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From: "acoplan at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/99960] New: MVE: Wrong code storing V2DI vector
Date: Wed, 07 Apr 2021 15:41:03 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99960

            Bug ID: 99960
           Summary: MVE: Wrong code storing V2DI vector
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: acoplan at gcc dot gnu.org
  Target Milestone: ---

For the following testcase:

typedef long long v2di __attribute((vector_size(16)));
void foo(v2di *p)
{
  *p =3D (v2di){ 1, 2 };
}

we miscompile it at -O2 -march=3Darmv8.1-m.main+mve -mfloat-abi=3Dhard. Loo=
king at
the generated code:

foo:
        @ args =3D 0, pretend =3D 0, frame =3D 0
        @ frame_needed =3D 0, uses_anonymous_args =3D 0
        @ link register save eliminated.
        vldr.64 d6, .L3
        vldr.64 d7, .L3+8
        vstr.64 d6, [r0]
        bx      lr
.L4:
        .align  3
.L3:
        .word   1
        .word   0
        .word   2
        .word   0
        .size   foo, .-foo

it looks like we're missing a store of d7. Here's a full testcase:

typedef long long v2di __attribute((vector_size(16)));

__attribute((noipa))
void stvec (v2di *p) {
  *p =3D (v2di){ 1, 2 };
}

int main () {
  v2di v;
  stvec(&v);
  if (v[1] !=3D 2)
    __builtin_abort ();
}

I originally noticed this while investigating an execution failure for
gcc.c-torture/execute/pr92618.c. FWIW, clang does:

foo:
        adr     r1, .LCPI0_0
        vldrw.u32       q0, [r1]
        vstrw.32        q0, [r0]
        bx      lr
.LCPI0_0:
        .long   1                               @ 0x1
        .long   0                               @ 0x0
        .long   2                               @ 0x2
        .long   0                               @ 0x0=