add comments for operator precedence

Author: changkhothuychung

clang/lib/Basic/OperatorPrecedence.cpp

@@ -54,6 +54,9 @@ prec::Level getBinOpPrecedence(tok::TokenKind Kind, bool GreaterThanIsOperator,
   case tok::pipepipe:             return prec::LogicalOr;
   case tok::ampamp:               return prec::LogicalAnd;
   case tok::pipe:                 return prec::InclusiveOr;
+  // this is for the case when ^^ appears where a binary operator is needed,
+  // and the first ^ is the actual binary operator,
+  // and the second is for a block.
   case tok::caretcaret:
   case tok::caret:                return prec::ExclusiveOr;
   case tok::amp:                  return prec::And;