[NFC][LoopFlatten][LoopInterchange] Do not explicitly forget subloops

[caojoshua]

Summary

We don't need to explicitly forget subloops because forgetting parent
loops will automatically forget their subloops

[caojoshua]

ping

[fhahn]

LGTM, thanks!

llvm/lib/Transforms/Scalar/LoopFlatten.cpp

if (FI.Widened)
                                        "flatten.trunciv");
 
     LLVM_DEBUG(dbgs() << "Replacing: "; V->dump(); dbgs() << "with:      ";
                OuterValue->dump());
     V->replaceAllUsesWith(OuterValue);
   }
 
   // Tell LoopInfo, SCEV and the pass manager that the inner loop has been
-  // deleted, and any information that have about the outer loop invalidated.
+  // deleted, and invalidate any outer loop information.
   SE->forgetLoop(FI.OuterLoop);
-  SE->forgetLoop(FI.InnerLoop);
   SE->forgetBlockAndLoopDispositions();
   if (U)
     U->markLoopAsDeleted(*FI.InnerLoop, FI.InnerLoop->getName());
   LI->erase(FI.InnerLoop);
 
   // Increment statistic value.
   NumFlattened++;
 

llvm/lib/Transforms/Scalar/LoopInterchange.cpp

void LoopInterchangeTransform::restructureLoops(
 
   // The preheader of the original outer loop becomes part of the new
   // outer loop.
   NewOuter->addBlockEntry(OrigOuterPreHeader);
   LI->changeLoopFor(OrigOuterPreHeader, NewOuter);
 
   // Tell SE that we move the loops around.
   SE->forgetLoop(NewOuter);
-  SE->forgetLoop(NewInner);
 }
 
 bool LoopInterchangeTransform::transform() {
   bool Transformed = false;
 
   if (InnerLoop->getSubLoops().empty()) {
     BasicBlock *InnerLoopPreHeader = InnerLoop->getLoopPreheader();
     LLVM_DEBUG(dbgs() << "Splitting the inner loop latch\n");