Combine `_CHECK_FUNCTION_EXACT_ARGS` and `_CHECK_STACK_SPACE` uops?

[gvanrossum]

These two uops always happen as a pair, and they contain a bunch of duplicate work (func = ... and code = ...). The second one doesn't use any cache entries. So they can be combined, hopefully saving a little bit of JIT template size (the combined template only needs to extract code once). Both only contain DEOPT_IF() calls.

A possible argument against would be that eventually we'd want to change one or the other to use EXIT_IF(). (Or can those coexist in one uop?)

CC: @brandtbucher @markshannon

Linked PRs

• gh-116976: Merge _CHECK_STACK_SPACE into preceding _CHECK_FUNCTION_EXACT_ARGS #116977

[gvanrossum]

Brandt looked at this briefly and it looks like the individual templates are ~125 and ~115 bytes, while the combined template is ~165 bytes, so a clear win.

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EDIT: On my M3, 172 + 128 vs. 212, so 88 bytes win.

[gvanrossum]

I imagine there might be another possible future downside though: _CHECK_STACK_SPACE uops have the potential of being eliminated when they're redundant. (We currently don't do that though.)

I'd really like @markshannon's opinion here.

[markshannon]

I'd rather keep them separate. Having the uops separate means that they can be optimized separately, and superinstructions will put them back together if they are a common(ish) pair.