[wasm] Remove kFinishedTopTierCompilation event

This fully removes the kFinishedTopTierCompilation event, and any
handling of it. In a dynamic tiering world, that event has no meaning
any more.

R=ahaas@chromium.org

Bug: v8:12899
Change-Id: I36484e36f7c36f2ac4fcb111e67a14509c2eefef
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3667081
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80930}

src/wasm/compilation-environment.h

@@ -111,14 +111,12 @@ class WireBytesStorage {
   virtual base::Optional<ModuleWireBytes> GetModuleBytes() const = 0;
 };
 
-// Callbacks will receive either {kFailedCompilation} or both
-// {kFinishedBaselineCompilation} and {kFinishedTopTierCompilation}, in that
-// order. If tier up is off, both events are delivered right after each other.
+// Callbacks will receive either {kFailedCompilation} or
+// {kFinishedBaselineCompilation}.
 enum class CompilationEvent : uint8_t {
   kFinishedBaselineCompilation,
   kFinishedExportWrappers,
   kFinishedCompilationChunk,
-  kFinishedTopTierCompilation,
   kFailedCompilation,
   kFinishedRecompilation
 };
@@ -169,7 +167,6 @@ class V8_EXPORT_PRIVATE CompilationState {
 
   bool failed() const;
   bool baseline_compilation_finished() const;
-  bool top_tier_compilation_finished() const;
   bool recompilation_finished() const;
 
   void set_compilation_id(int compilation_id);

src/wasm/module-compiler.cc

@@ -646,11 +646,6 @@ class CompilationStateImpl {
            outstanding_export_wrappers_ == 0;
   }
 
-  bool top_tier_compilation_finished() const {
-    base::MutexGuard guard(&callbacks_mutex_);
-    return outstanding_top_tier_functions_ == 0;
-  }
-
   bool recompilation_finished() const {
     base::MutexGuard guard(&callbacks_mutex_);
     return outstanding_recompilation_functions_ == 0;
@@ -873,10 +868,6 @@ bool CompilationState::baseline_compilation_finished() const {
   return Impl(this)->baseline_compilation_finished();
 }
 
-bool CompilationState::top_tier_compilation_finished() const {
-  return Impl(this)->top_tier_compilation_finished();
-}
-
 bool CompilationState::recompilation_finished() const {
   return Impl(this)->recompilation_finished();
 }
@@ -2371,11 +2362,6 @@ class AsyncCompileJob::CompilationStateCallback
         DCHECK(CompilationEvent::kFinishedBaselineCompilation == last_event_ ||
                CompilationEvent::kFinishedCompilationChunk == last_event_);
         break;
-      case CompilationEvent::kFinishedTopTierCompilation:
-        DCHECK(CompilationEvent::kFinishedBaselineCompilation == last_event_);
-        // At this point, the job will already be gone, thus do not access it
-        // here.
-        break;
       case CompilationEvent::kFailedCompilation:
         DCHECK(!last_event_.has_value() ||
                last_event_ == CompilationEvent::kFinishedExportWrappers);
@@ -2389,8 +2375,7 @@ class AsyncCompileJob::CompilationStateCallback
         }
         break;
       case CompilationEvent::kFinishedRecompilation:
-        // This event can happen either before or after
-        // {kFinishedTopTierCompilation}, hence don't remember this in
+        // This event can happen out of order, hence don't remember this in
         // {last_event_}.
         return;
     }
@@ -3295,13 +3280,6 @@ void CompilationStateImpl::InitializeCompilationProgressAfterDeserialization(
       // The {kFinishedBaselineCompilation} event is needed for module
       // compilation to finish.
       finished_events_.Add(CompilationEvent::kFinishedBaselineCompilation);
-      if (liftoff_functions.empty() && lazy_functions.empty()) {
-        // All functions exist now as TurboFan functions, so we can trigger the
-        // {kFinishedTopTierCompilation} event.
-        // The {kFinishedTopTierCompilation} event is needed for the C-API so
-        // that {serialize()} works after {deserialize()}.
-        finished_events_.Add(CompilationEvent::kFinishedTopTierCompilation);
-      }
     }
     compilation_progress_.assign(module->num_declared_functions,
                                  kProgressAfterTurbofanDeserialization);
@@ -3418,14 +3396,12 @@ void CompilationStateImpl::AddCallback(
   // Immediately trigger events that already happened.
   for (auto event : {CompilationEvent::kFinishedExportWrappers,
                      CompilationEvent::kFinishedBaselineCompilation,
-                     CompilationEvent::kFinishedTopTierCompilation,
                      CompilationEvent::kFailedCompilation}) {
     if (finished_events_.contains(event)) {
       callback->call(event);
     }
   }
   constexpr base::EnumSet<CompilationEvent> kFinalEvents{
-      CompilationEvent::kFinishedTopTierCompilation,
       CompilationEvent::kFailedCompilation};
   if (!finished_events_.contains_any(kFinalEvents)) {
     callbacks_.emplace_back(std::move(callback));
@@ -3636,17 +3612,17 @@ void CompilationStateImpl::TriggerCallbacks(
     triggered_events.Add(CompilationEvent::kFinishedExportWrappers);
     if (outstanding_baseline_units_ == 0) {
       triggered_events.Add(CompilationEvent::kFinishedBaselineCompilation);
-      if (!dynamic_tiering_ && outstanding_top_tier_functions_ == 0) {
-        triggered_events.Add(CompilationEvent::kFinishedTopTierCompilation);
-      }
     }
   }
 
