Add support for unevaluated compute! functions

`LazyBroadcast.jl` provides a way to return an unevaluated function.
This is useful in two cases:
1. reduce code verbosity to handle the `isnothing(out)` case
2. allow clustering all the broadcasted expressions in a single place

In turn, 2. is useful because it is the first step in fusing different
broadcasted calls.

This commit adds support for such functions.

Project.toml

@@ -20,6 +20,7 @@ ClimaCore = "0.13.4, 0.14"
 ClimaTimeSteppers = "0.7.10"
 Dates = "1"
 Documenter = "1"
+LazyBroadcast = "0.1.3"
 JuliaFormatter = "1"
 NCDatasets = "0.13.1, 0.14"
 Profile = "1"
@@ -35,10 +36,11 @@ BenchmarkTools = "6e4b80f9-dd63-53aa-95a3-0cdb28fa8baf"
 ClimaTimeSteppers = "595c0a79-7f3d-439a-bc5a-b232dc3bde79"
 Documenter = "e30172f5-a6a5-5a46-863b-614d45cd2de4"
 JuliaFormatter = "98e50ef6-434e-11e9-1051-2b60c6c9e899"
+LazyBroadcast = "9dccce8e-a116-406d-9fcc-a88ed4f510c8"
 Profile = "9abbd945-dff8-562f-b5e8-e1ebf5ef1b79"
 ProfileCanvas = "efd6af41-a80b-495e-886c-e51b0c7d77a3"
 SafeTestsets = "1bc83da4-3b8d-516f-aca4-4fe02f6d838f"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
-test = ["Aqua", "BenchmarkTools", "ClimaTimeSteppers", "Documenter", "JuliaFormatter", "Profile", "ProfileCanvas", "SafeTestsets", "Test"]
+test = ["Aqua", "BenchmarkTools", "ClimaTimeSteppers", "Documenter", "JuliaFormatter", "LazyBroadcast", "Profile", "ProfileCanvas", "SafeTestsets", "Test"]

src/clima_diagnostics.jl

@@ -18,6 +18,7 @@ struct DiagnosticsHandler{
     STORAGE <: Dict,
     ACC <: Dict,
     COUNT <: Dict,
+    BROAD <: Dict,
 }
     """An iterable with the `ScheduledDiagnostic`s that are scheduled."""
     scheduled_diagnostics::SD
@@ -34,6 +35,11 @@ struct DiagnosticsHandler{
     many times the given diagnostics was computed from the last time it was output to
     disk."""
     counters::COUNT
+
+    """Dictionary that maps a given `ScheduledDiagnostic` to a Base.Broadcast.Broadcasted
+    expression. This is used to allow lazy evaluation of expressions, which can lead to
+    reduce code verbosity and improved performance."""
+    broadcasted_expressions::BROAD
 end
 
 """
@@ -57,9 +63,11 @@ function DiagnosticsHandler(scheduled_diagnostics, Y, p, t; dt = nothing)
 
     # For diagnostics that perform reductions, the storage is used for the values computed
     # at each call. Reductions also save the accumulated value in accumulators.
+    # broadcasted_expressions maps diagnostics with LazyBroadcast objects.
     storage = Dict()
     accumulators = Dict()
     counters = Dict()
+    broadcasted_expressions = Dict()
 
     unique_scheduled_diagnostics = Tuple(unique(scheduled_diagnostics))
     if length(unique_scheduled_diagnostics) != length(scheduled_diagnostics)
@@ -90,8 +98,18 @@ function DiagnosticsHandler(scheduled_diagnostics, Y, p, t; dt = nothing)
         isa_time_reduction = !isnothing(diag.reduction_time_func)
 
         # The first time we call compute! we use its return value. All the subsequent times
-        # (in the callbacks), we will write the result in place
-        storage[diag] = variable.compute!(nothing, Y, p, t)
+        # (in the callbacks), we will write the result in place. ClimaDiagnostics supports
+        # LazyBroadcast.jl. In this case, the return value of `compute!` is a
+        # `Base.Broadcast.Broadcasted` and we have to manually materialize the result.
+        out_or_broadcasted_expr = variable.compute!(nothing, Y, p, t)
+        if out_or_broadcasted_expr isa Base.Broadcast.Broadcasted
+            broadcasted_expressions[diag] = out_or_broadcasted_expr
+            storage[diag] =
+                Base.Broadcast.materialize(broadcasted_expressions[diag])
+        else
+            storage[diag] = out_or_broadcasted_expr
+        end
+
         counters[diag] = 1
 
