[wasm] Refactor counters for unfinished compilation units

So far, we always finished the baseline units before finishing any
tiering unit. This will be refactored to finish all units from the
background threads, so the finishing can happen in any order.
Thus refactor the counters to count both separately, and trigger the
right events.

R=ahaas@chromium.org

Bug: v8:7921
Change-Id: Ia2d8ab3f70f9bc3406eff428da5d22580558887b
Reviewed-on: https://chromium-review.googlesource.com/c/1333669
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57608}

src/wasm/function-compiler.cc

@@ -91,6 +91,8 @@ void WasmCompilationUnit::ExecuteCompilation(
       }
       // Otherwise, fall back to turbofan.
       SwitchTier(ExecutionTier::kOptimized);
+      // TODO(wasm): We could actually stop or remove the tiering unit for this
+      // function to avoid compiling it twice with TurboFan.
       V8_FALLTHROUGH;
     case ExecutionTier::kOptimized:
       turbofan_unit_->ExecuteCompilation(env, func_body, counters, detected);

src/wasm/module-compiler.cc

@@ -126,7 +126,9 @@ class CompilationStateImpl {
     return baseline_compilation_finished_;
   }
 
-  bool has_outstanding_units() const { return outstanding_units_ > 0; }
+  bool has_outstanding_units() const {
+    return outstanding_tiering_units_ > 0 || outstanding_baseline_units_ > 0;
+  }
 
   CompileMode compile_mode() const { return compile_mode_; }
   WasmFeatures* detected_features() { return &detected_features_; }
@@ -274,8 +276,8 @@ class CompilationStateImpl {
 
   const size_t max_background_tasks_ = 0;
 
-  size_t outstanding_units_ = 0;
-  size_t num_tiering_units_ = 0;
+  size_t outstanding_baseline_units_ = 0;
+  size_t outstanding_tiering_units_ = 0;
 };
 
 void UpdateFeatureUseCounts(Isolate* isolate, const WasmFeatures& detected) {
@@ -639,11 +641,8 @@ bool FetchAndExecuteCompilationUnit(CompilationEnv* env,
       compilation_state->GetNextCompilationUnit();
   if (unit == nullptr) return false;
 
-  // TODO(kimanh): We need to find out in which tier the unit
-  // should be compiled in before compiling it, as it might fallback
-  // to Turbofan if it cannot be compiled using Liftoff. This can be removed
-  // later as soon as Liftoff can compile any function. Then, we can directly
-  // access {unit->tier()} within {ScheduleUnitForFinishing()}.
+  // Get the tier before starting compilation, as compilation can switch tiers
+  // if baseline bails out.
   ExecutionTier tier = unit->tier();
   unit->ExecuteCompilation(env, compilation_state->GetSharedWireBytesStorage(),
                            counters, detected);
@@ -2995,11 +2994,10 @@ void CompilationStateImpl::CancelAndWait() {
 
 void CompilationStateImpl::SetNumberOfFunctionsToCompile(size_t num_functions) {
   DCHECK(!failed());
-  outstanding_units_ = num_functions;
+  outstanding_baseline_units_ = num_functions;
 
   if (compile_mode_ == CompileMode::kTiering) {
-    outstanding_units_ += num_functions;
-    num_tiering_units_ = num_functions;
+    outstanding_tiering_units_ = num_functions;
   }
 }
 
@@ -3067,32 +3065,44 @@ bool CompilationStateImpl::HasCompilationUnitToFinish() {
 }
 
 void CompilationStateImpl::OnFinishedUnit() {
-  DCHECK_GT(outstanding_units_, 0);
-  --outstanding_units_;
-
-  if (outstanding_units_ == 0) {
-    background_task_manager_.CancelAndWait();
-    baseline_compilation_finished_ = true;
-
-    DCHECK(compile_mode_ == CompileMode::kRegular ||
-           compile_mode_ == CompileMode::kTiering);
-    NotifyOnEvent(compile_mode_ == CompileMode::kRegular
-                      ? CompilationEvent::kFinishedBaselineCompilation
-                      : CompilationEvent::kFinishedTopTierCompilation,
-                  nullptr);
-
-  } else if (outstanding_units_ == num_tiering_units_) {
-    DCHECK_EQ(compile_mode_, CompileMode::kTiering);
-    baseline_compilation_finished_ = true;
-
-    // TODO(wasm): For streaming compilation, we want to start top tier
-    // compilation before all functions have been compiled with Liftoff, e.g.
-    // in the case when all received functions have been compiled with Liftoff
-    // and we are waiting for new functions to compile.
-
-    // If we are in {kRegular} mode, {num_tiering_units_} is 0, therefore
-    // this case is already caught by the previous check.
-    NotifyOnEvent(CompilationEvent::kFinishedBaselineCompilation, nullptr);
+  // If we are *not* compiling in tiering mode, then all units are counted as
+  // baseline units.
+  bool is_tiering_mode = compile_mode_ == CompileMode::kTiering;
+  bool is_tiering_unit = is_tiering_mode && baseline_compilation_finished_;
+
+  // Sanity check: Baseline compilation cannot be finished if there are
+  // outstanding baseline units and tiering units.
+  DCHECK_IMPLIES(
+      outstanding_tiering_units_ > 0 && outstanding_baseline_units_ > 0,
+      !baseline_compilation_finished_);
+  // Sanity check: If we are not in tiering mode, there cannot be outstanding
+  // tiering units.
+  DCHECK_IMPLIES(!is_tiering_mode, outstanding_tiering_units_ == 0);
+
+  auto* units_counter = is_tiering_unit ? &outstanding_tiering_units_
+                                        : &outstanding_baseline_units_;
+  DCHECK_GT(*units_counter, 0);
+  --*units_counter;
+
+  if (*units_counter == 0) {
+    if (!baseline_compilation_finished_) {
+      baseline_compilation_finished_ = true;
+
+      // TODO(wasm): For streaming compilation, we want to start top tier
+      // compilation before all functions have been compiled with Liftoff, e.g.
+      // in the case when all received functions have been compiled with Liftoff
+      // and we are waiting for new functions to compile.
+
+      // If we are in {kRegular} mode, {num_tiering_units_} is 0, therefore
+      // this case is already caught by the previous check.
+      NotifyOnEvent(CompilationEvent::kFinishedBaselineCompilation, nullptr);
+      if (!is_tiering_mode) {
+        NotifyOnEvent(CompilationEvent::kFinishedTopTierCompilation, nullptr);
+      }
+    } else {
+      DCHECK(is_tiering_unit);
+      NotifyOnEvent(CompilationEvent::kFinishedTopTierCompilation, nullptr);
+    }
   }
 }