8242353: Shenandoah: micro-optimize region liveness handling

Reviewed-by: rkennke

Author: shipilev

src/hotspot/share/gc/shenandoah/shenandoahConcurrentMark.inline.hpp

@@ -75,20 +75,15 @@ inline void ShenandoahConcurrentMark::count_liveness(jushort* live_data, oop obj
   if (!region->is_humongous_start()) {
     assert(!region->is_humongous(), "Cannot have continuations here");
     size_t max = (1 << (sizeof(jushort) * 8)) - 1;
-    if (size >= max) {
-      // too big, add to region data directly
-      region->increase_live_data_gc_words(size);
+    jushort cur = live_data[region_idx];
+    size_t new_val = size + cur;
+    if (new_val >= max) {
+      // overflow, flush to region data
+      region->increase_live_data_gc_words(new_val);
+      live_data[region_idx] = 0;
     } else {
-      jushort cur = live_data[region_idx];
-      size_t new_val = cur + size;
-      if (new_val >= max) {
-        // overflow, flush to region data
-        region->increase_live_data_gc_words(new_val);
-        live_data[region_idx] = 0;
-      } else {
-        // still good, remember in locals
-        live_data[region_idx] = (jushort) new_val;
-      }
+      // still good, remember in locals
+      live_data[region_idx] = (jushort) new_val;
     }
   } else {
     shenandoah_assert_in_correct_region(NULL, obj);

src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp

@@ -3024,9 +3024,9 @@ void ShenandoahHeap::flush_liveness_cache(uint worker_id) {
   assert(_liveness_cache != NULL, "sanity");
   jushort* ld = _liveness_cache[worker_id];
   for (uint i = 0; i < num_regions(); i++) {
-    ShenandoahHeapRegion* r = get_region(i);
     jushort live = ld[i];
     if (live > 0) {
+      ShenandoahHeapRegion* r = get_region(i);
       r->increase_live_data_gc_words(live);
       ld[i] = 0;
     }