From d40c143eb4f19f1dfd0d0dcf9b718be6e495ca27 Mon Sep 17 00:00:00 2001
From: Sai Praveen Bangaru <31557731+saipraveenb25@users.noreply.github.com>
Date: Tue, 27 Aug 2024 15:00:43 -0400
Subject: Explicitly detach derivative when forming a non-differentiable struct
 out of differentiable args (#4901)

* Explicitly detach derivative when forming a non-differentiable struct out of differentiable args

This fixes an issue where initializer lists get optimized out and lose information about non-differentiability.

There are 2 places where this could have been fixed:
1. When coercing initializer-list exprs, we can check for non-differentiable aggregate types and use a detach derivative on all the args.
2. Add an extra case in the peephole optimization step that adds detach-derivative when simplifying a make-struct of a non-differentiable type.

Even though solution 2 is more elegant, this PR goes with solution 1 simply to avoid having to use a differentiable-type-conformance-context that is used in the auto-diff IR passes to check for differentiability.

* Change test name + add expected vals
---
 source/slang/slang-ast-expr.h | 8 ++++++++
 1 file changed, 8 insertions(+)

(limited to 'source/slang/slang-ast-expr.h')

diff --git a/source/slang/slang-ast-expr.h b/source/slang/slang-ast-expr.h
index c07f7f5b9..f9b8831f1 100644
--- a/source/slang/slang-ast-expr.h
+++ b/source/slang/slang-ast-expr.h
@@ -544,6 +544,13 @@ class OpenRefExpr : public Expr
     Expr* innerExpr = nullptr;
 };
 
+class DetachExpr : public Expr
+{
+    SLANG_AST_CLASS(DetachExpr)
+
+    Expr* inner = nullptr;
+};
+
     /// Base class for higher-order function application
     /// Eg: foo(fn) where fn is a function expression.
     ///
@@ -563,6 +570,7 @@ class DifferentiateExpr : public HigherOrderInvokeExpr
 {
     SLANG_ABSTRACT_AST_CLASS(DifferentiateExpr)
 };
+
     /// An expression of the form `__fwd_diff(fn)` to access the 
     /// forward-mode derivative version of the function `fn`
     ///
-- 
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