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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/102446] [9/10/11/12 Regression] wrong code at
 -O3 on x86_64-linux-gnu
Date: Wed, 22 Sep 2021 10:56:26 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102446

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
void m() {
  int aa =3D 0, i =3D 0;
  for (; i < 3; i++)
    if (k < 0)
      aa |=3D *j;

Dump of assembler code for function m:
   0x0000000000400540 <+0>:     mov    0x200b16(%rip),%edi        # 0x60105c
<k>
   0x0000000000400546 <+6>:     mov    0x200b13(%rip),%rax        # 0x601060
<j>
   0x000000000040054d <+13>:    sar    $0x1f,%edi
=3D> 0x0000000000400550 <+16>:    and    (%rax),%edi
   0x0000000000400552 <+18>:    cmpw   $0x0,0x200af6(%rip)        # 0x601050
<d>

so we're loading *j before checking k < 0.  On GIMPLE that's OK:

  <bb 2> [local count: 268435456]:
  k.5_1 =3D k;
  j.6_2 =3D j;
  if (k.5_1 < 0)
    goto <bb 3>; [41.00%]
  else
    goto <bb 4>; [59.00%]

  <bb 3> [local count: 110058537]:
  j.6__lsm0.31_28 =3D *j.6_2;

  <bb 4> [local count: 268435456]:
  # aa_9 =3D PHI <j.6__lsm0.31_28(3), 0(2)>

but RTL if-conversion makes the load unconditional.

(insn 13 12 35 3 (set (reg/v:SI 89 [ j.6__lsm0.31 ])
        (mem:SI (reg/f:DI 83 [ j.6_2 ]) [1 *j.6_2+0 S4 A32])) 77
{*movsi_internal}
     (expr_list:REG_DEAD (reg/f:DI 83 [ j.6_2 ])
        (nil)))

I don't see any flags marking it as not trapping?=