From 945409c4c6871c18aad24086c594cc66b5913733 Mon Sep 17 00:00:00 2001
From: Sai Praveen Bangaru <31557731+saipraveenb25@users.noreply.github.com>
Date: Thu, 17 Aug 2023 14:45:13 -0400
Subject: Initial support for differentiating existential types (#3111)

* Merge

* WIP: Complete auto-diff logic for existential types

* Revert "Add compiler option for generating representative hash"

This reverts commit 13b09ef4621e73844c96d64d9c111a8ed0d45aae.

* More fixes for fwd-mode AD on existential types

* Add anyValueSize inference pass

* Fix checking of `Differential.Differential==Differential`

* In-progress: infer any-value-size for existential types

* Existentials now work in forward-mode

* Overhaul handling of existential AD types. Fwd-mode works, reverse-mode requires front-end changes

* Reverse-mode now works on existentials

* Cleanup

* Remove diff rules for create existential object for now

* Revert treat-as-differentiable changes

* Fixes

* More fixes

* Cleanup

* more cleanup

* signed/unsigned

* Revert "Cleanup"

This reverts commit e4f7d71f07bb207736f90708961eeecd09a1b652.

* Cleanup (again)

* Remove public/export/keep-alive on null differential after AD pass

* Minor fix

* Update dictionary accessors

* Keep export decoration

* More fixes + Support for `kIROp_PackAnyValue`

* Merge upstream

* Update expected-failure.txt
---
 source/slang/diff.meta.slang | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

(limited to 'source/slang/diff.meta.slang')

diff --git a/source/slang/diff.meta.slang b/source/slang/diff.meta.slang
index ce0e72d34..423b6bfd0 100644
--- a/source/slang/diff.meta.slang
+++ b/source/slang/diff.meta.slang
@@ -25,6 +25,30 @@ attribute_syntax [DerivativeMember(memberName)] : DerivativeMemberAttribute;
 __attributeTarget(FunctionDeclBase)
 attribute_syntax [NoDiffThis] : NoDiffThisAttribute;
 
+// A 'none-type' that acts as a run-time sentinel for zero differentials.
+public struct NullDifferential : IDifferentiable
+{ 
+    // for now, we'll use at least one field to make sure the type is non-empty
+    uint dummy;
+    typedef NullDifferential Differential;
+
+    [Differentiable]
+    [ForceInline]
+    static Differential dzero() { return { 0 }; }
+
+    [Differentiable]
+    [ForceInline]
+    static Differential dadd(Differential, Differential) { return { 0 }; }
+
+    [Differentiable]
+    [ForceInline]
+    static Differential dmul<T: __BuiltinRealType>(T, Differential) { return { 0 }; }
+};
+
+// Existential check for null differential type
+__intrinsic_op($(kIROp_IsDifferentialNull))
+bool isDifferentialNull(IDifferentiable obj);
+
 /// Represents a GPU view of a tensor.
 __generic<T>
 __magic_type(TensorViewType)
-- 
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