Type instability for `PtrArray`s with `--check-bounds=no` and StrideArrays.jl (but not with StrideArraysCore.jl)

[sloede]

When using StrideArrays.jl with Julia v1.11 and --check-bounds=no, PtrArrays will cause a type instability that only manifests when loading StrideArrays.jl, but not when loading StrideArraysCore.jl.

I know all the arguments for and against --check-bounds=no, but this seems to me like it should work (or at least be fixable), which would likely mean that --check-bounds=no becomes usable again for us in Trixi-land...

MWE

For this I used Julia v1.11.3 on a Linux machine.

Install packages first with (only needed once)

julia --project=. --check-bounds=no -e 'using Pkg; Pkg.add(["StrideArrays", "StrideArraysCore"])'

This currently install StrideArrays.jl v0.1.29 with StrideArraysCore.jl v0.5.7.

Then, start the Julia REPL with julia --project=. --check-bounds=no and execute either

using StrideArraysCore: PtrArray, StaticInt

_u = zeros(1)
u = PtrArray(pointer(_u), (StaticInt(1),))

@code_warntype u[1]

or

using StrideArrays: PtrArray, StaticInt

_u = zeros(1)
u = PtrArray(pointer(_u), (StaticInt(1),))

@code_warntype u[1]

The first one (with StrideArraysCore.jl) will give you

MethodInstance for getindex(::PtrArray{Float64, 1, (1,), Tuple{StaticInt{1}}, Tuple{Nothing}, Tuple{StaticInt{1}}}, ::Int64)
  from getindex(A::PtrArray{T, 1}, i::Union{Int128, Int16, Int32, Int64, Int8, UInt128, UInt16, UInt32, UInt64, UInt8, StaticInt}) where T @ StrideArraysCore ~/.julia/packages/StrideArraysCore/Yyyvt/src/ptr_array.jl:1035
Static Parameters
  T = Float64
Arguments
  #self#::Core.Const(getindex)
  A::PtrArray{Float64, 1, (1,), Tuple{StaticInt{1}}, Tuple{Nothing}, Tuple{StaticInt{1}}}
  i::Int64
Body::Float64
1 ─      nothing
│   %2 = $(Expr(:boundscheck))::Bool
└──      goto #3 if not %2
2 ─ %4 = StrideArraysCore.checkbounds::Core.Const(checkbounds)
└──      (%4)(A, i)
3 ┄ %6 = StrideArraysCore.unsafe_getindex(A, i)::Float64
└──      return %6

while the second one will give you

MethodInstance for getindex(::PtrArray{Float64, 1, (1,), Tuple{StaticInt{1}}, Tuple{Nothing}, Tuple{StaticInt{1}}}, ::Int64)
  from getindex(A::PtrArray{T, 1}, i::Union{Int128, Int16, Int32, Int64, Int8, UInt128, UInt16, UInt32, UInt64, UInt8, StaticInt}) where T @ StrideArraysCore ~/.julia/packages/StrideArraysCore/Yyyvt/src/ptr_array.jl:1035
Static Parameters
  T = Float64
Arguments
  #self#::Core.Const(getindex)
  A::PtrArray{Float64, 1, (1,), Tuple{StaticInt{1}}, Tuple{Nothing}, Tuple{StaticInt{1}}}
  i::Int64
Body::Any
1 ─      nothing
│   %2 = $(Expr(:boundscheck))::Bool
└──      goto #3 if not %2
2 ─ %4 = StrideArraysCore.checkbounds::Core.Const(checkbounds)
└──      (%4)(A, i)
3 ┄ %6 = StrideArraysCore.unsafe_getindex(A, i)::Any
└──      return %6

That is, in the second version StrideArraysCore.unsafe_getindex(A, i)::Any is type unstable.

Note that you need to execute Julia in between, since once you've loaded StrideArrays.jl, there's no going back.

[ranocha]

This seems to be basically JuliaLang/julia#50985

[ranocha]

Loading StrideArrays.jl makes the final pointer arithmetic in StrideArraysCore.unsafe_getindex(u, 1) type unstable - I guess since some new methods are added and heuristics drop inferring further.

[sloede]

This seems to be basically JuliaLang/julia#50985

🤦 I guess it would have been sensible to check that first. However, given that I posted this already 1.5 years ago, I really didn't have it on the radar anymore :-/