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From: "hubicka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/106293] [13/14 Regression] 456.hmmer at
 -Ofast -march=native regressed by 19% on zen2 and zen3 in July 2022
Date: Thu, 27 Jul 2023 21:38:39 +0000
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X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 13.0
X-Bugzilla-Keywords: missed-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106293

--- Comment #16 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
It is really hard to make loop splitting to do something.
It does not like canonicalized invariant variables since loop exit condition
should not be NE_EXPR and it does not like when VRP turns LT/GT into NE.

This is what happens in hmmer.  There is loop iterating 100 times and split=
ting
happens just before last BB
int M =3D 100;

void
__attribute__ ((noinline,noipa))
do_something()
{
}
void
__attribute__ ((noinline,noipa))
do_something2()
{
}

__attribute__ ((noinline,noipa))
void test1 (int n)
{
  if (n <=3D 0 || n > 100000)
        return;=20
  for (int i =3D 0; i <=3D n; i++)
          if (i < n)
                  do_something ();
          else
                  do_something2 ();
}
int
main(int, char **)
{
        for (int i =3D 0 ; i < 1000; i++)
          test1(M);
        return 0;
}=