bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?

[Eli Zaretskii]

> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Sat, 4 Jul 2020 08:57:08 -0700
> Cc: Stefan Monnier <monnier@iro.umontreal.ca>,
>  Andrea Corallo <andrea_corallo@yahoo.it>, 42147@debbugs.gnu.org
> 
> This makes Emacs behavior more consistent across platforms,
> and should make some byte-code optimizations safer (Bug#42147).
> We can assume SSE2 by now, since it has been out for 20 years.
> * configure.ac: On x86 with GCC, default to -msse2 -mfpmath=sse.

This assumes that the system on which Emacs runs is the same as where
it was built, doesn't it?  Is that assumption valid enough to do this
by default?