Fix the order of destructors in LibLTOCodeGenerator

[steven_wu]

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.

[• rafael]

Needs a git-clang-format.

You should be able to write an unit test that calls lto_module_create_in_codegen_context. I would be very happy if you did, but I understand if you think it is not worth it.

[steven_wu]

Thanks Rafael for reviewing the change! I couldn't find a clean way to link against libLTO for testing in llvm repo. This might need to be fixed. I have some internal ld64 test case covering this for now.

Steven

include/llvm/LTO/LTOCodeGenerator.h

struct LTOCodeGenerator {
   /// threads.  Output files will be written to members of out. Returns true on
   /// success.
   bool compileOptimized(ArrayRef<raw_pwrite_stream *> Out);
 
   void setDiagnosticHandler(lto_diagnostic_handler_t, void *);
 
   LLVMContext &getContext() { return Context; }
 
+  void resetMergedModule() { MergedModule.reset(); }
+
 private:
   void initializeLTOPasses();
 
   bool compileOptimizedToFile(const char **Name);
   void applyScopeRestrictions();
   void applyRestriction(GlobalValue &GV, ArrayRef<StringRef> Libcalls,
                         std::vector<const char *> &MustPreserveList,
                         SmallPtrSetImpl<GlobalValue *> &AsmUsed,

tools/lto/lto.cpp

 // file.
 struct LibLTOCodeGenerator : LTOCodeGenerator {
   LibLTOCodeGenerator() : LTOCodeGenerator(*LTOContext) {
     setDiagnosticHandler(handleLibLTODiagnostic, nullptr); }
   LibLTOCodeGenerator(std::unique_ptr<LLVMContext> Context)
       : 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;
 };
 
 }
 
 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(LibLTOCodeGenerator, lto_code_gen_t)
 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(LTOModule, lto_module_t)