removing ModuleProvider from ExecutionEngine doesn't remove reverse global mappings #3537
Description
| Bugzilla Link | 3165 |
| Version | unspecified |
| OS | Linux |
| Attachments | Code to demonstrate the problem |
| Reporter | LLVM Bugzilla Contributor |
Extended Description
When a module provider is removed from the ExecutionEngine, forward mappings from the module's GlobalValues are removed, but the reverse mappings remain.
The problem seems to me to be in ExecutionEngine::clearGlobalMappingsFromModule. It loops over the module's global mappings, calling std::map<...>::erase(...) on both the forward and reverse maps. However, the variant of erase being called is the erase-by-key variant, and the GlobalValue * is passed to both calls. It's the key in the first map, but the value in the second.
The obvious fix would be to look up the GlobalValue * in the first map to get the void * address, then erase the address from the reverse map and the GlobalValue * from the forward map.
But: I've had one LLVM developer (Nickolas Lewycky) suggest to me, as a workaround for another problem, mapping multiple GlobalValue *'s to the same address. I'm not too worried about my particular workaround case, but if there are other more significant cases where multiple GlobalValue *'s map to the same address, then the whole notion of storing the reverse mapping in a single-valued map doesn't work.