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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/101755] [12 regression]
 gcc.target/arm/reg_equal_test.c fails on arm since r12-2637
Date: Mon, 09 Aug 2021 21:19:36 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101755

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
  d =3D a | -2;
  b =3D (d =3D=3D 0) ? c : (c % d);

d can never be 0, VRP figures this out now.
so we end up with:
d =3D a | -2;
b =3D 0xc7d24b5e % d;
if (b !=3D 0xc7d24b5e)
  abort();

and b cannot be 0xc7d24b5e because d is negative :).

So VRP is optimizing this all the way out.

The test was trying to make sure the value 0xc7d24b5e was emitted as a
REG_EQUAL note when splitting up the constant (for the forming) in RTL.

https://gcc.gnu.org/pipermail/gcc-patches/2015-June/422430.html
https://gcc.gnu.org/pipermail/gcc-patches/2015-June/422432.html=