From acd0c076aa17e7b799f6079529afba045b138b61 Mon Sep 17 00:00:00 2001
From: "Peter S. Housel" <housel@acm.org>
Date: Fri, 28 Jun 2024 21:49:52 -0700
Subject: [PATCH 1/3] dfmc-flow-graph: Properly maintain loop merge bookkeeping

* sources/dfmc/flow-graph/utilities.dylan
  (delete-computation! on <loop-merge>): Override to properly remove
   dead loop merges from the auxiliary collections kept within <loop>
   and <loop-call> nodes.
---
 sources/dfmc/flow-graph/utilities.dylan | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/sources/dfmc/flow-graph/utilities.dylan b/sources/dfmc/flow-graph/utilities.dylan
index 7b75616b9f..f7569c78eb 100644
--- a/sources/dfmc/flow-graph/utilities.dylan
+++ b/sources/dfmc/flow-graph/utilities.dylan
@@ -436,6 +436,14 @@ define method delete-computation! (c :: <unwind-protect>) => ();
   remove-computation-references!(c);
 end method;
 
+define method delete-computation! (c :: <loop-merge>) => ();
+  let loop :: <loop> = c.loop-merge-loop;
+  loop.loop-merges := remove!(loop.loop-merges, c);
+  let loop-call :: <loop-call> = c.loop-merge-call;
+  loop-call.loop-call-merges := remove!(loop-call.loop-call-merges, c);
+  next-method();
+end method;
+
 //// multiple computation interfaces
 
 define method insert-computations-after!

From 2b11414374ecb17bc8b6712982081b9531dd8851 Mon Sep 17 00:00:00 2001
From: "Peter S. Housel" <housel@acm.org>
Date: Fri, 28 Jun 2024 23:04:40 -0700
Subject: [PATCH 2/3] dylan-test-suite: Add a test for issue 1523

This adds a regression test for issue 1523, a compilation failure that
occurrs when loop merges are deleted as dead code.

* sources/dylan/tests/regressions.dylan (test issue-1523): New test
  with a loop merge eligible for deletion.
---
 sources/dylan/tests/regressions.dylan | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/sources/dylan/tests/regressions.dylan b/sources/dylan/tests/regressions.dylan
index c95cde3c19..d985d9b540 100644
--- a/sources/dylan/tests/regressions.dylan
+++ b/sources/dylan/tests/regressions.dylan
@@ -276,6 +276,20 @@ define test issue-1455 ()
   check-true("no other values were returned", empty?(more));
 end;
 
+define test issue-1523 ()
+  // Loop merge for a can be eliminated as dead code
+  let value
+    = iterate loop (a = #f, b = 1)
+        if (b == 3)
+          b
+        else
+          loop(b, b + 1)
+        end
+      end;
+  check-equal("Loop with dead iteration variables executes properly",
+              value, 3);
+end;
+
 define suite dylan-regressions-test-suite ()
   test bug-2766;
   test bug-5800;
@@ -299,4 +313,5 @@ define suite dylan-regressions-test-suite ()
   test issue-1091;
   test issue-1095;
   test issue-1455;
+  test issue-1523;
 end suite;

From f05ba9e551bd70ccea04e434cc5fb2ea2474ec51 Mon Sep 17 00:00:00 2001
From: "Peter S. Housel" <housel@acm.org>
Date: Sat, 29 Jun 2024 11:00:48 -0700
Subject: [PATCH 3/3] release-notes: Add entry for issue 1523 fix

---
 documentation/source/release-notes/2024.2.rst | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/documentation/source/release-notes/2024.2.rst b/documentation/source/release-notes/2024.2.rst
index c9562928ee..9f43db4161 100644
--- a/documentation/source/release-notes/2024.2.rst
+++ b/documentation/source/release-notes/2024.2.rst
@@ -39,6 +39,9 @@ Compiler
   the comparison can now be properly inlined because the first
   argument to :drm:`min` is known to be an :drm:`<integer>`.
 
+* `Issue 1523 <https://github.com/dylan-lang/opendylan/issues/1523>`_, which
+  could result in a compiler abort during code generation, has been fixed.
+
 Tools
 =====