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8254320: Shenandoah: C2 native LRB should activate for non-cset objects #580

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8254320: Shenandoah: C2 native LRB should activate for non-cset objects #580

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8254320: Shenandoah: C2 native LRB should activate for non-cset objects
Oct 9, 2020
05b2bee
Merge remote-tracking branch 'upstream/master' into 8254320
Oct 9, 2020
e5b1e89
Add comment why native-LRB doesn't need the cset-check
Oct 12, 2020
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13 changes: 10 additions & 3 deletions src/hotspot/share/gc/shenandoah/c2/shenandoahSupport.cpp
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Original file line number Diff line number Diff line change
@@ -1325,7 +1325,7 @@ void ShenandoahBarrierC2Support::pin_and_expand(PhaseIdealLoop* phase) {
assert(val->bottom_type()->make_oopptr(), "need oop");
assert(val->bottom_type()->make_oopptr()->const_oop() == NULL, "expect non-constant");

enum { _heap_stable = 1, _not_cset, _evac_path, PATH_LIMIT };
enum { _heap_stable = 1, _evac_path, _not_cset, PATH_LIMIT };
Node* region = new RegionNode(PATH_LIMIT);
Node* val_phi = new PhiNode(region, val->bottom_type()->is_oopptr());
Node* raw_mem_phi = PhiNode::make(region, raw_mem, Type::MEMORY, TypeRawPtr::BOTTOM);
@@ -1339,14 +1339,21 @@ void ShenandoahBarrierC2Support::pin_and_expand(PhaseIdealLoop* phase) {
val_phi->init_req(_heap_stable, val);
raw_mem_phi->init_req(_heap_stable, raw_mem);

// Test for in-cset.
// Test for in-cset, unless it's a native-LRB. Native LRBs need to return NULL
// even for non-cset objects to prevent ressurrection of such objects.
// Wires !in_cset(obj) to slot 2 of region and phis
Node* not_cset_ctrl = NULL;
test_in_cset(ctrl, not_cset_ctrl, val, raw_mem, phase);
if (!lrb->is_native()) {
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I think it deserves a comment why LRB-native is special.

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Yup, I added a comment there. Thanks!

test_in_cset(ctrl, not_cset_ctrl, val, raw_mem, phase);
}
if (not_cset_ctrl != NULL) {
region->init_req(_not_cset, not_cset_ctrl);
val_phi->init_req(_not_cset, val);
raw_mem_phi->init_req(_not_cset, raw_mem);
} else {
region->del_req(_not_cset);
val_phi->del_req(_not_cset);
raw_mem_phi->del_req(_not_cset);
}

// Resolve object when orig-value is in cset.