Fix an invalid transformation by the optimizer. Introduced by #2811.

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);
+                /* If we jumped to popax instead of calling it as a subroutine,
-              CS_InsertEntry (S, X, I);
+                ** 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;
 

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;
+    }
+}
+