[wasm] Introduce a caching threshold

With dynamic tiering, typically not all functions of a WebAssembly
module get compiled with TurboFan, and therefore the code caching would
never get triggered. With this CL code caching is triggered whenever
{FLAG_wasm_caching_threshold} bytes of TurboFan code are generated.

This new caching event is only triggered when --wasm-dynamic-tiering is
enabled.

R=clemensb@chromium.org

Bug: v8:12281
Change-Id: I939325aea7e4310aa76c936636799661c05d4079
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3202593Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77251}

src/flags/flag-definitions.h

@@ -955,6 +955,9 @@ DEFINE_BOOL(wasm_tier_up, true,
             "have an effect)")
 DEFINE_BOOL(wasm_dynamic_tiering, false,
             "enable dynamic tier up to the optimizing compiler")
+DEFINE_INT(
+    wasm_caching_threshold, 1000000,
+    "the amount of wasm top tier code that triggers the next caching event")
 DEFINE_DEBUG_BOOL(trace_wasm_decoder, false, "trace decoding of wasm code")
 DEFINE_DEBUG_BOOL(trace_wasm_compiler, false, "trace compiling of wasm code")
 DEFINE_DEBUG_BOOL(trace_wasm_interpreter, false,

src/wasm/compilation-environment.h

@@ -105,6 +105,7 @@ class WireBytesStorage {
 enum class CompilationEvent : uint8_t {
   kFinishedBaselineCompilation,
   kFinishedExportWrappers,
+  kFinishedCompilationChunk,
   kFinishedTopTierCompilation,
   kFailedCompilation,
   kFinishedRecompilation

src/wasm/module-compiler.cc

@@ -746,6 +746,9 @@ class CompilationStateImpl {
   int outstanding_baseline_units_ = 0;
   int outstanding_export_wrappers_ = 0;
   int outstanding_top_tier_functions_ = 0;
+  // The amount of generated top tier code since the last
+  // {kFinishedCompilationChunk} event.
+  size_t bytes_since_last_chunk = 0;
   std::vector<uint8_t> compilation_progress_;
 
   int outstanding_recompilation_functions_ = 0;
@@ -2095,8 +2098,12 @@ class AsyncCompileJob::CompilationStateCallback {
                                                   : nullptr);
         }
         break;
+      case CompilationEvent::kFinishedCompilationChunk:
+        DCHECK(CompilationEvent::kFinishedBaselineCompilation == last_event_ ||
+               CompilationEvent::kFinishedCompilationChunk == last_event_);
+        break;
       case CompilationEvent::kFinishedTopTierCompilation:
-        DCHECK_EQ(CompilationEvent::kFinishedBaselineCompilation, last_event_);
+        DCHECK(CompilationEvent::kFinishedBaselineCompilation == last_event_);
         // At this point, the job will already be gone, thus do not access it
         // here.
         break;
@@ -3191,6 +3198,10 @@ void CompilationStateImpl::CommitTopTierCompilationUnit(
 void CompilationStateImpl::AddTopTierPriorityCompilationUnit(
     WasmCompilationUnit unit, size_t priority) {
   compilation_unit_queues_.AddTopTierPriorityUnit(unit, priority);
+  {
+    base::MutexGuard guard(&callbacks_mutex_);
+    outstanding_top_tier_functions_++;
+  }
   compile_job_->NotifyConcurrencyIncrease();
 }
 
@@ -3303,6 +3314,9 @@ void CompilationStateImpl::OnFinishedUnits(
         DCHECK_GT(outstanding_baseline_units_, 0);
         outstanding_baseline_units_--;
       }
+      if (code->tier() == ExecutionTier::kTurbofan) {
+        bytes_since_last_chunk += code->instructions().size();
+      }
       if (reached_tier < required_top_tier &&
           required_top_tier <= code->tier()) {
         DCHECK_GT(outstanding_top_tier_functions_, 0);
@@ -3356,12 +3370,17 @@ void CompilationStateImpl::TriggerCallbacks(
     triggered_events.Add(CompilationEvent::kFinishedExportWrappers);
     if (outstanding_baseline_units_ == 0) {
       triggered_events.Add(CompilationEvent::kFinishedBaselineCompilation);
-      if (outstanding_top_tier_functions_ == 0) {
+      if (!FLAG_wasm_dynamic_tiering && outstanding_top_tier_functions_ == 0) {
         triggered_events.Add(CompilationEvent::kFinishedTopTierCompilation);
       }
     }
   }
 
+  if (static_cast<size_t>(FLAG_wasm_caching_threshold) <
+      bytes_since_last_chunk) {
+    triggered_events.Add(CompilationEvent::kFinishedCompilationChunk);
+    bytes_since_last_chunk = 0;
+  }
   if (compile_failed_.load(std::memory_order_relaxed)) {
     // *Only* trigger the "failed" event.
     triggered_events =
@@ -3372,9 +3391,11 @@ void CompilationStateImpl::TriggerCallbacks(
 
