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-check-expr.cpp | 7 +++++++
 1 file changed, 7 insertions(+)

(limited to 'source/slang/slang-check-expr.cpp')

diff --git a/source/slang/slang-check-expr.cpp b/source/slang/slang-check-expr.cpp
index 4d36299bb..3072c3257 100644
--- a/source/slang/slang-check-expr.cpp
+++ b/source/slang/slang-check-expr.cpp
@@ -3242,6 +3242,13 @@ namespace Slang
         return expr;
     }
 
+    Expr* SemanticsExprVisitor::visitDetachExpr(DetachExpr* expr)
+    {
+        expr->inner = CheckTerm(expr->inner);
+        expr->type = expr->inner->type;
+        return expr;
+    }
+
 
     static bool _isSizeOfType(Type* type)
     {
-- 
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