[PM] Preserve GlobalsAA for SROA

[davide]

Summary

Same question as GVN, is this really just an oversight or something intended?
Also, this should "preserve the CFG" but we all know there's no way to do that in the new PM yet etc..

[chandlerc]

LGTM

llvm/trunk/lib/Transforms/Scalar/SROA.cpp

do {
     }
 
     Changed |= promoteAllocas(F);
 
     Worklist = PostPromotionWorklist;
     PostPromotionWorklist.clear();
   } while (!Worklist.empty());
 
+  if (!Changed)
+    return PreservedAnalyses::all();
+
   // FIXME: Even when promoting allocas we should preserve some abstract set of
   // CFG-specific analyses.
-  return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
+  PreservedAnalyses PA;
+  PA.preserve<GlobalsAA>();
+  return PA;
 }
 
 PreservedAnalyses SROA::run(Function &F, AnalysisManager<Function> &AM) {
   return runImpl(F, AM.getResult<DominatorTreeAnalysis>(F),
                  AM.getResult<AssumptionAnalysis>(F));
 }
 
 /// A legacy pass for the legacy pass manager that wraps the \c SROA pass.