[Bug c/109393] Very trivial address calculation does not fold

["manolis.tsamis at vrull dot eu" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109393

--- Comment #6 from manolis.tsamis at vrull dot eu ---
(In reply to Richard Biener from comment #5)
> (In reply to manolis.tsamis from comment #4)
> > Given the original transform it should be valid to propagate the constant
> > addition through the cast?
> 
> Yes.  Note doing so loses information, we know i + 1 doesn't overflow
> (undefined behavior).  Widening preserves this knowledge I think, but if
> just an unsigned conversion would be propagated it would be lost.

So, is that the reason that this transform isn't already implemented as an
optimisation?

But then again isn't this information also lost in the code currently produced
by GCC, where the constant is already propagated? Although I can see how it is
different to do the propagation of constants in the front-end only vs doing it
anywhere while transforming the code; maybe that's the difference that matters.
But hopefully doing better canonicalization/constant folding on address
calculations and constants should also result in better optimisation
opportunities overall.