Revert "pp_split: RXf_NULL branch [...]"

"pp_split: RXf_NULL branch - separate out (gimme_scalar), reduce
unnecessary work" was causing CPAN failures such as github #18188,
which appear to be down to a change of behaviour in 'split //, $s, 2'.

This reverts commit 59892837454d0ca367c3f7c83b2a646c57333b9a.

1 files changed, 53 insertions, 47 deletions

diff --git a/pp.c b/pp.c
index 06de4e688d..58181f4e35 100644
--- a/pp.c
+++ b/pp.c
@@ -6174,56 +6174,62 @@ PP(pp_split)
 	}
     }
     else if (RX_EXTFLAGS(rx) & RXf_NULL && !(s >= strend)) {
-        /* This case boils down to deciding which is the smaller of:
-         * limit - effectively a number of characters
-         * slen - which already contains the number of characters in s
-         *
-         * The resulting number is the number of iters (for gimme_scalar)
-         * or the number of SVs to create (!gimme_scalar). */
-
-        /* setting it to -1 will trigger a panic in EXTEND() */
-        const SSize_t sslen = slen > SSize_t_MAX ?  -1 : (SSize_t)slen;
-        /*limit is not needed later, so can clobber it here */
-        limit--;
-        if (sslen < limit || limit < 0) {
-            iters = slen -1;
-            limit = slen;
-            /* Note: The same result is returned if the following block
-             * is removed, because of the "keep field after final delim?"
-             * adjustment, but having the following makes the "correct"
-             * behaviour more apparent. */
-            if (gimme_scalar) {
-                s = strend;
-                iters++;
+        /*
+          Pre-extend the stack, either the number of bytes or
+          characters in the string or a limited amount, triggered by:
+
+          my ($x, $y) = split //, $str;
+            or
+          split //, $str, $i;
+        */
+	if (!gimme_scalar) {
+	    const IV items = limit - 1;
+            /* setting it to -1 will trigger a panic in EXTEND() */
+            const SSize_t sslen = slen > SSize_t_MAX ?  -1 : (SSize_t)slen;
+	    if (items >=0 && items < sslen)
+		EXTEND(SP, items);
+	    else
+		EXTEND(SP, sslen);
+	}
+
+        if (do_utf8) {
+            while (--limit) {
+                /* keep track of how many bytes we skip over */
+                m = s;
+                s += UTF8SKIP(s);
+		if (gimme_scalar) {
+		    iters++;
+		    if (s-m == 0)
+			trailing_empty++;
+		    else
+			trailing_empty = 0;
+		} else {
+		    dstr = newSVpvn_flags(m, s-m, SVf_UTF8 | make_mortal);
+
+		    PUSHs(dstr);
+		}
+
+                if (s >= strend)
+                    break;
             }
         } else {
-            iters = limit;
-        }
+            while (--limit) {
+	        if (gimme_scalar) {
+		    iters++;
+		} else {
+		    dstr = newSVpvn(s, 1);
 
-        if (!gimme_scalar) {
-            /*
-              Pre-extend the stack, either the number of bytes or
-              characters in the string or a limited amount, triggered by:
-
-              my ($x, $y) = split //, $str;
-                or
-              split //, $str, $i;
-            */
-            EXTEND(SP, limit);
-
-            if (do_utf8) {
-                while (--limit) {
-                    m = s;
-                    s += UTF8SKIP(s);
-                    dstr = newSVpvn_flags(m, s-m, SVf_UTF8 | make_mortal);
-                    PUSHs(dstr);
-                }
-            } else {
-                while (--limit) {
-                    dstr = newSVpvn_flags(s, 1, make_mortal);
-                    PUSHs(dstr);
-                    s++;
-                }
+
+		    if (make_mortal)
+			sv_2mortal(dstr);
+
+		    PUSHs(dstr);
+		}
+
+                s++;
+
+                if (s >= strend)
+                    break;
             }
         }
     }