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Merged
merged 6 commits into from
Dec 5, 2024
Merged

Skip val register in ObjectBarrier impl #294

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31f6d2e
Fix compressed `val` register.
wks Dec 3, 2024
0748d71
Fix for no-fast-path code paths.
wks Dec 3, 2024
91f9da8
Add CI scripts
wks Dec 3, 2024
065e814
Revert changes to ci-test-only-normal.sh
wks Dec 3, 2024
914420c
Just set slot and target to nullptr
wks Dec 4, 2024
3816fde
Fix typo
wks Dec 5, 2024
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2 changes: 2 additions & 0 deletions .github/scripts/ci-test-minimal.sh
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Expand Up @@ -27,6 +27,8 @@ MMTK_PLAN=MarkSweep runbms_dacapo2006_with_heap_multiplier fop 8
MMTK_PLAN=NoGC runbms_dacapo2006_with_heap_size fop 1000 1000
# Test heap resizing
MMTK_PLAN=GenImmix runbms_dacapo2006_with_heap_size fop 20 100
# Test compressed oops with heap range > 4GB
MMTK_PLAN=GenImmix runbms_dacapo2006_with_heap_size fop 20 5000
# Test no compressed oop
MMTK_PLAN=GenImmix runbms_dacapo2006_with_heap_multiplier fop 4 -XX:-UseCompressedOops -XX:-UseCompressedClassPointers

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21 changes: 14 additions & 7 deletions openjdk/barriers/mmtkObjectBarrier.cpp
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Expand Up @@ -38,8 +38,11 @@ void MMTkObjectBarrierSetRuntime::object_reference_write_post(oop src, oop* slot

#define __ masm->

void MMTkObjectBarrierSetAssembler::object_reference_write_post(MacroAssembler* masm, DecoratorSet decorators, Address dst, Register val, Register tmp1, Register tmp2) const {
void MMTkObjectBarrierSetAssembler::object_reference_write_post(MacroAssembler* masm, DecoratorSet decorators, Address dst, Register val, Register tmp1, Register tmp2, bool compensate_val_reg) const {
if (can_remove_barrier(decorators, val, /* skip_const_null */ true)) return;

bool is_not_null = (decorators & IS_NOT_NULL) != 0;

Register obj = dst.base();
#if MMTK_ENABLE_BARRIER_FASTPATH
Label done;
Expand Down Expand Up @@ -67,17 +70,21 @@ void MMTkObjectBarrierSetAssembler::object_reference_write_post(MacroAssembler*
__ andptr(tmp2, 1);
__ cmpptr(tmp2, 1);
__ jcc(Assembler::notEqual, done);
#endif

__ movptr(c_rarg0, obj);
__ lea(c_rarg1, dst);
__ movptr(c_rarg2, val == noreg ? (int32_t) NULL_WORD : val);
__ call_VM_leaf_base(FN_ADDR(MMTkBarrierSetRuntime::object_reference_write_slow_call), 3);
__ xorptr(c_rarg1, c_rarg1);
// Note: If `compensate_val_reg == true && UseCompressedOops === true`, the `val` register will be
// holding a compressed pointer to the target object. If the write barrier needs to know the
// target, we will need to decompress it before passing it to the barrier slow path. However,
// since we know the semantics of `ObjectReference`, i.e. it logs the object without looking at
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@qinsoon qinsoon Dec 4, 2024

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Did you mean "the semantics of object remembering barrier"?

We need to a check to know this is object remembering barrier somewhere in the code. We can get it from https://github.com/mmtk/mmtk-core/blob/a75309373cd301acad473bbb8ea04670facd6e2a/src/plan/plan_constraints.rs#L35, and store the value somewhere for the C++ code to access.

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@wks wks Dec 4, 2024

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Did you mean "the semantics of object remembering barrier"?

Oops. That's a typo. I did mean ObjectBarrier.

We need to a check to know this is object remembering barrier somewhere in the code.

