Straw poll on shifts with out of range operands

[Andrew Pinski <pinskia@gmail.com>]

I am in the middle of improving the isolation path pass for shifts
with out of range operands.
There are 3 options we could do really:
1) isolate the path to __builtin_unreachable
2) isolate the path to __builtin_trap
    This is what is currently done for null pointer and divide by zero
3) isolate the path and turn the shift into zero constant
   This happens currently for explicit use in both match (in many
cases) and VRP for others.

All 3 are not hard to implement.
This comes up in the context of https://gcc.gnu.org/PR115636 where the
original requestor thinks it should be #3 but I suspect they didn't
realize it was undefined behavior then.
2 seems the best for user experience.
1 seems like the best for optimizations.
3 is more in line with how other parts of the compiler handle it.

So the question I have is which one should we go for? (is there
another option I missed besides not do anything)

Thanks,
Andrew Pinski