CONFIG: add named topoControls

etc/controlDict

@@ -147,6 +147,15 @@ OptimisationSwitches
     //  >= 3 : when there are more than N nodes
     nodeComms.min   0;
 
+    // Selection of topology-aware routines (bitmask)
+    //  0: disabled [default]
+    //  1: broadcast [MPI]
+    //  4: gather/all-gather [MPI]
+    // 16: combine (reduction) [manual algorithm]
+    // 32: mapGather (reduction) [manual algorithm]
+    // 64: gatherList/scatterList [manual algorithm]
+    topoControl     0;
+
     // Transfer double as float for processor boundaries. Mostly defunct.
     floatTransfer   0;
 

src/OpenFOAM/db/IOstreams/Pstreams/UPstream.C

@@ -106,7 +106,35 @@ void Foam::UPstream::printNodeCommsControl(Ostream& os)
 
 void Foam::UPstream::printTopoControl(Ostream& os)
 {
-    os  << "none";
+    unsigned count = 0;
+
+    if (UPstream::topologyControl_ > 0)
+    {
+        #undef  PrintControl
+        #define PrintControl(Ctrl, Name)                      \
+        if (UPstream::usingTopoControl(topoControls::Ctrl))   \
+        {                                                     \
+            os << (count++ ? ' ' : '(') << Name;              \
+        }
+
+        PrintControl(broadcast, "broadcast");
+        PrintControl(reduce, "reduce");
+        PrintControl(gather, "gather");
+        PrintControl(combine, "combine");
+        PrintControl(mapGather, "mapGather");
+        PrintControl(gatherList, "gatherList");
+
+        #undef PrintControl
+    }
+
+    if (count)
+    {
+        os << ')';  // End the list
+    }
+    else
+    {
+        os << "none";
+    }
 }