gcc
2017-04-05  Bernd Edlinger  <bernd.edlinger@hotmail.de>

	* doc/extend.texi: Document the always_alias type attribute.
	* alias.c (get_alias_set): Honor the always_alias attribute.
	(record_component_aliases): Don't ignore the always_alias attribute.
	* tree.c (build_pointer_type_for_mode,
	build_reference_type_for_mode): Add the always_alias attribute.

gcc/c-family
2017-04-05  Bernd Edlinger  <bernd.edlinger@hotmail.de>

	* c-attribs.c (c_common_attribute_tab): Add the always_alias attribute.

gcc/cp
2017-04-05  Bernd Edlinger  <bernd.edlinger@hotmail.de>

	* class.c (fixup_attribute_variants): Add the always_alias attribute.
	(finish_struct_1): Add an always_alias attribute if required by C++17.
	* decl.c (start_enum): Likewise.
	* pt.c (lookup_template_class_1): Add the always_alias attribute.
	* typeck2.c (cxx_type_contains_byte_buffer): New function.
	* cp-tree.h (cxx_type_contains_byte_buffer): Declare.