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From: "dave.anglin at bell dot net" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/106458] [12/13 Regression] glibc's
 malloc/tst-scratch_buffer.c test is miscompiled with gcc-12
Date: Wed, 10 Aug 2022 20:53:56 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106458

--- Comment #15 from dave.anglin at bell dot net ---
On 2022-08-10 9:30 a.m., rguenth at gcc dot gnu.org wrote:
> hen I try with a cc1 cross I see
>
>> ./cc1 -quiet t.i -fpreprocessed -O2 -g -std=3Dgnu11 -fgnu89-inline -fmer=
ge-all-constants -frounding-math -fno-stack-protector -fno-common -fmath-er=
rno    -fno-pie -fopt-info-vec
> and nothing actually vectorized.  Besides the PRE there seems to be a mis=
sed
> DSE at the end (when vectorization is enabled as after the change):
>
>     # DEBUG BEGIN_STMT
>     memset (&buf.__space.__c, 64, 1024);
>     # DEBUG BEGIN_STMT
> +  sizes[0] =3D 16;
>     sizes[1] =3D 1024;
>     sizes[2] =3D 1040;
>
> otherwise I see nothing suspicious in differences in .optimized when
> comparing -fdump-tree-optimized with/without -fno-tree-vectorize.
>
I'm not sure what's going on with the sizes[0] statement but the main
difference in .optimize with and without pre
seems to be in the handling of the old_length variable in do_test:

 =C2=A0Removing basic block 86
 =C2=A0int do_test ()
 =C2=A0{
-=C2=A0 unsigned int ivtmp.23;
-=C2=A0 size_t old_length;
+=C2=A0 unsigned int ivtmp.28;
 =C2=A0=C2=A0 void * r;
 =C2=A0=C2=A0 void * c;
 =C2=A0=C2=A0 size_t l;=