The changed code is in mmtkObjectBarrier.cpp which is dedicated to the object remembering barrier. The class MMTkObjectBarrierSetAssembler is only used if get_selected_barrier() in mmtkBarrierSet.cpp returns new MMTkObjectBarrier(); Therefore we don't need to check here, as long as the get_selected_barrier() chooses the right barrier.

// the `slot` or the `target` parameter at all, we simply pass nullptr to both parameters.
__ xorptr(c_rarg2, c_rarg2);

#if MMTK_ENABLE_BARRIER_FASTPATH
__ call_VM_leaf_base(FN_ADDR(MMTkBarrierSetRuntime::object_reference_write_slow_call), 3);
__ bind(done);
#else
__ movptr(c_rarg0, obj);
__ lea(c_rarg1, dst);
__ movptr(c_rarg2, val == noreg ? (int32_t) NULL_WORD : val);
__ call_VM_leaf_base(FN_ADDR(MMTkBarrierSetRuntime::object_reference_write_post_call), 3);
#endif
}
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2 changes: 1 addition & 1 deletion openjdk/barriers/mmtkObjectBarrier.hpp
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Expand Up @@ -30,7 +30,7 @@ class MMTkObjectBarrierSetRuntime: public MMTkBarrierSetRuntime {

class MMTkObjectBarrierSetAssembler: public MMTkBarrierSetAssembler {
protected:
virtual void object_reference_write_post(MacroAssembler* masm, DecoratorSet decorators, Address dst, Register val, Register tmp1, Register tmp2) const override;
virtual void object_reference_write_post(MacroAssembler* masm, DecoratorSet decorators, Address dst, Register val, Register tmp1, Register tmp2, bool compensate_val_reg) const override;
public:
virtual void arraycopy_prologue(MacroAssembler* masm, DecoratorSet decorators, BasicType type, Register src, Register dst, Register count) override;
virtual void arraycopy_epilogue(MacroAssembler* masm, DecoratorSet decorators, BasicType type, Register src, Register dst, Register count) override;
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7 changes: 5 additions & 2 deletions openjdk/mmtkBarrierSetAssembler_x86.hpp
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Expand Up @@ -16,7 +16,8 @@ class MMTkBarrierSetAssembler: public BarrierSetAssembler {
/// Full pre-barrier
virtual void object_reference_write_pre(MacroAssembler* masm, DecoratorSet decorators, Address dst, Register val, Register tmp1, Register tmp2) const {}
/// Full post-barrier
virtual void object_reference_write_post(MacroAssembler* masm, DecoratorSet decorators, Address dst, Register val, Register tmp1, Register tmp2) const {}
/// `compensate_val_reg` is true if this function is called after `BarrierSetAssembler::store_at` which compresses the pointer in the `val` register in place.
virtual void object_reference_write_post(MacroAssembler* masm, DecoratorSet decorators, Address dst, Register val, Register tmp1, Register tmp2, bool compensate_val_reg) const {}

/// Barrier elision test
virtual bool can_remove_barrier(DecoratorSet decorators, Register val, bool skip_const_null) const {
Expand All @@ -34,7 +35,9 @@ class MMTkBarrierSetAssembler: public BarrierSetAssembler {
virtual void store_at(MacroAssembler* masm, DecoratorSet decorators, BasicType type, Address dst, Register val, Register tmp1, Register tmp2) override {
if (type == T_OBJECT || type == T_ARRAY) object_reference_write_pre(masm, decorators, dst, val, tmp1, tmp2);
BarrierSetAssembler::store_at(masm, decorators, type, dst, val, tmp1, tmp2);
if (type == T_OBJECT || type == T_ARRAY) object_reference_write_post(masm, decorators, dst, val, tmp1, tmp2);
// BarrierSetAssembler::store_at modifies val and make it compressed if UseCompressedOops is true.
// We need to compensate for this change and decode it in object_reference_write_post.
if (type == T_OBJECT || type == T_ARRAY) object_reference_write_post(masm, decorators, dst, val, tmp1, tmp2, true);
}

/// Generate C1 write barrier slow-call stub
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