ARM64 read barrier support for concurrent GC in Optimizing.
This first implementation uses slow paths to instrument heap
reference loads and GC root loads for the concurrent copying
collector, respectively calling the artReadBarrierSlow and
artReadBarrierForRootSlow runtime entry points.
Notes:
- This implementation does not instrument HInvokeVirtual
nor HInvokeInterface instructions (for class reference
loads), as the corresponding read barriers are not stricly
required with the current concurrent copying collector.
- Intrinsics which may eventually call (on slow path) are
disabled when read barriers are enabled, as the current
slow path infrastructure does not support this case.
- When read barriers are enabled, the code generated for a
HArraySet instruction always go into the array set slow
path for object arrays (delegating the operation to the
runtime), as we are lacking a mechanism to keep a
temporary register live accross a runtime call (needed for
the instrumentation of type checking code, which requires
two successive read barriers).
Bug: 12687968
Change-Id: Icfb74f67bf23ae80e7723ee6a0c9ff34ba325d48
diff --git a/compiler/optimizing/intrinsics_arm64.cc b/compiler/optimizing/intrinsics_arm64.cc
index 059abf0..b04dcce 100644
--- a/compiler/optimizing/intrinsics_arm64.cc
+++ b/compiler/optimizing/intrinsics_arm64.cc
@@ -143,7 +143,23 @@
bool IntrinsicLocationsBuilderARM64::TryDispatch(HInvoke* invoke) {
Dispatch(invoke);
LocationSummary* res = invoke->GetLocations();
- return res != nullptr && res->Intrinsified();
+ if (res == nullptr) {
+ return false;
+ }
+ if (kEmitCompilerReadBarrier && res->CanCall()) {
+ // Generating an intrinsic for this HInvoke may produce an
+ // IntrinsicSlowPathARM64 slow path. Currently this approach
+ // does not work when using read barriers, as the emitted
+ // calling sequence will make use of another slow path
+ // (ReadBarrierForRootSlowPathARM64 for HInvokeStaticOrDirect,
+ // ReadBarrierSlowPathARM64 for HInvokeVirtual). So we bail
+ // out in this case.
+ //
+ // TODO: Find a way to have intrinsics work with read barriers.
+ invoke->SetLocations(nullptr);
+ return false;
+ }
+ return res->Intrinsified();
}
#define __ masm->
@@ -818,9 +834,12 @@
(type == Primitive::kPrimLong) ||
(type == Primitive::kPrimNot));
vixl::MacroAssembler* masm = codegen->GetAssembler()->vixl_masm_;
- Register base = WRegisterFrom(locations->InAt(1)); // Object pointer.
- Register offset = XRegisterFrom(locations->InAt(2)); // Long offset.
- Register trg = RegisterFrom(locations->Out(), type);
+ Location base_loc = locations->InAt(1);
+ Register base = WRegisterFrom(base_loc); // Object pointer.
+ Location offset_loc = locations->InAt(2);
+ Register offset = XRegisterFrom(offset_loc); // Long offset.
+ Location trg_loc = locations->Out();
+ Register trg = RegisterFrom(trg_loc, type);
bool use_acquire_release = codegen->GetInstructionSetFeatures().PreferAcquireRelease();
MemOperand mem_op(base.X(), offset);
@@ -837,13 +856,18 @@
if (type == Primitive::kPrimNot) {
DCHECK(trg.IsW());
- codegen->GetAssembler()->MaybeUnpoisonHeapReference(trg);
+ codegen->MaybeGenerateReadBarrier(invoke, trg_loc, trg_loc, base_loc, 0U, offset_loc);
}
}
static void CreateIntIntIntToIntLocations(ArenaAllocator* arena, HInvoke* invoke) {
+ bool can_call = kEmitCompilerReadBarrier &&
+ (invoke->GetIntrinsic() == Intrinsics::kUnsafeGetObject ||
+ invoke->GetIntrinsic() == Intrinsics::kUnsafeGetObjectVolatile);
LocationSummary* locations = new (arena) LocationSummary(invoke,
- LocationSummary::kNoCall,
+ can_call ?
+ LocationSummary::kCallOnSlowPath :
+ LocationSummary::kNoCall,
kIntrinsified);
locations->SetInAt(0, Location::NoLocation()); // Unused receiver.
locations->SetInAt(1, Location::RequiresRegister());
@@ -1057,6 +1081,9 @@
if (use_acquire_release) {
__ Bind(&loop_head);
__ Ldaxr(tmp_value, MemOperand(tmp_ptr));
+ // TODO: Do we need a read barrier here when `type == Primitive::kPrimNot`?
+ // Note that this code is not (yet) used when read barriers are
+ // enabled (see IntrinsicLocationsBuilderARM64::VisitUnsafeCASObject).
__ Cmp(tmp_value, expected);
__ B(&exit_loop, ne);
__ Stlxr(tmp_32, value, MemOperand(tmp_ptr));
@@ -1065,6 +1092,9 @@
__ Dmb(InnerShareable, BarrierWrites);
__ Bind(&loop_head);
__ Ldxr(tmp_value, MemOperand(tmp_ptr));
+ // TODO: Do we need a read barrier here when `type == Primitive::kPrimNot`?
+ // Note that this code is not (yet) used when read barriers are
+ // enabled (see IntrinsicLocationsBuilderARM64::VisitUnsafeCASObject).
__ Cmp(tmp_value, expected);
__ B(&exit_loop, ne);
__ Stxr(tmp_32, value, MemOperand(tmp_ptr));
@@ -1090,7 +1120,11 @@
// The UnsafeCASObject intrinsic does not always work when heap
// poisoning is enabled (it breaks run-test 004-UnsafeTest); turn it
// off temporarily as a quick fix.
+ //
// TODO(rpl): Fix it and turn it back on.
+ //
+ // TODO(rpl): Also, we should investigate whether we need a read
+ // barrier in the generated code.
if (kPoisonHeapReferences) {
return;
}