Allow Subzero to parse function blocks in parallel.

src/IceTranslator.cpp

Index: src/IceTranslator.cpp
diff --git a/src/IceTranslator.cpp b/src/IceTranslator.cpp
index ce54c218405d6c7466715f73b76ed27096728b75..181fd44c3dcb11e76d9fa7c61fa036c505205821 100644
--- a/src/IceTranslator.cpp
+++ b/src/IceTranslator.cpp
@@ -24,6 +24,20 @@
 
 namespace Ice {
 
+class CfgOptWorkItem final : public OptWorkItem {
+  CfgOptWorkItem() = delete;
+  CfgOptWorkItem(const CfgOptWorkItem &) = delete;
+  CfgOptWorkItem &operator=(const CfgOptWorkItem &) = delete;
+
+public:
+  CfgOptWorkItem(std::unique_ptr<Cfg> Func) : Func(std::move(Func)) {}
+  std::unique_ptr<Cfg> getParsedCfg() override { return std::move(Func); }
+  ~CfgOptWorkItem() override = default;
+
+private:
+  std::unique_ptr<Ice::Cfg> Func;
+};
+
 Translator::Translator(GlobalContext *Ctx)
     : Ctx(Ctx), NextSequenceNumber(GlobalContext::getFirstSequenceNumber()),
       ErrorStatus() {}
@@ -55,7 +69,7 @@ bool Translator::checkIfUnnamedNameSafe(const IceString &Name, const char *Kind,
 }
 
 void Translator::translateFcn(std::unique_ptr<Cfg> Func) {
-  Ctx->optQueueBlockingPush(std::move(Func));
+  Ctx->optQueueBlockingPush(makeUnique<CfgOptWorkItem>(std::move(Func)));
 }
 
 void Translator::lowerGlobals(