avoid stack-overflow in JuliaLang#46736

When we perform re-intersection_unionall, the `Union` bounds might be generated from `simple_join` thus not identical to the src `Union`.

src/subtype.c

@@ -2150,6 +2150,9 @@ static jl_value_t *intersect_aside(jl_value_t *x, jl_value_t *y, jl_stenv_t *e,
         return y;
     if (y == (jl_value_t*)jl_any_type && !jl_is_typevar(x))
         return x;
+    // band-aid for #46736
+    if (jl_egal(x, y))
+        return x;
 
     jl_saved_unionstate_t oldRunions; push_unionstate(&oldRunions, &e->Runions);
     int savedepth = e->invdepth, Rsavedepth = e->Rinvdepth;

test/subtype.jl

@@ -2296,6 +2296,14 @@ let S = Tuple{Type{T},Array{Union{T,Missing},N}} where {T,N},
     @test_broken I <: T
 end
 
+#issue 46736
+let S = Tuple{Val{T}, T} where {S1,T<:Val{Union{Nothing,S1}}},
+    T = Tuple{Val{Val{Union{Nothing, S2}}}, Any} where S2
+    @testintersect(S, T, !Union{})
+    # not ideal (`S1` should be unbounded)
+    @test_broken testintersect(S, T) == Tuple{Val{Val{Union{Nothing, S1}}}, Val{Union{Nothing, S1}}} where S1<:(Union{Nothing, S2} where S2)
+end
+
 @testset "known subtype/intersect issue" begin
     #issue 45874
     # Causes a hang due to jl_critical_error calling back into malloc...