+  // For dynamic tiering, trigger "compilation chunk finished" after a new chunk
+  // of size {FLAG_wasm_caching_threshold}.
   if (dynamic_tiering_ && 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 =
@@ -3670,8 +3646,6 @@ void CompilationStateImpl::TriggerCallbacks(
                        "wasm.ExportWrappersFinished"),
         std::make_pair(CompilationEvent::kFinishedBaselineCompilation,
                        "wasm.BaselineFinished"),
-        std::make_pair(CompilationEvent::kFinishedTopTierCompilation,
-                       "wasm.TopTierFinished"),
         std::make_pair(CompilationEvent::kFinishedCompilationChunk,
                        "wasm.CompilationChunkFinished"),
         std::make_pair(CompilationEvent::kFinishedRecompilation,
@@ -3854,15 +3828,8 @@ void CompilationStateImpl::WaitForCompilationEvent(
   };
 
   WaitForEventDelegate delegate{done};
-  // Everything except for top-tier units will be processed with kBaselineOnly
-  // (including wrappers). Hence we choose this for any event except
-  // {kFinishedTopTierCompilation}.
-  auto compile_tiers =
-      expect_event == CompilationEvent::kFinishedTopTierCompilation
-          ? kBaselineOrTopTier
-          : kBaselineOnly;
   ExecuteCompilationUnits(native_module_weak_, async_counters_.get(), &delegate,
-                          compile_tiers);
+                          kBaselineOnly);
   semaphore->Wait();
 }
 

src/wasm/streaming-decoder.cc

@@ -332,10 +332,7 @@ class CompilationChunkFinishedCallback : public CompilationEventCallback {
   }
 
   void call(CompilationEvent event) override {
-    if (event != CompilationEvent::kFinishedCompilationChunk &&
-        event != CompilationEvent::kFinishedTopTierCompilation) {
-      return;
-    }
+    if (event != CompilationEvent::kFinishedCompilationChunk) 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()) {

src/wasm/wasm-code-manager.cc

@@ -1705,15 +1705,11 @@ void NativeModule::SetWireBytes(base::OwnedVector<const uint8_t> wire_bytes) {
 }
 
 void NativeModule::UpdateCPUDuration(size_t cpu_duration, ExecutionTier tier) {
-  if (tier == WasmCompilationUnit::GetBaselineExecutionTier(this->module())) {
-    if (!compilation_state_->baseline_compilation_finished()) {
-      baseline_compilation_cpu_duration_.fetch_add(cpu_duration,
-                                                   std::memory_order_relaxed);
-    }
+  if (!compilation_state_->baseline_compilation_finished()) {
+    baseline_compilation_cpu_duration_.fetch_add(cpu_duration,
+                                                 std::memory_order_relaxed);
   } else if (tier == ExecutionTier::kTurbofan) {
-    if (!compilation_state_->top_tier_compilation_finished()) {
-      tier_up_cpu_duration_.fetch_add(cpu_duration, std::memory_order_relaxed);
-    }
+    tier_up_cpu_duration_.fetch_add(cpu_duration, std::memory_order_relaxed);
   }
 }
 

