[PM] Fix a bad invalid densemap iterator bug in the new invalidation

logic.

Yup, the invalidation logic has an invalid iterator bug. Can't make this
stuff up.

We can recursively insert things into the map so we can't cache the
iterator into that map across those recursive calls. We did this
differently in two places. I have an end-to-end test that triggers at
least one of them. I'm going to work on a nice minimal test case that
triggers these, but I didn't want to leave the bug in the tree while
I tried to trigger it.

Also, the dense map iterator checking stuff we have now is awesome. =D

llvm-svn: 288135

include/llvm/IR/PassManager.h

@@ -399,13 +399,11 @@ public:
     template <typename PassT>
     bool invalidate(IRUnitT &IR, const PreservedAnalyses &PA) {
       AnalysisKey *ID = PassT::ID();
-      SmallDenseMap<AnalysisKey *, bool, 8>::iterator IMapI;
-      bool Inserted;
-      std::tie(IMapI, Inserted) = IsResultInvalidated.insert({ID, false});
 
       // If we've already visited this pass, return true if it was invalidated
       // and false otherwise.
-      if (!Inserted)
+      auto IMapI = IsResultInvalidated.find(ID);
+      if (IMapI != IsResultInvalidated.end())
         return IMapI->second;
 
       // Otherwise look up the result object.
@@ -421,9 +419,16 @@ public:
           ResultModelT;
       auto &ResultModel = static_cast<ResultModelT &>(*RI->second->second);
 
-      // Mark in the map whether the result should be invalidated and return
-      // that.
-      IMapI->second = ResultModel.invalidate(IR, PA, *this);
+      // Insert into the map whether the result should be invalidated and
+      // return that. Note that we cannot re-use IMapI and must do a fresh
+      // insert here as calling the invalidate routine could (recursively)
+      // insert things into the map making any iterator or reference invalid.
+      bool Inserted;
+      std::tie(IMapI, Inserted) = IsResultInvalidated.insert(
+          {ID, ResultModel.invalidate(IR, PA, *this)});
+      (void)Inserted;
+      assert(Inserted && "Should not have already inserted this ID, likely "
+                         "indicates a dependency cycle!");
       return IMapI->second;
     }
 
@@ -593,16 +598,22 @@ public:
       AnalysisKey *ID = AnalysisResultPair.first;
       auto &Result = *AnalysisResultPair.second;
 
-      SmallDenseMap<AnalysisKey *, bool, 8>::iterator IMapI;
-      bool Inserted;
-      std::tie(IMapI, Inserted) = IsResultInvalidated.insert({ID, false});
-      if (!Inserted)
+      auto IMapI = IsResultInvalidated.find(ID);
+      if (IMapI != IsResultInvalidated.end())
         // This result was already handled via the Invalidator.
         continue;
 
       // Try to invalidate the result, giving it the Invalidator so it can
       // recursively query for any dependencies it has and record the result.
-      IMapI->second = Result.invalidate(IR, PA, Inv);
+      // Note that we cannot re-use 'IMapI' here or pre-insert the ID as the
+      // invalidate method may insert things into the map as well, invalidating
+      // any iterator or pointer.
+      bool Inserted =
+          IsResultInvalidated.insert({ID, Result.invalidate(IR, PA, Inv)})
+              .second;
+      (void)Inserted;
+      assert(Inserted && "Should never have already inserted this ID, likely "
+                         "indicates a cycle!");
     }
 
     // Now erase the results that were marked above as invalidated.