipation of a 3rd type being added for block param proxy support.

The code that's generated is very slightly different (I believe better, especially for the cfunc case). The new CFP is written to relative to the caller CFP instead of using a temporary register (a temporary register derived from a memory addition and a memory load for cfunc) in both cases. This takes the function call block of 1.itself (a cfunc) from 177 bytes to 159 bytes on x86_64 (for iseq calls a more modest 3 bytes of savings 😅). I wasn't able to see a difference in performance, but would be curious to see on an Intel machine (vs my AMD zen 2).

[k0kubun]

Cirrus Graviton2 YJIT jobs failed with both gcc and clang. Is this failure related to your change?

[jhawthorn]

I think it is related. I can reproduce (inconsistently) locally. I'll investigate tomorrow.

[noahgibbs]

I definitely like the readability and maintainability of this more.

[jhawthorn]

Figured it out! I had mistakenly dropped a cast from cme -> usize -> VALUE -> Opnd and only did cme -> usize -> Opnd so it wasn't being compacted/moved correctly. Should be fixed now! 🤞

[maximecb]

I support this effort, it's a good idea 👍

Wrote two very minor comments.