From 380c3f810e87ab2ee26af7d4196e1d036dd08e1b Mon Sep 17 00:00:00 2001
From: Kugel Fuhr <98353208+kugelfuhr@users.noreply.github.com>
Date: Thu, 5 Mar 2026 18:38:34 +0100
Subject: [PATCH 1/2] Fix an invalid transformation by the optimizer.
 Introduced by #2811.

---
 src/cc65/coptmisc.c | 17 ++++++++++-------
 test/val/bug2937.c  | 27 +++++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 7 deletions(-)
 create mode 100644 test/val/bug2937.c

diff --git a/src/cc65/coptmisc.c b/src/cc65/coptmisc.c
index deca3fbe5..b9a018899 100644
--- a/src/cc65/coptmisc.c
+++ b/src/cc65/coptmisc.c
@@ -1213,21 +1213,24 @@ unsigned OptTosPushPop (CodeSeg* S)
         /* Get the next entry */
         const CodeEntry* E = CS_GetEntry (S, I);
 
-        /* Check for decspn, incspn, subysp or addysp */
+        /* Check for pushax/popax */
         if (CE_IsCallTo (E, "pushax")                              &&
             (N = CS_GetNextEntry (S, I)) != 0                      &&
             (CE_IsCallTo (N, "popax") || CE_IsJumpTo (N, "popax")) &&
             !CE_HasLabel (N)) {
 
-            /* Insert an rts if jmp popax */
             if (N->OPC == OP65_JMP) {
-              CodeEntry* X = NewCodeEntry (OP65_RTS, AM65_IMP, 0, 0, E->LI);
-              CS_InsertEntry (S, X, I);
+                /* If we jumped to popax instead of calling it as a subroutine,
+                ** add an RTS before removing the sequence.
+                */
+                CodeEntry* X = NewCodeEntry (OP65_RTS, AM65_IMP, 0, 0, E->LI);
+                CS_InsertEntry (S, X, I);
+                CS_DelEntries (S, I+1, 2);
+            } else {
+                /* Otherwise just remove the sequence */
+                CS_DelEntries (S, I, 2);
             }
 
-            /* Delete the old code */
-            CS_DelEntries (S, I+1, 2);
-
             /* Remember we had changes */
             ++Changes;
 
diff --git a/test/val/bug2937.c b/test/val/bug2937.c
new file mode 100644
index 000000000..57f6e927c
--- /dev/null
+++ b/test/val/bug2937.c
@@ -0,0 +1,27 @@
+/* Note: This test is rather fragile since it depends on how the compiler
+** handles certain sequences and return codes. It checks for exactly one
+** optimizer problem introduced in #2937. If it fails in some future version,
+** do not hesitate to remove it.
+*/
+
+#include <stdio.h>
+
+static unsigned char test(unsigned v)
+{
+    (void)v;
+    asm("jsr popax");
+    asm("lda #0");
+    return __A__;
+}
+
+int main(void)
+{
+    if (test(1)) {
+        printf("Test failed\n");
+        return 1;
+    } else {
+        printf("Test ok\n");
+        return 0;
+    }
+}
+

From 3d26a7e1febc0abed859b21c3ea1cc059f04d24e Mon Sep 17 00:00:00 2001
From: Kugel Fuhr <98353208+kugelfuhr@users.noreply.github.com>
Date: Thu, 5 Mar 2026 18:44:33 +0100
Subject: [PATCH 2/2] Correct test name and test comment.

---
 test/val/{bug2937.c => bug2811.c} | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
 rename test/val/{bug2937.c => bug2811.c} (88%)

diff --git a/test/val/bug2937.c b/test/val/bug2811.c
similarity index 88%
rename from test/val/bug2937.c
rename to test/val/bug2811.c
index 57f6e927c..8f0ff2e48 100644
--- a/test/val/bug2937.c
+++ b/test/val/bug2811.c
@@ -1,6 +1,6 @@
 /* Note: This test is rather fragile since it depends on how the compiler
 ** handles certain sequences and return codes. It checks for exactly one
-** optimizer problem introduced in #2937. If it fails in some future version,
+** optimizer problem introduced in #2811. If it fails in some future version,
 ** do not hesitate to remove it.
 */