avoid method proliferation for Tuple functions

base/essentials.jl

@@ -531,8 +531,12 @@ julia> Base.tail(())
 ERROR: ArgumentError: Cannot call tail on an empty tuple.
 ```
 """
-tail(x::Tuple) = argtail(x...)
-tail(::Tuple{}) = throw(ArgumentError("Cannot call tail on an empty tuple."))
+function tail(x::Tuple)
+    if x === ()
+        throw(ArgumentError("Cannot call tail on an empty tuple."))
+    end
+    argtail(x...)
+end
 
 function unwrap_unionall(@nospecialize(a))
     @_foldable_meta

base/operators.jl

@@ -223,13 +223,6 @@ isless(x::AbstractFloat, y::AbstractFloat) = (!isnan(x) & (isnan(y) | signless(x
 isless(x::Real,          y::AbstractFloat) = (!isnan(x) & (isnan(y) | signless(x, y))) | (x < y)
 isless(x::AbstractFloat, y::Real         ) = (!isnan(x) & (isnan(y) | signless(x, y))) | (x < y)
 
-# Performance optimization to reduce branching
-# This is useful for sorting tuples of integers
-# TODO: remove this when the compiler can optimize the generic version better
-# See #48724 and #48753
-isless(a::Tuple{BitInteger, BitInteger}, b::Tuple{BitInteger, BitInteger}) =
-    isless(a[1], b[1]) | (isequal(a[1], b[1]) & isless(a[2], b[2]))
-
 """
     isgreater(x, y)
 

base/tuple.jl

@@ -268,9 +268,12 @@ end
 
 @eval split_rest(t::Tuple, n::Int, i=1) = ($(Expr(:meta, :aggressive_constprop)); _split_tuple(t, length(t)-n, Int(i)))
 
-# Use dispatch to avoid a branch in first
-first(::Tuple{}) = throw(ArgumentError("tuple must be non-empty"))
-first(t::Tuple) = t[1]
+function first(t::Tuple)
+    if t === ()
+        throw(ArgumentError("tuple must be non-empty"))
+    end
+    t[1]
+end
 
 # eltype
 
@@ -575,71 +578,104 @@ function _eq(t1::Any32, t2::Any32)
 end
 
 const tuplehash_seed = UInt === UInt64 ? 0x77cfa1eef01bca90 : 0xf01bca90
-hash(::Tuple{}, h::UInt) = h ⊻ tuplehash_seed
-hash(t::Tuple, h::UInt) = hash(t[1], hash(tail(t), h))
-function hash(t::Any32, h::UInt)
-    out = h ⊻ tuplehash_seed
-    for i = length(t):-1:1
-        out = hash(t[i], out)
+function hash(t::Tuple, h::UInt)
+    function f(t::Tuple, h::UInt)
+        if t === ()
+            h ⊻ tuplehash_seed
+        else
+            hash(t[1], hash(tail(t), h))
+        end
     end
-    return out
+    function f(t::Any32, h::UInt)
+        out = h ⊻ tuplehash_seed
+        for i = length(t):-1:1
+            out = hash(t[i], out)
+        end
+        return out
+    end
+    f(t, h)
 end
 
-<(::Tuple{}, ::Tuple{}) = false
-<(::Tuple{}, ::Tuple) = true
-<(::Tuple, ::Tuple{}) = false
 function <(t1::Tuple, t2::Tuple)
-    a, b = t1[1], t2[1]
-    eq = (a == b)
-    if ismissing(eq)
-        return missing
-    elseif !eq
-        return a < b
-    end
-    return tail(t1) < tail(t2)
-end
-function <(t1::Any32, t2::Any32)
-    n1, n2 = length(t1), length(t2)
-    for i = 1:min(n1, n2)
-        a, b = t1[i], t2[i]
+    function f(t1::Tuple, t2::Tuple)
+        if t2 === ()
+            return false
+        end
+        if t1 === ()
+            return true
+        end
+        a, b = t1[1], t2[1]
         eq = (a == b)
         if ismissing(eq)
             return missing
         elseif !eq
-           return a < b
+            return a < b
         end
+        return tail(t1) < tail(t2)
     end
-    return n1 < n2
+    function f(t1::Any32, t2::Any32)
+        n1, n2 = length(t1), length(t2)
+        for i = 1:min(n1, n2)
+            a, b = t1[i], t2[i]
+            eq = (a == b)
+            if ismissing(eq)
+                return missing
+            elseif !eq
+                return a < b
+            end
+        end
+        return n1 < n2
+    end
+    f(t1, t2)
 end
 
-isless(::Tuple{}, ::Tuple{}) = false
-isless(::Tuple{}, ::Tuple) = true
-isless(::Tuple, ::Tuple{}) = false
+# copy of `BitInteger` defined later during bootstrap in int.jl
+const _BitInteger = Union{
+    Int8, Int16, Int32, Int64, Int128,
+    UInt8, UInt16, UInt32, UInt64, UInt128,
+}
 
 """
     isless(t1::Tuple, t2::Tuple)
 
 Return `true` when `t1` is less than `t2` in lexicographic order.
