Incorrect bitfield aliasing with Tree SSA

[Eric Botcazou]

> 	* tree.h (struct tree_struct_field_tag): Add new field alias_set.
> 	(SFT_NONADDRESSABLE_P, SFT_ALIAS_SET): New macros.
> 	* tree-flow.h (struct fieldoff): Add new field alias_set.
> 	* tree-ssa-structalias.c (push_fields_onto_fieldstack): Add new
> 	argument addressable_type.  Set alias_set of fieldoff.
> 	* tree-ssa-alias.c (create_sft): Add new argument alias_set.
> 	(create_overlap_variables_for): Pass alias_set from fieldoff to
> 	create_sft.
> 	* alias.c (get_alias_set): Use alias_set from SFT if set.

Thanks for crafting this.  Btw, could you add

  PR tree-optimization/25737

on top of the ChangeLog entry when you commit it?

-- 
Eric Botcazou