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From: "juzhe.zhong at rivai dot ai" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/113134] gcc does not version loops with early
 break conditions that don't have side-effects
Date: Fri, 02 Feb 2024 03:38:54 +0000
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X-Bugzilla-Component: tree-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113134

--- Comment #21 from JuzheZhong <juzhe.zhong at rivai dot ai> ---
Hi, Richard. I looked into ivcanon.

I found that:

      /* If the loop has more than one exit, try checking all of them
         for # of iterations determinable through scev.  */
      if (!exit)
        niter =3D find_loop_niter (loop, &exit);

In find_loop_niter, we iterate 2 exit edges:

1. bb 5 -> bb 6 with niter =3D (unsigned int) N_13(D).
2. bb 3 -> bb 6 with niter =3D 1001.

It just skip niter =3D (unsigned int) N_13(D) in:
      if (!integer_zerop (desc.may_be_zero))
        continue;

find_loop_niter (loop, &exit) return 1001 with skipping  (unsigned int)
N_13(D).

Should it return MIN (1001, (unsigned int) N_13(D)).

I prefer fix it in ivcanon since I believe it would be more elegant than fi=
x it
in loop splitter.

I am still investigating, any guides will be really appreciated.

Thanks.=