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fix CyclePadding(::DataType) #50719

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Jul 31, 2023
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fix CyclePadding(::DataType) #50719

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4 changes: 3 additions & 1 deletion base/reinterpretarray.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -720,7 +720,9 @@ function CyclePadding(T::DataType)
a, s = datatype_alignment(T), sizeof(T)
as = s + (a - (s % a)) % a
pad = padding(T)
s != as && push!(pad, Padding(s, as - s))
if s != as
pad = Core.svec(pad..., Padding(s, as - s))
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Is this function still inferable? It seems like as - s might need to be an argument to padding

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Yes, I think it's still inferrable:

julia> only(code_typed(Base.CyclePadding, (DataType,); optimize=false))
CodeInfo(
1 ─ %1  = Base.datatype_alignment(T)::Int64
│   %2  = Base.sizeof(T)::Int64
│         (a = %1)::Int64
│         (s = %2)::Int64
│   %5  = s::Int64
│   %6  = a::Int64
│   %7  = (s % a)::Int64
│   %8  = (%6 - %7)::Int64
│   %9  = (%8 % a)::Int64
│         (as = %5 + %9)::Int64
│         (pad = Base.padding(T))::Core.SimpleVector
│   %12 = (s != as)::Bool
└──       goto #3 if not %12
2 ─ %14 = Core.svec::Core.Const(Core.svec)
│   %15 = pad::Core.SimpleVector
│   %16 = s::Int64
│   %17 = (as - s)::Int64
│   %18 = Base.Padding(%16, %17)::Base.Padding
│   %19 = Core.tuple(%18)::Tuple{Base.Padding}
└──       (pad = Core._apply_iterate(Base.iterate, %14, %15, %19))::Core.SimpleVector
3 ┄ %21 = Base.CyclePadding(pad, as)::Base.CyclePadding{Core.SimpleVector}
└──       return %21
) => Base.CyclePadding{Core.SimpleVector}

julia> code_typed(; optimize=false) do
           Base.CyclePadding(Int)
       end
1-element Vector{Any}:
 CodeInfo(
1 ─ %1 = Base.CyclePadding::Core.Const(Base.CyclePadding)
│   %2 = (%1)(Main.Int)::Core.Const(Base.CyclePadding{Core.SimpleVector}(svec(), 8))
└──      return %2
) => Base.CyclePadding{Core.SimpleVector}

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@vtjnash vtjnash Jul 31, 2023 •
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This code isn't reachable for as == s, but generally seems pretty hard to trigger anyways? I don't fully understand this code's (expected/observed) behavior:

julia> code_typed(; optimize=false) do
                  Base.CyclePadding(Tuple{Int64,Int8,Int16})
              end
1-element Vector{Any}:
 CodeInfo(
    @ REPL[12]:2 within `#19`
1 ─ %1 = Base.CyclePadding::Core.Const(Base.CyclePadding)
│   %2 = Core.apply_type(Main.Tuple, Main.Int64, Main.Int8, Main.Int16)::Core.Const(Tuple{Int64, Int8, Int16})
│   %3 = (%1)(%2)::Core.Const(Base.CyclePadding{Core.SimpleVector}(svec(Base.Padding(10, 1), Base.Padding(16, 4)), 16))
└──      return %3
) => Base.CyclePadding{Core.SimpleVector}
julia> primitive type Int24 24 end

julia> Base.CyclePadding(Int24)
ERROR: MethodError: no method matching push!(::Core.SimpleVector, ::Base.Padding)

Closest candidates are:
  push!(::Any, ::Any, ::Any)
   @ Base abstractarray.jl:3399
  push!(::Any, ::Any, ::Any, ::Any...)
   @ Base abstractarray.jl:3400
  push!(::BitVector, ::Any)
   @ Base bitarray.jl:752
  ...

Stacktrace:
 [1] Base.CyclePadding(T::DataType)
   @ Base ./reinterpretarray.jl:723
 [2] top-level scope
   @ REPL[11]:1

end
CyclePadding(pad, as)
end

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