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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/104550] bogus warning from -Wuninitialized +
 -ftrivial-auto-var-init=pattern
Date: Thu, 17 Feb 2022 16:53:42 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104550

--- Comment #15 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to qinzhao from comment #11)
> (In reply to Jakub Jelinek from comment #10)
> > Even in that case, filling the memory with pattern & mask instead of fi=
lling
> > the memory with pattern + __builtin_clear_padding afterwards seems like=
 a
> > win.
>=20
> So, you mean It's better to do the following for pattern init:
>=20
> 1. add call to .DEFERRED_INIT(, pattern, ) during gimplification;
> 2. during RTL expansion, fill the memory with pattern & mask if the varia=
ble
> is in memory.=20
>=20
> how to implement "fill the memory with pattern & mask" during RTL expansi=
on?
> currently, we use memset to fill the memory when the variable is in memor=
y,
> pattern & mask might not fit to a BYTE-repeatable pattern that can be used
> for memset?

You can populate a buffer with the pattern and then clear_type_padding_in_m=
ask.
Then you can create a STRING_CST out from that array and store_expr
(the_STRING_CST, DECL_RTL (var), false, false, false) - at least when DECL_=
RTL
(var) is a MEM.=