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False positive for local variable in multiple if statements with the same condition #801
Description
JET v0.11 seems to generate false positive warnings for the following setup, where multiple branches with a shared condition are used:
using JET
module MWE
function f(m, n)
condition = m < n
if condition
some_variable = 3
end
mn = m + n
if condition
mn += some_variable
end
return mn
end
end
using .MWE
@report_call target_modules = (MWE,) MWE.f(1, 2)While I agree that this might be a hard issue to solve in general, would there be a way to rewrite this such that JET can recognize that this is never an issue, or is there a fix for JET that can detect this?
I'm struggling to come up with a code pattern that can avoid this in a satisfactory manner.
The simplest approach seems to be to just define some_variable = nothing in the else branches, ensuring that the variable is always defined.
However, I don't think this guarantees that the compiler is always able to optimize away the resulting (union-split) type instability, and while in this specific case it is easy to create a dummy variable of the same type, this is not always easy or cheap (e.g. might require allocations).
This is a duplicate of #795 but with a simpler MWE, I wasn't sure if this needs its own issue or should be attached there.
Activity
Avoid conditionally defined local variables (#2443)