Subzero: Fixed deadlock with _start but no globals

src/IceInstrumentation.h

 //===- subzero/src/IceInstrumentation.h - ICE instrumentation ---*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 12 matching lines @@
 /// subclass is still responsible for driving the instrumentation, but it can
 /// use other Instrumentation subclasses however it needs to.
 ///
 //===----------------------------------------------------------------------===//
 
 #ifndef SUBZERO_SRC_ICEINSTRUMENTATION_H
 #define SUBZERO_SRC_ICEINSTRUMENTATION_H
 
 #include "IceDefs.h"
 
+#include <condition_variable>
+
 namespace Ice {
 
 class LoweringContext;
 
 class Instrumentation {
   Instrumentation() = delete;
   Instrumentation(const Instrumentation &) = delete;
   Instrumentation &operator=(const Instrumentation &) = delete;
 
 public:
   Instrumentation(GlobalContext *Ctx) : Ctx(Ctx) {}
+  virtual ~Instrumentation() = default;
   virtual void instrumentGlobals(VariableDeclarationList &) {}
   void instrumentFunc(Cfg *Func);
+  void setHasSeenGlobals();
 
 protected:
   virtual void instrumentInst(LoweringContext &Context);
+  LockedPtr<VariableDeclarationList> getGlobals();
 
 private:
   virtual bool isInstrumentable(Cfg *) { return true; }
   virtual void instrumentFuncStart(LoweringContext &) {}
   virtual void instrumentAlloca(LoweringContext &, class InstAlloca *) {}
   virtual void instrumentArithmetic(LoweringContext &, class InstArithmetic *) {
   }
   virtual void instrumentBr(LoweringContext &, class InstBr *) {}
   virtual void instrumentCall(LoweringContext &, class InstCall *) {}
   virtual void instrumentCast(LoweringContext &, class InstCast *) {}
@@ skipping 12 matching lines @@
   virtual void instrumentStore(LoweringContext &, class InstStore *) {}
   virtual void instrumentSwitch(LoweringContext &, class InstSwitch *) {}
   virtual void instrumentUnreachable(LoweringContext &,
                                      class InstUnreachable *) {}
   virtual void instrumentStart(Cfg *) {}
   virtual void instrumentLocalVars(Cfg *) {}
   virtual void finishFunc(Cfg *) {}
 
 protected:
   GlobalContext *Ctx;
+
+private:
+  bool HasSeenGlobals = false;
+  std::mutex GlobalsSeenMutex;
+  std::condition_variable GlobalsSeenCV;
 };
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEINSTRUMENTATION_H