a few compiler improvements

- improve fieldtype_nothrow for vararg tuple types
- remove UnionAll construction code from tuple_type_head
- add specializations to avoid some common generated functions

base/compiler/tfuncs.jl

@@ -876,12 +876,12 @@ function _fieldtype_nothrow(@nospecialize(s), exact::Bool, name::Const)
     isa(fld, Int) || return false
     ftypes = datatype_fieldtypes(u)
     nf = length(ftypes)
-    (fld >= 1 && fld <= nf) || return false
     if u.name === Tuple.name && fld >= nf && isvarargtype(ftypes[nf])
-        # The length of the tuple will be determined at runtime, we can't say
-        # anything
-        return false
+        # If we don't know the exact type, the length of the tuple will be determined
+        # at runtime and we can't say anything.
+        return exact
     end
+    (fld >= 1 && fld <= nf) || return false
     return true
 end
 

base/essentials.jl

@@ -205,7 +205,7 @@ 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."))
 
-tuple_type_head(T::Type) = (@_pure_meta; fieldtype(T::Type{<:Tuple}, 1))
+tuple_type_head(T::Type) = (@_pure_meta; fieldtype(T, 1))
 
 function tuple_type_tail(T::Type)
     @_pure_meta

base/multidimensional.jl

@@ -758,8 +758,7 @@ function _unsafe_getindex(::IndexStyle, A::AbstractArray, I::Vararg{Union{Real,
     return dest
 end
 
-# Always index with the exactly indices provided.
-@generated function _unsafe_getindex!(dest::AbstractArray, src::AbstractArray, I::Vararg{Union{Real, AbstractArray}, N}) where N
+function _generate_unsafe_getindex!_body(N::Int)
     quote
         @_inline_meta
         D = eachindex(dest)
@@ -776,6 +775,20 @@ end
     end
 end
 
+# Always index with the exactly indices provided.
+@generated function _unsafe_getindex!(dest::AbstractArray, src::AbstractArray, I::Vararg{Union{Real, AbstractArray}, N}) where N
+    _generate_unsafe_getindex!_body(N)
+end
+
+# manually written-out specializations for 1 and 2 arguments to save compile time
+@eval function _unsafe_getindex!(dest::AbstractArray, src::AbstractArray, I::Vararg{Union{Real, AbstractArray},1})
+    $(_generate_unsafe_getindex!_body(1))
+end
+
+@eval function _unsafe_getindex!(dest::AbstractArray, src::AbstractArray, I::Vararg{Union{Real, AbstractArray},2})
+    $(_generate_unsafe_getindex!_body(2))
+end
+
 @noinline throw_checksize_error(A, sz) = throw(DimensionMismatch("output array is the wrong size; expected $sz, got $(size(A))"))
 
 ## setindex! ##
@@ -786,8 +799,7 @@ function _setindex!(l::IndexStyle, A::AbstractArray, x, I::Union{Real, AbstractA
     A
 end
 
-@generated function _unsafe_setindex!(::IndexStyle, A::AbstractArray, x, I::Union{Real,AbstractArray}...)
-    N = length(I)
+function _generate_unsafe_setindex!_body(N::Int)
     quote
         x′ = unalias(A, x)
         @nexprs $N d->(I_d = unalias(A, I[d]))
@@ -806,6 +818,18 @@ end
     end
 end
 
+@generated function _unsafe_setindex!(::IndexStyle, A::AbstractArray, x, I::Vararg{Union{Real,AbstractArray}, N}) where N
+    _generate_unsafe_setindex!_body(N)
+end
+
+@eval function _unsafe_setindex!(::IndexStyle, A::AbstractArray, x, I::Vararg{Union{Real,AbstractArray},1})
+    $(_generate_unsafe_setindex!_body(1))
+end
+
+@eval function _unsafe_setindex!(::IndexStyle, A::AbstractArray, x, I::Vararg{Union{Real,AbstractArray},2})
+    $(_generate_unsafe_setindex!_body(2))
+end
+
 diff(a::AbstractVector) = diff(a, dims=1)
 
 """

base/namedtuple.jl

@@ -248,7 +248,9 @@ function merge(a::NamedTuple{an}, b::NamedTuple{bn}) where {an, bn}
     end
 end
 
-merge(a::NamedTuple{()}, b::NamedTuple) = b
+merge(a::NamedTuple,     b::NamedTuple{()}) = a
+merge(a::NamedTuple{()}, b::NamedTuple{()}) = a
+merge(a::NamedTuple{()}, b::NamedTuple)     = b
 
 merge(a::NamedTuple, b::Iterators.Pairs{<:Any,<:Any,<:Any,<:NamedTuple}) = merge(a, b.data)
 
@@ -320,6 +322,8 @@ function structdiff(a::NamedTuple{an}, b::Union{NamedTuple{bn}, Type{NamedTuple{
     end
 end
 
+structdiff(a::NamedTuple{an}, b::Union{NamedTuple{an}, Type{NamedTuple{an}}}) where {an} = (;)
+
 """
     setindex(nt::NamedTuple, val, key::Symbol)
 

test/compiler/inference.jl

@@ -655,6 +655,9 @@ let fieldtype_tfunc = Core.Compiler.fieldtype_tfunc,
     @test fieldtype_nothrow(Union{Type{Base.RefValue{<:Real}}, Type{Base.RefValue{Any}}}, Const(:x))
     @test fieldtype_nothrow(Const(Union{Base.RefValue{<:Real}, Base.RefValue{Any}}), Const(:x))
     @test fieldtype_nothrow(Type{Union{Base.RefValue{T}, Base.RefValue{Any}}} where {T<:Real}, Const(:x))
+    @test fieldtype_nothrow(Type{Tuple{Vararg{Int}}}, Const(1))
+    @test fieldtype_nothrow(Type{Tuple{Vararg{Int}}}, Const(42))
+    @test !fieldtype_nothrow(Type{<:Tuple{Vararg{Int}}}, Const(1))
 end
 
 # issue #11480