Transpiler having troubles with broadcast

[ChrisRackauckas]

uprev = GPUArray(rand(Float32, 32, 32))
k1 = GPUArray(rand(Float32, 32, 32))
k2 = GPUArray(rand(Float32, 32, 32))
k3 = GPUArray(rand(Float32, 32, 32))
k4 = GPUArray(rand(Float32, 32, 32))
dt = 1.2f0
b1 = 1.3f0
b2 = 1.4f0
b3 = 1.5f0
b4 = 1.6f0
utilde = similar(uprev)
@. utilde = uprev + dt*(b1*k1 + b2*k2 + b3*k3 + b4*k4)

OpenCL backend

[ChrisRackauckas]

Here's another expression where it has trouble:

@. u = uprev + dt*duprev + dt^2*(1//2*ku)

where dt is a scalar and the rest are matching GPUArrays.

[SimonDanisch]

The first one is pretty weird...
Seems to all work fine, but the return type of the broadcast lambda doesn't seem to propagate.

using Transpiler, Sugar, GPUArrays
lambda = getfield(Main, Symbol("##7#8")) # taken from backtrace
m = Transpiler.CLMethod((GPUArrays.broadcast_kernel!, Tuple{
    Float32, lambda,
    Transpiler.CLIntrinsics.CLArray{Float32,2}, Tuple{UInt32,UInt32}, UInt32,
    Tuple{GPUArrays.BroadcastDescriptorN{Array,2},GPUArrays.BroadcastDescriptorN{Any,0},
    GPUArrays.BroadcastDescriptorN{Any,0},GPUArrays.BroadcastDescriptorN{Array,2},
    GPUArrays.BroadcastDescriptorN{Any,0},GPUArrays.BroadcastDescriptorN{Array,2},
    GPUArrays.BroadcastDescriptorN{Any,0},GPUArrays.BroadcastDescriptorN{Array,2},
    GPUArrays.BroadcastDescriptorN{Any,0},GPUArrays.BroadcastDescriptorN{Array,2}},
    Transpiler.CLIntrinsics.CLArray{Float32,2},
    Float32,
    Float32,
    Transpiler.CLIntrinsics.CLArray{Float32,2},
    Float32,
    Transpiler.CLIntrinsics.CLArray{Float32,2},
    Float32, Transpiler.CLIntrinsics.CLArray{Float32,2},
    Float32, Transpiler.CLIntrinsics.CLArray{Float32,2}
}))

ci = code_typed(m.signature..., optimize=false)[1][1]
println(ci.code)

Variables:
  #self#::GPUArrays.#broadcast_kernel!
  state::Float32
  func::##7#8
  B::Transpiler.CLIntrinsics.CLArray{Float32,2}
  shape::Tuple{UInt32,UInt32}
  len::UInt32
  descriptor::Tuple{GPUArrays.BroadcastDescriptorN{Array,2},GPUArrays.BroadcastDescriptorN{Any,0},GPUArrays.BroadcastDescriptorN{Any,0},GPUArrays.BroadcastDescriptorN{Array,2},GPUArrays.BroadcastDescriptorN{Any,0},GPUArrays.BroadcastDescriptorN{Array,2},GPUArrays.BroadcastDescriptorN{Any,0},GPUArrays.BroadcastDescriptorN{Array,2},GPUArrays.BroadcastDescriptorN{Any,0},GPUArrays.BroadcastDescriptorN{Array,2}}
  A_1::Transpiler.CLIntrinsics.CLArray{Float32,2}
  A_2::Float32
  A_3::Float32
  A_4::Transpiler.CLIntrinsics.CLArray{Float32,2}
  A_5::Float32
  A_6::Transpiler.CLIntrinsics.CLArray{Float32,2}
  A_7::Float32
  A_8::Transpiler.CLIntrinsics.CLArray{Float32,2}
  A_9::Float32
  A_10::Transpiler.CLIntrinsics.CLArray{Float32,2}
  ilin::UInt32

Body:
  begin 
      SSAValue(2) = $(Expr(:invoke, MethodInstance for ret(::Type{UInt32}), :(Transpiler.CLIntrinsics.ret), :(Transpiler.CLIntrinsics.Cuint)))

      SSAValue(1) = (Base.checked_trunc_uint)(UInt32, 1)::UInt32
      ilin::UInt32 = (Base.add_int)(SSAValue(2), SSAValue(1))::UInt32 # line 149:
      unless (Base.ule_int)(ilin::UInt32, len::UInt32)::Bool goto 15 # line 150:

      SSAValue(0) = $(Expr(:invoke, MethodInstance for apply_broadcast(::UInt32, ::Float32, ::##7#8, ::Tuple{UInt32,UInt32}, ::UInt32, ::Tuple{GPUArrays.BroadcastDescriptorN{Array,2},GPUArrays.BroadcastDescriptorN{Any,0},GPUArrays.BroadcastDescriptorN{Any,0},GPUArrays.BroadcastDescriptorN{Array,2},GPUArrays.BroadcastDescriptorN{Any,0},GPUArrays.BroadcastDescriptorN{Array,2},GPUArrays.BroadcastDescriptorN{Any,0},GPUArrays.BroadcastDescriptorN{Array,2},GPUArrays.BroadcastDescriptorN{Any,0},GPUArrays.BroadcastDescriptorN{Array,2}}, ::Transpiler.CLIntrinsics.CLArray{Float32,2}, ::Float32, ::Float32, ::Transpiler.CLIntrinsics.CLArray{Float32,2}, ::Float32, ::Transpiler.CLIntrinsics.CLArray{Float32,2}, ::Float32, ::Transpiler.CLIntrinsics.CLArray{Float32,2}, ::Float32, ::Transpiler.CLIntrinsics.CLArray{Float32,2}), :(GPUArrays.apply_broadcast), :(ilin), :(state), :(func), :(shape), :(len), :(descriptor), :(A_1), :(A_2), :(A_3), :(A_4), :(A_5), :(A_6), :(A_7), :(A_8), :(A_9), :(A_10)))

      (GPUArrays.setindex!)(B::Transpiler.CLIntrinsics.CLArray{Float32,2}, SSAValue(0), ilin::UInt32)::ANY
      return
  end::Void

You can see that everything infers nicely, but:

call = ci.code[8].args[2]
m2 = Transpiler.CLMethod((GPUArrays.apply_broadcast,
    Tuple{map(x-> Sugar.expr_type(m, x), call.args[2:end])...}
))
Base.Core.Inference.return_type(m2.signature...) == Float32
# BUT:
Sugar.expr_type(m, SSAValue(0)) == Any # The variable that gets the call assigned

No idea why SSAValue(0) is inferred as Any.
Need to figure out if that's a problem with GPUArrays, or maybe even a corner case in type inference.

The second one is a classic break down of Transpiler.jl and can be worked around with:

u .= uprev .+ dt .* duprev .+ Float32(dt ^ 2) .* (Float32(Cint(1)//Cint(2)) .* ku)

I will see if I can fix that in Transpiler in the next days!
Btw, you should do these promotions/conversions before the broadcast call anyways, so that they don't happen in the hot loop.

[SimonDanisch]

Okay, 2 should be fixed, while I'm pretty sure that 1 is JuliaLang/julia#22255

[maleadt]

Transpiler is not maintained anymore.