in inference, disallow 3-element Unions if one elt is abstract (JuliaLang#36200)

Author: JeffBezanson

base/compiler/typelimits.jl

@@ -268,8 +268,11 @@ function type_more_complex(@nospecialize(t), @nospecialize(c), sources::SimpleVe
     return true
 end
 
+union_count_abstract(x::Union) = union_count_abstract(x.a) + union_count_abstract(x.b)
+union_count_abstract(@nospecialize(x)) = !isdispatchelem(x)
+
 function issimpleenoughtype(@nospecialize t)
-    return unionlen(t) <= MAX_TYPEUNION_LENGTH && unioncomplexity(t) <= MAX_TYPEUNION_COMPLEXITY
+    return unionlen(t)+union_count_abstract(t) <= MAX_TYPEUNION_LENGTH && unioncomplexity(t) <= MAX_TYPEUNION_COMPLEXITY
 end
 
 # pick a wider type that contains both typea and typeb,

test/compiler/inference.jl

@@ -91,10 +91,10 @@ tmerge_test(Tuple{ComplexF64, ComplexF64, ComplexF32}, Tuple{Vararg{Union{Comple
     Tuple{Vararg{Complex}}, false)
 tmerge_test(Tuple{}, Tuple{Complex, Vararg{Union{ComplexF32, ComplexF64}}},
     Tuple{Vararg{Complex}})
-@test Core.Compiler.tmerge(Tuple{}, Union{Int16, Nothing, Tuple{ComplexF32, ComplexF32}}) ==
-    Union{Int16, Nothing, Tuple{Vararg{ComplexF32}}}
-@test Core.Compiler.tmerge(Union{Int32, Nothing, Tuple{ComplexF32}}, Union{Int32, Nothing, Tuple{ComplexF32, ComplexF32}}) ==
-    Union{Int32, Nothing, Tuple{Vararg{ComplexF32}}}
+@test Core.Compiler.tmerge(Tuple{}, Union{Nothing, Tuple{ComplexF32, ComplexF32}}) ==
+    Union{Nothing, Tuple{Vararg{ComplexF32}}}
+@test Core.Compiler.tmerge(Union{Nothing, Tuple{ComplexF32}}, Union{Nothing, Tuple{ComplexF32, ComplexF32}}) ==
+    Union{Nothing, Tuple{Vararg{ComplexF32}}}
 
 # issue 9770
 @noinline x9770() = false