[Bug middle-end/84747] alias analysis reports may-conflict for references to disjoint address spaces

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84747

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |jakub at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
On some targets where the address spaces are really separate, one kind of
memory and another kind of memory, I can see why assuming non-aliasing is fine.
But exactly on x86_64 I don't see how that could be safe, %fs/%gs simply are
the given addresses plus the segment base.  You can access the same memory both
with
%gs:ptr1 and ptr2 where ptr2 is ptr1 + gs_segment_base, e.g. glibc uses for TLS
heavily both kinds of accesses.