--- a/src/hotspot/share/opto/superword.cpp	Mon Sep 30 13:27:55 2019 +0200
+++ b/src/hotspot/share/opto/superword.cpp	Mon Sep 30 13:28:33 2019 +0200
@@ -2045,12 +2045,11 @@
         for (uint k = 0; k < use->req(); k++) {
           Node* n = use->in(k);
           if (def == n) {
-            // reductions should only have a Phi use at the the loop
-            // head and out of loop uses
+            // Reductions should only have a Phi use at the loop head or a non-phi use
+            // outside of the loop if it is the last element of the pack (e.g. SafePoint).
             if (def->is_reduction() &&
                 ((use->is_Phi() && use->in(0) == _lpt->_head) ||
-                 !_lpt->is_member(_phase->get_loop(_phase->ctrl_or_self(use))))) {
-              assert(i == p->size()-1, "must be last element of the pack");
+                 (!_lpt->is_member(_phase->get_loop(_phase->ctrl_or_self(use))) && i == p->size()-1))) {
               continue;
             }
             if (!is_vector_use(use, k)) {

--- a/src/hotspot/share/runtime/arguments.cpp	Mon Sep 30 13:27:55 2019 +0200
+++ b/src/hotspot/share/runtime/arguments.cpp	Mon Sep 30 13:28:33 2019 +0200
@@ -533,6 +533,7 @@
   { "FieldsAllocationStyle",        JDK_Version::jdk(14), JDK_Version::jdk(15), JDK_Version::jdk(16) },
   { "CompactFields",                JDK_Version::jdk(14), JDK_Version::jdk(15), JDK_Version::jdk(16) },
   { "MonitorBound",                 JDK_Version::jdk(14), JDK_Version::jdk(15), JDK_Version::jdk(16) },
+  { "G1RSetScanBlockSize",          JDK_Version::jdk(14), JDK_Version::jdk(15), JDK_Version::jdk(16) },
 
   // --- Deprecated alias flags (see also aliased_jvm_flags) - sorted by obsolete_in then expired_in:
   { "DefaultMaxRAMFraction",        JDK_Version::jdk(8),  JDK_Version::undefined(), JDK_Version::undefined() },