datadeps: Support field access in Deps

docs/src/datadeps.md

@@ -179,9 +179,20 @@ Dagger.spawn_datadeps() do
 end
 ```
 
-You can pass any number of aliasing modifiers to `Deps`. This is particularly
-useful for declaring aliasing with `Diagonal`, `Bidiagonal`, `Tridiagonal`, and
-`SymTridiagonal` access, as these "wrappers" make a copy of their parent array
-and thus can't be used to "mask" access to the parent like `UpperTriangular`
-and `UnitLowerTriangular` can (which is valuable for writing memory-efficient,
-generic algorithms in Julia).
+We call `InOut(Diagonal)` an "aliasing modifier". The purpose of `Deps` is to
+pass an argument (here, `A`) as-is, while specifying to Datadeps what portions
+of the argument will be accessed (in this case, the diagonal elements) and how
+(read/write/both). You can pass any number of aliasing modifiers to `Deps`.
+
+`Deps` is particularly useful for declaring aliasing with `Diagonal`,
+`Bidiagonal`, `Tridiagonal`, and `SymTridiagonal` access, as these "wrappers"
+make a copy of their parent array and thus can't be used to "mask" access to the
+parent like `UpperTriangular` and `UnitLowerTriangular` can (which is valuable
+for writing memory-efficient, generic algorithms in Julia).
+
+### Supported Aliasing Modifiers
+
+- Any function that returns the original object or a view of the original object
+- `UpperTriangular`/`LowerTriangular`/`UnitUpperTriangular`/`UnitLowerTriangular`
+- `Diagonal`/`Bidiagonal`/`Tridiagonal`/`SymTridiagonal` (via `Deps`, e.g. to read from the diagonal of `X`: `Dagger.@spawn sum(Deps(X, In(Diagonal)))`)
+- `Symbol` for field access (via `Deps`, e.g. to write to `X.value`: `Dagger.@spawn setindex!(Deps(X, InOut(:value)), :value, 42)`

src/memory-spaces.jl

@@ -162,7 +162,12 @@ function memory_spans(oa::ObjectAliasing)
     return [span]
 end
 
-aliasing(x, T) = aliasing(T(x))
+function aliasing(x, dep_mod)
+    if dep_mod isa Symbol
+        return aliasing(getfield(x, dep_mod))
+    end
+    return aliasing(dep_mod(x))
+end
 function aliasing(x::T) where T
     if isbits(x)
         return NoAliasing()

test/datadeps.jl

@@ -109,6 +109,7 @@ function test_task_dominators(logs::Dict, tid::Int, doms::Vector; all_tids::Vect
 end
 
 @everywhere do_nothing(Xs...) = nothing
+@everywhere mut_ref!(R) = (R[] .= 0;)
 function test_datadeps(;args_chunks::Bool,
                         args_thunks::Bool,
                         args_loc::Int,
@@ -425,10 +426,17 @@ function test_datadeps(;args_chunks::Bool,
     end
 
     # Inner Scope
-    @test_throws Dagger.Sch.SchedulingException Dagger.spawn_datadeps() do 
+    @test_throws Dagger.Sch.SchedulingException Dagger.spawn_datadeps() do
         Dagger.@spawn scope=Dagger.ExactScope(Dagger.ThreadProc(1, 5000)) 1+1
     end
 
+    # Field aliasing
+    X = Ref(rand(1000))
+    @test all(x->x==0, fetch(Dagger.spawn_datadeps() do
+        Dagger.@spawn mut_ref!(Deps(X, InOut(:x)))
+        Dagger.@spawn getfield(Deps(X, In(:x)), :x)
+    end))
+
     # Add-to-copy
     A = rand(1000)
     B = rand(1000)