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From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/104550] bogus warning from -Wuninitialized +
 -ftrivial-auto-var-init=pattern
Date: Fri, 18 Feb 2022 06:53:00 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104550

--- Comment #16 from rguenther at suse dot de <rguenther at suse dot de> ---
On Thu, 17 Feb 2022, jakub at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104550
>=20
> --- 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 =
filling
> > > the memory with pattern + __builtin_clear_padding afterwards seems li=
ke 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 var=
iable
> > is in memory.=20
> >=20
> > how to implement "fill the memory with pattern & mask" during RTL expan=
sion?
> > currently, we use memset to fill the memory when the variable is in mem=
ory,
> > pattern & mask might not fit to a BYTE-repeatable pattern that can be u=
sed
> > for memset?
>=20
> You can populate a buffer with the pattern and then clear_type_padding_in=
_mask.
> 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 DEC=
L_RTL
> (var) is a MEM.

It would of course be _highly_ desirable to _not_ need to build a
STRING_CST here.  The problematical cases are all when DECL_RTL isn't
a MEM, of course.=