This patch fixes the following bug:

$ awk 'BEGIN{s="";a[1]=7;split("",b,split("",a));print a[1]}'
7

--- gawk-3.1.1/field.c.orig	Mon May 13 14:56:04 2002
+++ gawk-3.1.1/field.c	Mon May 13 14:55:17 2002
@@ -855,6 +855,16 @@ do_split(NODE *tree)
 		 * Skip the work if first arg is the null string.
 		 * Check after clearing the array, to preserve
 		 * correct semantics.
+		 *
+		 * But if sep is not FS, evaluate it, since it may have
+		 * sideeffects.
+		 */
+		if ((sep->re_flags & FS_DFLT) == 0)
+			free_temp(tree_eval(sep->re_exp));
+		/*
+		 * FIXME: the above call should be also avoided in other
+		 * cases when it's clear that sep has no side effects.
+		 * (That would require an analysis during the compile time.)
 		 */
 		tmp = tmp_number((AWKNUM) 0);
 		goto out;