ScalarEvolution: Make required passes transitive to prevent dangling pointers

[srking]

Summary

ScalarEvolution stores long lived raw pointers to objects owned by unique_ptrs in other passes. In ScalarEvolution, change addRequired() to addRequiredTransitive() to prevent required passes from being freed and thus preven dangling raw pointers.

IMHO, the current design needs a FIXME to eliminate the long lived raw pointers altogether. Barring that, some way to assert() if the raw pointers becomes dangling would help.

[hfinkel]

LGTM.

[craig.topper]

Committed in r242989

lib/Analysis/ScalarEvolution.cpp

void ScalarEvolution::releaseMemory() {
   UnsignedRanges.clear();
   SignedRanges.clear();
   UniqueSCEVs.clear();
   SCEVAllocator.Reset();
 }
 
 void ScalarEvolution::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.setPreservesAll();
-  AU.addRequired<AssumptionCacheTracker>();
+  AU.addRequiredTransitive<AssumptionCacheTracker>();
   AU.addRequiredTransitive<LoopInfoWrapperPass>();
   AU.addRequiredTransitive<DominatorTreeWrapperPass>();
-  AU.addRequired<TargetLibraryInfoWrapperPass>();
+  AU.addRequiredTransitive<TargetLibraryInfoWrapperPass>();
 }
 
 bool ScalarEvolution::hasLoopInvariantBackedgeTakenCount(const Loop *L) {
   return !isa<SCEVCouldNotCompute>(getBackedgeTakenCount(L));
 }
 
 static void PrintLoopInfo(raw_ostream &OS, ScalarEvolution *SE,
                           const Loop *L) {