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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug rtl-optimization/105338] [12 Regression] Regression: jump or
 cmove generated for pattern (x ? CST : 0)
Date: Fri, 22 Apr 2022 11:20:08 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105338

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #5)
> (In reply to Jakub Jelinek from comment #3)
> > Before fwprop1, the code looks roughly the same except for the swapped
> > branches,
> > so in C
> >   if (tmp83 !=3D 0)
> >     tmp82 =3D 5;
> >   else
> >     tmp82 =3D tmp83;
> > vs.
> >   if (tmp83 =3D=3D 0)
> >     tmp82 =3D tmp83;
> >   else
> >     tmp82 =3D 5;
>=20
> Specifically for this we could also look to canonicalize this in
> uncprop which introduces the copies, making sure to rewrite this into
> an equality compare?

When un-propagating into a PHI in uncprop_into_successor_phis mark the
BB of the PHI node.

In uncprop_dom_walker::before_dom_children, when it is marked, match
a diamond/half-diamond with the immediate dominator and do the rewrite
of the conditional and swapping of edge flags.=