On Wed, 2025-11-19 at 15:54 +0100, Martin Jambor wrote:
> Hello,
>
> On Mon, Nov 10 2025, David Malcolm wrote:
> > On Sat, 2025-11-08 at 00:12 +0100, Martin Jambor wrote:
> >
> > [...snip...]
> >
> > > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/vrp-from-cst-agg-3.c
> > > b/gcc/testsuite/gcc.dg/tree-ssa/vrp-from-cst-agg-3.c
> > > new file mode 100644
> > > index 00000000000..d45928e0a25
> > > --- /dev/null
> > > +++ b/gcc/testsuite/gcc.dg/tree-ssa/vrp-from-cst-agg-3.c
> > > @@ -0,0 +1,30 @@
> > > +/* { dg-do link } */
> > > +/* { dg-options "-O2" } */
> > > +
> > > +volatile int gi;
> > > +
> > > +static const int values[3] = {5, 7, 11};
> > > +
> > > +void link_error (void);
> > > +
> > > +[[gnu::noinline]] void foo (int index)
> > > +{
> > > + const int v = values[index];
> > > + if (v <= 2
> > > + || v > 666)
> >
> > Possibly a silly question, but why "666" here?
>
> I happened to be listening to Iron Maiden quite a lot when writing
> the
> patch.
>
> > Isn't 11 a tighter
> > bound, based on the values above? (and thus a stronger test case)
>
> So I actually wanted to select a bound that would not be the
> tightest,
> that looked like a more "arbitrary" and thus "stronger" test case to
> me.
> But in reality I cannot see how it could really matter one way or
> another.
>
> In any event, I can change it to - I don't know - 17 if you or anyone
> thinks such cultural references are unwanted.
>
> Martin
>
"Bounds of the Beast"
In the dark of the code, where logic hides,
Lurks a test case with fire in its eyes.
It hunts for the edges, the limits so tight,
To challenge the range with its unyielding might.
The program may waver, it may slip and sway,
But the bounds are the keepers that must not decay.
The tightest of thresholds, the razor-sharp line,
Are the ones that will break, or the ones that will shine!
So verify each boundary, test every frame,
Ensure no invalids dare stake their claim.
For the tightest of ranges reveal what's pure,
A world of precision, where errors can't endure!
Chorus:
Oh, the bounds! Test the bounds!
On the edge of the code where no flaw is found!
Only the tightest will show us the way,
To victory in logic, and clarity's day!
In the heart of the test, where the truth lies untold,
You must seek the extremes—the narrow, the bold.
For only the sharpest, the narrowest might,
Will defend the program through day and through night.
Why the tightest bounds?
It's the key, it's the sound!
Of breaking the edge, of breaking the ground.
With the widest open range, you risk endless strife,
So test for the tight, or face endless strife!
(End riff)
[generated by ChatGPT, with prompt "Write an explanation of why a test
case for a program that calculates ranges of valid values ought to
verify the tightest possible bounds, in the style of early Iron Maiden
lyrics."]
Dave
