split HIP: the RCCL default stays quiet when the peer push is off

src/split/src/hip/rccl_dl.hpp

@@ -69,7 +69,7 @@ inline RcclDecision rccl_decide(const char* env, bool peer_on, bool default_on,
     const bool wanted = env ? std::strcmp(env, "0") != 0 : default_on;
     if (!wanted) return d;
     if (!peer_on) {
-        d.line = "RCCL is not used for the prompt sums: the peer push between the cards is off, so the host exchange stays.";
+        if (env) d.line = "RCCL is not used for the prompt sums: the peer push between the cards is off, so the host exchange stays.";   // (asked for: say so; the default stays quiet)
         return d;
     }
     std::string why;

src/split/tools/rccl_policy_test.cpp

@@ -26,6 +26,11 @@ int main() {
     // =1 without the peer push: the host exchange stays, one line, no open
     d = rccl_decide("1", false, false, pass);
     CHECK(!d.use && calls == 0 && d.line == "RCCL is not used for the prompt sums: the peer push between the cards is off, so the host exchange stays.");
+    // the default alone (unset) without the peer push: the host exchange, quiet
+    calls = 0;
+    d = rccl_decide(nullptr, false, true, pass);
+    CHECK(!d.use && calls == 0 && d.line.empty());
+    calls = 0;
     // =1 with the peer push and a library that opens: used, the line says which
     d = rccl_decide("1", true, false, pass);
     CHECK(d.use && calls == 1 && d.line == "The prompt sums use RCCL (librccl.so.1).");