This finishes the work begun in gh-107760. When, while projecting a superblock, we encounter a call to a short, simple function, the superblock will now enter the function using `_PUSH_FRAME`, continue through it, and leave it using `_POP_FRAME`, and then continue through the original code. Multiple frame pushes and pops are even possible. It is also possible to stop appending to the superblock in the middle of a called function, when running out of space or encountering an unsupported bytecode.
This fixes two tiny defects in analysis.py that I didn't catch on time in #107564:
- `get_var_names` in `check_macro_consistency` should skip `UNUSED` names.
- Fix an occurrence of `is UNUSED` (should be `==`).
Introducing a new file, stacking.py, that takes over several responsibilities related to symbolic evaluation of push/pop operations, with more generality.
This mostly extracts a whole bunch of stuff out of generate_cases.py into separate files, but there are a few other things going on here.
- analysis.py: `Analyzer` etc.
- instructions.py: `Instruction` etc.
- flags.py: `InstructionFlags`, `variable_used`, `variable_used_unspecialized`
- formatting.py: `Formatter` etc.
- Rename parser.py to parsing.py, to avoid conflict with stdlib parser.py
- Blackify most things
- Fix most mypy errors
- Remove output filenames from Generator state, add them to `write_instructions()` etc.
- Fix unit tests