Re: fixing AC_OPENMP for Apple clang

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On Mon, Mar 02, 2026 at 12:55:43PM -0500, Ben Boeckel wrote:
> On Mon, Mar 02, 2026 at 19:07:26 +0200, Andrew W. Nosenko wrote:
> > On Mon, 2 Mar 2026 at 18:14, Dima Pasechnik <[email protected]> wrote:
> > > Homebrew is the de-facto macOS package manager (supported by Apple, in
> > > fact, albeit not
> > > too publicly), see https://brew.sh/
> >=20
> > Sorry, but I slightly confused now, what OS do you targeting?  Because I
> > use Clang (installed from MacPorts) + Autotools on macOS without any ex=
tra
> > dances, just with regular AC_OPENMP, which results in plain -fopenmp, f=
or
> > years (just since Clang obtained OpenMP support)
>=20
> Xcode's Clang build uses its own versioning scheme. MacPorts' Clang is
> upstream Clang and its versioning scheme.

Indeed, I am talking about the "native" Apple clang (which they aliased
to gcc, to make it even more confusing), the one that comes with Apple's XC=
ode suite.

% gcc -v
Apple clang version 17.0.0 (clang-1700.6.3.2)
Target: x86_64-apple-darwin24.6.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDe=
fault.xctoolchain/usr/bin
% clang -v
Apple clang version 17.0.0 (clang-1700.6.3.2)
Target: x86_64-apple-darwin24.6.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDe=
fault.xctoolchain/usr/bin

It does need "-Xpreprocessor -fopenmp":

% echo "#include <stdio.h>" > foo.c=20
% clang  -fopenmp -c foo.c          # oops...
clang: error: unsupported option '-fopenmp'
%
% clang -Xpreprocessor -fopenmp -c foo.c # is OK.
%

Homebrew, just as MacPorts, allows one to install the llvm (upstream)
clang.

% /usr/local/opt/llvm/bin/clang -v
Homebrew clang version 22.1.0
Target: x86_64-apple-darwin24.6.0
Thread model: posix
InstalledDir: /usr/local/Cellar/llvm/22.1.0/bin
Configuration file: /usr/local/etc/clang/x86_64-apple-darwin24.cfg
System configuration file directory: /usr/local/etc/clang
User configuration file directory: /Users/dima/.config/clang

And it doesn't mind the normal "-fopenmp" option:

% /usr/local/opt/llvm/bin/clang -fopenmp -c foo.c # is OK.
%

HTH
Dima


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