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[vm/compiler] Fix incorrect write-barrier elimination

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If there is a GC-triggering instruction between array allocation and
store into array we cannot omit the barrier. This worked for stores
where the receiver is a direct array allocation, but not if it's a phi.

Closes https://github.com/dart-lang/sdk/issues/43786
Closes https://github.com/dart-lang/sdk/issues/43770

Change-Id: I28de29cf85842a9d3ae3189bb8e6426969fe4279
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/167570
Commit-Queue: Martin Kustermann <kustermann@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
This commit is contained in:
Martin Kustermann 2020-10-15 10:40:43 +00:00 committed by commit-bot@chromium.org
parent 1f3c76ccdd
commit 32dfefbea1
2 changed files with 72 additions and 4 deletions
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22
runtime/vm/compiler/write_barrier_elimination.cc
View File

@ -192,6 +192,8 @@ void WriteBarrierElimination::SaveResults() {
void WriteBarrierElimination::IndexDefinitions(Zone* zone) {
BitmapBuilder array_allocations;
GrowableArray<Definition*> create_array_worklist;
for (intptr_t i = 0; i < block_order_->length(); ++i) {
BlockEntryInstr* const block = block_order_->At(i);
if (auto join_block = block->AsJoinEntry()) {
@ -209,8 +211,12 @@ void WriteBarrierElimination::IndexDefinitions(Zone* zone) {
for (ForwardInstructionIterator it(block); !it.Done(); it.Advance()) {
if (Definition* current = it.Current()->AsDefinition()) {
if (IsUsable(current)) {
array_allocations.Set(definition_count_, current->IsCreateArray());
const bool is_create_array = current->IsCreateArray();
array_allocations.Set(definition_count_, is_create_array);
definition_indices_.Insert({current, definition_count_++});
if (is_create_array) {
create_array_worklist.Add(current);
}
#if defined(DEBUG)
if (tracing_) {
THR_Print("Definition (%" Pd ") has index %" Pd ".\n",
@ -222,6 +228,20 @@ void WriteBarrierElimination::IndexDefinitions(Zone* zone) {
}
}
while (!create_array_worklist.is_empty()) {
auto instr = create_array_worklist.RemoveLast();
for (Value::Iterator it(instr->input_use_list()); !it.Done();
it.Advance()) {
if (auto phi_use = it.Current()->instruction()->AsPhi()) {
const intptr_t index = Index(phi_use);
if (!array_allocations.Get(index)) {
array_allocations.Set(index, /*can_be_create_array=*/true);
create_array_worklist.Add(phi_use);
}
}
}
}
vector_ = new (zone) BitVector(zone, definition_count_);
vector_->SetAll();
array_allocations_mask_ = new (zone) BitVector(zone, definition_count_);

54
runtime/vm/compiler/write_barrier_elimination_test.cc
View File

@ -12,7 +12,8 @@ namespace dart {
DEBUG_ONLY(DECLARE_FLAG(bool, trace_write_barrier_elimination);)
ISOLATE_UNIT_TEST_CASE(IRTest_WriteBarrierElimination_JoinSuccessors) {
DEBUG_ONLY(FLAG_trace_write_barrier_elimination = true);
DEBUG_ONLY(
SetFlagScope<bool> sfs(&FLAG_trace_write_barrier_elimination, true));
const char* nullable_tag = TestCase::NullableTag();
const char* null_assert_tag = TestCase::NullAssertTag();
@ -82,7 +83,8 @@ ISOLATE_UNIT_TEST_CASE(IRTest_WriteBarrierElimination_JoinSuccessors) {
}
ISOLATE_UNIT_TEST_CASE(IRTest_WriteBarrierElimination_AtLeastOnce) {
DEBUG_ONLY(FLAG_trace_write_barrier_elimination = true);
DEBUG_ONLY(
SetFlagScope<bool> sfs(&FLAG_trace_write_barrier_elimination, true));
// Ensure that we process every block at least once during the analysis
// phase so that the out-sets will be initialized. If we don't process
// each block at least once, the store "c.next = n" will be marked
@ -137,7 +139,8 @@ ISOLATE_UNIT_TEST_CASE(IRTest_WriteBarrierElimination_AtLeastOnce) {
}
ISOLATE_UNIT_TEST_CASE(IRTest_WriteBarrierElimination_Arrays) {
DEBUG_ONLY(FLAG_trace_write_barrier_elimination = true);
DEBUG_ONLY(
SetFlagScope<bool> sfs(&FLAG_trace_write_barrier_elimination, true));
const char* nullable_tag = TestCase::NullableTag();
// Test that array allocations are not considered usable after a
@ -204,4 +207,49 @@ ISOLATE_UNIT_TEST_CASE(IRTest_WriteBarrierElimination_Arrays) {
EXPECT(store_into_array->ShouldEmitStoreBarrier() == true);
}
ISOLATE_UNIT_TEST_CASE(IRTest_WriteBarrierElimination_Regress43786) {
DEBUG_ONLY(
SetFlagScope<bool> sfs(&FLAG_trace_write_barrier_elimination, true));
const char* kScript = R"(
foo() {
final root = List<dynamic>.filled(128, null);
List<dynamic> last = root;
for (int i = 0; i < 10 * 1024; ++i) {
final nc = List(128);
last[0] = nc;
last = nc;
}
}
main() { foo(); }
)";
const auto& root_library = Library::Handle(LoadTestScript(kScript));
Invoke(root_library, "main");
const auto& function = Function::Handle(GetFunction(root_library, "foo"));
TestPipeline pipeline(function, CompilerPass::kJIT);
FlowGraph* flow_graph = pipeline.RunPasses({});
auto entry = flow_graph->graph_entry()->normal_entry();
EXPECT(entry != nullptr);
StoreIndexedInstr* store_into_phi = nullptr;
ILMatcher cursor(flow_graph, entry);
RELEASE_ASSERT(cursor.TryMatch(
{
kMatchAndMoveCreateArray,
kMatchAndMoveGoto,
kMatchAndMoveBranchTrue,
kMatchAndMoveCreateArray,
{kMatchAndMoveStoreIndexed, &store_into_phi},
},
kMoveGlob));
EXPECT(store_into_phi->array()->definition()->IsPhi());
EXPECT(store_into_phi->ShouldEmitStoreBarrier());
}
} // namespace dart