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From: "qinzhao at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/102586] [12 Regression] ICE in
 clear_padding_type, at gimple-fold.c:4798 since r12-3433-ga25e0b5e6ac8a77a
Date: Fri, 11 Feb 2022 17:36:35 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102586

qinzhao at gcc dot gnu.org changed:

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

--- Comment #25 from qinzhao at gcc dot gnu.org ---
(In reply to Jakub Jelinek from comment #24)
> I bet with the default -flifetime-dse=3D2 we would then have a
>   var =3D {};
>   var =3D{v} {CLOBBER}; // Start of ctor clobber
>   var.whatever =3D ...; // Ctor content
> and the zero initialization would be optimized away then.
> I guess ideal would be to emit such zero initialization in the complete
> object ctors right after the -flifetime-dse=3D2 beginning clobber and ide=
ally
> one that clearly says to the gimplifier and rest of middle-end that it mu=
st
> initialize even padding bits.
> Because right now gimplification of var =3D {} will often happily lower t=
hat to
>   var.a =3D 0; var.b =3D 0; var.c =3D 0;
> even when there are padding bits,

oh right, I recall that this was the reason why adding "var =3D {}" to init=
ialize
the whole structure didn't work well for initialize all paddings. therefore=
 we
have to explicitly call __builtin_clear_padding for clear all paddings.=