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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/106331] [12/13 Regression] Whole array assignment of
 empty string segfaults with -Og
Date: Mon, 18 Jul 2022 08:10:38 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106331

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
                 CC|                            |rguenth at gcc dot gnu.org
             Target|                            |x86_64-*-*

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed - we get

  # S.0_3 =3D PHI <1(2), S.0_7(4)>
  if (S.0_3 > 2)
    goto <bb 5>; [33.33%]
  else
    goto <bb 4>; [66.67%]

  _1 =3D S.0_3 + -1;
  _2 =3D &a[_1];
  __builtin_memset (_2, 32, 24);
  S.0_7 =3D S.0_3 + 1;
  goto <bb 3>; [100.00%]

but somehow we fail to see that while the first [24] is 16 byte aligned, the
second is not:

.L4:
        leaq    -3(%rax,%rax,2), %rcx
        leaq    0(,%rcx,8), %rdx
        leaq    -56(%rsp,%rdx), %rdx
        movdqa  .LC0(%rip), %xmm0
        movaps  %xmm0, (%rdx)
        movabsq $2314885530818453536, %rsi
        movq    %rsi, 16(%rdx)
        addq    $1, %rax
.L3:
        cmpq    $2, %rax
        jle     .L4

we shouldn't have used movaps %xmm0, (%rdx) here.  Probably middle-end but
bisection will show.=