   // Don't trigger past events again.
   triggered_events -= finished_events_;
-  // Recompilation can happen multiple times, thus do not store this.
-  finished_events_ |=
-      triggered_events - CompilationEvent::kFinishedRecompilation;
+  // Recompilation can happen multiple times, thus do not store this. There can
+  // also be multiple compilation chunks.
+  finished_events_ |= triggered_events -
+                      CompilationEvent::kFinishedRecompilation -
+                      CompilationEvent::kFinishedCompilationChunk;
 
   for (auto event :
        {std::make_pair(CompilationEvent::kFailedCompilation,
@@ -3385,6 +3406,8 @@ void CompilationStateImpl::TriggerCallbacks(
                        "wasm.BaselineFinished"),
         std::make_pair(CompilationEvent::kFinishedTopTierCompilation,
                        "wasm.TopTierFinished"),
+        std::make_pair(CompilationEvent::kFinishedCompilationChunk,
+                       "wasm.CompilationChunkFinished"),
         std::make_pair(CompilationEvent::kFinishedRecompilation,
                        "wasm.RecompilationFinished")}) {
     if (!triggered_events.contains(event.first)) continue;
@@ -3395,7 +3418,11 @@ void CompilationStateImpl::TriggerCallbacks(
     }
   }
 
-  if (outstanding_baseline_units_ == 0 && outstanding_export_wrappers_ == 0 &&
+  // With dynamic tiering, we don't know if we can ever delete the callback.
+  // TODO(https://crbug.com/v8/12289): Release some callbacks also when dynamic
+  // tiering is enabled.
+  if (!FLAG_wasm_dynamic_tiering && outstanding_baseline_units_ == 0 &&
+      outstanding_export_wrappers_ == 0 &&
       outstanding_top_tier_functions_ == 0 &&
       outstanding_recompilation_functions_ == 0) {
     // Clear the callbacks because no more events will be delivered.

src/wasm/streaming-decoder.cc

@@ -312,33 +312,29 @@ void AsyncStreamingDecoder::Abort() {
 
 namespace {
 
-class TopTierCompiledCallback {
+class CompilationChunkFinishedCallback {
  public:
-  TopTierCompiledCallback(
+  CompilationChunkFinishedCallback(
       std::weak_ptr<NativeModule> native_module,
       AsyncStreamingDecoder::ModuleCompiledCallback callback)
       : native_module_(std::move(native_module)),
         callback_(std::move(callback)) {}
 
   void operator()(CompilationEvent event) const {
-    if (event != CompilationEvent::kFinishedTopTierCompilation) return;
+    if (event != CompilationEvent::kFinishedCompilationChunk &&
+        event != CompilationEvent::kFinishedTopTierCompilation) {
+      return;
+    }
     // If the native module is still alive, get back a shared ptr and call the
     // callback.
     if (std::shared_ptr<NativeModule> native_module = native_module_.lock()) {
       callback_(native_module);
     }
-#ifdef DEBUG
-    DCHECK(!called_);
-    called_ = true;
-#endif
   }
 
  private:
   const std::weak_ptr<NativeModule> native_module_;
   const AsyncStreamingDecoder::ModuleCompiledCallback callback_;
-#ifdef DEBUG
-  mutable bool called_ = false;
-#endif
 };
 
 }  // namespace
@@ -347,7 +343,7 @@ void AsyncStreamingDecoder::NotifyNativeModuleCreated(
     const std::shared_ptr<NativeModule>& native_module) {
   if (!module_compiled_callback_) return;
   auto* comp_state = native_module->compilation_state();
-  comp_state->AddCallback(TopTierCompiledCallback{
+  comp_state->AddCallback(CompilationChunkFinishedCallback{
       std::move(native_module), std::move(module_compiled_callback_)});
   module_compiled_callback_ = {};
 }

test/cctest/cctest.status

@@ -1240,4 +1240,13 @@
   'test-calls-with-arraylike-or-spread/*': [SKIP],
 }],
 
+################################################################################
+['variant == stress', {
+  # The 'stress' variants sets the '--stress-opt' d8 flag, which executes 2 runs
+  # in debug mode and 5 runs in release mode. Hence the module will be cached
+  # between runs, and the correct caching behavior cannot be observed anymore in
+  # the later runs.
+  'test-streaming-compilation/AsyncTestIncrementalCaching': [SKIP],
+  'test-streaming-compilation/SingleThreadedTestIncrementalCaching': [SKIP],
+}],
 ]

test/cctest/wasm/test-streaming-compilation.cc

@@ -20,6 +20,7 @@
 #include "test/common/wasm/flag-utils.h"
 #include "test/common/wasm/test-signatures.h"
 #include "test/common/wasm/wasm-macro-gen.h"
+#include "test/common/wasm/wasm-module-runner.h"
 
 namespace v8 {
 namespace internal {
@@ -1108,6 +1109,105 @@ STREAM_TEST(TestModuleWithImportedFunction) {
   CHECK(tester.IsPromiseFulfilled());
 }
 
