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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/101197] __builtin_memmove does not perform constant
 optimizations
Date: Fri, 25 Jun 2021 07:53:22 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101197

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

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

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I guess it can be expanded inline iff it is done through a modified
move_by_pieces - one that instead of emitting read store read store read st=
ore
emits all the reads first and then all the stores.  And hopefully the alias=
ing
info will make it clear for all the following RTL passes that it can overlap
and thus scheduling etc. can't reorder the stores with the reads.
emit_block_move_hints will need some small tweaks.
Currently for might_overlap it only tries emit_block_move_via_pattern and p=
unts
if that fails.
I think we'd need some m_* flag and adjust the run method so that if that is
true, it emits the stores in a separate sequence from the reads.=