Add support for non-nullable tables and init expressions

[pufferfish101007]

Resolves #5628

Adds support for non-nullable tables with init expressions. I'm not totally sure how I should go about adding new tests, but manual test cases are below. I have also unignored previously ignored spec tests instance.wast, ref_is_null.wast, table.wast, i31.wast, which now all pass. I have also changed the reason for ignoring array.wast as it does not (and has not in the past, AFAICT) rely on non-nullable table types.

This introduces a breaking change in the C api, as it adds an extra argument to addTable. Is this ok? Should a new method be added instead? (e.g. addTableWithInit?)

Manual tests

The validation ones might overlap with the spec tests. Unchecked boxes indicate tests that currently fail.

• Nullable tables should continue to round-trip correctly:

(module
 (type $0 (func (param i32)))
 (table $0 0 funcref)
 (elem $0 (i32.const 0))
 (func $0 (param $0 i32)
 )
)

• Non-nullable tables with init expr should round-trip correctly:

(module
 (type $0 (func (param i32)))
 (table $0 0 (ref $0) (ref.func $0))
 (func $0 (param $0 i32)
 )
)

• Non-nullable table without an init expr should fail validation:

(module
 (type $0 (func (param i32)))
 (table $0 0 (ref $0))
 (func $0 (param $0 i32)
 )
)

Correctly fails with [wasm-validator error in module] unexpected false: tables with non-nullable types require an initializer expression, on table

• Nullable table with init expr should rountrip correctly:

(module
 (type $0 (func (param i32)))
 (table $0 0 funcref (ref.func $0))
 (func $0 (type $0) (param $0 i32)
 )
)

• Non-nullable table init expr should be validated to be a subtype of the table type

(module
 (type $0 (func (param i32)))
 (table $0 0 (ref $0) (i32.const 0))
 (func $0 (param $0 i32)
 )
)

Correctly fails with [wasm-validator error in module] init expression must be a subtype of the table type, on (i32.const 0)

• Nullable table init expr (if present) should be validated to be a subtype of the table type

(module
 (type $0 (func (param i32)))
 (table $0 0 funcref (i32.const 0))
 (func $0 (param $0 i32)
 )
)

Correctly fails with [wasm-validator error in module] init expression must be a subtype of the table type, on (i32.const 0)

• wasm-opt doesn't remove init expr as dead code

(module
 (type $0 (func (param i32)))
 (table $0 0 funcref (ref.func $0))
 (export "table" (table $0))
 (func $0 (type $0) (param $0 i32)
 )
)

• spec test global.wast fails at the following (validation succeeds), although I don't understand why the module should be invalid:

(assert_invalid
  (module
    (global $g funcref (ref.null func))
    (table $t 10 funcref (global.get $g))
  )
  "unknown global"
)

[stevenfontanella]

I have also unignored previously ignored spec tests instance.wast, ref_is_null.wast, table.wast, i31.wast, which now all pass. I have also changed the reason for ignoring array.wast as it does not (and has not in the past, AFAICT) rely on non-nullable table types.

I don't see these changes in shared.py, can we add them?

[stevenfontanella]

Add a CHANGELOG.md entry under Current Trunk describing the breakage and how to fix it for C/JS library users.

[stevenfontanella]

setMemory has a default param for null but most other cases seem to rely on unset params being implicitly undefined in JS, maybe we should do the same here?

i.e.

function(..., init) {
  return preserveStack(() => Module['_BinaryenAddTable'](..., init)
}

(or check for undefined if needed)

cc @kripken if you have any opinion

[pufferfish101007]

I think optional parameters need to come after all non-optional parameters, so init would need to come before type. To me, that seems less nice, both because adding it at the end isn't breaking for the JS api, and because the init expression would naturally come at the end when writing WAT.

[stevenfontanella]

Great!