test/cctest/wasm/test-run-wasm-module.cc

@@ -195,7 +195,6 @@ TEST(Run_WasmModule_CompilationHintsNoTiering) {
     CHECK_EQ(expected_tier, actual_tier);
     auto* compilation_state = native_module->compilation_state();
     CHECK(compilation_state->baseline_compilation_finished());
-    CHECK(compilation_state->top_tier_compilation_finished());
   }
   Cleanup();
 }
@@ -247,19 +246,14 @@ TEST(Run_WasmModule_CompilationHintsTierUp) {
       CHECK(compilation_state->baseline_compilation_finished());
     }
 
-    // Busy wait for top tier compilation to finish.
-    while (!compilation_state->top_tier_compilation_finished()) {
-    }
-
-    // Expect top tier code.
+    // Tier-up is happening in the background. Eventually we should have top
+    // tier code.
     ExecutionTier top_tier = ExecutionTier::kTurbofan;
-    {
+    ExecutionTier actual_tier = ExecutionTier::kNone;
+    while (actual_tier != top_tier) {
       CHECK(native_module->HasCode(kFuncIndex));
       WasmCodeRefScope code_ref_scope;
-      ExecutionTier actual_tier = native_module->GetCode(kFuncIndex)->tier();
-      CHECK_EQ(top_tier, actual_tier);
-      CHECK(compilation_state->baseline_compilation_finished());
-      CHECK(compilation_state->top_tier_compilation_finished());
+      actual_tier = native_module->GetCode(kFuncIndex)->tier();
     }
   }
   Cleanup();
@@ -301,23 +295,19 @@ TEST(Run_WasmModule_CompilationHintsLazyBaselineEagerTopTier) {
     NativeModule* native_module = module.ToHandleChecked()->native_module();
     auto* compilation_state = native_module->compilation_state();
 
-    // Busy wait for top tier compilation to finish.
-    while (!compilation_state->top_tier_compilation_finished()) {
-    }
-
-    // Expect top tier code.
+    // We have no code initially (because of lazy baseline), but eventually we
+    // should have TurboFan ready (because of eager top tier).
     static_assert(ExecutionTier::kLiftoff < ExecutionTier::kTurbofan,
                   "Assume an order on execution tiers");
-    static const int kFuncIndex = 0;
-    ExecutionTier top_tier = ExecutionTier::kTurbofan;
-    {
-      CHECK(native_module->HasCode(kFuncIndex));
-      WasmCodeRefScope code_ref_scope;
-      ExecutionTier actual_tier = native_module->GetCode(kFuncIndex)->tier();
-      CHECK_EQ(top_tier, actual_tier);
-      CHECK(compilation_state->baseline_compilation_finished());
-      CHECK(compilation_state->top_tier_compilation_finished());
+    constexpr int kFuncIndex = 0;
+    WasmCodeRefScope code_ref_scope;
+    while (true) {
+      auto* code = native_module->GetCode(kFuncIndex);
+      if (!code) continue;
+      CHECK_EQ(ExecutionTier::kTurbofan, code->tier());
+      break;
     }
+    CHECK(compilation_state->baseline_compilation_finished());
   }
   Cleanup();
 }

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

@@ -1322,6 +1322,11 @@ STREAM_TEST(TestFunctionSectionWithoutCodeSection) {
 }
 
 STREAM_TEST(TestSetModuleCompiledCallback) {
+  // The "module compiled" callback (to be renamed to "top tier chunk finished"
+  // or similar) will only be triggered with dynamic tiering, so skip this test
+  // if dynamic tiering is disabled.
+  if (!FLAG_wasm_dynamic_tiering) return;
+
   // Reduce the caching threshold so that our three small functions trigger
   // caching.
   FlagScope<int> caching_treshold(&FLAG_wasm_caching_threshold, 10);