Backport fix for what may be a memory-alignment issue?

[timholy]

Does anyone happen to know which PR likely fixed this, and whether it's backportable? I can do a bisect if it would be helpful.

julia> using Images

julia> input = Matrix{RGB{N0f8}}(undef, 5, 5);

julia> fill!(input, RGB(0, 0, 0));

julia> useother = trues(size(input));

julia> function transfermask(input, useother, othervalue)
           combined = similar(input)
           for idx in eachindex(combined)
               combined[idx] = ifelse(
                   useother[idx],
                   RGB{Float64}(othervalue),
                   input[idx]
               )
           end
           return combined
       end
transfermask (generic function with 1 method)

Buggy result (at least julia 1.0.5 and julia 1.2.0, maybe others):

julia> transfermask(input, useother, RGB{N0f8}(1.0,1.0,1.0))
5×5 Array{RGB{N0f8},2} with eltype RGB{Normed{UInt8,8}}:
 RGB{N0f8}(1.0,0.0,0.0)  RGB{N0f8}(1.0,0.0,0.0)  RGB{N0f8}(1.0,0.0,0.0)  RGB{N0f8}(1.0,0.0,0.0)  RGB{N0f8}(1.0,0.0,0.0)
 RGB{N0f8}(1.0,0.0,0.0)  RGB{N0f8}(1.0,0.0,0.0)  RGB{N0f8}(1.0,0.0,0.0)  RGB{N0f8}(1.0,0.0,0.0)  RGB{N0f8}(1.0,0.0,0.0)
 RGB{N0f8}(1.0,0.0,0.0)  RGB{N0f8}(1.0,0.0,0.0)  RGB{N0f8}(1.0,0.0,0.0)  RGB{N0f8}(1.0,0.0,0.0)  RGB{N0f8}(1.0,0.0,0.0)
 RGB{N0f8}(1.0,0.0,0.0)  RGB{N0f8}(1.0,0.0,0.0)  RGB{N0f8}(1.0,0.0,0.0)  RGB{N0f8}(1.0,0.0,0.0)  RGB{N0f8}(1.0,0.0,0.0)
 RGB{N0f8}(1.0,0.0,0.0)  RGB{N0f8}(1.0,0.0,0.0)  RGB{N0f8}(1.0,0.0,0.0)  RGB{N0f8}(1.0,0.0,0.0)  RGB{N0f8}(1.0,0.0,0.0)

Correct result (at least 1.3.1 and master, maybe others):

julia> transfermask(input, useother, RGB{N0f8}(1.0,1.0,1.0))
5×5 Array{RGB{N0f8},2} with eltype RGB{Normed{UInt8,8}}:
 RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)
 RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)
 RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)
 RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)
 RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)

xref JuliaImages/Images.jl#814

[vtjnash]

#33706 perhaps?

[kimikage]

I'm not familiar with LLVM, so I'm not sure #33706 is exactly what we are looking for.
FWIW, the following tests are all passed even on v1.0.5:

julia/test/compiler/codegen.jl

Lines 422 to 428 in 53ba0cc

	# issue 33590
	function f33590(b, x)
	y = b ? nothing : (x[1] + 1,)
	return something(ifelse(b, x, y))
	end
	@test f33590(true, (3,)) == (3,)
	@test f33590(false, (3,)) == (4,)

Also, FWIW, the following is a minimal code without Images.jl.

julia> Float64[ifelse(i > 1, 2//3, -1.0) for i=1:2] # v1.3.1 (or v1.3.0)
2-element Array{Float64,1}:
 -1.0
  0.6666666666666666

julia> Float64[ifelse(i > 1, 2//3, -1.0) for i=1:2] # v1.0.5 (the result depends on the uninitialized stack)
2-element Array{Float64,1}:
 -1.0
  0.9976410051612077

[galenlynch]

Array assignment isn't necessary to get strange behavior:

julia> for i = 1:2 # julia1.2
       display(ifelse(i > 1, 1//3, -1.0))
       end
-1.0
1//140412727051408

[kimikage]

You are right. I just thought it would be better not to depend on Images.jl, if someone runs the bisect. There are no further implications. 😄

[galenlynch]

The buggy display behavior seems to happen in Julia 1.0.5 as well

[timholy]

I tried applying #33706 to release-1.2 but it doesn't apply cleanly.

[kimikage]

It might be a good idea to resolve it as a part of #34011.
I'm sorry I cannot be of any help due to insufficient resources.

[brenhinkeller]

Looks like it has been long enough that a backport is presumably no longer relevant. Can confirm we're still getting the correct behaviour nowadays on 1.8.3:

julia> transfermask(input, useother, RGB{N0f8}(1.0,1.0,1.0))
5×5 Array{RGB{N0f8},2} with eltype RGB{N0f8}:
 RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)
 RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)
 RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)
 RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)
 RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)  RGB{N0f8}(1.0,1.0,1.0)