Re: BUG #15844: MIPS: remove .set mips2 in s_lock.h to fix r6 build

PG Bug reporting form <noreply@postgresql.org> writes:
> MIPS r6 changes the encoding of LL/SC instruction,
> while the .set mips2 will force assembler to generate
> old encoding.
> This patch can fix this problem.

So I have a bunch of questions about this patch.

1. What problem is this actually solving?  We have what I think are
reasonably modern MIPS machines in the buildfarm (frogfish,
topminnow) and they aren't complaining.

2. What toolchains define __mips_isa_rev at all?  Seems like we could
be trading one portability issue for another one.

3. If we actually need something here, don't we need a run-time probe
rather than a compile-time check?  Distro packagers, for example,
can't assume that their packages will be run on exactly the hardware
they build on.

            regards, tom lane