ARM 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: I92e8db414d029f952c07f3d3a98069e46dfdbc2a
diff --git a/compiler/optimizing/intrinsics_arm.cc b/compiler/optimizing/intrinsics_arm.cc
index 0a5acc3..d2017da 100644
--- a/compiler/optimizing/intrinsics_arm.cc
+++ b/compiler/optimizing/intrinsics_arm.cc
@@ -44,7 +44,23 @@
bool IntrinsicLocationsBuilderARM::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
+ // IntrinsicSlowPathARM slow path. Currently this approach
+ // does not work when using read barriers, as the emitted
+ // calling sequence will make use of another slow path
+ // (ReadBarrierForRootSlowPathARM for HInvokeStaticOrDirect,
+ // ReadBarrierSlowPathARM 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 __ assembler->
@@ -662,20 +678,23 @@
(type == Primitive::kPrimLong) ||
(type == Primitive::kPrimNot));
ArmAssembler* assembler = codegen->GetAssembler();
- Register base = locations->InAt(1).AsRegister<Register>(); // Object pointer.
- Register offset = locations->InAt(2).AsRegisterPairLow<Register>(); // Long offset, lo part only.
+ Location base_loc = locations->InAt(1);
+ Register base = base_loc.AsRegister<Register>(); // Object pointer.
+ Location offset_loc = locations->InAt(2);
+ Register offset = offset_loc.AsRegisterPairLow<Register>(); // Long offset, lo part only.
+ Location trg_loc = locations->Out();
if (type == Primitive::kPrimLong) {
- Register trg_lo = locations->Out().AsRegisterPairLow<Register>();
+ Register trg_lo = trg_loc.AsRegisterPairLow<Register>();
__ add(IP, base, ShifterOperand(offset));
if (is_volatile && !codegen->GetInstructionSetFeatures().HasAtomicLdrdAndStrd()) {
- Register trg_hi = locations->Out().AsRegisterPairHigh<Register>();
+ Register trg_hi = trg_loc.AsRegisterPairHigh<Register>();
__ ldrexd(trg_lo, trg_hi, IP);
} else {
__ ldrd(trg_lo, Address(IP));
}
} else {
- Register trg = locations->Out().AsRegister<Register>();
+ Register trg = trg_loc.AsRegister<Register>();
__ ldr(trg, Address(base, offset));
}
@@ -684,14 +703,18 @@
}
if (type == Primitive::kPrimNot) {
- Register trg = locations->Out().AsRegister<Register>();
- __ 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());
@@ -936,6 +959,7 @@
__ Bind(&loop_head);
__ ldrex(tmp_lo, tmp_ptr);
+ // TODO: Do we need a read barrier here when `type == Primitive::kPrimNot`?
__ subs(tmp_lo, tmp_lo, ShifterOperand(expected_lo));
@@ -964,7 +988,11 @@
// 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;
}
@@ -1400,6 +1428,10 @@
}
}
+// TODO: Implement read barriers in the SystemArrayCopy intrinsic.
+// Note that this code path is not used (yet) because we do not
+// intrinsify methods that can go into the IntrinsicSlowPathARM
+// slow path.
void IntrinsicCodeGeneratorARM::VisitSystemArrayCopy(HInvoke* invoke) {
ArmAssembler* assembler = GetAssembler();
LocationSummary* locations = invoke->GetLocations();