gh-87092: create a 'jump target label' abstraction so that the compiler's codegen stage does not work directly with basic blocks

[iritkatriel]

This does two things:

(1) prepares the code for moving codegen from basicblock to proper labels (which are replaced by basicblock refs before the optimization stage).
(2) reduces boilerplate and tightens error checking in a few places.

• Issue: Split compiler into code-gen, optimizer and assembler. #87092

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @iritkatriel for commit 863f188 🤖

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[markshannon]

Nice.

Could you rename SET_LABEL to something a bit more meaningful?

Logically we are emitting labels in the same way as we are emitting instructions.
However, we aren't really doing that physically.

I'd be happy with EMIT_LABEL or EMIT_LABEL_HERE, assuming the implementation will match the concept soon enough.
Or we could use USE as the old code was compiler_use_next_block.
Either USE_LABEL or USE_LABEL_HERE?

It's your call, but "set" has so many meanings as to be meaningless.

[bedevere-bot]

When you're done making the requested changes, leave the comment: I have made the requested changes; please review again.

[iritkatriel]

I have made the requested changes; please review again.

I also made a few more changes that make this refactor more complete - we now have both a target_label and a target (block) on the instruction. The label is set by the frontend and the block is calculated before optimisations. They have different types to make sure we know which one we are using when.

Eventually the i_target can move off the instruction to the basicblock (there is only one per BB). Once the label becomes an int we can use the oparg field for it, so the instruction won't need either of these two fields.

[bedevere-bot]

Thanks for making the requested changes!

@markshannon: please review the changes made to this pull request.

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @iritkatriel for commit 0b8075e 🤖

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[iritkatriel]

Buildbots are happy with this.

[iritkatriel]

With the last change the front end's labels are int rather than basicblock*.. (reverted a couple of commits - test_venv hanged).

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @iritkatriel for commit 5415722 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.

[iritkatriel]

I found the bug that caused the reverted commit to fail, but I think we should merge this PR as is and continue in another one.

This PR currently touches a lot of the code, but the changes are simple. The next step is a bit more sensitive so it's better to have it in a smaller PR.

[markshannon]

OK, let's merge this.