Reland "[heap] Turn on parallel compaction"

src/flag-definitions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file defines all of the flags.  It is separated into different section,
 // for Debug, Release, Logging and Profiling, etc.  To add a new flag, find the
 // correct section, and use one of the DEFINE_ macros, without a trailing ';'.
 //
 // This include does not have a guard, because it is a template-style include,
 // which can be included multiple times in different modes.  It expects to have
@@ skipping 656 matching lines @@
             "old code (required for code flushing)")
 DEFINE_BOOL(incremental_marking, true, "use incremental marking")
 DEFINE_BOOL(finalize_marking_incrementally, true,
             "finalize marking in incremental steps")
 DEFINE_INT(min_progress_during_incremental_marking_finalization, 32,
            "keep finalizing incremental marking as long as we discover at "
            "least this many unmarked objects")
 DEFINE_INT(max_incremental_marking_finalization_rounds, 3,
            "at most try this many times to finalize incremental marking")
 DEFINE_BOOL(concurrent_sweeping, true, "use concurrent sweeping")
-DEFINE_BOOL(parallel_compaction, false, "use parallel compaction")
+DEFINE_BOOL(parallel_compaction, true, "use parallel compaction")
 DEFINE_BOOL(trace_incremental_marking, false,
             "trace progress of the incremental marking")
 DEFINE_BOOL(track_gc_object_stats, false,
             "track object counts and memory usage")
 DEFINE_BOOL(trace_gc_object_stats, false,
             "trace object counts and memory usage")
 DEFINE_IMPLICATION(trace_gc_object_stats, track_gc_object_stats)
 DEFINE_BOOL(track_detached_contexts, true,
             "track native contexts that are expected to be garbage collected")
 DEFINE_BOOL(trace_detached_contexts, false,
@@ skipping 432 matching lines @@
 #undef DEFINE_ALIAS_FLOAT
 #undef DEFINE_ALIAS_ARGS
 
 #undef FLAG_MODE_DECLARE
 #undef FLAG_MODE_DEFINE
 #undef FLAG_MODE_DEFINE_DEFAULTS
 #undef FLAG_MODE_META
 #undef FLAG_MODE_DEFINE_IMPLICATIONS
 
 #undef COMMA