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

llvm-svn: 255092
diff --git a/llvm/tools/lto/lto.cpp b/llvm/tools/lto/lto.cpp
index d13de57..d8f99c0 100644
--- a/llvm/tools/lto/lto.cpp
+++ b/llvm/tools/lto/lto.cpp
@@ -124,6 +124,10 @@
       : 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;
 };