[serializer] print use count of external references.

R=peria@chromium.org, vogelheim@chromium.org
BUG=chromium:617892
NOPRESUBMIT=true

Review-Url: https://codereview.chromium.org/2495213003
Cr-Commit-Position: refs/heads/master@{#40979}

src/api.cc

@@ -559,6 +559,10 @@ StartupData SnapshotCreator::CreateBlob(
   }
   data->contexts_.Clear();
 
+#ifdef DEBUG
+  i::ExternalReferenceTable::instance(isolate)->ResetCount();
+#endif  // DEBUG
+
   i::StartupSerializer startup_serializer(isolate, function_code_handling);
   startup_serializer.SerializeStrongReferences();
 
@@ -572,6 +576,13 @@ StartupData SnapshotCreator::CreateBlob(
   }
 
   startup_serializer.SerializeWeakReferencesAndDeferred();
+
+#ifdef DEBUG
+  if (i::FLAG_external_reference_stats) {
+    i::ExternalReferenceTable::instance(isolate)->PrintCount();
+  }
+#endif  // DEBUG
+
   i::SnapshotData startup_snapshot(&startup_serializer);
   StartupData result =
       i::Snapshot::CreateSnapshotBlob(&startup_snapshot, &context_snapshots);

src/external-reference-table.cc

@@ -11,6 +11,11 @@
 #include "src/deoptimizer.h"
 #include "src/ic/stub-cache.h"
 
+#if defined(DEBUG) && defined(V8_OS_LINUX) && !defined(V8_OS_ANDROID)
+#define SYMBOLIZE_FUNCTION
+#include <execinfo.h>
+#endif  // DEBUG && V8_OS_LINUX && !V8_OS_ANDROID
+
 namespace v8 {
 namespace internal {
 
@@ -43,6 +48,28 @@ ExternalReferenceTable::ExternalReferenceTable(Isolate* isolate) {
   AddApiReferences(isolate);
 }
 
+#ifdef DEBUG
+void ExternalReferenceTable::ResetCount() {
+  for (ExternalReferenceEntry& entry : refs_) entry.count = 0;
+}
+
+void ExternalReferenceTable::PrintCount() {
+  for (int i = 0; i < refs_.length(); i++) {
+    v8::base::OS::Print("index=%5d count=%5d  %-60s\n", i, refs_[i].count,
+                        refs_[i].name);
+  }
+}
+#endif  // DEBUG
+
+// static
+const char* ExternalReferenceTable::ResolveSymbol(void* address) {
+#ifdef SYMBOLIZE_FUNCTION
+  return backtrace_symbols(&address, 1)[0];
+#else
+  return "<unresolved>";
+#endif  // SYMBOLIZE_FUNCTION
+}
+
 void ExternalReferenceTable::AddReferences(Isolate* isolate) {
   // Miscellaneous
   Add(ExternalReference::roots_array_start(isolate).address(),
@@ -336,22 +363,24 @@ void ExternalReferenceTable::AddAccessors(Isolate* isolate) {
   };
 
   static const AccessorRefTable getters[] = {
-#define ACCESSOR_INFO_DECLARATION(name) \
-  {FUNCTION_ADDR(&Accessors::name##Getter), "Accessors::" #name "Getter"},
-      ACCESSOR_INFO_LIST(ACCESSOR_INFO_DECLARATION)
+#define ACCESSOR_INFO_DECLARATION(name)     \
+  { FUNCTION_ADDR(&Accessors::name##Getter), \
+    "Redirect to Accessors::" #name "Getter"},
+  ACCESSOR_INFO_LIST(ACCESSOR_INFO_DECLARATION)
 #undef ACCESSOR_INFO_DECLARATION
   };
   static const AccessorRefTable setters[] = {
 #define ACCESSOR_SETTER_DECLARATION(name) \
-  {FUNCTION_ADDR(&Accessors::name), "Accessors::" #name},
-      ACCESSOR_SETTER_LIST(ACCESSOR_SETTER_DECLARATION)
+  { FUNCTION_ADDR(&Accessors::name), "Accessors::" #name},
+  ACCESSOR_SETTER_LIST(ACCESSOR_SETTER_DECLARATION)
 #undef ACCESSOR_INFO_DECLARATION
   };
 
   for (unsigned i = 0; i < arraysize(getters); ++i) {
-    Add(getters[i].address, getters[i].name);
+    const char* name = getters[i].name + 12;  // Skip "Redirect to " prefix.
+    Add(getters[i].address, name);
     Add(AccessorInfo::redirect(isolate, getters[i].address, ACCESSOR_GETTER),
-        "");
+        getters[i].name);
   }
 
   for (unsigned i = 0; i < arraysize(setters); ++i) {
@@ -412,7 +441,8 @@ void ExternalReferenceTable::AddApiReferences(Isolate* isolate) {
   intptr_t* api_external_references = isolate->api_external_references();
   if (api_external_references != nullptr) {
     while (*api_external_references != 0) {
-      Add(reinterpret_cast<Address>(*api_external_references), "<embedder>");
+      Address address = reinterpret_cast<Address>(*api_external_references);
+      Add(address, ResolveSymbol(address));
       api_external_references++;
     }
   }

src/external-reference-table.h

@@ -23,12 +23,24 @@ class ExternalReferenceTable {
   Address address(uint32_t i) { return refs_[i].address; }
   const char* name(uint32_t i) { return refs_[i].name; }
 
