typemap: improve quality of leaf split (#48925)

Introduce another optional layer of indirection, doing lookup on first
typename always, then leaftypes. This lets the intersection-iterators
skip a lot of jl_isa queries later.

base/reflection.jl

@@ -1070,29 +1070,31 @@ function visit(f, mt::Core.MethodTable)
  nothing
 end
 function visit(f, mc::Core.TypeMapLevel)
- if mc.targ !== nothing
- e = mc.targ::Vector{Any}
+ function avisit(f, e::Array{Any,1})
  for i in 2:2:length(e)
- isassigned(e, i) && visit(f, e[i])
+ isassigned(e, i) || continue
+ ei = e[i]
+ if ei isa Vector{Any}
+ for j in 2:2:length(ei)
+ isassigned(ei, j) || continue
+ visit(f, ei[j])
+ end
+ else
+ visit(f, ei)
+ end
  end
  end
+ if mc.targ !== nothing
+ avisit(f, mc.targ::Vector{Any})
+ end
  if mc.arg1 !== nothing
- e = mc.arg1::Vector{Any}
- for i in 2:2:length(e)
- isassigned(e, i) && visit(f, e[i])
- end
+ avisit(f, mc.arg1::Vector{Any})
  end
  if mc.tname !== nothing
- e = mc.tname::Vector{Any}
- for i in 2:2:length(e)
- isassigned(e, i) && visit(f, e[i])
- end
+ avisit(f, mc.tname::Vector{Any})
  end
  if mc.name1 !== nothing
- e = mc.name1::Vector{Any}
- for i in 2:2:length(e)
- isassigned(e, i) && visit(f, e[i])
- end
+ avisit(f, mc.name1::Vector{Any})
  end
  mc.list !== nothing && visit(f, mc.list)
  mc.any !== nothing && visit(f, mc.any)

src/julia.h

@@ -639,10 +639,10 @@ typedef struct _jl_typemap_level_t {
  // next split may be on Type{T} as LeafTypes then TypeName's parents up to Any
  // next split may be on LeafType
  // next split may be on TypeName
- _Atomic(jl_array_t*) arg1; // contains LeafType
- _Atomic(jl_array_t*) targ; // contains Type{LeafType}
- _Atomic(jl_array_t*) name1; // contains non-abstract TypeName, for parents up to (excluding) Any
- _Atomic(jl_array_t*) tname; // contains a dict of Type{TypeName}, for parents up to Any
+ _Atomic(jl_array_t*) arg1; // contains LeafType (in a map of non-abstract TypeName)
+ _Atomic(jl_array_t*) targ; // contains Type{LeafType} (in a map of non-abstract TypeName)
+ _Atomic(jl_array_t*) name1; // a map for a map for TypeName, for parents up to (excluding) Any
+ _Atomic(jl_array_t*) tname; // a map for Type{TypeName}, for parents up to (including) Any
  // next a linear list of things too complicated at this level for analysis (no more levels)
  _Atomic(jl_typemap_entry_t*) linear;
  // finally, start a new level if the type at offs is Any