On Wed, Apr 10, 2024 at 11:44 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> ... On my Mac laptop
> (Apple clang version 15.0.0), the compile time for preproc.o went from
> 6.7sec to 5.5sec.
Having seen multi-minute compile times on FreeBSD (where clang is the
system compiler) and Debian (where I get packages from apt.llvm.org),
I have been quietly waiting for this issue to hit Mac users too (where
a clang with unknown proprietary changes is the system compiler), but
it never did. Huh.
I tried to understand a bit more about Apple's version soup. This
seems to be an up-to-date table (though I don't understand their
source of information):
https://en.wikipedia.org/wiki/Xcode#Xcode_15.0_-_(since_visionOS_support)_2
According to cc -v on my up-to-date MacBook Air, it has "Apple clang
version 15.0.0 (clang-1500.3.9.4)", which, if the table is correct,
means that it's using LLVM 16.0.0 (note, not 16.0.6, the final version
of that branch of [open] LLVM, and the version I saw the issue with on
FreeBSD and Debian). They relabel everything to match the Xcode
version that shipped it, and they're currently off by one.
I wondered if perhaps the table just wasn't accurate in the final
digits, so I looked for clues in strings in the binary, and sure
enough it contains "LLVM 15.0.0". My guess would be that they've
clobbered the major version, but not the rest: the Xcode version is
15.3, and I don't see a 3, so I guess this is really derived from LLVM
16.0.0.
One explanation would be that they rebase their proprietary bits and
pieces over the .0 version of each major release, and then cherry-pick
urgent fixes and stuff later, not pulling in the whole minor release;
they also presumably have to maintain it for much longer than the LLVM
project's narrow support window. Who knows. So now I wonder if it
could be that LLVM 16.0.6 does this, but LLVM 16.0.0 doesn't.
I installed clang-16 (16.0.6) with MacPorts, and it does show the problem.