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When no value can flow out of a function (its body is unreachable, it
has no return with a value, and it does not tail-call a function with a
possible result), `LUB::getResultsLUB` notes nothing and DAE left the
result type alone. Such functions are common in compiled code (e.g.
wrappers that just throw an exception), and since `getResultsLUB` notes
the declared result type of `return_call` targets, every function that
tail-calls them also kept its imprecise result type.
For example, with `--dae`:
(func $fail (param $0 (ref eq)) (result (ref eq))
(throw $exn (local.get $0)))
(func $f (param $0 i32) (result (ref eq))
(if (local.get $0)
(then (return (ref.i31 (i32.const 0)))))
(return_call $fail (global.get $msg)))
`$f` stayed at `(ref eq)` although it can only return an i31.
When the result is a single reference type and no value is noted,
refine it to the non-nullable bottom type of its hierarchy (e.g. `(ref
none)`), under the same conditions as other result refinements (all
calls are known). `$fail` now returns `(ref none)` and `$f` `(ref i31)`
(chains of tail calls are refined over the DAE iterations). The callers
see an uninhabitable call result, so with dae-optimizing the code after
the call becomes unreachable, and a call whose result is dropped gets
an `unreachable` after it when the result is later removed.
Multivalue results are left alone.
Some existing tests relied on never-returning helper functions keeping
their declared result types; export those helpers to preserve what the
tests check.
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Looks good to me! Can you run the fuzzer for a few thousand iterations to see if it finds any issues? (scripts/fuzz_opt.py or scripts/monitor_fuzz.py -j --max-iters=5000)
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When no value can flow out of a function, DAE leaves the result type alone. Such functions are common in compiled code (e.g. functions that just throw an exception).
For example, with
--dae:$fstayed at(ref eq)although it can only return an i31.When the result is a single reference type and no value is noted, we refine it to the non-nullable bottom type of its hierarchy (e.g.
(ref none)), under the same conditions as other result refinements (all calls are known).$failnow returns(ref none)and$f(ref i31).