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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug debug/108656] [12/13 Regression] '-fcompare-debug' failure
 (length) w/ -O2 -fno-ipa-pure-const -fno-tree-dce --param
 early-inlining-insns=0 since r12-5236
Date: Mon, 06 Feb 2023 09:56:50 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108656

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #6)
> (In reply to Jakub Jelinek from comment #5)
> > Created attachment 54412 [details]
> > gcc13-pr108656.patch
> >=20
> > So shall we fix it like this then?
>=20
> But isn't this the wrong "side"?  returns_twice means it is the abnormal
> control _receiver_, it doesn't perform an abnormal goto itself.
>=20
> stmt_starts_bb_p is correct here, so where does it go wrong?

I think it needs both.  The thing is, when it returns the second time, it d=
oes
that again by returning from itself, not through returning from some unrela=
ted
function.
Say, if we have pure + returns_twice call and no other call in a function, =
the
abnormal edge to the pure + returns_twice call would be optimized away, even
when the call remains, because there would be no edge from some call to the
.ABNORMAL_DISPATCHER block.
__attribute__((pure, returns_twice)) int foo (void);

int
bar (void)
{
  for (int i =3D 0; i < 64; ++i)
    {
      int x =3D foo ();
      if (x =3D=3D 26)
        return -42;
    }
  return 42;
}
doesn't even have because of this any abnormal edges created.
Or, if there is some other non-pure call somewhere else, we model through t=
he
abnormal
edges that that other call can pass control back to the start of the
returns_twice call to make it return again.=