From 0717a9454d7eb2275575d22f97962d9d9f1e95e2 Mon Sep 17 00:00:00 2001
From: Jameson Nash <vtjnash@gmail.com>
Date: Tue, 6 Aug 2024 06:53:10 -0400
Subject: [PATCH] Revert "better type inference for several functions taking
 `NTuple` args" (#55375)

Reverts JuliaLang/julia#55124 as this turns out to hurt performance
quite a bit

Closes #55374
---
 base/essentials.jl |  8 +-------
 base/ntuple.jl     |  2 +-
 base/tuple.jl      | 16 +++-------------
 test/tuple.jl      |  7 -------
 4 files changed, 5 insertions(+), 28 deletions(-)

diff --git a/base/essentials.jl b/base/essentials.jl
index 2e76235cba9a6..50017b3d7927d 100644
--- a/base/essentials.jl
+++ b/base/essentials.jl
@@ -501,13 +501,7 @@ julia> Base.tail(())
 ERROR: ArgumentError: Cannot call tail on an empty tuple.
 ```
 """
-function tail(x::Tuple{Any,Vararg})
-    y = argtail(x...)::Tuple
-    if x isa NTuple  # help the type inference
-        y = y::NTuple
-    end
-    y
-end
+tail(x::Tuple) = argtail(x...)
 tail(::Tuple{}) = throw(ArgumentError("Cannot call tail on an empty tuple."))
 
 function unwrap_unionall(@nospecialize(a))
diff --git a/base/ntuple.jl b/base/ntuple.jl
index 4adab38a8ee82..f81d2686b9764 100644
--- a/base/ntuple.jl
+++ b/base/ntuple.jl
@@ -95,5 +95,5 @@ end
 function reverse(t::NTuple{N}) where N
     ntuple(Val{N}()) do i
         t[end+1-i]
-    end::NTuple
+    end
 end
diff --git a/base/tuple.jl b/base/tuple.jl
index 5f74d486e1e69..fc213410cfd7c 100644
--- a/base/tuple.jl
+++ b/base/tuple.jl
@@ -340,15 +340,9 @@ ERROR: ArgumentError: Cannot call front on an empty tuple.
 """
 function front(t::Tuple)
     @inline
-    if t === ()
-        throw(ArgumentError("Cannot call front on an empty tuple."))
-    end
-    r = _front(t...)::Tuple
-    if t isa NTuple  # help the type inference
-        r = r::NTuple
-    end
-    r
+    _front(t...)
 end
+_front() = throw(ArgumentError("Cannot call front on an empty tuple."))
 _front(v) = ()
 function _front(v, t...)
     @inline
@@ -705,9 +699,5 @@ function circshift(x::Tuple{Any,Any,Any,Vararg{Any,N}}, shift::Integer) where {N
     @inline
     len = N + 3
     j = mod1(shift, len)
-    y = ntuple(k -> getindex(x, k-j+ifelse(k>j,0,len)), Val(len))::Tuple
-    if x isa NTuple  # help the type inference
-        y = y::NTuple
-    end
-    y
+    ntuple(k -> getindex(x, k-j+ifelse(k>j,0,len)), Val(len))::Tuple
 end
diff --git a/test/tuple.jl b/test/tuple.jl
index 59897c8adfdb2..b1894bd2bb6ce 100644
--- a/test/tuple.jl
+++ b/test/tuple.jl
@@ -845,10 +845,3 @@ end
         end
     end
 end
-
-@testset "abstract return type inference for homogeneous tuples" begin
-    @test NTuple == Core.Compiler.return_type(Base.tail, Tuple{NTuple})
-    @test NTuple == Core.Compiler.return_type(Base.front, Tuple{NTuple})
-    @test NTuple == Core.Compiler.return_type(reverse, Tuple{NTuple})
-    @test NTuple == Core.Compiler.return_type(circshift, Tuple{NTuple,Int})
-end