Make dss and weighted_dss no-ops for empty fields.

Author: sriharshakandala

src/Spaces/dss.jl

@@ -63,7 +63,9 @@ function create_dss_buffer(
     convert_to_array = DA isa Array ? false : true
     (_, _, _, Nv, nelems) = Base.size(data)
     Np = Spaces.nperimeter(perimeter)
-    Nf = cld(length(parent(data)), (Nij * Nij * Nv * nelems))
+    Nf =
+        length(parent(data)) == 0 ? 0 :
+        cld(length(parent(data)), (Nij * Nij * Nv * nelems))
     nfacedof = Nij - 2
     T = eltype(parent(data))
     TS = _transformed_type(data, local_geometry, local_weights, DA) # extract transformed type
@@ -269,6 +271,7 @@ function weighted_dss_start!(
     hspace::SpectralElementSpace2D{<:Topology2D},
     dss_buffer::DSSBuffer,
 )
+    length(parent(data)) == 0 && return nothing
     device = ClimaComms.device(hspace.topology)
     dss_transform!(
         device,
@@ -335,6 +338,7 @@ function weighted_dss_internal!(
     hspace::AbstractSpectralElementSpace,
     dss_buffer::Union{DSSBuffer, Nothing},
 )
+    length(parent(data)) == 0 && return nothing
     if hspace isa SpectralElementSpace1D
         dss_1d!(
             hspace.topology,
@@ -413,6 +417,7 @@ function weighted_dss_ghost!(
     hspace::SpectralElementSpace2D{<:Topology2D},
     dss_buffer::DSSBuffer,
 )
+    length(parent(data)) == 0 && return data
     device = ClimaComms.device(hspace.topology)
     ClimaComms.finish(dss_buffer.graph_context)
     load_from_recv_buffer!(device, dss_buffer)
@@ -1002,6 +1007,7 @@ end
 Computed unweighted/pure DSS of `data`.
 """
 function dss!(data, topology, quadrature_style)
+    length(parent(data)) == 0 && return nothing
     device = ClimaComms.device(topology)
     perimeter = Perimeter2D(Quadratures.degrees_of_freedom(quadrature_style))
     # create dss buffer

test/Spaces/ddss1.jl

@@ -2,7 +2,14 @@ using Logging
 using Test
 
 import ClimaCore:
-    Domains, Fields, Geometry, Meshes, Operators, Spaces, Topologies
+    Domains,
+    Fields,
+    Geometry,
+    Meshes,
+    Operators,
+    Spaces,
+    Topologies,
+    DataLayouts
 
 using ClimaComms
 const device = ClimaComms.device()
@@ -39,6 +46,9 @@ function distributed_space(
     return (space, context)
 end
 
+init_state_scalar(local_geometry, p) = (; ρ = 1.0)
+init_state_vector(local_geometry, p) = Geometry.Covariant12Vector(1.0, -1.0)
+
 #=
  _
 |1|
@@ -61,41 +71,54 @@ end
     @test Topologies.local_neighboring_elements(space.topology, 3) == [2, 4]
     @test Topologies.local_neighboring_elements(space.topology, 4) == [1, 3]
 
-    init_state(local_geometry, p) = (ρ = 1.0)
-    y0 = init_state.(Fields.local_geometry_field(space), Ref(nothing))
+    y0 = init_state_scalar.(Fields.local_geometry_field(space), Ref(nothing))
     nel = Topologies.nlocalelems(Spaces.topology(space))
     yarr = parent(y0)
     yarr .= reshape(1:(Nq * Nq * nel), (Nq, Nq, 1, nel))
 
-    dss2_buffer = Spaces.create_dss_buffer(y0)
-    Spaces.weighted_dss!(y0, dss2_buffer) # DSS2
+    dss_buffer = Spaces.create_dss_buffer(y0)
+    Spaces.weighted_dss!(y0, dss_buffer) # DSS2
 #! format: off
     @test Array(yarr[:]) == [18.5, 5.0, 9.5, 18.5, 5.0, 9.5, 18.5, 5.0, 9.5, 9.5, 
                              14.0, 18.5, 9.5, 14.0, 18.5, 9.5, 14.0, 18.5, 18.5, 
                              23.0, 27.5, 18.5, 23.0, 27.5, 18.5, 23.0, 27.5, 27.5, 
                              32.0, 18.5, 27.5, 32.0, 18.5, 27.5, 32.0, 18.5]
 #! format: on
 
-    p = @allocated Spaces.weighted_dss!(y0, dss2_buffer)
+    p = @allocated Spaces.weighted_dss!(y0, dss_buffer)
     @show p
     #=
     @test p == 0
     =#
 end
 
-@testset "4x1 element mesh on 2 processes - vector field" begin
+@testset "test if dss is no-op on an empty field" begin
+    Nq = 3
+    space, comms_ctx = distributed_space((4, 1), (true, true), (Nq, 1, 1))
+    y0 = init_state_scalar.(Fields.local_geometry_field(space), Ref(nothing))
+
+    dims = (Nq, Nq, 0, 4)
+    array = similar(parent(y0), dims)
+    data = DataLayouts.rebuild(Fields.field_values(y0), array)
+    space = axes(y0)
+    empty_field = similar(y0, Tuple{})
+    dss_buffer = Spaces.create_dss_buffer(empty_field)
+    @test empty_field == Spaces.weighted_dss!(empty_field)
+end
+
+
+@testset "4x1 element mesh on 1 process - vector field" begin
     Nq = 3
     space, comms_ctx = distributed_space((4, 1), (true, true), (Nq, 1, 2))
-    init_state(local_geometry, p) = Geometry.Covariant12Vector(1.0, -1.0)
-    y0 = init_state.(Fields.local_geometry_field(space), Ref(nothing))
+    y0 = init_state_vector.(Fields.local_geometry_field(space), Ref(nothing))
     yx = copy(y0)
 
-    dss2_buffer = Spaces.create_dss_buffer(y0)
-    Spaces.weighted_dss!(y0, dss2_buffer)
+    dss_buffer = Spaces.create_dss_buffer(y0)
+    Spaces.weighted_dss!(y0, dss_buffer)
 
     @test parent(yx) ≈ parent(y0)
 
-    p = @allocated Spaces.weighted_dss!(y0, dss2_buffer)
+    p = @allocated Spaces.weighted_dss!(y0, dss_buffer)
     @show p
     #@test p == 0
 end