https://sourceforge.net/p/sdcc/bugs/4153/

Index: src/mcs51/ralloc.c
===================================================================
--- src/mcs51/ralloc.c	(revision 17011)
+++ src/mcs51/ralloc.c	(working copy)
@@ -1208,7 +1208,7 @@
   int change = 0;
 
   /* if the result has been spilt then cannot share */
-  if (opsym->isspilt)
+  if (result->isspilt || opsym->isspilt)
     return 0;
 
   for (;;)