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Disable thunks for 2nd order AD #683

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Merged
merged 6 commits into from
Jan 3, 2025
Merged

Disable thunks for 2nd order AD #683

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6586c90
Allow disabling thunking
pxl-th Jan 2, 2025
e01ec21
Bump to 1.25.1
pxl-th Jan 2, 2025
2564fc1
Simplify
pxl-th Jan 2, 2025
9439257
Unconditionally disable thunks for 2nd order AD
pxl-th Jan 2, 2025
2bd5843
Add comment
pxl-th Jan 2, 2025
d32aa01
Fixes
pxl-th Jan 2, 2025
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2 changes: 1 addition & 1 deletion Project.toml
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
name = "ChainRulesCore"
uuid = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
version = "1.25.0"
version = "1.25.1"

[deps]
Compat = "34da2185-b29b-5c13-b0c7-acf172513d20"
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16 changes: 15 additions & 1 deletion src/tangent_types/thunks.jl
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Original file line number Diff line number Diff line change
@@ -1,3 +1,7 @@
# Disable thunks for 2nd order AD.
_usethunks() = true
rrule(::typeof(_usethunks)) = false, (NoTangent(),)

abstract type AbstractThunk <: AbstractTangent end

struct MutateThunkException <: Exception end
Expand Down Expand Up @@ -141,7 +145,11 @@ macro thunk(body)
# Basically `:(Thunk(() -> $(esc(body))))` but use the location where it is defined.
# so we get useful stack traces if it errors.
func = Expr(:->, Expr(:tuple), Expr(:block, __source__, body))
Comment on lines 145 to 147
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@mcabbott mcabbott Jan 3, 2025

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This could go further and generate a name for the thunk, based on source location, instead of anon. () ->. I think the name will be seen sometimes where the code line info is not?

But not this PR perhaps...

return :(Thunk($(esc(func))))
return quote
$(esc(_usethunks))() ?
Thunk($(esc(func))) :
$(esc(func))()
end
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@mcabbott mcabbott Jan 2, 2025

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Comments on this approach over :(_usethunks() ? Thunk($(esc(func))) : $(esc(body))), from #568? My hope there was that including the body directly, instead of making and calling a function, might be slightly simpler for e.g. Zygote to understand.

end

"""
Expand Down Expand Up @@ -233,6 +241,12 @@ and destroy its inplacability.
struct InplaceableThunk{T<:Thunk,F} <: AbstractThunk
add!::F
val::T

function InplaceableThunk(add!::F, val::T) where {F, T}
_usethunks() ?
new{T, F}(add!, val) :
val
end
end

unthunk(x::InplaceableThunk) = unthunk(x.val)
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