[Bug target/94103] Wrong optimization: reading value of a variable changes its representation for optimizer

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94103

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |marxin at gcc dot gnu.org

--- Comment #9 from Martin Liška <marxin at gcc dot gnu.org> ---
commit r10-7145-g1dc00a8ec9aeba86b74b16bff6f171824bb7b4a1
Author: Richard Biener <rguenther@suse.de>
Date:   Thu Mar 12 14:18:35 2020 +0100

    tree-optimization/94103 avoid CSE of loads with padding

    VN currently replaces a load of a 16 byte entity 128 bits of precision
    (TImode) with the result of a load of a 16 byte entity with 80 bits of
    mode precision (XFmode).  That will go downhill since if the padding
    bits are not actually filled with memory contents those bits are
    missing.

    2020-03-12  Richard Biener  <rguenther@suse.de>

            PR tree-optimization/94103
            * tree-ssa-sccvn.c (visit_reference_op_load): Avoid type
            punning when the mode precision is not sufficient.

            * gcc.target/i386/pr94103.c: New testcase.