Fix a use-iterator-after-invalidate error

[sanjoy]

Summary

As far as I can tell, AnalysysResult::getResultImpl reuses an iterator into a DenseMap after inserting elements into it. This change recomputes the iterator before the second use.

(caveat: I'm not familiar with this bit of code, so it possible that I'm misreading it)

[sanjoy]

Checked in without pre-commit review since it looks fairly obvious.

include/llvm/IR/PassManager.h

ResultConceptT &getResultImpl(void *PassID, IRUnitT &IR) {
     // If we don't have a cached result for this function, look up the pass and
     // run it to produce a result, which we then add to the cache.
     if (Inserted) {
       auto &P = this->lookupPass(PassID);
       if (DebugLogging)
         dbgs() << "Running analysis: " << P.name() << "\n";
       AnalysisResultListT &ResultList = AnalysisResultLists[&IR];
       ResultList.emplace_back(PassID, P.run(IR, this));
+
+      // P.run may have inserted elements into AnalysisResults and invalidated
+      // RI.
+      RI = AnalysisResults.find(std::make_pair(PassID, &IR));
+      assert(RI != AnalysisResults.end() && "we just inserted it!");
+
       RI->second = std::prev(ResultList.end());
     }
 
     return *RI->second->second;
   }
 
   /// \brief Get a cached analysis result or return null.
   ResultConceptT *getCachedResultImpl(void *PassID, IRUnitT &IR) const {