add description of updateCycleLoopInfo

Author: ro-i

llvm/lib/Transforms/Utils/ControlFlowUtils.cpp

@@ -346,6 +346,14 @@ std::pair<BasicBlock *, bool> ControlFlowHub::finalize(
   return {FirstGuardBlock, true};
 }
 
+/// Helper function to update the cycle or loop information after inserting a
+/// new block between a callbr instruction and one of its target blocks.  Adds
+/// the new block to the innermost cycle or loop that the callbr instruction and
+/// the original target block share.
+/// \p LCI            cycle or loop information to update
+/// \p CallBrBlock    block containing the callbr instruction
+/// \p CallBrTarget   new target block of the callbr instruction
+/// \p Succ           original target block of the callbr instruction
 template <typename TI, typename T>
 static bool updateCycleLoopInfo(TI *LCI, BasicBlock *CallBrBlock,
                                 BasicBlock *CallBrTarget, BasicBlock *Succ) {