fix JuliaLang#31663, long inference time printing large tree structure (

JuliaLang#31680)

- avoid exponential search in `is_derived_type` when parameters are
  used as field types
- avoid inferring `show_default`
- improve a fast path in subtyping

base/compiler/typelimits.jl

@@ -66,7 +66,10 @@ function is_derived_type(@nospecialize(t), @nospecialize(c), mindepth::Int)
             # it cannot have a reference cycle in the type graph
             cF = c.types
             for f in cF
-                is_derived_type(t, f, mindepth) && return true
+                # often a parameter is also a field type; avoid searching twice
+                if !contains_is(c.parameters, f)
+                    is_derived_type(t, f, mindepth) && return true
+                end
             end
         end
     end

base/essentials.jl

@@ -794,6 +794,9 @@ function invokelatest(@nospecialize(f), @nospecialize args...; kwargs...)
     Core._apply_latest(inner)
 end
 
+# TODO: possibly make this an intrinsic
+inferencebarrier(@nospecialize(x)) = Ref{Any}(x)[]
+
 """
     isempty(collection) -> Bool
 

base/show.jl

@@ -326,7 +326,10 @@ show(x) = show(stdout::IO, x)
 
 show(io::IO, @nospecialize(x)) = show_default(io, x)
 
-function show_default(io::IO, @nospecialize(x))
+# avoid inferring show_default on the type of `x`
+show_default(io::IO, @nospecialize(x)) = _show_default(io, inferencebarrier(x))
+
+function _show_default(io::IO, @nospecialize(x))
     t = typeof(x)::DataType
     show(io, t)
     print(io, '(')

src/subtype.c

@@ -193,6 +193,7 @@ static int obviously_egal(jl_value_t *a, jl_value_t *b)
     if (jl_is_datatype(a)) {
         jl_datatype_t *ad = (jl_datatype_t*)a, *bd = (jl_datatype_t*)b;
         if (ad->name != bd->name) return 0;
+        if (ad->isconcretetype || bd->isconcretetype) return 0;
         size_t i, np = jl_nparams(ad);
         if (np != jl_nparams(bd)) return 0;
         for(i=0; i < np; i++) {

test/compiler/inference.jl

@@ -2325,3 +2325,26 @@ h28762(::Type{X}) where {X} = Array{f28762(X)}(undef, 0)
     @inferred g28762(Array)
     @inferred h28762(Array)
 end
+
+# issue #31663
+module I31663
+abstract type AbstractNode end
+
+struct Node{N1<:AbstractNode, N2<:AbstractNode} <: AbstractNode
+    a::N1
+    b::N2
+end
+
+struct Leaf <: AbstractNode
+end
+
+function gen_nodes(qty::Integer) :: AbstractNode
+    @assert qty > 0
+    result = Leaf()
+    for i in 1:qty
+        result = Node(result, Leaf())
+    end
+    return result
+end
+end
+@test count(==('}'), string(I31663.gen_nodes(50))) == 1275