`methods` returns wrong result for triangular dispatch

[yuyichao]

See below, methods returns two methods even though only the second one (the first in the returned array) can possibly be called. This is the reason we are doing a dynamic dispatch at all in #18331 . (and without this fixed allocation elimination can't fully work either)

julia> f{T<:Any}(::Type{T}, x) = 1
f (generic function with 1 method)

julia> f{T<:Any}(::Type{T}, x::T) = 2
f (generic function with 2 methods)

julia> methods(f, Tuple{Type{Any},Any})
#2 methods for generic function "f":
f{T}(::Type{T}, x::T) at REPL[2]:1
f{T}(::Type{T}, x) at REPL[1]:1

[yuyichao]

Ah....... Just notice this is the first thing @vtjnash mentioned in #18331 (comment) (Didn't realized that since this is also the case on 0.4 and is not the regression........... The regression is still the performance of the dynamic dispatch itself.)

[JeffBezanson]

closed by #18457