Update bias_act.jl (#618)

Author: mcabbott

src/bias_act.jl

@@ -8,7 +8,7 @@ const RCR = RuleConfig{>:HasReverseMode}
 @inline only_derivative(y,f::F,x) where F = only(only(ChainRulesCore.derivatives_given_output(y, f, x)))
 
 # This has no methods, used for testing whether `derivatives_given_output(Ω, f, x)`
-# is independent of `x`, as `_return_type` says `Union{}` when calling is an error.
+# is independent of `x`, as `return_type` says `Union{}` when calling is an error.
 struct NotaNumber <: Real end
 
 """
@@ -57,7 +57,7 @@ function ChainRulesCore.rrule(cfg::RCR, ::typeof(bias_act!), σ::F, x::AbstractA
     end
 
     # Fast path: it is now safe to overwrite x, since this is not needed for gradient of σ
-    if isconcretetype(Core.Compiler._return_type(only_derivative, Tuple{T, F, NotaNumber}))
+    if isconcretetype(Core.Compiler.return_type(only_derivative, Tuple{T, F, NotaNumber}))
         Ω = bias_act!(σ, x, b)  # now x === Ω, when x isa StridedArray{<:AbstractFloat}
         function bias_act!_fastback(Δ)
             # Tempting to overwrite x again, but only safe if you call pullback at most once,
@@ -70,7 +70,7 @@ function ChainRulesCore.rrule(cfg::RCR, ::typeof(bias_act!), σ::F, x::AbstractA
 
     # # Slower path: can't overwrite x, but can use derivatives_given_output
     # # This case is WRONG and tests fail, but not sure why
-    # elseif isconcretetype(Core.Compiler._return_type(only_derivative, Tuple{T, F, T}))
+    # elseif isconcretetype(Core.Compiler.return_type(only_derivative, Tuple{T, F, T}))
     #     Ω2 = fast_act(σ, x).(x) .+ b
     #     @show σ b
     #     function bias_act!_back2(Δ)