Do type checks in ArraySet without read barriers.
This approach is valid in the case of Baker and non-Baker
read barriers.
Benchmarks (ARM64) score variations on Nexus 5X with CPU
cores clamped at 960000 Hz (aosp_bullhead-userdebug build,
medians of 10 runs for each suite):
- Ritzperf - average (lower is better): -0.44% (virtually unchanged)
- CaffeineMark - average (higher is better): -0.20% (virtually unchanged)
- DeltaBlue (lower is better): -4.08% (slightly better)
- Richards - average (lower is better): -0.57% (virtually unchanged)
- SciMark2 - average (higher is better): -0.52% (virtually unchanged)
Details about Ritzperf benchmarks with meaningful variations
(lower is better):
- GenericCalcActions.MemAllocTest: +3.02% (slightly worse)
Details about Richards benchmarks with meaningful variations
(lower is better):
- gibbons -5.01% (better)
Boot image code size variation on Nexus 5X
(aosp_bullhead-userdebug build):
- total ARM64 framework Oat files size change:
83127840 bytes -> 83082656 bytes (-45184 bytes, -0.05%)
- total ARM framework Oat files size change:
72571872 bytes -> 72522796 bytes (-49076 bytes, -0.07%)
Test: ART_USE_READ_BARRIER=true ART_HEAP_POISONING=true m test-art-host
Test: ART_USE_READ_BARRIER=true ART_HEAP_POISONING=true m test-art-target
Bug: 29516974
Bug: 12687968
Change-Id: I8fe130156ace87dd2e4a15d9f8b4111287e735b3
diff --git a/compiler/optimizing/code_generator_arm.cc b/compiler/optimizing/code_generator_arm.cc
index d8866a9..b9f2056 100644
--- a/compiler/optimizing/code_generator_arm.cc
+++ b/compiler/optimizing/code_generator_arm.cc
@@ -4619,7 +4619,6 @@
}
if (needs_write_barrier) {
// Temporary registers for the write barrier.
- // These registers may be used for Baker read barriers too.
locations->AddTemp(Location::RequiresRegister()); // Possibly used for ref. poisoning too.
locations->AddTemp(Location::RequiresRegister());
}
@@ -4737,127 +4736,42 @@
__ Bind(&non_zero);
}
- if (kEmitCompilerReadBarrier) {
- if (!kUseBakerReadBarrier) {
- // When (non-Baker) read barriers are enabled, the type
- // checking instrumentation requires two read barriers
- // generated by CodeGeneratorARM::GenerateReadBarrierSlow:
- //
- // __ Mov(temp2, temp1);
- // // /* HeapReference<Class> */ temp1 = temp1->component_type_
- // __ LoadFromOffset(kLoadWord, temp1, temp1, component_offset);
- // codegen_->GenerateReadBarrierSlow(
- // instruction, temp1_loc, temp1_loc, temp2_loc, component_offset);
- //
- // // /* HeapReference<Class> */ temp2 = value->klass_
- // __ LoadFromOffset(kLoadWord, temp2, value, class_offset);
- // codegen_->GenerateReadBarrierSlow(
- // instruction, temp2_loc, temp2_loc, value_loc, class_offset, temp1_loc);
- //
- // __ cmp(temp1, ShifterOperand(temp2));
- //
- // However, the second read barrier may trash `temp`, as it
- // is a temporary register, and as such would not be saved
- // along with live registers before calling the runtime (nor
- // restored afterwards). So in this case, we bail out and
- // delegate the work to the array set slow path.
- //
- // TODO: Extend the register allocator to support a new
- // "(locally) live temp" location so as to avoid always
- // going into the slow path when read barriers are enabled?
- //
- // There is no such problem with Baker read barriers (see below).
- __ b(slow_path->GetEntryLabel());
- } else {
- Register temp3 = IP;
- Location temp3_loc = Location::RegisterLocation(temp3);
+ // Note that when read barriers are enabled, the type checks
+ // are performed without read barriers. This is fine, even in
+ // the case where a class object is in the from-space after
+ // the flip, as a comparison involving such a type would not
+ // produce a false positive; it may of course produce a false
+ // negative, in which case we would take the ArraySet slow
+ // path.
- // Note: `temp3` (scratch register IP) cannot be used as
- // `ref` argument of GenerateFieldLoadWithBakerReadBarrier
- // calls below (see ReadBarrierMarkSlowPathARM for more
- // details).
