[wasm] Implement parallel compilation.

src/wasm/wasm-opcodes.cc

 // Copyright 2015 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.
 
 #include "src/wasm/wasm-opcodes.h"
 #include "src/messages.h"
 #include "src/signature.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 61 matching lines @@
 
 // Initialize the signature table.
 static void InitSigTable() {
 #define SET_SIG_TABLE(name, opcode, sig) \
   kSimpleExprSigTable[opcode] = static_cast<int>(kSigEnum_##sig) + 1;
   FOREACH_SIMPLE_OPCODE(SET_SIG_TABLE);
   FOREACH_ASMJS_COMPAT_OPCODE(SET_SIG_TABLE);
 #undef SET_SIG_TABLE
 }
 
+class SigTable {
+ public:
+  SigTable() {
+    // TODO(ahaas): Move {InitSigTable} into the class.
+    InitSigTable();
+  }
+  FunctionSig* Signature(WasmOpcode opcode) const {
+    return const_cast<FunctionSig*>(
+        kSimpleExprSigs[kSimpleExprSigTable[static_cast<byte>(opcode)]]);
+  }
+};
+
+static base::LazyInstance<SigTable>::type sig_table = LAZY_INSTANCE_INITIALIZER;
+
 FunctionSig* WasmOpcodes::Signature(WasmOpcode opcode) {
-  // TODO(titzer): use LazyInstance to make this thread safe.
-  if (kSimpleExprSigTable[kExprI32Add] == 0) InitSigTable();
-  return const_cast<FunctionSig*>(
-      kSimpleExprSigs[kSimpleExprSigTable[static_cast<byte>(opcode)]]);
+  return sig_table.Get().Signature(opcode);
 }
 
 // TODO(titzer): pull WASM_64 up to a common header.
 #if !V8_TARGET_ARCH_32_BIT || V8_TARGET_ARCH_X64
 #define WASM_64 1
 #else
 #define WASM_64 0
 #endif
 
 int WasmOpcodes::TrapReasonToMessageId(TrapReason reason) {
   switch (reason) {
 #define TRAPREASON_TO_MESSAGE(name) \
   case k##name:                     \
     return MessageTemplate::kWasm##name;
     FOREACH_WASM_TRAPREASON(TRAPREASON_TO_MESSAGE)
 #undef TRAPREASON_TO_MESSAGE
     default:
       return MessageTemplate::kNone;
   }
 }
 
 const char* WasmOpcodes::TrapReasonMessage(TrapReason reason) {
   return MessageTemplate::TemplateString(TrapReasonToMessageId(reason));
 }
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8