Specialize lu_instance for CuArray and add generic fallback

Author: YingboMa

src/ArrayInterface.jl

@@ -420,6 +420,13 @@ Return the number.
 """
 lu_instance(a::Number) = a
 
+"""
+    lu_instance(a::Any) -> lu(a, check=false)
+
+Return the number.
+"""
+lu_instance(a::Any) = lu(a, check=false)
+
 """
 safevec(v)
 
@@ -520,6 +527,10 @@ function __init__()
     @require Adapt="79e6a3ab-5dfb-504d-930d-738a2a938a0e" begin
       include("cuarrays.jl")
     end
+    @require DiffEqBase="2b5f629d-d688-5b77-993f-72d75c75574e" begin
+      # actually do QR
+      lu_instance(A::CuArrays.CuMatrix{T}) where T = CuArrays.CUSOLVER.CuQR(similar(A, 0, 0), similar(A, 0))
+    end
   end
 
   @require BandedMatrices="aae01518-5342-5314-be14-df237901396f" begin