A bitcast was inserted when the receiver of the call wasn't a *i8. This
is a pretty common case, and did not play well with goroutines.
Avoid this bitcast by changing each call to a direct call, after
unpacking the receiver type from the *i8 parameter. This might also fix
some undefined behavior in the resulting program, as it is technically
not allowed to call a function with a different signature (even if the
signature is compatible).
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