Fix loop merge bookkeeping

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
 =====
 

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!

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;