[Bug middle-end/71654] [6/7 Regression] missing VRP optimization on c++ unsigned char and short expressions

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71654

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
The regression is because in GCC 5 we shorten the (int) i <= 3 compare
early during FE folding while it survives as integer compare in GCC 6.
This makes (int) i redundant in the conditional block.