[MRG] Detecting openmp flags on macOS (with libomp from brew) (#789)

* Detecting openmp flags on macOS (with libomp from brew)

* Detecting openmp flags on macOS (with libomp from brew) --lint

* Release.md update

Author: dcoeurjo

RELEASES.md

@@ -17,6 +17,7 @@ This new release adds support for sparse cost matrices and a new lazy EMD solver
 - Fix deprecated JAX function in `ot.backend.JaxBackend` (PR #771, Issue #770)
 - Add test for build from source (PR #772, Issue #764)
 - Fix device for batch Ot solver in `ot.batch` (PR #784, Issue #783)
+- Fix openmp flags on macOS (PR #789)
 
 ## 0.9.6.post1
 

ot/helpers/openmp_helpers.py

@@ -33,7 +33,18 @@ def get_openmp_flag(compiler):
         # Default flag for GCC and clang:
         omp_flag = ["-fopenmp"]
         if sys.platform.startswith("darwin"):
-            omp_flag += ["-Xpreprocessor", "-lomp"]
+            omp_flag = ["-Xpreprocessor", "-fopenmp"]
+            omp_flag += ["-I/usr/local/opt/libomp/include"]
+            #  Assuming `brew install libomp` on recent macOS
+            if os.path.isfile("/opt/homebrew/opt/libomp/lib/libomp.dylib"):
+                omp_flag += ["-I/opt/homebrew/opt/libomp/include"]
+                omp_flag += ["/opt/homebrew/opt/libomp/lib/libomp.dylib"]
+            else:
+                # Assuming `brew install libomp` on old macOS
+                if os.path.isfile("/usr/local/opt/libomp/lib/libomp.dylib"):
+                    omp_flag += ["-I/usr/local/opt/libomp/include"]
+                    omp_flag += ["/usr/local/opt/libomp/lib/libomp.dylib"]
+
     return omp_flag