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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/110449] Vect: use a small step to calculate
 the loop induction if the loop is unrolled during loop vectorization
Date: Thu, 06 Jul 2023 16:05:31 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110449

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jeff Law <law@gcc.gnu.org>:

https://gcc.gnu.org/g:224fd59b2dc8a5fa78a309a09863afe9b3cf2111

commit r14-2367-g224fd59b2dc8a5fa78a309a09863afe9b3cf2111
Author: Hao Liu OS <hliu@os.amperecomputing.com>
Date:   Thu Jul 6 10:04:46 2023 -0600

    Vect: use a small step to calculate induction for the unrolled loop (PR
tree-optimization/110449)

    If a loop is unrolled by n times during vectoriation, two steps are use=
d to
    calculate the induction variable:
      - The small step for the unrolled ith-copy: vec_1 =3D vec_iv + (VF/n *
Step)
      - The large step for the whole loop: vec_loop =3D vec_iv + (VF * Step)

    This patch calculates an extra vec_n to replace vec_loop:
      vec_n =3D vec_prev + (VF/n * S) =3D vec_iv + (VF/n * S) * n =3D vec_l=
oop.

    So that we can save the large step register and related operations.

    gcc/ChangeLog:

            PR tree-optimization/110449
            * tree-vect-loop.cc (vectorizable_induction): use vec_n to repl=
ace
            vec_loop for the unrolled loop.

    gcc/testsuite/ChangeLog:

            * gcc.target/aarch64/pr110449.c: New testcase.=