From d74f5c6f09704a86ca1b87d6acf8cb6c1d09ba24 Mon Sep 17 00:00:00 2001
From: yangguo <yangguo@chromium.org>
Date: Tue, 17 Mar 2015 04:04:12 -0700
Subject: [PATCH] Serializer: Cache FlagList::Hash result.

R=vogelheim@chromium.org

Review URL: https://codereview.chromium.org/1011703003

Cr-Commit-Position: refs/heads/master@{#27234}
---
 src/flags.cc                  | 23 +++++++++++++++--------
 src/flags.h                   |  3 ++-
 test/cctest/test-serialize.cc |  2 ++
 3 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/src/flags.cc b/src/flags.cc
index d498c28240..7386238090 100644
--- a/src/flags.cc
+++ b/src/flags.cc
@@ -543,15 +543,10 @@ void FlagList::PrintHelp() {
 }
 
 
-// static
-void FlagList::EnforceFlagImplications() {
-#define FLAG_MODE_DEFINE_IMPLICATIONS
-#include "src/flag-definitions.h"
-#undef FLAG_MODE_DEFINE_IMPLICATIONS
-}
+static uint32_t flag_hash = 0;
 
 
-uint32_t FlagList::Hash() {
+void ComputeFlagListHash() {
   std::ostringstream modified_args_as_string;
 #ifdef DEBUG
   modified_args_as_string << "debug";
@@ -564,7 +559,19 @@ uint32_t FlagList::Hash() {
     }
   }
   std::string args(modified_args_as_string.str());
-  return static_cast<uint32_t>(
+  flag_hash = static_cast<uint32_t>(
       base::hash_range(args.c_str(), args.c_str() + args.length()));
 }
+
+
+// static
+void FlagList::EnforceFlagImplications() {
+#define FLAG_MODE_DEFINE_IMPLICATIONS
+#include "src/flag-definitions.h"
+#undef FLAG_MODE_DEFINE_IMPLICATIONS
+  ComputeFlagListHash();
+}
+
+
+uint32_t FlagList::Hash() { return flag_hash; }
 } }  // namespace v8::internal
diff --git a/src/flags.h b/src/flags.h
index 9ec5d30119..545c172d36 100644
--- a/src/flags.h
+++ b/src/flags.h
@@ -58,7 +58,8 @@ class FlagList {
   // Set flags as consequence of being implied by another flag.
   static void EnforceFlagImplications();
 
-  // Hash of current flags (to quickly determine flag changes).
+  // Hash of flags (to quickly determine mismatching flag expectations).
+  // This hash is calculated during V8::Initialize and cached.
   static uint32_t Hash();
 };
 
diff --git a/test/cctest/test-serialize.cc b/test/cctest/test-serialize.cc
index 71e5d82181..88711b8429 100644
--- a/test/cctest/test-serialize.cc
+++ b/test/cctest/test-serialize.cc
@@ -1372,7 +1372,9 @@ TEST(SerializeToplevelFlagChange) {
   v8::ScriptCompiler::CachedData* cache = ProduceCache(source);
 
   v8::Isolate* isolate2 = v8::Isolate::New();
+
   FLAG_allow_natives_syntax = true;  // Flag change should trigger cache reject.
+  FlagList::EnforceFlagImplications();
   {
     v8::Isolate::Scope iscope(isolate2);
     v8::HandleScope scope(isolate2);