[issue25414] Drop unnecessary size limit test from deques on builds with 64-bit numbers

[Raymond Hettinger]

New submission from Raymond Hettinger:

The following test can never succeed when PY_SSIZE_T_MAX is 63-bits (as that number of allocations would exceed possible time and memory).

    #define MAX_DEQUE_LEN (PY_SSIZE_T_MAX - 3*BLOCKLEN)

    if (len >= MAX_DEQUE_LEN) {
        PyErr_SetString(PyExc_OverflowError,
                        "cannot add more blocks to the deque");
        return NULL;
    }

Removing the test saves a recurring block of code through-out the module.  The block adds register pressure, triggers an unnecessary memory access and has a predictable test-and-jump.

Conditional compilation can leave the test in for builds with size_t under 64-bits.

----------
messages: 253053
nosy: rhettinger
priority: normal
severity: normal
status: open
title: Drop unnecessary size limit test from deques on builds with 64-bit numbers
versions: Python 3.6

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue25414>
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