fix a s/non-utf8/is-utf8/ bit of nastiness

Commit 3e462cdc2087ddf90984010fabd80c30db92bfa0 provided a fix
for the  s/non-utf8/is-utf8/ case by upgrading TARG to UTF8 after the
match, but before the substitution. It used sv_utf8_upgrade() rather than
sv_utf8_upgrade_nomg(), so for example, with a tied variable, FETCH would
get called again, and all the char* pointers such as s would be left
dangling. If the length of the string was unchanged, the code wouldn't
notice this.

Fix by using the _nomg() variant, and by checking whether the string
has been reallocated

1 files changed, 3 insertions, 2 deletions

diff --git a/pp_hot.c b/pp_hot.c
index 5a920d4d4d..7316c5aabb 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -2185,12 +2185,13 @@ PP(pp_subst)
 	 * http://www.nntp.perl.org/group/perl.perl5.porters/2010/04/msg158809.html
 	 */
 	if (matched && DO_UTF8(dstr) && ! DO_UTF8(TARG)) {
-	    const STRLEN new_len = sv_utf8_upgrade(TARG);
+	    char * const orig_pvx =  SvPVX(TARG);
+	    const STRLEN new_len = sv_utf8_upgrade_nomg(TARG);
 
 	    /* If the lengths are the same, the pattern contains only
 	     * invariants, can keep going; otherwise, various internal markers
 	     * could be off, so redo */
-	    if (new_len != len) {
+	    if (new_len != len || orig_pvx != SvPVX(TARG)) {
 		goto setup_match;
 	    }
 	}