web runtimes should enforce int types on bit operations

[rakudrama]

The DDC and dart2js runtimes implement the bit operations like & and << on (JavaScript) Number rather than on Dart int.
They should be upgraded to enforce int receiver and argument types. The lack of enforcement is a hold-over from Dart 1, where the extra cost of int checks would be too expensive. The enforcement is now mostly static.

The lack of enforcement does not affect statically typed code since the int interface enforces the receiver and argument types at compile time.

Dynamic code fails to check both the receiver and argument for being int, allowing non-integer floating point numbers into the calculation (where they are truncated according to the JavaScript ToInt32 operation).

The main benefit of better enforcement of the int types would be more uniform behaviour in testing, e.g. #45419.

The main disadvantage is that there will be performance regressions on paths that do the extra checks, and these regressions would need to be fixed

• dynamic calls
• calls that are not lowered to more basic operations (more of an issue with shifts that bit-wise operations)

DDC would need to go first, since the extra checks should not be a surprise in production.

[johnniwinther]

To enforce this, the CFE constant evaluator needs to be augmented with knowledge of the "static type" of a constant value. Currently all integer and double literals are encoded as DoubleConstant values and these values are allowed as integers where the value is not infinite and truncates to itself (i.e. has no fractional part).

To enforce this new behavior we would need to retain integer as IntegerConstant values but evaluate them as their corresponding double values (notably taking the integer precision limit of the double encoding into account).

[rakudrama]

@johnniwinther I don't think the CFE has to do anything. It already ready shows an error for this:

const dynamic a = 2.3;
const b = a << 1;

The issue is about preventing the current sketchy behaviour in the runtime of returning 4 (aka 4.0) for the above with non-const variables.