Speed up isinstance on union types #91603
Description
PEP 604 allows isinstance on union types but it much slower compared to a tuple of types. This can be speed up with a fast path. Currently it is almost 4x slower, so there is room for improvement.
Benchmarks:
@kumaraditya303 ➜ /workspaces/cpython (fast-iter-str) $ ./python -m timeit "isinstance(1, (int, str))"
5000000 loops, best of 5: 54.6 nsec per loop
@kumaraditya303 ➜ /workspaces/cpython (fast-iter-str) $ ./python -m timeit "isinstance(1, int|str)"
1000000 loops, best of 5: 202 nsec per loop