Make ArrayExpressionType a DeclRefType and define its autodiff extension in stdlib. (#2615)

* Allow array parameters in forward diff.

* Use type canonicalization instead of coersion.

* Reimplement array type.

* Fix.

* Update test case.

---------

Co-authored-by: Yong He <yhe@nvidia.com>

1 files changed, 35 insertions, 0 deletions

diff --git a/source/slang/diff.meta.slang b/source/slang/diff.meta.slang
index c732d1a5e..adbf8ae48 100644
--- a/source/slang/diff.meta.slang
+++ b/source/slang/diff.meta.slang
@@ -127,6 +127,41 @@ void updatePair<T : IDifferentiable>(inout DifferentialPair<T> p, T newPrimal, T
     p = DifferentialPair<T>(newPrimal, newDiff);
 }
 
+__generic<T, let N:int>
+__intrinsic_op($(kIROp_MakeArrayFromElement))
+Array<T,N> makeArrayFromElement(T element);
+
+
+__generic<T:IDifferentiable, let N:int>
+extension Array<T, N> : IDifferentiable
+{
+    typedef Array<T.Differential, N> Differential;
+
+    [__unsafeForceInlineEarly]
+    static Differential dzero()
+    {
+        return makeArrayFromElement<T.Differential, N>(T.dzero());
+    }
+
+    [__unsafeForceInlineEarly]
+    static Differential dadd(Differential a, Differential b)
+    {
+        Array<T.Differential, N> result;
+        for (int i = 0; i < N; i++)
+            result[i] = T.dadd(a[i], b[i]);
+        return result;
+    }
+
+    [__unsafeForceInlineEarly]
+    static Differential dmul(This a, Differential b)
+    {
+        Array<T.Differential, N> result;
+        for (int i = 0; i < N; i++)
+            result[i] = T.dmul(a[i], b[i]);
+        return result;
+    }
+}
+
 // vector-matrix
 __generic<T : __BuiltinFloatingPointType, let N : int, let M : int>
 [ForceInline]