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From: "avieira at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/108177] New: MVE predicated stores to same address get
 optimized away
Date: Mon, 19 Dec 2022 14:29:38 +0000
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X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: 12.0
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X-Bugzilla-Status: UNCONFIRMED
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108177

            Bug ID: 108177
           Summary: MVE predicated stores to same address get optimized
                    away
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: avieira at gcc dot gnu.org
  Target Milestone: ---

GCC currently generates wrong code for predicated MVE stores to the same
address. Like:

#include <arm_mve.h>

uint8x16_t foo (uint8x16_t a, uint8_t *pa, mve_pred16_t p1, mve_pred16_t p2)
{
    vstrbq_p_u8 (pa, a, p1);
    vstrbq_p_u8 (pa, a, p2);
}

with 'gcc -mcpu=3Dcortex-m55 -mfloat-abi=3Dhard -O3' it will only generate =
the
second MVE store. Though if (p2 | p1) !=3D p2 then the second store will not
fully overwrite the first.=