Select barrier based on active plan (#225)

* Add barrier configuration to PlanConstraints
* Remove `needs_write_barrier`

Author: wenyuzhao

src/plan/barriers.rs

@@ -4,6 +4,12 @@ use crate::scheduler::WorkBucketStage;
 use crate::util::*;
 use crate::MMTK;
 
+#[derive(Copy, Clone, Debug)]
+pub enum BarrierSelector {
+    NoBarrier,
+    ObjectBarrier,
+}
+
 /// For field writes in HotSpot, we cannot always get the source object pointer and the field address
 pub enum WriteTarget {
     Object(ObjectReference),

src/plan/gencopy/global.rs

@@ -1,6 +1,5 @@
 use super::gc_work::{GenCopyCopyContext, GenCopyMatureProcessEdges, GenCopyNurseryProcessEdges};
 use super::mutator::ALLOCATOR_MAPPING;
-use crate::mmtk::MMTK;
 use crate::plan::global::BasePlan;
 use crate::plan::global::CommonPlan;
 use crate::plan::global::GcStatus;
@@ -25,6 +24,7 @@ use crate::util::side_metadata::meta_bytes_per_chunk;
 use crate::util::OpaquePointer;
 use crate::vm::ObjectModel;
 use crate::vm::*;
+use crate::{mmtk::MMTK, plan::barriers::BarrierSelector};
 use enum_map::EnumMap;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::Arc;
@@ -49,7 +49,7 @@ pub const GENCOPY_CONSTRAINTS: PlanConstraints = PlanConstraints {
     gc_header_bits: 2,
     gc_header_words: 0,
     num_specialized_scans: 1,
-    needs_write_barrier: true,
+    barrier: BarrierSelector::ObjectBarrier,
     ..PlanConstraints::default()
 };
 

src/plan/plan_constraints.rs

@@ -1,3 +1,4 @@
+use crate::plan::barriers::BarrierSelector;
 use crate::util::constants::*;
 
 /// This struct defines plan-specific constraints.
@@ -10,9 +11,9 @@ pub struct PlanConstraints {
     pub gc_header_words: usize,
     pub num_specialized_scans: usize,
     pub max_non_los_copy_bytes: usize,
-    pub needs_write_barrier: bool,
     pub needs_log_bit_in_header: bool,
     pub needs_log_bit_in_header_num: usize,
+    pub barrier: BarrierSelector,
     // the following seems unused for now
     pub needs_linear_scan: bool,
     pub needs_concurrent_workers: bool,
@@ -28,13 +29,13 @@ impl PlanConstraints {
             gc_header_words: 0,
             num_specialized_scans: 0,
             max_non_los_copy_bytes: MAX_INT,
-            needs_write_barrier: false,
             needs_log_bit_in_header: false,
             needs_log_bit_in_header_num: 0,
             needs_linear_scan: SUPPORT_CARD_SCANNING || LAZY_SWEEP,
             needs_concurrent_workers: false,
             generate_gc_trace: false,
             needs_forward_after_liveness: false,
+            barrier: BarrierSelector::NoBarrier,
         }
     }
 }