[issue39223] Fold constant slicing with slices

[Batuhan]

Batuhan <batuhanosmantaskaya at gmail.com> added the comment:

It looks like we have some usage for normal indexing (not this PR, the original optimization);

cpython/cpython/Lib/base64.py:382
cpython/cpython/Lib/base64.py:382
cpython/cpython/Lib/base64.py:393
cpython/cpython/Lib/base64.py:397
cpython/cpython/Lib/pickle.py:306
cpython/cpython/Lib/pickle.py:1291
cpython/cpython/Lib/glob.py:155
cpython/cpython/Lib/test/test_mmap.py:59
cpython/cpython/Lib/test/test_mmap.py:63
cpython/cpython/Lib/test/test_mmap.py:574
cpython/cpython/Lib/test/test_codecs.py:2317
cpython/cpython/Lib/test/test_codecs.py:2323
cpython/cpython/Lib/test/test_contextlib.py:1025
cpython/cpython/Lib/test/test_struct.py:645

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue39223>
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