op is one of: TOK.lessThan, TOK.lessOrEqual, TOK.greaterThan, TOK.greaterOrEqual
http://dlang.org/spec/expression.html#relation_expressions
The types for a binary expression are incompatible. Print error message.
Mark the operands as will never be dereferenced, which is useful info for @safe checks. Do before semantic() on operands rewrites them.
See Implementation
op is one of: TOK.lessThan, TOK.lessOrEqual, TOK.greaterThan, TOK.greaterOrEqual
http://dlang.org/spec/expression.html#relation_expressions