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Subject: [Bug middle-end/101062] [10/11/12 Regression] wrong code with "-O2
 -fno-toplevel-reorder -frename-registers"
Date: Wed, 16 Jun 2021 10:18:41 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101062

--- Comment #12 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:b4b50bf2864e09f028a39a3f460222632c4d7348

commit r12-1527-gb4b50bf2864e09f028a39a3f460222632c4d7348
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Jun 16 12:17:55 2021 +0200

    stor-layout: Create DECL_BIT_FIELD_REPRESENTATIVE even for bitfields in
unions [PR101062]

    The following testcase is miscompiled on x86_64-linux, the bitfield sto=
re
    is implemented as a RMW 64-bit operation at d+24 when the d variable has
    size of only 28 bytes and scheduling moves in between the R and W part
    a store to a different variable that happens to be right after the d
    variable.

    The reason for this is that we weren't creating
    DECL_BIT_FIELD_REPRESENTATIVEs for bitfields in unions.

    The following patch does create them, but treats all such bitfields as =
if
    they were in a structure where the particular bitfield is the only fiel=
d.

    2021-06-16  Jakub Jelinek  <jakub@redhat.com>

            PR middle-end/101062
            * stor-layout.c (finish_bitfield_representative): For fields in
unions
            assume nextf is always NULL.
            (finish_bitfield_layout): Compute bit field representatives als=
o in
            unions, but handle it as if each bitfield was the only field in=
 the
            aggregate.

            * gcc.dg/pr101062.c: New test.=