[Bug target/101384] [9/10/11/12 Regression] wrong code at -Og and above with vector shift/multiply

cvs-commit at gcc dot gnu.org gcc-bugzilla@gcc.gnu.org
Tue Jul 20 14:43:55 GMT 2021


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101384

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:dc386b020869ad0095cf58f8c76a40ea457e7a2c

commit r11-8789-gdc386b020869ad0095cf58f8c76a40ea457e7a2c
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Jul 20 16:41:29 2021 +0200

    rs6000: Fix up easy_vector_constant_msb handling [PR101384]

    The following gcc.dg/pr101384.c testcase is miscompiled on
    powerpc64le-linux.
    easy_altivec_constant has code to try construct vector constants with
    different element sizes, perhaps different from CONST_VECTOR's mode.  But
as
    written, that works fine for vspltis[bhw] cases, but not for the vspltisw
    x,-1; vsl[bhw] x,x,x case, because that creates always a V16QImode,
V8HImode
    or V4SImode constant containing broadcasted constant with just the MSB set.
    The vspltis_constant function etc. expects the vspltis[bhw] instructions
    where the small [-16..15] or even [-32..30] constant is sign-extended to
the
    remaining step bytes, but that is not the case for the 0x80...00 constants,
    with step 1 we can't handle e.g.
    { 0x80, 0xff, 0xff, 0xff, 0x80, 0xff, 0xff, 0xff, 0x80, 0xff, 0xff, 0xff,
0x80, 0xff, 0xff, 0xff }
    vectors but do want to handle e.g.
    { 0, 0, 0, 0x80, 0, 0, 0, 0x80, 0, 0, 0, 0x80, 0, 0, 0, 0x80 }
    and similarly with copies 1 we do want to handle e.g.
    { 0x80808080, 0x80808080, 0x80808080, 0x80808080 }.

    This is a simpler version of the fix for backports, which limits the
EASY_VECTOR_MSB case
    matching to step == 1 && copies == 1, because that is the only case the
    splitter handles correctly.

    2021-07-20  Jakub Jelinek  <jakub@redhat.com>

            PR target/101384
            * config/rs6000/rs6000.c (vspltis_constant): Accept EASY_VECTOR_MSB
            only if step and copies are equal to 1.

            * gcc.dg/pr101384.c: New test.


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