Split hot and cold parts of the templates.

[markshannon]

Linked PRs

• GH-116422: Tier2 hot/cold splitting #116813
• GH-116422: Factor out eval breaker checks at end of calls into its own micro-op. #116817
• GH-116422: Modify a few uops so that they can be supported by tier 2 with hot/cold splitting #116832

[markshannon]

In order to split out the cold parts of instructions we will need to support jumps within executors.
Something like:

tier2 op(_JUMP_TIER2, (offset/4 --)) {
    JUMP_BY(offset);
}

@brandtbucher How much effort to support this in the JIT?
I assume not that much as the prototype must have supported _POP_JUMP_IF_FALSE.

[brandtbucher]

Not hard. We already loop once to get the total size before compiling, so collecting offsets during that same step isn't difficult.

[brandtbucher]

And yeah, the prototype already did this at one point back when we had exit stubs.

[brandtbucher]

Maybe not worth pursuing yet, but just realized: if we make all jumps backwards (meaning, put cold stubs before the entry point) then we can emit the entire thing in one forward pass once we have a slab allocator. But probably more trouble than it's worth right now.