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Track when the asm interpreter transitions into C++ interpreter #436

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We can measure which opcodes do this most frequently with bpftrace. This lets us see, for example, that we should probably implement a handler for LOAD_ATTR_INSTANCE_SLOT_DESCR (included in this PR).

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UNPACK_SEQUENCE looks like an easy enough next target if we specialize for list/tuple.

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LOAD_ATTR_MODULE, too.

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LIST_APPEND, too.

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tekknolagi commented Apr 17, 2023

And BUILD_SLICE and ROT_THREE and ROT_FOUR.

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In debug(opt) mode, register a bpftrace event that fires when the
assembly interpreter switches to the C++ interpreter. This also includes
opcodes that have no assembly implementation (and therefore always
switch to C++).
For richards.py this occurs 25330 times, according to the bpftrace
script. It is not the hottest, but it is easy to implement.

(smaller)
...
@interpreter_deopt[usdt:./build/bin/python:python:InterpreterDeopt_COMPARE_IN_MONOMORPHIC]: 14073
@interpreter_deopt[usdt:./build/bin/python:python:InterpreterDeopt_COMPARE_EQ_STR]: 17581
@interpreter_deopt[usdt:./build/bin/python:python:InterpreterDeopt_LOAD_ATTR_INSTANCE_TYPE]: 19845
@interpreter_deopt[usdt:./build/bin/python:python:InterpreterDeopt_LOAD_ATTR_INSTANCE_SLOT_DESCR]: 25330
@interpreter_deopt[usdt:./build/bin/python:python:InterpreterDeopt_BUILD_TUPLE]: 27540
@interpreter_deopt[usdt:./build/bin/python:python:InterpreterDeopt_GET_ITER]: 44881
@interpreter_deopt[usdt:./build/bin/python:python:InterpreterDeopt_INPLACE_OP_MONOMORPHIC]: 56030
@interpreter_deopt[usdt:./build/bin/python:python:InterpreterDeopt_BINARY_FLOORDIV_SMALLINT]: 57701
@interpreter_deopt[usdt:./build/bin/python:python:InterpreterDeopt_BINARY_OP_MONOMORPHIC]: 58618
(higher)
This brings it down from 19727 to 4101 transitions from asm to C++.
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