The compiler has a type to represent integer values of arbitrary size and sign: ScalarInt. It comes with a bunch of useful helpers and is used throughout the interpreter, CTFE, and valtrees.
However, The SwitchInt terminator stores the variants as u128 rather than a ScalarInt. I think this is mostly for historical reasons, it is older than ScalarInt. However ScalarInt is also 1 byte bigger than u128 due to a size that is stored, largely as sanity check.
I think ideally we'd change SwitchTarget to use ScalarInt. If the extra byte per arm is too much (in fact it might be more, SmallVec is ptr-aligned so it will probably add padding), then alternatively we could add APIs to SwitchTarget that let one work with it as-if it was a ScalarInt, hiding the u128 from sight.
Cc @rust-lang/wg-mir-opt
The compiler has a type to represent integer values of arbitrary size and sign: ScalarInt. It comes with a bunch of useful helpers and is used throughout the interpreter, CTFE, and valtrees.
However, The SwitchInt terminator stores the variants as
u128rather than a ScalarInt. I think this is mostly for historical reasons, it is older than ScalarInt. However ScalarInt is also 1 byte bigger than u128 due to a size that is stored, largely as sanity check.I think ideally we'd change SwitchTarget to use ScalarInt. If the extra byte per arm is too much (in fact it might be more, SmallVec is ptr-aligned so it will probably add padding), then alternatively we could add APIs to SwitchTarget that let one work with it as-if it was a ScalarInt, hiding the u128 from sight.
Cc @rust-lang/wg-mir-opt