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From: "kungfujesus06 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/108498] ppc64 big endian generates
 uninitialized reads with -fstore-merging
Date: Mon, 23 Jan 2023 18:18:15 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108498

--- Comment #15 from Adam Stylinski <kungfujesus06 at gmail dot com> ---
(In reply to Adam Stylinski from comment #14)
> (In reply to Andrew Pinski from comment #13)
> > Ok, this seems wrong:
> >=20
> > New sequence of 1 stores to replace old one of 10 stores
> > # .MEM_102 =3D VDEF <.MEM_101>
> > MEM <char[8]> [(void *)&insn] =3D "\x02\x00\xff\x03\x00\x01\x02\x03";
> > Exceeded original number of stmts (2).  Not profitable to emit new sequ=
ence.
> >=20
> >=20
> > The size should be 9 rather 8 ...
>=20
> Ah cool.  I guess the suboptimality is probably a bug in its own right.  =
Any
> reason it's using so many stores to memory?  The clang version can
> accomplish it almost entirely in GPRs.

I guess "entirely in GPRs" isn't very true.  Clang does it in 7 stores, with
the last being the return value on the stack.  GCC is doing it in 16 stores=
 and
quite a few loads.  The stack churn is a bit unnerving, is there anything t=
hat
can be done to improve this?=