[Bug tree-optimization/114635] OpenMP reductions fail dependency analysis

["rsandifo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114635

--- Comment #19 from Richard Sandiford <rsandifo at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #14)
> Usually targets do have a limit on the actual length but I see
> constant_upper_bound_with_limit doesn't query such.  But it would
> be a more appropriate way to say there might be an actual target limit here?
The discussion has moved on, but FWIW: this was a deliberate choice.
The thinking at the time was that VLA code should be truly “agnostic”
and not hard-code an upper limit.  Hard-coding a limit would be hard-coding
an assumption that the architectural maximum would never increase in future.

(The main counterargument was that any uses of the .B form of TBL would
break down for >256-byte vectors.  We hardly use such TBLs for autovec
though, and could easily choose not to use them at all.)

That decision is 8 or 9 years old at this point, so it might seem overly
dogmatic now.  Even so, I think we should have a strong reason to change tack.
It shouldn't just be about trying to avoid poly_ints :)