RFA (tree.c): PATCH for may_alias vs. TYPE_CANONICAL, related to c++/50800

[Richard Biener]

On Thu, Apr 23, 2015 at 5:49 PM, Jason Merrill <jason@redhat.com> wrote:
> In general, TYPE_CANONICAL of a type strips all attributes.  An exception to
> this seems to be that TYPE_REF_CAN_ALIAS_ALL remains set on the
> TYPE_CANONICAL of a pointer/reference type even though its TREE_TYPE no
> longer has the may_alias attribute, and is inconsistent with
> "affects_type_identity" being false for may_alias.  This seems to have been
> a mistake in the patch that first introduced TYPE_CANONICAL, rather than a
> deliberate choice.
>
> I'm also planning to fix 50800 in the front end, but this patch still seems
> like an improvement.
>
> Tested x86-64-pc-linux-gnu, OK for trunk?

Looks good to me.  We eventually were confused by alias.c get_alias_set
dropping to TYPE_CANONICAL (TYPE_MAIN_VARIANT (T)) before determining
the alias set of a type T.  But of course ref-all is only relevant for
the alias-set
of type *T.

Richard.