         # If it is not a reduction, call the output writer as well
@@ -115,6 +133,7 @@ function DiagnosticsHandler(scheduled_diagnostics, Y, p, t; dt = nothing)
         storage,
         accumulators,
         counters,
+        broadcasted_expressions,
     )
 end
 
@@ -153,13 +172,40 @@ function orchestrate_diagnostics(
         active_compute[diag_index] || continue
         diag = scheduled_diagnostics[diag_index]
 
-        diag.variable.compute!(
+        diagnostic_handler.counters[diag] += 1
+
+        # ClimaDiagnostics supports LazyBroadcast.jl. When used, the return value of
+        # `compute!` is a `Base.Broadcast.Broadcasted`. We materialize the output to
+        # diagnostic_handler.storage[diag] in the next for loop.
+
+        out_or_broadcasted_expr = diag.variable.compute!(
             diagnostic_handler.storage[diag],
             integrator.u,
             integrator.p,
             integrator.t,
         )
-        diagnostic_handler.counters[diag] += 1
+        if out_or_broadcasted_expr isa Base.Broadcast.Broadcasted
+            diagnostic_handler.broadcasted_expressions[diag] =
+                out_or_broadcasted_expr
+        end
+    end
+
+    # Evaluate the lazy compute (aka, materialize everything)
+    for diag_index in 1:length(scheduled_diagnostics)
+        active_compute[diag_index] || continue
+        diag = scheduled_diagnostics[diag_index]
+        haskey(diagnostic_handler.broadcasted_expressions, diag) || continue
+
+        Base.Broadcast.materialize!(
+            diagnostic_handler.storage[diag],
+            diagnostic_handler.broadcasted_expressions[diag],
+        )
+    end
+
+    # Process possible time reductions (now we have evaluated storage[diag])
+    for diag_index in 1:length(scheduled_diagnostics)
+        active_compute[diag_index] || continue
+        diag = scheduled_diagnostics[diag_index]
 
         isa_time_reduction = !isnothing(diag.reduction_time_func)
         if isa_time_reduction

test/integration_test.jl

@@ -12,6 +12,8 @@ import ClimaComms
     ClimaComms.@import_required_backends
 end
 
+import LazyBroadcast: @lazy
+
 const context = ClimaComms.context()
 ClimaComms.init(context)
 
@@ -41,7 +43,15 @@ function setup_integrator(output_dir; context, more_compute_diagnostics = 0)
     )
 
     function compute_my_var!(out, u, p, t)
-        ClimaDiagnostics.@assign out copy(u.my_var)
+        if isnothing(out)
+            return copy(u.my_var)
+        else
+            out .= u.my_var
+        end
+    end
+
+    function compute_my_var_lazy!(out, u, p, t)
+        return @lazy @. out = copy(u.my_var)
     end
 
     simple_var = ClimaDiagnostics.DiagnosticVariable(;
@@ -50,6 +60,12 @@ function setup_integrator(output_dir; context, more_compute_diagnostics = 0)
         long_name = "YO YO",
     )
 
+    simple_var_lazy = ClimaDiagnostics.DiagnosticVariable(;
+        compute! = compute_my_var_lazy!,
+        short_name = "YO LAZY",
+        long_name = "YO YO LAZY",
+    )
+
     average_diagnostic = ClimaDiagnostics.ScheduledDiagnostic(
         variable = simple_var,
         output_writer = nc_writer,
@@ -61,6 +77,10 @@ function setup_integrator(output_dir; context, more_compute_diagnostics = 0)
         variable = simple_var,
         output_writer = nc_writer,
     )
+    inst_diagnostic_lazy = ClimaDiagnostics.ScheduledDiagnostic(
+        variable = simple_var_lazy,
+        output_writer = nc_writer,
+    )
     inst_every3s_diagnostic = ClimaDiagnostics.ScheduledDiagnostic(
         variable = simple_var,
         output_writer = nc_writer,
@@ -76,6 +96,7 @@ function setup_integrator(output_dir; context, more_compute_diagnostics = 0)
     scheduled_diagnostics = [
         average_diagnostic,
         inst_diagnostic,
+        inst_diagnostic_lazy,
         inst_diagnostic_h5,
         inst_every3s_diagnostic,
     ]