Re: fixing AC_OPENMP for Apple clang

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On Wed, Mar 04, 2026 at 01:33:10AM +0100, Bruno Haible wrote:
> See also the ticket <https://savannah.gnu.org/support/?111055>.
> There, two facts were mentioned:
>=20
> * While libtool (version 2.5.3) does not support "-Xpreprocessor -fopenmp=
",
>   it does support "-Wp,-fopenmp".
>=20
> * On macOS 26.2, with cc being "Apple clang version 17.0.0 (clang-1700.6.=
3.2)",
>   "cc -help" reports that the option '-fopenmp' exists.
>   Therefore it looks like trying "-Wp,-fopenmp" is only needed for older
>   versions of Apple clang (which ones?).

Apple lies to us here!
I have "Apple clang version 17.0.0 (clang-1700.6.3.2)" on the latest versio=
n of Intel macOS=20

  % uname -a
  Darwin OUCL13243.local 24.6.0 Darwin Kernel Version 24.6.0: Mon Jan 19 22=
:00:10 PST 2026; root:xnu-11417.140.69.708.3~1/RELEASE_X86_64 x86_64

  % cc -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/Xcode=
Default.xctoolchain/usr/bin

and "cc -help" reports that "-fopenmp" is an option,

   % cc --help | grep "fopenmp "
  -fopenmp                Parse OpenMP pragmas and generate parallel code.


yet it does not work:

% cat foo.c
#include <stdio.h>

% cc -c foo.c -fopenmp
clang: error: unsupported option '-fopenmp'

% cc -c foo.c -Xclang -fopenmp # this is OK
% cc -c foo.c -Xpreprocessor -fopenmp # OK too

And I do have reports from people running the latest macOS 26 and clang
17.0.0, who say the same, that "-fopenmp" doesn't work with the extra
prefix of "-Xpreprocessor".


By the way, does anyone here knows the difference between "-Xpreprocessor" =
and "-Xclang" ?

Dima


>=20
> Bruno
>=20
>=20
>=20

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