More performance fixes

src/tangents.jl

@@ -610,7 +610,9 @@ Add `x` to `y`. If `ismutabletype(T)`, then `increment!!(x, y) === x` must hold.
 That is, `increment!!` will mutate `x`.
 This must apply recursively if `T` is a composite type whose fields are mutable.
 """
-increment!!(x::T, y::T) where {T} = increment_internal!!(IdDict{Any,Bool}(), x, y)
+function increment!!(x::T, y::T) where {T}
+    return increment_internal!!(isbitstype(T) ? NoCache() : IdDict{Any,Bool}(), x, y)
+end
 
 increment_internal!!(::IncCache, ::NoTangent, ::NoTangent) = NoTangent()
 increment_internal!!(::IncCache, x::T, y::T) where {T<:IEEEFloat} = x + y
@@ -619,10 +621,11 @@ function increment_internal!!(::IncCache, x::Ptr{T}, y::Ptr{T}) where {T}
 end
 @generated function increment_internal!!(c::IncCache, x::T, y::T) where {T<:Tuple}
     inc_exprs = map(n -> :(increment_internal!!(c, x[$n], y[$n])), 1:fieldcount(T))
-    return Expr(:(::), Expr(:call, :tuple, inc_exprs...), T)
+    return Expr(:call, :tuple, inc_exprs...)
 end
-function increment_internal!!(c::IncCache, x::T, y::T) where {T<:NamedTuple}
-    return T(tuple_map((x, y) -> increment_internal!!(c, x, y), x, y))
+@generated function increment_internal!!(c::IncCache, x::T, y::T) where {T<:NamedTuple}
+    inc_exprs = map(n -> :(increment_internal!!(c, x[$n], y[$n])), 1:fieldcount(T))
+    return Expr(:new, T, inc_exprs...)
 end
 function increment_internal!!(c::IncCache, x::T, y::T) where {T<:PossiblyUninitTangent}
     is_init(x) && is_init(y) && return T(increment_internal!!(c, val(x), val(y)))