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

[Segher Boessenkool <segher@kernel.crashing.org>]

On Thu, Jun 03, 2021 at 11:11:53AM -0600, Jeff Law wrote:
> On 6/3/2021 2:00 AM, Segher Boessenkool wrote:
> >The whole point of requiring the split condition to start with && is so
> >it will become harder to mess things up (it will make the gen* code a
> >tiny little bit simpler as well).  And there is no transition period or
> >anything like that needed either.  Just the bunch that will break will
> >need fixing.  So let's find out how many of those there are :-)
> Exactly.   While these empty conditions or those not starting with "&&" 
> are technically valid, they're all suspicious from a port correctness 
> standpoint, particularly if the main condition is non-empty.

And note that this is also the case if you wrote the insn condition as
an empty string, but you used some iterator with a condition.  I found
many of these in rs6000.  This will need to be fixed before we do
anything else.

> Having made that mistake when converting the H8 away from CC0, I can say 
> fairly confidently that if we had this in place a year ago that those 
> mistakes would likely have been avoided.  Thankfully the H8 isn't a 
> heavily used port and has limped along until I stumbled over the issue a 
> week or so ago while polishing some improvements to the port.

I've noticed unexpected splits in rs6000 only a few times over the
years. That doesn't mean more didn't happen, they just didn't cause
obvious enough problems :-)


Segher