From: Tom Lane <tgl@sss.pgh.pa.us>
To: Thomas Munro <thomas.munro@gmail.com>
cc: Michael Paquier <michael@paquier.xyz>, Noah Misch <noah@leadboat.com>,
        Vik Fearing <vik@postgresfriends.org>,
 cary huang <hcary328@gmail.com>,
        pgsql-hackers@lists.postgresql.org
Subject: Re: Add support for AT LOCAL
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Comments: In-reply-to Thomas Munro <thomas.munro@gmail.com>
	message dated "Wed, 18 Oct 2023 12:11:35 +1300"
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Date: Tue, 17 Oct 2023 23:15:14 -0400
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Thomas Munro <thomas.munro@gmail.com> writes:
> On Wed, Oct 18, 2023 at 11:54 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Should we be testing against xlclang instead?

> I hesitated to suggest it because it's not my animal/time we're
> talking about but it seems to make more sense.  It appears to be IBM's
> answer to the nothing-builds-with-this-thing phenomenon, since it
> accepts a lot of GCCisms via Clang's adoption of them.  From a quick
> glance at [1], it lacks the atomics builtins but we have our own
> assembler magic for POWER.  So maybe it'd all just work™.

FWIW, I tried a test build with xlclang 16.1 on cfarm111, and
it does seem like it Just Works, modulo a couple of oddities:

* <netinet/tcp.h> fails to compile, due to references to struct
in6_addr, unless <netinet/in.h> is included first.  Most of our
references to tcp.h already do that, but not libpq-be.h and
fe-protocol3.c.  I'm a bit at a loss why we've not seen this
with the existing BF animals on this machine, because AFAICS
they're all using the same /usr/include tree.

* configure recognizes this as gcc but not Clang, which may or may
not be fine:
...
checking whether we are using the GNU C compiler... yes
...
checking whether xlclang is Clang... no
...
This doesn't seem to break anything, but it struck me as odd.
configure seems to pick a sane set of compiler options anyway.

Interestingly, xlclang shows the same failure with the pre-19fa97731
versions of timetz_zone/timetz_izone as plain xlc does.  I guess
this is not so astonishing since they presumably share the same
codegen backend.  But maybe somebody ought to file a bug with IBM?

			regards, tom lane