Feature

As discussed in #3056 (comment) we allow const instructions with values that are way too large for their type (i.e. 0xff00 for an i8). We should reject these modules in the CLIF validator.

Benefit

Rejecting these modules is a good way to prevent bugs in code generators using cranelift as a backend. As well as preventing issues where backends are not expecting constant values larger than the instruction type. Similar to #3056 (although this one is "legal") but with even more surprising values.

Implementation

The ideal place to implement this is in the CLIF validator, so that we can reject these CLIF modules.

Because CLIF values do not have signedness until time of use, we must allow both signed and unsigned ranges of values (-128..127 or 0..255 in the i8 case).

Alternatives

We can keep ignoring the issue (as we do now), or we can define some other behavior, such as masking the bottom bits depending on the type. But this has all the hallmarks of a bug in whatever code generator is producing this code, so we should probably not silently allow these modules.