On Tue, 15 Apr 2025, Jakub Jelinek wrote:
> On Mon, Mar 31, 2025 at 03:34:07PM +0200, Martin Jambor wrote:
> > This patch just introduces a form of dumping of widest ints that only
> > have zeros in the lowest 128 bits so that instead of printing
> > thousands of f's the output looks like:
> >
> > Bits: value = 0xffff, mask = all ones folled by
> > 0xffffffffffffffffffffffffffff0000
> >
> > and then makes sure we use the function not only to print bits but
> > also to print masks where values like these can also occur.
>
> Shouldn't that be followed by instead?
> And the widest_int checks seems to be quite expensive (especially for
> large widest_ints), I think for the first one we can just == -1
> and for the second one wi::arshift (value, 128) == -1 and the zero extension
> by using wi::zext.
>
> Anyway, I wonder if it wouldn't be better to use something shorter,
> the variant patch uses 0xf..f prefix before the 128-bit hexadecimal
> number (maybe we could also special case the even more common bits 64+
> are all ones case). Or it could be 0xf*f prefix. Or printing such
> numbers as -0x prefixed negative, though that is not a good idea for masks.
I'd accept 0xf..f as reasonable, possibly 0xf<repeated N times>f
when there are more than sizeof("repeated N times") fs inbetween.
It does make matching up masks more difficult when tracking changes
(from my experience with bit-CCP debugging, where such large masks
appear as well). So IMO we can live with large 0xffffff but for
all-ones we could print -1 if that's the common noisy thing.
Richard.
