Re: [PATCH] Rename nonzero_bits to known_zero_bits.

[Jakub Jelinek <jakub@redhat.com>]

On Fri, Oct 21, 2022 at 11:45:33AM -0500, Segher Boessenkool wrote:
> On Fri, Oct 21, 2022 at 03:14:26PM +0200, Aldy Hernandez via Gcc-patches wrote:
> > The name nonzero_bits is confusing.  We're not tracking nonzero bits.
> > We're tracking known-zero bits, or at the worst we're tracking "maye
> > nonzero bits".  But really, the only thing we're sure about in the
> > "nonzero" bits are the bits that are zero, which are known to be 0.
> > We're not tracking nonzero bits.
> 
> Indeed.
> 
> > I know we've been carrying around this name forever, but the fact that
> > both of the maintainers of the code *HATE* it, should be telling.
> > Also, we'd also like to track known-one bits in the irange, so it's
> > best to keep the nomenclature consistent.
> 
> And that as well.
> 
> However:
> 
> > 	* asan.cc (handle_builtin_alloca): Rename *nonzero* to *known_zero*.
> 
> Our "nonzero" means "not known to be zero", not "known to be zero", so
> this renaming makes it worse than it was.  Rename it to

Agreed.

I think maybe_nonzero_bits would be fine.

Anyway, the reason it is called this way is that we have similar APIs
on the RTL side, nonzero_bits* in rtlanal.cc.
So if we rename, it should be renamed consistently.

> "not_known_zero", make that a thin wrapper around a new "known_zero",
> and slowly get rid of not_known_zero?

	Jakub