Base.has_fast_linear_indexing needs a method for Ref

[chengchingwen]

has_fast_linear_indexingfor Broadcasted check all the arguments,

julia/base/reducedim.jl

Lines 194 to 198 in 58ffe7e

	has_fast_linear_indexing(a::AbstractArrayOrBroadcasted) = false
	has_fast_linear_indexing(a::Array) = true
	has_fast_linear_indexing(::Number) = true # for Broadcasted
	has_fast_linear_indexing(bc::Broadcast.Broadcasted) =
	all(has_fast_linear_indexing, bc.args)

but broadcasting literal_pow has Base.RefValue{typeof(^)}(^) and Base.RefValue{Val{2}}(Val{2}()) in its argument, which cause MethodError

MWE:

using LazyArrays
bc = @~ x .^ 2 # use LazyArrays to get the Broadcasted object
sum(bc, dims=1) # MethodError for has_fast_linear_indexing(::Base.RefValue{typeof(^)})

versioninfo:

julia> versioninfo()
Julia Version 1.6.1
Commit 6aaedecc44 (2021-04-23 05:59 UTC)
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: Intel(R) Core(TM) i7-7800X CPU @ 3.50GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-11.0.1 (ORCJIT, skylake-avx512)
Environment:
  JULIA_NUM_THREADS = 8

[stevengj]

Sounds like it need a method for RefValue? i.e. just add

has_fast_linear_indexing(bc::Ref) = true

(Note that if I add the above method, or just change your test case to bc = @~ x .+ 2 to avoid literal_pow, then sum(bc, dims=1) gives me a different MethodError, this time for reducedim_init on a Broadcasted object. But that's an unrelated problem—sum(bc, dims=1, init=0.0) succeeds. I see you already filed that as #41054.)

[stevengj]

(It doesn't seem related to literal_pow specifically, so I changed the issue title.)