Updating zygote errors? MethodError: no method matching getindex(::Nothing, ::String)
#3
Comments
|
Thanks for the report, but although Zygote does break a lot of things I don't expect this to be my fault :) Please can you report this to Pkg.jl. |
Keno
added a commit
that referenced
this issue
Feb 24, 2019
Right now Zygote inserts stacks whenever it needs to use an ssa value
not defined in the first basic block. This is of course unnecessary.
The condition for needing stacks is that the basic block that defines
it is self-reachable (i.e. in a loop). Otherwise, we can simply insert
phi nodes to thread the desired SSA value through to the exit block
(we don't need to do anything in the adjoint, since the reversal of
the CFG ensures dominance). Removing stacks allows for both more
efficient code generation and enables higher order auto-diff (since
we use control flow in Zygote, but can't handle differentiating code
that contains stacks). The headline example is something like the following:
```
function foo(b, x)
if b
sin(x)
else
cos(x)
end
end
```
Then looking at `@code_typed derivative(x->foo(true, x), 1.0)`, we get:
Before:
```
CodeInfo(
1 ── %1 = $(Expr(:foreigncall, :(:jl_alloc_array_1d), Array{Int8,1}, svec(Any, Int64), :(:ccall), 2, Array{Int8,1}, 0, 0))::Array{Int8,1}
│ %2 = $(Expr(:foreigncall, :(:jl_alloc_array_1d), Array{Any,1}, svec(Any, Int64), :(:ccall), 2, Array{Any,1}, 0, 0))::Array{Any,1}
│ %3 = $(Expr(:foreigncall, :(:jl_alloc_array_1d), Array{Any,1}, svec(Any, Int64), :(:ccall), 2, Array{Any,1}, 0, 0))::Array{Any,1}
│ %4 = Base.sin::typeof(sin)
│ invoke %4(_3::Float64)::Float64
│ %6 = %new(##334#335{Float64}, x)::##334#335{Float64}
│ %7 = %new(##758#back#336{##334#335{Float64}}, %6)::##758#back#336{##334#335{Float64}}
[snip]
23 ─ %52 = invoke %47(1::Int8)::Tuple{Nothing,Nothing,Any}
│ %53 = Base.getfield(%52, 3, true)::Any
└─── goto #24
24 ─ return %53
) => Any
```
After:
```
CodeInfo(
1 ─ %1 = Base.sin::typeof(sin)
│ invoke %1(_3::Float64)::Float64
│ %3 = Core.Intrinsics.not_int(true)::Bool
└── goto #3 if not %3
2 ─ invoke Zygote.notnothing(nothing::Nothing)::Union{}
└── $(Expr(:unreachable))::Union{}
3 ┄ %7 = invoke Zygote.cos(_3::Float64)::Float64
│ %8 = Base.mul_float(1.0, %7)::Float64
└── goto #4
4 ─ goto #5
5 ─ goto #6
6 ─ goto #7
7 ─ return %8
) => Float64
```
Which is essentially perfect (there's a bit of junk left over, but LLVM
can take care of that. The only thing that doesn't get removed is the
useless invocation of `sin`, but that's a separate and known issue).
Keno
added a commit
that referenced
this issue
Mar 6, 2019
Right now Zygote inserts stacks whenever it needs to use an ssa value
not defined in the first basic block. This is of course unnecessary.
The condition for needing stacks is that the basic block that defines
it is self-reachable (i.e. in a loop). Otherwise, we can simply insert
phi nodes to thread the desired SSA value through to the exit block
(we don't need to do anything in the adjoint, since the reversal of
the CFG ensures dominance). Removing stacks allows for both more
efficient code generation and enables higher order auto-diff (since
we use control flow in Zygote, but can't handle differentiating code
that contains stacks). The headline example is something like the following:
```
function foo(b, x)
if b
sin(x)
else
cos(x)
end
end
```
Then looking at `@code_typed derivative(x->foo(true, x), 1.0)`, we get:
Before:
```
CodeInfo(
1 ── %1 = $(Expr(:foreigncall, :(:jl_alloc_array_1d), Array{Int8,1}, svec(Any, Int64), :(:ccall), 2, Array{Int8,1}, 0, 0))::Array{Int8,1}
│ %2 = $(Expr(:foreigncall, :(:jl_alloc_array_1d), Array{Any,1}, svec(Any, Int64), :(:ccall), 2, Array{Any,1}, 0, 0))::Array{Any,1}
│ %3 = $(Expr(:foreigncall, :(:jl_alloc_array_1d), Array{Any,1}, svec(Any, Int64), :(:ccall), 2, Array{Any,1}, 0, 0))::Array{Any,1}
│ %4 = Base.sin::typeof(sin)
│ invoke %4(_3::Float64)::Float64
│ %6 = %new(##334#335{Float64}, x)::##334#335{Float64}
│ %7 = %new(##758#back#336{##334#335{Float64}}, %6)::##758#back#336{##334#335{Float64}}
[snip]
23 ─ %52 = invoke %47(1::Int8)::Tuple{Nothing,Nothing,Any}
│ %53 = Base.getfield(%52, 3, true)::Any
└─── goto #24
24 ─ return %53
) => Any
```
After:
```
CodeInfo(
1 ─ %1 = Base.sin::typeof(sin)
│ invoke %1(_3::Float64)::Float64
│ %3 = Core.Intrinsics.not_int(true)::Bool
└── goto #3 if not %3
2 ─ invoke Zygote.notnothing(nothing::Nothing)::Union{}
└── $(Expr(:unreachable))::Union{}
3 ┄ %7 = invoke Zygote.cos(_3::Float64)::Float64
│ %8 = Base.mul_float(1.0, %7)::Float64
└── goto #4
4 ─ goto #5
5 ─ goto #6
6 ─ goto #7
7 ─ return %8
) => Float64
```
Which is essentially perfect (there's a bit of junk left over, but LLVM
can take care of that. The only thing that doesn't get removed is the
useless invocation of `sin`, but that's a separate and known issue).
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