On Sat, Apr 04, 2026 at 10:18:59AM -0400, Zack Weinberg wrote: > On Sat, Apr 4, 2026, at 12:07 AM, Dima Pasechnik wrote: > > What I am confused about is that there seems to be no way in the current > > AC_OPENMP to tell whether the call was a success. Note that there is > > case in the macro where no flags are needed. Then the test may succeed, > > or may fail. > ... > > Only by reading the macro code, or by doing a trial run and looking at > > config.log, one can conclude that to test for failure > > (say, with current language C) > > one has to test ac_cv_prog_c_openmp for being equal to 'unsupported'. > > > > Should the manual be more clear on this? > > Yes, this should be clarified. However, the reason it's not documented right > now is that it was assumed the rest of the configure script *wouldn't need to > know* whether OpenMP support is actually available or not. That information > is available to the *program* by checking whether the preprocessor macro > `_OPENMP` is defined, and the people who wrote AC_OPENMP originally (before > my time) assumed that was good enough.
Some legacy code we have uses GNU gengetopt to set up options for an interactive code at configure time, by filling an .ggo.in template, so it needs to know whether to emable an OpenMP-related option or not. Testing $ac_cv_prog_c_openmp is the most natural thing to do in this case, it seems. Dima
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