[issue42246] Implement PEP 626

[Mark Shannon]

Mark Shannon <mark at hotpy.org> added the comment:

The following code is completely eliminated by the macros.

1. if 0:
2.     secret_debugging_code()

PEP 626 says that all executed lines of code must generate trace events,
so we need to emit an instruction for line 1.

Dead code elimination will remove the `secret_debugging_code()`, but leave the test. The peephole optimiser can then reduce it to a NOP, but won't eliminate it as it is the only instruction for line 1.

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stage: patch review -> 

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue42246>
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