--- old/src/hotspot/cpu/x86/gc/shenandoah/shenandoahBarrierSetAssembler_x86.cpp	2020-04-06 16:01:02.566780904 +0200
+++ new/src/hotspot/cpu/x86/gc/shenandoah/shenandoahBarrierSetAssembler_x86.cpp	2020-04-06 16:01:02.460780972 +0200
@@ -79,9 +79,11 @@
 
       // Avoid runtime call when not active.
       Address gc_state(thread, in_bytes(ShenandoahThreadLocalData::gc_state_offset()));
-      int flags = ShenandoahHeap::HAS_FORWARDED;
-      if (ShenandoahStoreValEnqueueBarrier || !dest_uninitialized) {
-        flags |= ShenandoahHeap::MARKING;
+      int flags;
+      if (ShenandoahSATBBarrier && dest_uninitialized) {
+        flags = ShenandoahHeap::HAS_FORWARDED;
+      } else {
+        flags = ShenandoahHeap::HAS_FORWARDED | ShenandoahHeap::MARKING;
       }
       __ testb(gc_state, flags);
       __ jcc(Assembler::zero, done);
--- old/src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp	2020-04-06 16:01:03.173780515 +0200
+++ new/src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp	2020-04-06 16:01:03.061780586 +0200
@@ -409,6 +409,19 @@
     ShouldNotReachHere();
   }
   _gc_mode->initialize_flags();
+  if (_gc_mode->is_diagnostic() && !UnlockDiagnosticVMOptions) {
+    vm_exit_during_initialization(
+            err_msg("GC mode \"%s\" is diagnostic, and must be enabled via -XX:+UnlockDiagnosticVMOptions.",
+                    _gc_mode->name()));
+  }
+  if (_gc_mode->is_experimental() && !UnlockExperimentalVMOptions) {
+    vm_exit_during_initialization(
+            err_msg("GC mode \"%s\" is experimental, and must be enabled via -XX:+UnlockExperimentalVMOptions.",
+                    _gc_mode->name()));
+  }
+  log_info(gc, init)("Shenandoah GC mode: %s",
+                     _gc_mode->name());
+
   _heuristics = _gc_mode->initialize_heuristics();
 
   if (_heuristics->is_diagnostic() && !UnlockDiagnosticVMOptions) {
--- old/src/hotspot/share/gc/shenandoah/shenandoahIUMode.hpp	2020-04-06 16:01:03.796780116 +0200
+++ new/src/hotspot/share/gc/shenandoah/shenandoahIUMode.hpp	2020-04-06 16:01:03.689780184 +0200
@@ -32,6 +32,10 @@
 class ShenandoahIUMode : public ShenandoahNormalMode {
 public:
   virtual void initialize_flags() const;
+
+  virtual const char* name()     { return "Incremental-Update"; }
+  virtual bool is_diagnostic()   { return false; }
+  virtual bool is_experimental() { return true; }
 };
 
 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHIUMODE_HPP
--- old/src/hotspot/share/gc/shenandoah/shenandoahMode.hpp	2020-04-06 16:01:04.388779737 +0200
+++ new/src/hotspot/share/gc/shenandoah/shenandoahMode.hpp	2020-04-06 16:01:04.278779807 +0200
@@ -33,6 +33,9 @@
 public:
   virtual void initialize_flags() const = 0;
   virtual ShenandoahHeuristics* initialize_heuristics() const = 0;
+  virtual const char* name() = 0;
+  virtual bool is_diagnostic() = 0;
+  virtual bool is_experimental() = 0;
 };
 
 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHMODE_HPP
--- old/src/hotspot/share/gc/shenandoah/shenandoahNormalMode.hpp	2020-04-06 16:01:04.971779363 +0200
+++ new/src/hotspot/share/gc/shenandoah/shenandoahNormalMode.hpp	2020-04-06 16:01:04.868779429 +0200
@@ -33,6 +33,9 @@
 public:
   virtual void initialize_flags() const;
   virtual ShenandoahHeuristics* initialize_heuristics() const;
+  virtual const char* name()     { return "Normal"; }
+  virtual bool is_diagnostic()   { return false; }
+  virtual bool is_experimental() { return false; }
 };
 
 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHNORMALMODE_HPP
--- old/src/hotspot/share/gc/shenandoah/shenandoahPassiveMode.hpp	2020-04-06 16:01:05.553778990 +0200
+++ new/src/hotspot/share/gc/shenandoah/shenandoahPassiveMode.hpp	2020-04-06 16:01:05.446779058 +0200
@@ -31,6 +31,10 @@
 public:
   virtual void initialize_flags() const;
   virtual ShenandoahHeuristics* initialize_heuristics() const;
+
+  virtual const char* name()     { return "Passive"; }
+  virtual bool is_diagnostic()   { return true; }
+  virtual bool is_experimental() { return false; }
 };
 
 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHNORMALMODE_HPP
--- old/test/hotspot/jtreg/gc/shenandoah/options/TestHeuristicsUnlock.java	2020-04-06 16:01:06.149778608 +0200
+++ new/test/hotspot/jtreg/gc/shenandoah/options/TestHeuristicsUnlock.java	2020-04-06 16:01:06.039778679 +0200
@@ -49,7 +49,7 @@
         testWith("-XX:ShenandoahGCHeuristics=static", Mode.PRODUCT);
         testWith("-XX:ShenandoahGCHeuristics=compact", Mode.PRODUCT);
 
-        testWith("-XX:ShenandoahGCMode=iu", Mode.PRODUCT);
+        testWith("-XX:ShenandoahGCMode=iu", Mode.EXPERIMENTAL);
 
         testWith("-XX:ShenandoahGCHeuristics=aggressive", Mode.DIAGNOSTIC);
         testWith("-XX:ShenandoahGCHeuristics=passive", Mode.DIAGNOSTIC);