Hi,

After switching my C++ app from a glibc-based build to a static build using musl, I've noticed significant differences in performance with certain loading operations, which seems to be related to using std::map with a case-insensitive UTF-8 sorting algorithm. For example, parsing a XML file with a flat listing of ~350k directory items and mapping them by name takes about 3 seconds with glibc vs 13 seconds with musl. After modifying the sort algorithm by removing all calls to towlower, the loading time with musl drops to 3.5 seconds.

I put together a C++ benchmark with the same sorting algorithm, which seems to produce similar results (GCC 6.3, 64 bit, -O3):

https://gist.github.com/maksis/92ad04f525d69043283350675d04f160

glibc: ~2 seconds (Arch Linux)
musl: ~7 seconds (Alpine Linux 3.6.0)


What might be causing the difference?