Reland "[wasm][debug] Fix tier down during streaming compilation"

This is a reland of 3cc981cb with a
fix for data race detected by TSan.

Original change's description:
> [wasm][debug] Fix tier down during streaming compilation
>
> If the debugger is enabled while streaming compilation is happening, we
> won't correctly tier down to Liftoff. This is because during streaming
> compilation, we always compile for no debugging. Fixing that is a bit
> tricky, since when the debugger is enabled, functions can either already
> have finished compiling, or they are currently being compiled, or their
> wire bytes are not received yet.
> Instead of handling this correctly while streaming compilation is
> running, we just recompile the whole module with Liftoff after streaming
> compilation finished.
>
> For testing this, we use the existing tests for async compilation, and
> enable --wasm-test-streaming, which compiles via the streaming decoder
> even in the async compilation case.
>
> R=thibaudm@chromium.org
>
> Bug: v8:10531
> Change-Id: I0177248a9ad2e90f83faee965d6746de05423f1f
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2207133
> Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
> Commit-Queue: Clemens Backes <clemensb@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#67882}

Bug: v8:10531, v8:10544
Change-Id: I884922b6ac55543e6ff9b1046438f6b3abab6f64
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2207187Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67896}

src/wasm/module-compiler.cc

@@ -802,6 +802,9 @@ class CompilationUnitBuilder {
     ExecutionTierPair tiers = GetRequestedExecutionTiers(
         native_module_->module(), compilation_state()->compile_mode(),
         native_module_->enabled_features(), func_index);
+    // Compile everything for non-debugging initially. If needed, we will tier
+    // down when the module is fully compiled. Synchronization would be pretty
+    // difficult otherwise.
     baseline_units_.emplace_back(func_index, tiers.baseline_tier, kNoDebugging);
     if (tiers.baseline_tier != tiers.top_tier) {
       tiering_units_.emplace_back(func_index, tiers.top_tier, kNoDebugging);
@@ -1773,8 +1776,11 @@ class AsyncCompileJob::CompilationStateCallback {
       case CompilationEvent::kFailedCompilation:
         DCHECK(!last_event_.has_value());
         if (job_->DecrementAndCheckFinisherCount()) {
+          // Don't update {job_->native_module_} to avoid data races with other
+          // compilation threads. Use a copy of the shared pointer instead.
+          std::shared_ptr<NativeModule> native_module = job_->native_module_;
           job_->isolate_->wasm_engine()->UpdateNativeModuleCache(
-              true, &job_->native_module_, job_->isolate_);
+              true, &native_module, job_->isolate_);
           job_->DoSync<CompileFailed>();
         }
         break;
@@ -2407,6 +2413,13 @@ void AsyncStreamingProcessor::OnFinishedStream(OwnedVector<uint8_t> bytes) {
   }
   const bool needs_finish = job_->DecrementAndCheckFinisherCount();
   DCHECK_IMPLIES(!has_code_section, needs_finish);
+  // We might need to recompile the module for debugging, if the debugger was
+  // enabled while streaming compilation was running. Since handling this while
+  // compiling via streaming is tricky, we just tier down now, before publishing
+  // the module.
+  if (job_->native_module_->IsTieredDown()) {
+    job_->native_module_->TriggerRecompilation();
+  }
   if (needs_finish) {
     const bool failed = job_->native_module_->compilation_state()->failed();
     if (!cache_hit) {

test/debugger/debug/wasm/debug-enabled-tier-down-wasm-streaming.js

+// Copyright 2020 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --wasm-test-streaming
+
+load('test/debugger/debug/wasm/debug-enabled-tier-down-wasm.js');