I wrote:
> ... I wonder whether Apple are using more
> aggressive optimization flags than other people. OTOH, while it would
> not surprise me if Apple put some work into making zlib go fast, it
> seems less likely that they'd expend effort or risk on xsltproc.
I checked Fedora 26 and found that it's using an identical source
version of xsltproc:
$ xsltproc --version
Using libxml 20904, libxslt 10129 and libexslt 817
xsltproc was compiled against libxml 20904, libxslt 10129 and libexslt 817
libxslt 10129 was compiled against libxml 20904
libexslt 817 was compiled against libxml 20904
Its time to build the HTML docs ... 46 seconds. This is on a machine
intermediate in speed between the Sierra and High Sierra machines whose
timings I quoted before. So we can definitively discard the idea that
Apple sprinkled any magic pixie dust on their xsltproc build. Your
MacPorts build is the outlier, leaving us with the theories that it was
built at -O0 or there's a performance bug in the newer source releases.
I have no doubt that xmlsoft.org would be interested if you can narrow
it down to the latter.
regards, tom lane