The compilation is very slow when using HS_FLAG_UTF8 and HS_FLAG_CASELESS

I compiling my patterns using the api of hs_compile_multi(). Compilation takes a long time when seting the pattern flags is HS_FLAG_UTF8 and HS_FLAG_CASELESS than only seting the patter flags is HS_FLAG_UTF8 or HS_FLAG_CASELESS . I use the vesion is 5.1.0

Start by reproducing the reported comparison through hs_compile_multi() with HS_FLAG_UTF8 and HS_FLAG_CASELESS, using the same pattern and Hyperscan 5.1.0 if available. Measure compilation times for each flag combination, then identify the relevant compiler path; done means the cause is established and a regression measurement or documented limitation is provided.

Written by the indexing model from the issue text.