Semantics for operation evaluation

[dkcumming]

Here are some semantics for evaluation of operations with Scalar values that map to integers. Pointers and floats are not considered yet. For each instruction I will add some links to reasons why I interpreted it as I have:

• Unchecked_: throw_ub_overflow, if throw_ub_on_overflow throw (for shifts), if throw_ub_on_overflow throw (for signed), if throw_ub_on_overflow throw (for unsigned)
• Add, Sub, Mul, Shl, Shr: smir conversion of mir, smir split overflow instructions, shift overflow signed, shift overflow unsigned, arith overflow signed, arith overflow unsigned
• Cmp: entry point, Ordering: -1, 0, 1, bitwidth 1, bitwidth 2

• chop for signed integers: I have no reference for this, Stephen and I investigated this in a call. There is likely an equivalent solution with less operations available.