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

[Segher Boessenkool]

On Thu, Jun 03, 2021 at 11:25:49AM +0100, Richard Sandiford wrote:
> We shouldn't just add "&&" to all define_insn_and_splits that currently
> lack them.

My previous post shows that this *already* is required.

> IMO it's not reasonable to ask Kewen to do that for all ports.  So the
> process I suggested was a way of mechanically changing existing ports in
> a way that would not require input from target maintainers, or extensive
> testing on affected targets.

I fear it will end up as Yet Another unfinished transition this way :-(

> >> I don't know.  "&& 1" looks kind of weird to me.
> >
> > We have it in rs6000.md since 2004.  sparc has had it since 2002.  i386
> > has had it since 2001.  arm still does not have it :-)
> 
> Sure, this syntax goes back 20 years.  I don't think that answers the
> point though.  The question was whether a split condition "&& 1" is
> more readable than a condition "", given that "" means "always" in other
> contexts.  Given the choice, IMO "" is more readable and "&& 1" looks
> weird/inconsistent.

In most ports "&& 1" is all over the place and well-known already.  Sure
we could change to "" meaning always, but that is not what it currently
means!

If we could just start all over we could do it perfectly (but see
second-system syndrome, heh).  But we cannot.  IMO we should especially
avoid everything that uses new semantics for old syntax.


Segher