Dedicated SV copying code in place of Perl_sv_setsv_flags

av.c

@@ -475,6 +475,8 @@ Perl_av_make(pTHX_ SSize_t size, SV **strp)
         AvALLOC(av) = ary;
         AvARRAY(av) = ary;
         AvMAX(av) = size - 1;
+        SSize_t *fillp = &AvFILLp(av);
+
         /* avoid av being leaked if croak when calling magic below */
         EXTEND_MORTAL(1);
         PL_tmps_stack[++PL_tmps_ix] = (SV*)av;
@@ -486,12 +488,8 @@ Perl_av_make(pTHX_ SSize_t size, SV **strp)
             /* Don't let sv_setsv swipe, since our source array might
                have multiple references to the same temp scalar (e.g.
                from a list slice) */
-
-            SvGETMAGIC(*strp); /* before newSV, in case it dies */
-            AvFILLp(av)++;
-            ary[i] = newSV_type(SVt_NULL);
-            sv_setsv_flags(ary[i], *strp,
-                           SV_DO_COW_SVSETSV|SV_NOSTEAL);
+            ary[i] = newSVsv_flags(*strp, SV_DO_COW_SVSETSV|SV_NOSTEAL|SV_GMAGIC);
+            *fillp = i;
             strp++;
         }
         /* disarm av's leak guard */

embed.fnc

@@ -2347,7 +2347,10 @@ ARdp	|OP *	|newSVREF	|NN OP *o
 Adp	|SV *	|newSVrv	|NN SV * const rv			\
 				|NULLOK const char * const classname
 ARdmp	|SV *	|newSVsv	|NULLOK SV * const old
-ARdp	|SV *	|newSVsv_flags	|NULLOK SV * const old			\
+ARdip	|SV *	|newSVsv_flags	|NULLOK SV * const old			\
+				|I32 flags
+ARdp	|SV *	|newSVsv_flags_NN					\
+				|NN SV * const old			\
 				|I32 flags
 ARdmp	|SV *	|newSVsv_nomg	|NULLOK SV * const old
 ARdp	|SV *	|newSV_true

embed.h

@@ -462,6 +462,7 @@
 # define newSVpvz(a)                            Perl_newSVpvz(aTHX_ a)
 # define newSVrv(a,b)                           Perl_newSVrv(aTHX_ a,b)
 # define newSVsv_flags(a,b)                     Perl_newSVsv_flags(aTHX_ a,b)
+# define newSVsv_flags_NN(a,b)                  Perl_newSVsv_flags_NN(aTHX_ a,b)
 # define newSVuv(a)                             Perl_newSVuv(aTHX_ a)
 # define newTRYCATCHOP(a,b,c,d)                 Perl_newTRYCATCHOP(aTHX_ a,b,c,d)
 # define newUNOP(a,b,c)                         Perl_newUNOP(aTHX_ a,b,c)

pod/perldelta.pod

@@ -423,6 +423,19 @@ memory saving is unrealistic.
 C<sv_vcatpvfn_flags()> now substitutes the Unicode REPLACEMENT CHARACTER
 for malformed input.  Previously it used the NUL character.
 
+=item *
+
+L<perlapi/C<newSVsv_flags_NN>> is a new function for creating a new SV
+and assigning the value(s) of an existing SV to it.
+
+Historically, C<Perl_newSVsv_flags> and C<Perl_sv_mortalcopy_flags> would
+pass a new SV head and the original SV to C<Perl_sv_setsv_flags>. However,
+the latter contains many branches of no relevance to a fresh SV, so they
+now make use of the new function to streamline the process.
+
+C<Perl_newSVsv_flags> is now essentially a NULL pointer check and wrapper
+around the new function, so has been moved into F<sv_inline.h>.
+
 =back
 
 =head1 Selected Bug Fixes

pp.c

@@ -6419,10 +6419,11 @@ PP(pp_push)
         PL_delaymagic = DM_DELAY;
         for (++MARK; MARK <= PL_stack_sp; MARK++) {
             SV *sv;
-            if (*MARK) SvGETMAGIC(*MARK);
-            sv = newSV_type(SVt_NULL);
-            if (*MARK)
-                sv_setsv_nomg(sv, *MARK);
+            if (*MARK) {
+                sv = newSVsv_flags(*MARK, SV_DO_COW_SVSETSV|SV_GMAGIC);
+            } else
+                sv = newSV_type(SVt_NULL);
+
             av_store(ary, AvFILLp(ary)+1, sv);
         }
         if (PL_delaymagic & DM_ARRAY_ISA)

pp_ctl.c

@@ -4418,13 +4418,11 @@ S_doopen_pm(pTHX_ SV *name)
         return NULL;
 
     if (memENDPs(p, namelen, ".pm")) {
-        SV *const pmcsv = sv_newmortal();
-        PerlIO * pmcio;
+        SV *const pmcsv = sv_mortalcopy_flags(name, SV_GMAGIC|SV_NOSTEAL|SV_DO_COW_SVSETSV);
 
-        SvSetSV_nosteal(pmcsv,name);
         sv_catpvs(pmcsv, "c");
 
-        pmcio = check_type_and_open(pmcsv);
+        PerlIO * pmcio = check_type_and_open(pmcsv);
         if (pmcio)
             return pmcio;
     }
@@ -4816,8 +4814,7 @@ S_require_file(pTHX_ SV *sv)
                     }
 
                     if (SvPADTMP(nsv)) {
-                        nsv = sv_newmortal();
-                        SvSetSV_nosteal(nsv,sv);
+                        nsv = sv_mortalcopy_flags(sv, SV_GMAGIC|SV_NOSTEAL|SV_DO_COW_SVSETSV);
                     }
 
                     const char *method = NULL;

pp_hot.c

@@ -5374,8 +5374,7 @@ PP(pp_subst)
     if (dstr) {
         /* replacement needing upgrading? */
         if (DO_UTF8(TARG) && !doutf8) {
-             nsv = sv_newmortal();
-             SvSetSV(nsv, dstr);
+             nsv = sv_mortalcopy_flags(dstr, SV_GMAGIC|SV_DO_COW_SVSETSV);
              sv_utf8_upgrade(nsv);
              c = SvPV_const(nsv, clen);
              doutf8 = TRUE;