Re: [PATCH] use zero as the lower bound for a signed-unsigned range (PR 79327)

[Martin Sebor <msebor at gmail dot com>]

> > So far I haven't done full bootstrap/regtest on this, just
> > make check-gcc -j16 -k RUNTESTFLAGS=tree-ssa.exp
> > which revealed the need for gcc.dg/tree-ssa/builtin-sprintf-warn-1.c hunk
> > below.  Here it is turned into a short wrong-code without the patch
> > below:
> > volatile int a;
> >
> > int
> > main (void)
> > {
> >   int i;
> >   char buf[64];
> >   if (__builtin_sprintf (buf, "%#hho", a) > 1)
> >     __builtin_abort ();
> >   if (__builtin_sprintf (buf, "%#hhx", a) > 1)
> >     __builtin_abort ();
> >   return 0;
> > }
> > Current trunk as well as trunk + your patch computes ranges [2, 4] and
> > [3, 4], but the correct ranges are [1, 4] and [1, 4], because for a 0
> > (or say -131072 etc.) it sets buf to "0" in both cases.
>
> That's right.  This is a good find.  This case is being tested in
> builtin-sprintf-warn-1.c but the assertions (on lines 1154 and
> 1155) seem to expect the wrong numbers.  I would expect your fix
> to cause failures here. (And now that I've read the rest of the
> patch I see it does.)
...
> > -  T (2, "%#hho",        a);     /* { dg-warning "nul past the end" } */
> > -  T (2, "%#hhx",        a);     /* { dg-warning ".%#hhx. directive
> > writing between 3 and . bytes into a region of size 2" } */
> > +  T (2, "%#hho",        a);
> > +  T (2, "%#hhx",        a);

On reflection, this isn't quite the right fix.  We want to both set
the correct range and warn because the call will likely overflow.
This is an example of why the likely/unlikely counters have been
introduced.  By setting min = 1 and likely = 2 for the %#hho and
3 for the %#hhx we get the desired result.

Martin