+STREAM_TEST(TestIncrementalCaching) {
+  FLAG_VALUE_SCOPE(wasm_dynamic_tiering, true);
+  FLAG_VALUE_SCOPE(wasm_tier_up, false);
+  constexpr int threshold = 10;
+  FlagScope<int> caching_treshold(&FLAG_wasm_caching_threshold, threshold);
+  StreamTester tester(isolate);
+  int call_cache_counter = 0;
+  tester.stream()->SetModuleCompiledCallback(
+      [&call_cache_counter](
+          const std::shared_ptr<i::wasm::NativeModule>& native_module) {
+        call_cache_counter++;
+      });
+
+  ZoneBuffer buffer(tester.zone());
+  TestSignatures sigs;
+  WasmModuleBuilder builder(tester.zone());
+  builder.SetMinMemorySize(1);
+
+  base::Vector<const char> function_names[] = {
+      base::CStrVector("f0"), base::CStrVector("f1"), base::CStrVector("f2")};
+  for (int i = 0; i < 3; ++i) {
+    WasmFunctionBuilder* f = builder.AddFunction(sigs.v_v());
+
+    constexpr int64_t val = 0x123456789abc;
+    constexpr int index = 0x1234;
+    uint8_t store_mem[] = {
+        WASM_STORE_MEM(MachineType::Int64(), WASM_I32V(index), WASM_I64V(val))};
+    constexpr uint32_t kStoreLength = 20;
+    CHECK_EQ(kStoreLength, arraysize(store_mem));
+
+    // Produce a store {threshold} many times to reach the caching threshold.
+    constexpr uint32_t kCodeLength = kStoreLength * threshold + 1;
+    uint8_t code[kCodeLength];
+    for (int j = 0; j < threshold; ++j) {
+      memcpy(code + (j * kStoreLength), store_mem, kStoreLength);
+    }
+    code[kCodeLength - 1] = WasmOpcode::kExprEnd;
+    f->EmitCode(code, kCodeLength);
+    builder.AddExport(function_names[i], f);
+  }
+  builder.WriteTo(&buffer);
+  tester.OnBytesReceived(buffer.begin(), buffer.end() - buffer.begin());
+  tester.FinishStream();
+  tester.RunCompilerTasks();
+  CHECK(tester.IsPromiseFulfilled());
+  tester.native_module();
+  constexpr base::Vector<const char> kNoSourceUrl{"", 0};
+  Isolate* i_isolate = reinterpret_cast<i::Isolate*>(isolate);
+  Handle<Script> script = GetWasmEngine()->GetOrCreateScript(
+      i_isolate, tester.native_module(), kNoSourceUrl);
+  Handle<FixedArray> export_wrappers = i_isolate->factory()->NewFixedArray(3);
+  Handle<WasmModuleObject> module_object = WasmModuleObject::New(
+      i_isolate, tester.native_module(), script, export_wrappers);
+  ErrorThrower thrower(i_isolate, "Instantiation");
+  // We instantiated before, so the second instantiation must also succeed:
+  Handle<WasmInstanceObject> instance =
+      GetWasmEngine()
+          ->SyncInstantiate(i_isolate, &thrower, module_object, {}, {})
+          .ToHandleChecked();
+  CHECK(!thrower.error());
+
+  WasmCodeRefScope code_scope;
+  CHECK(tester.native_module()->GetCode(0)->is_liftoff());
+  CHECK(tester.native_module()->GetCode(1)->is_liftoff());
+  CHECK(tester.native_module()->GetCode(2)->is_liftoff());
+  // No TurboFan compilation happened yet, and therefore no call to the cache.
+  CHECK_EQ(0, call_cache_counter);
+  bool exception = false;
+  // The tier-up threshold is hard-coded right now.
+  constexpr int tier_up_threshold = 4;
+  for (int i = 0; i < tier_up_threshold; ++i) {
+    testing::CallWasmFunctionForTesting(i_isolate, instance, "f0", 0, nullptr,
+                                        &exception);
+  }
+  tester.RunCompilerTasks();
+  CHECK(!tester.native_module()->GetCode(0)->is_liftoff());
+  CHECK(tester.native_module()->GetCode(1)->is_liftoff());
+  CHECK(tester.native_module()->GetCode(2)->is_liftoff());
+  CHECK_EQ(1, call_cache_counter);
+  size_t serialized_size;
+  {
+    i::wasm::WasmSerializer serializer(tester.native_module().get());
+    serialized_size = serializer.GetSerializedNativeModuleSize();
+  }
+  for (int i = 0; i < tier_up_threshold; ++i) {
+    testing::CallWasmFunctionForTesting(i_isolate, instance, "f1", 0, nullptr,
+                                        &exception);
+  }
+  tester.RunCompilerTasks();
+  CHECK(!tester.native_module()->GetCode(0)->is_liftoff());
+  CHECK(!tester.native_module()->GetCode(1)->is_liftoff());
+  CHECK(tester.native_module()->GetCode(2)->is_liftoff());
+  CHECK_EQ(2, call_cache_counter);
+  {
+    i::wasm::WasmSerializer serializer(tester.native_module().get());
+    CHECK_LT(serialized_size, serializer.GetSerializedNativeModuleSize());
+  }
+}
+
 STREAM_TEST(TestModuleWithErrorAfterDataSection) {
   StreamTester tester(isolate);