Fix an op undef error and add test

Author: chriselrod

Project.toml

@@ -1,7 +1,7 @@
 name = "LoopVectorization"
 uuid = "bdcacae8-1622-11e9-2a5c-532679323890"
 authors = ["Chris Elrod <[email protected]>"]
-version = "0.12.46"
+version = "0.12.47"
 
 [deps]
 ArrayInterface = "4fba245c-0d91-5ea0-9b3e-6abc04ee57a9"

src/modeling/graphs.jl

@@ -1413,7 +1413,7 @@ Returns `-1` if not an outerreduction.
 function isouterreduction(ls::LoopSet, op::Operation)
   if isconstant(op) # equivalent to checking if length(loopdependencies(op)) == 0
     instr = op.instruction
-    instr == LOOPCONSTANT && return 0
+    instr == LOOPCONSTANT && return Core.ifelse(length(loopdependencies(op)) == 0, 0, -1)
     instr.mod === GLOBALCONSTANT && return -1
     ops = operations(ls)
     for or ∈ ls.outer_reductions

test/outer_reductions.jl

@@ -54,9 +54,20 @@ function test_awmean(::Type{T}) where {T}
     end
 end
 
+function not_an_outer_reduct!(r, N::Int, x = 2.0, y= nothing) # there was a bug where this was classified as one
+  @turbo for i ∈ eachindex(r)
+    acc = y === nothing ? x : r[i]
+    for n ∈ 1:N
+      acc += 0
+    end
+    r[i] = acc
+  end
+  r
+end
 @testset "Outer Reductions" begin
   for T ∈ [Float32,Float64,Int32,Int64]
     test_awmean(T)
   end
+  @test all(==(7.4), not_an_outer_reduct!(Vector{Float64}(undef, 5), 17, 7.4))
 end