add commend

Author: ro-i

llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h

@@ -612,6 +612,8 @@ LLVM_ABI void InvertBranch(BranchInst *PBI, IRBuilderBase &Builder);
 // br/brcond/unreachable/ret
 LLVM_ABI bool hasOnlySimpleTerminator(const Function &F);
 
+/// Print BasicBlock \p BB as an operand or print "<nullptr>" if \p BB is a
+/// nullptr.
 LLVM_ABI Printable printBasicBlock(const BasicBlock *BB);
 
 } // end namespace llvm