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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,104 @@ | ||
| const chainrules_fallback = which(rrule, Tuple{Any}) | ||
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| """ | ||
| has_chain_rrule(T) | ||
| For a type-tuple `T` e.g. `Tuple{typeof(f), Int, Float64}`, checks if there is a `rrule` defined for it. | ||
| Excluding the generic fallback. | ||
| The first return value is `true` if the `rrule` exists, `false` otherwise. | ||
| If it does not, then the second argument is a list of edges to attach to the CodeInfo for a generated function, | ||
| such that if a suitable rule is defined later, the generated function will recompile. | ||
| """ | ||
| function has_chain_rrule(T) | ||
| m = meta(Tuple{typeof(rrule),T.parameters...}) | ||
| if m.method !== chainrules_fallback | ||
| # found a rrule, no need to add any edges | ||
| return true, nothing | ||
| end | ||
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| return false, m.instance | ||
| end | ||
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| """ | ||
| is_kwfunc(sigt...) | ||
| Determines if `sigt` is the type signature of a kwfunction. | ||
| Each element of `sigt` should be a type. | ||
| Either the first 3 types are a kwfunc type, a NamedTuple and the matching base function type, | ||
| or the first argument is the base function type and it is not a kwfunction. | ||
| the remaining types in `sigt` are the types of the argument. | ||
| """ | ||
| is_kwfunc(::Vararg{Any}) = false | ||
| is_kwfunc(k, ::Type{<:NamedTuple}, f, args...) = k===Core.kwftype(f) | ||
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| """ | ||
| wrap_chainrules_output(x) | ||
| Convert `x` from the differentials types ChainRules uses to the format Zygote uses internally | ||
| (including conjugating complex gradients). | ||
| """ | ||
| @inline wrap_chainrules_output(x) = conj(unthunk(x)) # For now we are just not going to deal with thunks | ||
| @inline wrap_chainrules_output(x::Tuple) = map(wrap_chainrules_output, x) | ||
| @inline wrap_chainrules_output(x::ChainRules.AbstractZero) = nothing | ||
| for T_outer in (:Tuple, :NamedTuple) | ||
| # we create separate methods rather than using a `Union` + an `if` so that we avoid a | ||
| # branch that changes output type, because nested AD on that kinda thing makes Zygote less | ||
| # than happy. | ||
| @eval @inline function wrap_chainrules_output(x::ChainRules.Composite{P, T}) where {P, T<:$T_outer} | ||
| xp = map(wrap_chainrules_output, x) | ||
| convert($T_outer, xp) | ||
| end | ||
| end | ||
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| """ | ||
| wrap_chainrules_input(x) | ||
| Convert `x` from the format Zygote uses internally (including conjugated complex gradients) | ||
| to differentials types ChainRules uses. | ||
| """ | ||
| @inline wrap_chainrules_input(x) = conj(x) | ||
| @inline wrap_chainrules_input(::Nothing) = ChainRules.Zero() | ||
| @inline function wrap_chainrules_input(xs::Union{Tuple, NamedTuple}) | ||
| xp = map(wrap_chainrules_input, xs) | ||
| ChainRules.Composite{Any, typeof(xp)}(xp) | ||
| end | ||
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| """ | ||
| ZBack{F}(back) <: Function | ||
| Wrapper for a ChainRules pullback `back`, that causes it to follow Zygote conventions. | ||
| (A functor here is used rather than a closure to avoid boxing issues); | ||
| """ | ||
| struct ZBack{F} <: Function | ||
| back::F | ||
| end | ||
| @inline (s::ZBack)(dy) = wrap_chainrules_output(s.back(wrap_chainrules_input(dy))) | ||
| # `nothing->nothing` can be deleted after https://github.com/FluxML/Zygote.jl/issues/603 | ||
| # though it might be worth keeping as a performance optimization (benchmarking pending) | ||
| @inline (s::ZBack)(::Nothing) = nothing | ||
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| """ | ||
| chain_rrule(f, args...) | ||
| Returns a the (primal) value of `f(args...)` and a pullback, by invoking `ChainRulesCore.rrule(f, args...)`. | ||
| The pullback is appropriately wrapped up to follow Zygote conventions. | ||
| """ | ||
| @inline function chain_rrule(f, args...) | ||
| y, back = rrule(f, args...) | ||
| return y, ZBack(back) | ||
| end | ||
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| """ | ||
| chain_rrule_kw(kwf, kwargs, f, args...) | ||
| As per [`chain_rrule`](@ref) but with support for kwargs. | ||
| `kwf` should be the kwfunc matching to `f`, and `kwargs` are a `NamedTuple` of keyword arguments. | ||
| """ | ||
| @inline function chain_rrule_kw(kwf, kwargs, f, args...) | ||
| y, back = rrule(f, args...; kwargs...) | ||
| kw_zpullback(dy) = (nothing, nothing, ZBack(back)(dy)...) # first two nothings are for kwfunc and kwargs | ||
| return y, kw_zpullback | ||
| end |
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