Re: Garbage collection durint pcall.

[Andrew Gierth <andrew@...>]

>>>>> "Francisco" == Francisco Olarte <folarte@peoplecall.com> writes:

 >> A general observation: An optimizing implementation of Lua could do
 >> variable liveness analysis and reuse stack slots, resulting in the
 >> following:

 >> function f(x)
 >>   print(x)
 >>   local y = g() -- this overwrites x, making it collectable
 >>   print(y)
 >> end

 Francisco> I think this would be a faulty optimizer. To be exact, I
 Francisco> think doing this and allowing the value to be collected
 Francisco> would be an optimizer error. I have not tried to understand
 Francisco> the spec in detail, but, in a language with finalizers which
 Francisco> can be observed, this changes the semantics of the program.

There's a specific idiom that this kind of optimization would break,
which is when one fetches a key or value from a weak table into a local
variable purely to ensure it does not get collected during some process.
In this case the local variable might never be referenced at all after
assigning it.

-- 
Andrew.