Type Bounds

Some Wasm opcodes, such as local.set, have polymorphic arguments. Users can restrict matching such probe locations to a specific type using a type bound.

Here’s an example using a type bound:

wasm:opcode:call(arg0: i32):before {
    report unshared var all_arg0s: map<i32, i32>;
    all_arg0s[arg0]++;
}

This probe only matches call sites whose first argument is an i32; to also handle i64, f32, etc., you would write one type-bound probe per type.

To instead match multiple types with a single probe by binding an operand’s type to a type parameter that is resolved per match site, see Polymorphism.