+ // /* HeapReference<Class> */ temp1 = array->klass_
+ __ LoadFromOffset(kLoadWord, temp1, array, class_offset);
+ codegen_->MaybeRecordImplicitNullCheck(instruction);
+ __ MaybeUnpoisonHeapReference(temp1);
- // /* HeapReference<Class> */ temp1 = array->klass_
- codegen_->GenerateFieldLoadWithBakerReadBarrier(instruction,
- temp1_loc,
- array,
- class_offset,
- temp3_loc,
- /* needs_null_check */ true);
+ // /* HeapReference<Class> */ temp1 = temp1->component_type_
+ __ LoadFromOffset(kLoadWord, temp1, temp1, component_offset);
+ // /* HeapReference<Class> */ temp2 = value->klass_
+ __ LoadFromOffset(kLoadWord, temp2, value, class_offset);
+ // If heap poisoning is enabled, no need to unpoison `temp1`
+ // nor `temp2`, as we are comparing two poisoned references.
+ __ cmp(temp1, ShifterOperand(temp2));
- // /* HeapReference<Class> */ temp1 = temp1->component_type_
- codegen_->GenerateFieldLoadWithBakerReadBarrier(instruction,
- temp1_loc,
- temp1,
- component_offset,
- temp3_loc,
- /* needs_null_check */ false);
- // Register `temp1` is not trashed by the read barrier
- // emitted by GenerateFieldLoadWithBakerReadBarrier below,
- // as that method produces a call to a ReadBarrierMarkRegX
- // entry point, which saves all potentially live registers,
- // including temporaries such a `temp1`.
- // /* HeapReference<Class> */ temp2 = value->klass_
- codegen_->GenerateFieldLoadWithBakerReadBarrier(instruction,
- temp2_loc,
- value,
- class_offset,
- temp3_loc,
- /* needs_null_check */ false);
- // If heap poisoning is enabled, `temp1` and `temp2` have
- // been unpoisoned by the the previous calls to
- // CodeGeneratorARM::GenerateFieldLoadWithBakerReadBarrier.
- __ cmp(temp1, ShifterOperand(temp2));
-
- if (instruction->StaticTypeOfArrayIsObjectArray()) {
- Label do_put;
- __ b(&do_put, EQ);
- // We do not need to emit a read barrier for the
- // following heap reference load, as `temp1` is only used
- // in a comparison with null below, and this reference
- // is not kept afterwards.
- // /* HeapReference<Class> */ temp1 = temp1->super_class_
- __ LoadFromOffset(kLoadWord, temp1, temp1, super_offset);
- // If heap poisoning is enabled, no need to unpoison
- // `temp`, as we are comparing against null below.
- __ CompareAndBranchIfNonZero(temp1, slow_path->GetEntryLabel());
- __ Bind(&do_put);
- } else {
- __ b(slow_path->GetEntryLabel(), NE);
- }
- }
- } else {
- // Non read barrier code.
-
- // /* HeapReference<Class> */ temp1 = array->klass_
- __ LoadFromOffset(kLoadWord, temp1, array, class_offset);
- codegen_->MaybeRecordImplicitNullCheck(instruction);
+ if (instruction->StaticTypeOfArrayIsObjectArray()) {
+ Label do_put;
+ __ b(&do_put, EQ);
+ // If heap poisoning is enabled, the `temp1` reference has
+ // not been unpoisoned yet; unpoison it now.
__ MaybeUnpoisonHeapReference(temp1);
- // /* HeapReference<Class> */ temp1 = temp1->component_type_
- __ LoadFromOffset(kLoadWord, temp1, temp1, component_offset);
- // /* HeapReference<Class> */ temp2 = value->klass_
- __ LoadFromOffset(kLoadWord, temp2, value, class_offset);
- // If heap poisoning is enabled, no need to unpoison `temp1`
- // nor `temp2`, as we are comparing two poisoned references.
- __ cmp(temp1, ShifterOperand(temp2));
-
- if (instruction->StaticTypeOfArrayIsObjectArray()) {
- Label do_put;
- __ b(&do_put, EQ);
- // If heap poisoning is enabled, the `temp1` reference has
- // not been unpoisoned yet; unpoison it now.
- __ MaybeUnpoisonHeapReference(temp1);
-
- // /* HeapReference<Class> */ temp1 = temp1->super_class_
- __ LoadFromOffset(kLoadWord, temp1, temp1, super_offset);
- // If heap poisoning is enabled, no need to unpoison
- // `temp1`, as we are comparing against null below.
- __ CompareAndBranchIfNonZero(temp1, slow_path->GetEntryLabel());
- __ Bind(&do_put);
- } else {
- __ b(slow_path->GetEntryLabel(), NE);
- }
+ // /* HeapReference<Class> */ temp1 = temp1->super_class_
+ __ LoadFromOffset(kLoadWord, temp1, temp1, super_offset);
+ // If heap poisoning is enabled, no need to unpoison
+ // `temp1`, as we are comparing against null below.
+ __ CompareAndBranchIfNonZero(temp1, slow_path->GetEntryLabel());
+ __ Bind(&do_put);
+ } else {
+ __ b(slow_path->GetEntryLabel(), NE);
}
}