Improve precision of nfields_tfunc on Union
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base/compiler/tfuncs.jl
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| @@ -381,6 +381,9 @@ function nfields_tfunc(@nospecialize(x)) | |||
| return Const(isdefined(x, :types) ? length(x.types) : length(x.name.names)) | |||
| end | |||
| end | |||
| if isa(x, Union) | |||
| return tmerge(nfields_tfunc(x.a), nfields_tfunc(x.b)) | |||
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Could optimize a bit for larger unions by returning immediately if nfields_tfunc(x.a)==Int and only recursing down nfields_tfunc(x.b)otherwise (or vice versa). Not sure if worth it.
`nfields_tfunc(Tuple{Int, Union{Int, Float64}})` gave `Const(2)`,
but `nfields_tfunc(Union{Tuple{Int, Float64}, Tuple{Int, Int}})` gave
`Int`. In general, it's not great for the tfuncs to give different
answers when given `==` types, because other parts of the system
will happily substitute such types without changes to the user code,
which can change the inference result and lead to instability.
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nfields_tfunc(Tuple{Int, Union{Int, Float64}})gaveConst(2),but
nfields_tfunc(Union{Tuple{Int, Float64}, Tuple{Int, Int}})gaveInt. In general, it's not great for the tfuncs to give differentanswers when given
==types, because other parts of the systemwill happily substitute such types without changes to the user code,
which can change the inference result and lead to instability.