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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/103808] [12 Regression] '-fcompare-debug' failure
 (length) w/ -O2 -ftrapv
Date: Wed, 22 Dec 2021 23:57:29 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103808

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I think this is a latent bug exposed by my match.pd patch (r12-5392).

In GCC 11.2.0 we had:
  y_18 =3D iftmp.0_10 > a_14 ? 2 : 0;

While on the trunk we have:
  y_18 =3D prephitmp_29 * 2;

But doing this:

void
foo (__int128 x, int y)
{
  for (;;)
    {
      __int128 a, b;

      x |=3D !!y;
      a =3D x + 1;
      b =3D y ? ++y : ++x;
      y =3D a < b;
      asm("":"+r"(y));
      if (x >> 2)
        y *=3D 2;

      if (y =3D=3D b)
        __builtin_unreachable ();
    }
}

Which causes the IR to be the same out of 11 and 12, does not produce compa=
re
debug in 11 but does in 12.=