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Subject: [Bug target/61837] missed loop invariant expression optimization
Date: Fri, 15 May 2020 03:27:11 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D61837

--- Comment #11 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Xiong Hu Luo <luoxhu@gcc.gnu.org>:

https://gcc.gnu.org/g:8a15faa730f99100f6f3ed12663563356ec5a2c0

commit r11-407-g8a15faa730f99100f6f3ed12663563356ec5a2c0
Author: Xionghu Luo <luoxhu@linux.ibm.com>
Date:   Thu May 14 21:03:24 2020 -0500

    Fold (add -1; zero_ext; add +1) operations to zero_ext when not
overflow(PR37451, PR61837)

    This "subtract/extend/add" existed for a long time and still annoying us
    (PR37451, part of PR61837) when converting from 32bits to 64bits, as the
ctr
    register is used as 64bits on powerpc64, Andraw Pinski had a patch but
    caused some issue and reverted by Joseph S. Myers(PR37451, PR37782).

    Andraw:
    http://gcc.gnu.org/ml/gcc-patches/2008-09/msg01070.html
    http://gcc.gnu.org/ml/gcc-patches/2008-10/msg01321.html
    Joseph:
    https://gcc.gnu.org/legacy-ml/gcc-patches/2011-11/msg02405.html

    We still can do the simplification from "subtract/zero_ext/add" to
"zero_ext"
    when loop iterations is known to be LT than MODE_MAX (only do simplify
    when counter+0x1 NOT overflow).

    Bootstrap and regression tested pass on Power8-LE.

    gcc/ChangeLog

            2020-05-15  Xiong Hu Luo  <luoxhu@linux.ibm.com>

            PR rtl-optimization/37451, part of PR target/61837
            * loop-doloop.c (doloop_simplify_count): New function.  Simplify
            (add -1; zero_ext; add +1) to zero_ext when not wrapping.
            (doloop_modify): Call doloop_simplify_count.

    gcc/testsuite/ChangeLog

            2020-05-15  Xiong Hu Luo  <luoxhu@linux.ibm.com>

            PR rtl-optimization/37451, part of PR target/61837
            * gcc.target/powerpc/doloop-2.c: New test.=