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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug ipa/93385] [10 Regression] wrong code with u128 modulo at -O2
 -fno-dce -fno-ipa-cp -fno-tree-dce
Date: Tue, 21 Apr 2020 13:00:32 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D93385

--- Comment #32 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
For debug stmts when DCE isn't involved, we already seem to do the right th=
ing,
consider -O2 -g:
__attribute__((noinline)) static void
foo (int a)
{
  int b =3D 2 * a;
  int c =3D 3 * a;
  a =3D a + 4;
  asm volatile ("" : : : "memory");
}

void
bar (void)
{
  foo (1);
  foo (7);
  foo (16);
}

The clone materializes into:
  <bb 3> [local count: 1073741824]:
  # DEBUG D#5 s=3D> a
  # DEBUG a =3D> D#5

  <bb 2> [local count: 1073741824]:
  # DEBUG D#1 s=3D> a
  # DEBUG BEGIN_STMT
  # DEBUG b =3D> D#1 * 2
  # DEBUG BEGIN_STMT
  # DEBUG c =3D> D#1 * 3
  # DEBUG BEGIN_STMT
  # DEBUG a =3D> D#1 + 4
  # DEBUG BEGIN_STMT
  __asm__ __volatile__("" :  :  : "memory");
  return;
I thought only the first two debug stmts would appear, would need to look up
where the a_1(D) is replaced with the D#1 copy and where the corresponding
debug source bind is created.
Bet we want similar testcase also for when this DCE is used, and no, debug
stmts shouldn't be marked as something that should be thrown away, but inst=
ead
might be reset if we can't do anything better with them.=