Calling sv_backoff() on something that's about to be free()d will

memmov() memory that's about to be freed. Seems wasteful.

p4raw-id: //depot/perl@24344

diff --git a/sv.c b/sv.c
index 0757341..5353df2 100644 (file)
--- a/sv.c
+++ b/sv.c
@@ -4416,9 +4416,16 @@ Perl_sv_setsv_flags(pTHX_ SV *dstr, register SV *sstr, I32 flags)
                return;
            }
            if (SvPVX(dstr)) {
-               (void)SvOOK_off(dstr);          /* backoff */
-               if (SvLEN(dstr))
-                   Safefree(SvPVX(dstr));
+               if (SvLEN(dstr)) {
+                   /* Unwrap the OOK offset by hand, to save a needless
+                      memmove on memory that's about to be free()d.  */
+                   char *pv = SvPVX(dstr);
+                   if (SvOOK(dstr)) {
+                       pv -= SvIVX(dstr);
+                       SvFLAGS(dstr) &= ~SVf_OOK;
+                   }
+                   Safefree(pv);
+               }
                SvLEN_set(dstr, 0);
                 SvCUR_set(dstr, 0);
            }
@@ -5945,7 +5952,11 @@ Perl_sv_clear(pTHX_ register SV *sv)
     case SVt_PVNV:
     case SVt_PVIV:
       freescalar:
-       SvOOK_off(sv);
+       /* Don't bother with SvOOK_off(sv); as we're only going to free it.  */
+       if (SvOOK(sv)) {
+           SvPV_set(sv, SvPVX(sv) - SvIVX(sv));
+           /* Don't even bother with turning off the OOK flag.  */
+       }
        /* FALL THROUGH */
     case SVt_PV:
     case SVt_RV: