Expand macOS detection for OpenMP

Author: eddelbuettel

configure

@@ -3294,6 +3294,9 @@ printf "%s\n" "found" >&6; }
         { printf "%s\n" "$as_me:${as_lineno-$LINENO}: WARNING: OpenMP unavailable and turned off." >&5
 printf "%s\n" "$as_me: WARNING: OpenMP unavailable and turned off." >&2;}
         can_use_openmp="no"
+    else
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: not found" >&5
+printf "%s\n" "not found" >&6; }
     fi
 else
     { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: not found" >&5
@@ -3303,9 +3306,15 @@ fi
 if test x"${can_use_openmp}" = x"yes"; then
     { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for OpenMP" >&5
 printf %s "checking for OpenMP... " >&6; }
-    ## if R has -fopenmp we should be good
-    allldflags=$(${R_HOME}/bin/R CMD config --ldflags)
-    hasOpenMP=$(echo ${allldflags} | grep -- -fopenmp)
+    if test x"${RSysinfoName}" = x"Darwin"; then
+        ## if R has ~/.R/Makevars set we might good on macOS
+        allldflags=$(${R_HOME}/bin/R CMD config --ldflags)
+        hasOpenMP=$(echo ${allldflags} | grep -- -fopenmp)
+    else
+        ## if R has -fopenmp we should be good (non macOS)
+        allldflags=$(${R_HOME}/bin/R CMD config --ldflags)
+        hasOpenMP=$(echo ${allldflags} | grep -- -lomp)
+    fi
     if test x"${hasOpenMP}" = x""; then
         { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: missing" >&5
 printf "%s\n" "missing" >&6; }

configure.ac

@@ -87,16 +87,24 @@ if test x"${RSysinfoName}" = x"Darwin"; then
         AC_MSG_RESULT([found])
         AC_MSG_WARN([OpenMP unavailable and turned off.])
         can_use_openmp="no"
+    else
+        AC_MSG_RESULT([not found])
     fi
 else
     AC_MSG_RESULT([not found])
 fi
 
 if test x"${can_use_openmp}" = x"yes"; then
     AC_MSG_CHECKING([for OpenMP])
-    ## if R has -fopenmp we should be good
-    allldflags=$(${R_HOME}/bin/R CMD config --ldflags)
-    hasOpenMP=$(echo ${allldflags} | grep -- -fopenmp)
+    if test x"${RSysinfoName}" = x"Darwin"; then
+        ## if R has ~/.R/Makevars set we might good on macOS
+        allldflags=$(${R_HOME}/bin/R CMD config --ldflags)
+        hasOpenMP=$(echo ${allldflags} | grep -- -fopenmp)
+    else
+        ## if R has -fopenmp we should be good (non macOS)
+        allldflags=$(${R_HOME}/bin/R CMD config --ldflags)
+        hasOpenMP=$(echo ${allldflags} | grep -- -lomp)
+    fi
     if test x"${hasOpenMP}" = x""; then
         AC_MSG_RESULT([missing])
         arma_have_openmp="#define ARMA_DONT_USE_OPENMP 1"