// a (possibly parenthesized) built-in function.
func (tv TypeAndValue) IsBuiltin() bool {
	return tv.mode == builtin
}

// IsValue reports whether the corresponding expression is a value.
// Builtins are not considered values. Constant values have a non-
// nil Value.
func (tv TypeAndValue) IsValue() bool {
	switch tv.mode {
	case constant_, variable, mapindex, value, nilvalue, commaok, commaerr:
		return true
	}

		if _, ok := astutil.Unparen(star.X).(*ast.CallExpr); ok {
			// A call may return a pointer to a zero value.
			return nil
		}
	}
	if tv, ok := pass.TypesInfo.Types[x]; ok && tv.IsValue() {
		return lockPath(pass.Pkg, tv.Type, nil)
	}
	return nil
}

// lockPath returns a typePath describing the location of a lock value
// contained in typ. If there is no contained lock, it returns nil.
//