Subzero: Fixed deadlock with _start but no globals

src/IceInstrumentation.cpp

 //===- subzero/src/IceInstrumentation.cpp - ICE instrumentation framework -===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 100 matching lines @@
   case Inst::Unreachable:
     instrumentUnreachable(Context, llvm::cast<InstUnreachable>(Instr));
     break;
   default:
     // Only instrument high-level ICE instructions
     assert(false && "Instrumentation encountered an unexpected instruction");
     break;
   }
 }
 
+void Instrumentation::setHasSeenGlobals() {
+  {
+    std::unique_lock<std::mutex> _(GlobalsSeenMutex);
+    HasSeenGlobals = true;
+  }
+  GlobalsSeenCV.notify_all();
+}
+
+LockedPtr<VariableDeclarationList> Instrumentation::getGlobals() {
+  std::unique_lock<std::mutex> GlobalsLock(GlobalsSeenMutex);
+  GlobalsSeenCV.wait(GlobalsLock, [this] { return HasSeenGlobals; });
+  return Ctx->getGlobals();
+}
+
 } // end of namespace Ice