[issue17615] String comparison performance regression

[Neil Hodgson]

Neil Hodgson added the comment:

Including the wmemcmp patch did not improve the times on MSC v.1600 32 bit - if anything, the performance was a little slower for the test I used:

a=['C:/Users/Neil/Documents/λ','C:/Users/Neil/Documents/η']156
specialised:
[0.9125948707773204, 0.8990815272107868, 0.9055365478250721]
wmemcmp:
[0.9287715478844594, 0.926606017373151, 0.9155132192031097]

Looking at the assembler, there is a real call to wmemcmp which adds some time and wmemcmp does not seem to be optimized compared to a simple loop.

However, the use of memcmp for 1:1 is a big win. Replacing the memcmp with COMPARE(Py_UCS1, Py_UCS1) shows memcmp is 45% faster on 100 character strings. memcmp doesn't generate a real call: instead there is an inline unrolled (4 bytes per iteration) loop.

----------

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue17615>
_______________________________________