Will Emacs 27.2 do? If you must see results from an optimized build
of Emacs 28, I'll have to build one first.
As mentioned, mine was not an optimized build, on the contrary.
FWIW, I ran this same test with `sm-c-mode` (which should handle `xdisp.c`
about as well as CC-mode, but solves an easier problem since it doesn't
try to handle as much of C as CC-mode does (e.g. no support for K&R, no
highlighting of types), nor does it try to handle C++, Java, ...), and
most of the times for it are between 0.02 and 0.04.
That is much better, but still too slow, IMO. Think: it's the time
that it takes us to fontify a single windowful, only a couple of
dozens of lines. Why does it take so long?
For comparison, here it is for lisp/subr.el: it seems actually slightly
slower than what I for with xdisp.c when using sm-c-mode.
Stefan
0.075539393
0.030856317
0.040824289
0.029961978
0.012222597
0.020277377
0.08354889
0.027791121
0.040834603
0.029304419
0.040401518
0.042230931
0.041249748
0.041759172
0.022928028
0.088205301
0.01791448
0.039915906
0.041701691
0.036885006
0.037948645
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0.03723824
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let: End of buffer