Integrate/merge mainline with further efficiency tweak to sv.c's utf8 stuff.

p4raw-id: //depot/perlio@8093

diff --cc sv.c
index e29d1b4,e29d1b4..7c9c4db
--- 1/sv.c
--- 2/sv.c
+++ b/sv.c
@@@ -2390,36 -2390,36 +2390,37 @@@ Convert the PV of an SV to its UTF8-enc
  void
  Perl_sv_utf8_upgrade(pTHX_ register SV *sv)
  {
--    char *s, *t;
--    int hibit = FALSE;
++    char *s, *t, *e;
++    int  hibit = 0;
  
      if (!sv || !SvPOK(sv) || SvUTF8(sv))
        return;
  
      /* This function could be much more efficient if we had a FLAG in SVs
       * to signal if there are any hibit chars in the PV.
++     * Given that there isn't make loop fast as possible
       */
--    for (s = t = SvPVX(sv); t < SvEND(sv) && !hibit; t++) {
--      if (*t & 0x80) {
--          hibit = TRUE;
++    s = SvPVX(sv);
++    e = SvEND(sv);
++    t = s;
++    while (t < e) {
++      if ((hibit = *t++ & 0x80))
            break;
--      }
      }
  
      if (hibit) {
        STRLEN len;
        if (SvREADONLY(sv) && SvFAKE(sv)) {
--          Perl_warn(aTHX_ "%d s=%p t=%p e=%p",(int)hibit,s,t,SvEND(sv));
--          sv_dump(sv);
            sv_force_normal(sv);
            s = SvPVX(sv);
        }
        len = SvCUR(sv) + 1; /* Plus the \0 */
        SvPVX(sv) = (char*)bytes_to_utf8((U8*)s, &len);
        SvCUR(sv) = len - 1;
++      if (SvLEN(sv) != 0)
++          Safefree(s); /* No longer using what was there before. */
        SvLEN(sv) = len; /* No longer know the real size. */
        SvUTF8_on(sv);
--      Safefree(s); /* No longer using what was there before. */
      }
  }
  
@@@ -2482,6 -2482,6 +2483,7 @@@ Perl_sv_utf8_decode(pTHX_ register SV *
  {
      if (SvPOK(sv)) {
          char *c;
++        char *e;
          bool has_utf = FALSE;
          if (!sv_utf8_downgrade(sv, TRUE))
            return FALSE;
@@@ -2492,8 -2492,8 +2494,8 @@@
          c = SvPVX(sv);
        if (!is_utf8_string((U8*)c, SvCUR(sv)+1))
            return FALSE;
--
--        while (c < SvEND(sv)) {
++        e = SvEND(sv);
++        while (c < e) {
              if (*c++ & 0x80) {
                SvUTF8_on(sv);
                break;