lmul/rmul support for Diagonals (#671)

Author: kshyatt

src/host/linalg.jl

@@ -683,6 +683,7 @@ function generic_rmul!(X::AbstractArray, s::Number)
 end
 
 LinearAlgebra.rmul!(A::AbstractGPUArray, b::Number) = generic_rmul!(A, b)
+LinearAlgebra.rmul!(A::Diagonal{T, <:AbstractGPUArray}, b::Number) where {T} = generic_rmul!(A.diag, b)
 
 function generic_lmul!(s::Number, X::AbstractArray)
     @kernel function lmul_kernel!(X, s)
@@ -694,6 +695,7 @@ function generic_lmul!(s::Number, X::AbstractArray)
 end
 
 LinearAlgebra.lmul!(a::Number, B::AbstractGPUArray) = generic_lmul!(a, B)
+LinearAlgebra.lmul!(a::Number, B::Diagonal{T, <:AbstractGPUArray}) where {T} = generic_lmul!(a, B.diag)
 
 
 ## permutedims

test/testsuite/linalg.jl

@@ -437,6 +437,21 @@ end
         A_empty = randn(Float32, 0, 0)
         @test compare(f, AT, A_empty, d)
     end
+
+    @testset "rmul!/lmul! with diagonal and number" begin
+        n = 32
+        h_d = rand(Float32, n)
+        h_D = Diagonal(h_d)
+        d = AT(h_d)
+        D = Diagonal(d)
+        a = rand(Float32)
+        rmul!(D, a)
+        rmul!(h_D, a)
+        @test collect(D) ≈ h_D
+        lmul!(a, D)
+        lmul!(a, h_D)
+        @test collect(D) ≈ h_D
+    end
 end
 
 @testsuite "linalg/mul!/vector-matrix" (AT, eltypes)->begin