RFR (XS) 8242213: Shenandoah: remove unused ShenandoahHeuristics::_bytes_in_cset

[Aleksey Shipilev]

RFE:
  https://bugs.openjdk.java.net/browse/JDK-8242213

That field does not seem to be used for anything, yet we update it on critical path during cset
selection. We should ditch the field and all "uses" of it. Cursory examination seems to indicate it
was there since the initial integration.

Fix:

diff -r f30c66ecc928 src/hotspot/share/gc/shenandoah/heuristics/shenandoahAdaptiveHeuristics.cpp
--- a/src/hotspot/share/gc/shenandoah/heuristics/shenandoahAdaptiveHeuristics.cpp       Mon Apr 06
14:46:40 2020 +0200
+++ b/src/hotspot/share/gc/shenandoah/heuristics/shenandoahAdaptiveHeuristics.cpp       Mon Apr 06
15:04:29 2020 +0200
@@ -78,3 +78,2 @@
   size_t cur_garbage = 0;
-  _bytes_in_cset = 0;

@@ -92,3 +91,2 @@
       cset->add_region(r);
-      _bytes_in_cset += r->used();
       cur_cset = new_cset;
diff -r f30c66ecc928 src/hotspot/share/gc/shenandoah/shenandoahHeuristics.cpp
--- a/src/hotspot/share/gc/shenandoah/shenandoahHeuristics.cpp  Mon Apr 06 14:46:40 2020 +0200
+++ b/src/hotspot/share/gc/shenandoah/shenandoahHeuristics.cpp  Mon Apr 06 15:04:29 2020 +0200
@@ -48,3 +48,2 @@
   _successful_cycles_in_a_row(0),
-  _bytes_in_cset(0),
   _cycle_start(os::elapsedTime()),
@@ -260,3 +259,3 @@
 void ShenandoahHeuristics::record_allocation_failure_gc() {
-  _bytes_in_cset = 0;
+  // Do nothing.
 }
@@ -264,4 +263,2 @@
 void ShenandoahHeuristics::record_requested_gc() {
-  _bytes_in_cset = 0;
-
   // Assume users call System.gc() when external state changes significantly,
diff -r f30c66ecc928 src/hotspot/share/gc/shenandoah/shenandoahHeuristics.hpp
--- a/src/hotspot/share/gc/shenandoah/shenandoahHeuristics.hpp  Mon Apr 06 14:46:40 2020 +0200
+++ b/src/hotspot/share/gc/shenandoah/shenandoahHeuristics.hpp  Mon Apr 06 15:04:29 2020 +0200
@@ -84,4 +84,2 @@

-  size_t _bytes_in_cset;
-
   double _cycle_start;

Testing: hotspot_gc_shenandoah

-- 
Thanks,
-Aleksey