[mypyc] Borrow references during chained attribute access #12805
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refactor test case to make rebasing easier
ilevkivskyi
approved these changes
May 18, 2022
mypyc/irbuild/ll_builder.py
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| self.blocks: List[BasicBlock] = [] | ||
| # Stack of except handler entry blocks | ||
| self.error_handlers: List[Optional[BasicBlock]] = [None] | ||
| # Values that we need to keet alive as long as we have borrowed |
JukkaL
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May 19, 2022
Borrow an operand such as `x.y` (attribute of a native class) in various contexts when it's safe to do so. This reduces the number of incref/decref operations we need to perform. This continues work started in #12805. These cases now support borrowing (for some subexpressions, in some contexts): * `x.y is None` * Cast source value * `len(x.y)` (if the operand is a list) * `isinstance(x.y, C)` * `x.y[a.b]` * `x.y.z = 1`
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If we have multiple native attribute access operations in succession, we
can borrow the temporaries. This avoids an incref and decref. For
example, when evaluating
x.y.z, we don't need to incref the resultof
x.y.We need to make sure that the objects from which we borrow
values are not freed too early by adding
keep_aliveops.This is part of a wider reference counting optimization workstream.
All the improvements together produced around 5% performance
improvement in the richards benchmark.
In carefully constructed microbenchmarks 50+% improvements are
possible.