Fix the order of destructors in LibLTOCodeGenerator

Summary:
The order of destructors in LTOCodeGenerator gets changed in r254696.
It is possible for LTOCodeGenerator to have a MergedModule created in
the OwnedContext, in which case the module must be destructed before
the context.

Reviewers: rafael, dexonsmith

Subscribers: llvm-commits, joker.eph

Differential Revision: http://reviews.llvm.org/D15346

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@255092 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/LTO/LTOCodeGenerator.h

@@ -148,6 +148,8 @@ struct LTOCodeGenerator {
 
   LLVMContext &getContext() { return Context; }
 
+  void resetMergedModule() { MergedModule.reset(); }
+
 private:
   void initializeLTOPasses();
 

tools/lto/lto.cpp

@@ -124,6 +124,10 @@ struct LibLTOCodeGenerator : LTOCodeGenerator {
       : LTOCodeGenerator(*Context), OwnedContext(std::move(Context)) {
     setDiagnosticHandler(handleLibLTODiagnostic, nullptr); }
 
+  // Reset the module first in case MergedModule is created in OwnedContext.
+  // Module must be destructed before its context gets destructed.
+  ~LibLTOCodeGenerator() { resetMergedModule(); }
+
   std::unique_ptr<MemoryBuffer> NativeObjectFile;
   std::unique_ptr<LLVMContext> OwnedContext;
 };