 """
 function isless(t1::Tuple, t2::Tuple)
-    a, b = t1[1], t2[1]
-    isless(a, b) || (isequal(a, b) && isless(tail(t1), tail(t2)))
-end
-function isless(t1::Any32, t2::Any32)
-    n1, n2 = length(t1), length(t2)
-    for i = 1:min(n1, n2)
-        a, b = t1[i], t2[i]
-        if !isequal(a, b)
-            return isless(a, b)
+    function f(t1::Tuple, t2::Tuple)
+        if t2 === ()
+            return false
+        end
+        if t1 === ()
+            return true
+        end
+        a, b = t1[1], t2[1]
+        isless(a, b) || (isequal(a, b) && isless(tail(t1), tail(t2)))
+    end
+    function f(t1::Any32, t2::Any32)
+        n1, n2 = length(t1), length(t2)
+        for i = 1:min(n1, n2)
+            a, b = t1[i], t2[i]
+            if !isequal(a, b)
+                return isless(a, b)
+            end
         end
+        return n1 < n2
     end
-    return n1 < n2
+    # Performance optimization to reduce branching
+    # This is useful for sorting tuples of integers
+    # TODO: remove this when the compiler can optimize the generic version better
+    # See #48724 and #48753
+    function f(a::Tuple{_BitInteger, _BitInteger}, b::Tuple{_BitInteger, _BitInteger})
+        isless(a[1], b[1]) | (isequal(a[1], b[1]) & isless(a[2], b[2]))
+    end
+    f(t1, t2)
 end
 
 ## functions ##
 
-isempty(x::Tuple{}) = true
-isempty(@nospecialize x::Tuple) = false
+function isempty(x::Tuple)
+    x === ()
+end
 
 revargs() = ()
 revargs(x, r...) = (revargs(r...)..., x)
@@ -677,11 +713,19 @@ empty(@nospecialize x::Tuple) = ()
 foreach(f, itr::Tuple) = foldl((_, x) -> (f(x); nothing), itr, init=nothing)
 foreach(f, itr::Tuple, itrs::Tuple...) = foldl((_, xs) -> (f(xs...); nothing), zip(itr, itrs...), init=nothing)
 
-circshift((@nospecialize t::Union{Tuple{},Tuple{Any}}), @nospecialize _::Integer) = t
-circshift(t::Tuple{Any,Any}, shift::Integer) = iseven(shift) ? t : reverse(t)
-function circshift(x::Tuple{Any,Any,Any,Vararg{Any,N}}, shift::Integer) where {N}
+function circshift(x::Tuple, shift::Integer)
     @inline
-    len = N + 3
+    if (x === ()) || (x isa Tuple{Any})
+        return x
+    end
+    if x isa Tuple{Any,Any}
+        return if iseven(shift)
+            x
+        else
+            reverse(x)
+        end
+    end
+    len = length(x)
     j = mod1(shift, len)
     ntuple(k -> getindex(x, k-j+ifelse(k>j,0,len)), Val(len))::Tuple
 end

test/tuple.jl

@@ -855,6 +855,18 @@ end
 @test Val{Tuple{Int64, Vararg{Int32,N}} where N} === Val{Tuple{Int64, Vararg{Int32}}}
 @test Val{Tuple{Int32, Vararg{Int64}}} === Val{Tuple{Int32, Vararg{Int64,N}} where N}
 
+@testset "avoid method proliferation" begin
+    t = isone ∘ length ∘ methods
+    @test t(circshift, Tuple{Tuple, Integer})
+    @test t(hash, Tuple{Tuple, UInt})
+    for f in (Base.tail, first, isempty)
+        @test t(f, Tuple{Tuple})
+    end
+    for f in (<, isless, ==, isequal)
+        @test t(f, Tuple{Tuple, Tuple})
+    end
+end
+
 @testset "from Pair, issue #52636" begin
     pair = (1 => "2")
     @test (1, "2") == @inferred Tuple(pair)