Remove _extrema_rf optimization for AbstractFloat (follow advise)

Add TODO

apply suggestions

Update NEWS.md

Co-Authored-By: Takafumi Arakaki <takafumi.a@gmail.com>
Co-Authored-By: Takafumi Arakaki <29282+tkf@users.noreply.github.com>

Author: N5N3

NEWS.md

@@ -96,7 +96,7 @@ Standard library changes
   arithmetic to error if the result may be wrapping. Or use a package such as SaferIntegers.jl when
   constructing the range. ([#40382])
 * TCP socket objects now expose `closewrite` functionality and support half-open mode usage ([#40783]).
-* `extrema` now supports `init` keyword argument ([#36265]).
+* `extrema` now supports `init` keyword argument ([#36265], [#43604]).
 * Intersect returns a result with the eltype of the type-promoted eltypes of the two inputs ([#41769]).
 * `Iterators.countfrom` now accepts any type that defines `+`. ([#37747])
 

base/mpfr.jl

@@ -706,17 +706,6 @@ function min(x::BigFloat, y::BigFloat)
     return z
 end
 
-# We don't want allocations during `extrema`.
-# TODO: avoid allocations in `min/max`
-function Base._extrema_rf(x::NTuple{2,BigFloat}, y::NTuple{2,BigFloat})
-    (x1, x2), (y1, y2) = x, y
-    isnan(x1) && return x
-    isnan(y1) && return y
-    z1 = x1 < y1 || signbit(x1) > signbit(y1) ? x1 : y1
-    z2 = x2 < y2 || signbit(x2) > signbit(y2) ? y2 : x2
-    z1, z2
-end
-
 function modf(x::BigFloat)
     zint = BigFloat()
     zfloat = BigFloat()

base/reduce.jl

@@ -847,15 +847,8 @@ end
 ExtremaMap(::Type{T}) where {T} = ExtremaMap{Type{T}}(T)
 @inline (f::ExtremaMap)(x) = (y = f.f(x); (y, y))
 
+# TODO: optimize for inputs <: AbstractFloat
 @inline _extrema_rf((min1, max1), (min2, max2)) = (min(min1, min2), max(max1, max2))
-# optimization for AbstractFloat
-function _extrema_rf(x::NTuple{2,T}, y::NTuple{2,T}) where {T<:AbstractFloat}
-    (x1, x2), (y1, y2) = x, y
-    anynan = isnan(x1)|isnan(y1)
-    z1 = ifelse(anynan, x1-y1, ifelse(signbit(x1-y1), x1, y1))
-    z2 = ifelse(anynan, x1-y1, ifelse(signbit(x2-y2), y2, x2))
-    z1, z2
-end
 
 ## findmax, findmin, argmax & argmin
 

base/reducedim.jl

@@ -80,7 +80,6 @@ for (Op, initfun) in ((:(typeof(add_sum)), :zero), (:(typeof(mul_prod)), :one))
     @eval initarray!(a::AbstractArray{T}, ::Any, ::$(Op), init::Bool, src::AbstractArray) where {T} = (init && fill!(a, $(initfun)(T)); a)
 end
 
-# for min/max copyfirst is not correct for initialization, use `mapfirst!` instead
 initarray!(a::AbstractArray{T}, f, ::Union{typeof(min),typeof(max),typeof(_extrema_rf)},
     init::Bool, src::AbstractArray) where {T} = (init && mapfirst!(f, a, src); a)