+#ifdef DEBUG
+  void increment_count(uint32_t i) { refs_[i].count++; }
+  int count(uint32_t i) { return refs_[i].count; }
+  void ResetCount();
+  void PrintCount();
+#endif  // DEBUG
+
+  static const char* ResolveSymbol(void* address);
+
   static const int kDeoptTableSerializeEntryCount = 64;
 
  private:
   struct ExternalReferenceEntry {
     Address address;
     const char* name;
+#ifdef DEBUG
+    int count;
+#endif  // DEBUG
   };
 
   explicit ExternalReferenceTable(Isolate* isolate);

src/flag-definitions.h

@@ -627,6 +627,10 @@ DEFINE_BOOL(serialize_toplevel, true, "enable caching of toplevel scripts")
 DEFINE_BOOL(serialize_eager, false, "compile eagerly when caching scripts")
 DEFINE_BOOL(serialize_age_code, false, "pre age code in the code cache")
 DEFINE_BOOL(trace_serializer, false, "print code serializer trace")
+#ifdef DEBUG
+DEFINE_BOOL(external_reference_stats, false,
+            "print statistics on external references used during serialization")
+#endif  // DEBUG
 
 // compiler.cc
 DEFINE_INT(min_preparse_length, 1024,

src/snapshot/serializer-common.cc

@@ -8,25 +8,21 @@
 #include "src/ic/stub-cache.h"
 #include "src/list-inl.h"
 
-#if defined(DEBUG) && defined(V8_OS_LINUX) && !defined(V8_OS_ANDROID)
-#define SYMBOLIZE_FUNCTION
-#include <execinfo.h>
-#endif  // DEBUG && V8_OS_LINUX && !V8_OS_ANDROID
-
 namespace v8 {
 namespace internal {
 
 ExternalReferenceEncoder::ExternalReferenceEncoder(Isolate* isolate) {
   map_ = isolate->external_reference_map();
+#ifdef DEBUG
+  table_ = ExternalReferenceTable::instance(isolate);
+#endif  // DEBUG
   if (map_ != nullptr) return;
   map_ = new AddressToIndexHashMap();
   ExternalReferenceTable* table = ExternalReferenceTable::instance(isolate);
   for (uint32_t i = 0; i < table->size(); ++i) {
     Address addr = table->address(i);
-    // We expect no duplicate external references entries in the table.
-    // AccessorRefTable getter may have duplicates, indicated by an empty string
-    // as name.
-    DCHECK(table->name(i)[0] == '\0' || map_->Get(addr).IsNothing());
+    DCHECK(map_->Get(addr).IsNothing() ||
+           strncmp(table->name(i), "Redirect to ", 12) == 0);
     map_->Set(addr, i);
     DCHECK(map_->Get(addr).IsJust());
   }
@@ -36,13 +32,14 @@ ExternalReferenceEncoder::ExternalReferenceEncoder(Isolate* isolate) {
 uint32_t ExternalReferenceEncoder::Encode(Address address) const {
   Maybe<uint32_t> maybe_index = map_->Get(address);
   if (maybe_index.IsNothing()) {
-    void* function_addr = address;
-    v8::base::OS::PrintError("Unknown external reference %p.\n", function_addr);
-#ifdef SYMBOLIZE_FUNCTION
-    v8::base::OS::PrintError("%s\n", backtrace_symbols(&function_addr, 1)[0]);
-#endif  // SYMBOLIZE_FUNCTION
+    void* addr = address;
+    v8::base::OS::PrintError("Unknown external reference %p.\n", addr);
+    v8::base::OS::PrintError("%s", ExternalReferenceTable::ResolveSymbol(addr));
     v8::base::OS::Abort();
   }
+#ifdef DEBUG
+  table_->increment_count(maybe_index.FromJust());
+#endif  // DEBUG
   return maybe_index.FromJust();
 }
 

src/snapshot/serializer-common.h

@@ -24,6 +24,9 @@ class ExternalReferenceEncoder {
 
  private:
   AddressToIndexHashMap* map_;
+#ifdef DEBUG
+  ExternalReferenceTable* table_;
+#endif  // DEBUG
 
   DISALLOW_COPY_AND_ASSIGN(ExternalReferenceEncoder);
 };