How sticky are TYPE_MIN_VALUE and TYPE_MAX_VALUE? Is it possible to get rid of their effect using a NOP_EXPR, CONVERT_EXPR or VIEW_CONVERT_EXPR?
If this is impossible, the Ada front end should probably stop setting these fields because it assumes that it can use values outside that range: <http://gcc.gnu.org/onlinedocs/gcc-4.0.0/gnat_ugn_unw/Validity-Checking.html> Current mainline does not optimize array range checks away (even with -ftree-vrp), but I'm not sure if this is just a missed optimization opportunity as far as the optimizers are concerned, or something which is guaranteed to work in the future.
