[LoopFlatten] Do not report CFG analyses as up-to-date

[yrouban]

Summary

Re-enabling PreservedCFGChecker (D91327) the LoopFlatten was found as reporting Preserved<CFGAnalyses> while changed CFG.
This fix just removes CFGAnalyses from the returned preserved analyses set.

[dmgreen]

Certainly sound more correct. LGTM. Thanks for the patch.

llvm/lib/Transforms/Scalar/LoopFlatten.cpp

PreservedAnalyses LoopFlattenPass::run(Function &F,
   auto *LI = &AM.getResult<LoopAnalysis>(F);
   auto *SE = &AM.getResult<ScalarEvolutionAnalysis>(F);
   auto *AC = &AM.getResult<AssumptionAnalysis>(F);
   auto *TTI = &AM.getResult<TargetIRAnalysis>(F);
 
   if (!Flatten(DT, LI, SE, AC, TTI))
     return PreservedAnalyses::all();
 
-  PreservedAnalyses PA;
-  PA.preserveSet<CFGAnalyses>();
-  return PA;
+  return PreservedAnalyses::none();
 }
 
 namespace {
 class LoopFlattenLegacyPass : public FunctionPass {
 public:
   static char ID; // Pass ID, replacement for typeid
   LoopFlattenLegacyPass() : FunctionPass(ID) {
     initializeLoopFlattenLegacyPassPass(*PassRegistry::getPassRegistry());