[PATCH 2/3] Add simplify rules for wrapped binary operations.

[Robin Dapp]

> So - which case is it?  IIRC we want to handle small signed
> constants but the code can end up unsigned.  For the
> above we could write (unsigned long)((int)a + 1 - 1) and thus
> sign-extend?  Or even avoid this if we know the range.
> That is, it becomes the first case again (operation performed
> in a smaller type).

Both :) But in order to move forward the second transform suffices to
get rid of the redundant subtraction/addition of the ivopts candidate.

Attached is a new version as single file that disregards the other
possible cases (3/3 from before), only performs this transform and
checks for gimple_simplified in vrp2 after ivopts now.

Bootstrapped, no regressions on s390 and x86.

Regards
 Robin
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