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Let tmerge form a Union more often #27843

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Merged
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Jan 12, 2021
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Let tmerge form a Union more often #27843

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2c45fc2
Let tmerge form a Union more often
martinholters Jun 28, 2018
6b7e0cc
Add an inference monotonicity related test
martinholters Jan 12, 2021
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7 changes: 4 additions & 3 deletions base/compiler/typelimits.jl
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Expand Up @@ -355,9 +355,10 @@ function tmerge(@nospecialize(typea), @nospecialize(typeb))
return Any
end
typea == typeb && return typea
# it's always ok to form a Union of two concrete types
if (isconcretetype(typea) || isType(typea)) && (isconcretetype(typeb) || isType(typeb))
return Union{typea, typeb}
# it's always ok to form a Union of two Union-free types
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@vtjnash vtjnash Jun 29, 2018

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I think an alternate literal translation of this would be isa(unwrap_unionall(T), DataType)

u = Union{typea, typeb}
if unioncomplexity(u) <= 1
return u
end
# collect the list of types from past tmerge calls returning Union
# and then reduce over that list
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10 changes: 10 additions & 0 deletions test/compiler/inference.jl
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Expand Up @@ -2033,6 +2033,16 @@ let rt = Base.return_types(splat27434, (NamedTuple{(:x,), Tuple{T}} where T,))
@test !Base.has_free_typevars(rt[1])
end

# PR #27843
bar27843(x, y::Bool) = fill(x, 0)
bar27843(x, y) = fill(x, ntuple(_ -> 0, y))::Array{typeof(x)}
foo27843(x, y) = bar27843(x, y)
@test Core.Compiler.return_type(foo27843, Tuple{Union{Float64,Int}, Any}) == Union{Array{Float64}, Array{Int}}
let atypes1 = Tuple{Union{IndexCartesian, IndexLinear}, Any, Union{Tuple{}, Tuple{Any,Vararg{Any,N}} where N}, Tuple},
atypes2 = Tuple{Union{IndexCartesian, IndexLinear}, Any, Tuple, Tuple}
@test Core.Compiler.return_type(SubArray, atypes1) <: Core.Compiler.return_type(SubArray, atypes2)
end

# issue #27078
f27078(T::Type{S}) where {S} = isa(T, UnionAll) ? f27078(T.body) : T
T27078 = Vector{Vector{T}} where T
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