[RFC/PATCH 00/11] Fix up some unexpected empty split conditions

[Richard Biener]

On Tue, Jun 8, 2021 at 4:10 AM Kewen.Lin via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Hi Segher,
>
> on 2021/6/8 上午7:50, Segher Boessenkool wrote:
> > Hi!
> >
> > On Fri, Jun 04, 2021 at 10:57:51AM +0800, Kewen.Lin via Gcc-patches wrote:
> >> To find out those need fixing seems to be the critical part.  It's
> >> not hard to add one explicit "&&" to those that don't have it now, but
> >> even with further bootstrapped and regression tested I'm still not
> >> confident the adjustments are safe enough, since the testing coverage
> >> could be limited.  It may need more efforts to revisit, or/and test
> >> with more coverages, and port maintainers' reviews.
> >
> > https://gcc.gnu.org/pipermail/gcc-patches/2021-June/572120.html
> >
> > This adds an "&&" everywhere (or in fact, it just skips any existing
> > one, it just has the same effect of adding it everywhere).  I tested it
> > with building gcc and Linux for all supported targets (31 of them; I do
> > some with multiple configs, mostly 32-bit and 64-bit).  None had any
> > difference before and after the change.
> >
> > So I am no longer worried that there will be any fallout from doing
> > this.  There are many things that *could* go wrong, but I don't think
> > there will be enough at all to be an impediment to just throwing the
> > switch.
> >
> > If we go this way no target will need any significant fixing, maybe none
> > at all will be needed across all targets.  And no changes will be needed
> > anywhere immediately.  We could make leading "&&" deprecated, and the
> > same for split condition "1" (which was "&& 1").  This is easy to change
> > automatically as well.
> >
> Thanks very much for doing this!
>
> I guess we are not going to backport this?  If we won't, it seems to need
> some way to ensure the implied "&&" will show up explicitly when backporting
> some define_insn_and_split.

For this reason I'd prefer the explicit "&& ", Seghers testing means
mass-changing all define_insn_and_split is reasonable.

Richard.

> BR,
> Kewen