memory leak in LegacyPassManager.cpp

[huiwu]

Summary

in function MPPassManager::addLowerLevelRequiredPass in file LegacyPassManager.cpp, there is a memory leak found.

[mehdi_amini]

You should add llvm-commits as subscriber.

[mehdi_amini]

Is there a way to reproduce? Should we pass a unique_ptr in?

[huiwu]

If we add a pass twice into a ModulePass (for example, if a ModulePass depends on two FunctionPasses, and the second FunctionPass also depends on the first one), this leak can happen.

I think using unique_ptr can work, but need touch the key data structure of the pass management, and will be a much more complex fix.

lib/IR/LegacyPassManager.cpp

     // that we checked for an available analysis above.
     FPP->add(RequiredPass);
   }
+  else
+  {
+    delete RequiredPass;
+  }
   // Register P as the last user of FoundPass or RequiredPass.
   SmallVector<Pass *, 1> LU;
   LU.push_back(FoundPass);