Inlined newSV_type(SVt_NULL) leaner than non-inlined newSV(0)

When a function outside of sv.c creates a SV via newSV(0):
 * There is a call to Perl_newSV
 * A SV head is uprooted and its flags set
 * A runtime check is made to effectively see if 0 > 0
 * The new SV* is returned

Replacing newSV(0) with newSV_type(SVt_NULL) should be more efficient,
because (assuming there are SV heads to uproot), the only step is:
 * A SV head is uprooted and its flags set

av.c

@@ -292,7 +292,7 @@ Perl_av_fetch(pTHX_ AV *av, SSize_t key, I32 lval)
 
     if (!AvARRAY(av)[key]) {
       emptyness:
-        return lval ? av_store(av,key,newSV(0)) : NULL;
+        return lval ? av_store(av,key,newSV_type(SVt_NULL)) : NULL;
     }
 
     return &AvARRAY(av)[key];
@@ -473,7 +473,7 @@ Perl_av_make(pTHX_ SSize_t size, SV **strp)
 
             SvGETMAGIC(*strp); /* before newSV, in case it dies */
             AvFILLp(av)++;
-            ary[i] = newSV(0);
+            ary[i] = newSV_type(SVt_NULL);
             sv_setsv_flags(ary[i], *strp,
                            SV_DO_COW_SVSETSV|SV_NOSTEAL);
             strp++;
@@ -1124,7 +1124,7 @@ Perl_av_iter_p(pTHX_ AV *av) {
 
 SV *
 Perl_av_nonelem(pTHX_ AV *av, SSize_t ix) {
-    SV * const sv = newSV(0);
+    SV * const sv = newSV_type(SVt_NULL);
     PERL_ARGS_ASSERT_AV_NONELEM;
     if (!av_store(av,ix,sv))
         return sv_2mortal(sv); /* has tie magic */

dump.c

@@ -2674,7 +2674,7 @@ S_append_gv_name(pTHX_ GV *gv, SV *out)
         sv_catpvs_nomg(out, "<NULLGV>");
         return;
     }
-    sv = newSV(0);
+    sv = newSV_type(SVt_NULL);
     gv_fullname4(sv, gv, NULL, FALSE);
     Perl_sv_catpvf(aTHX_ out, "$%" SVf, SVfARG(sv));
     SvREFCNT_dec_NN(sv);

gv.c

@@ -202,7 +202,7 @@ Perl_newGP(pTHX_ GV *const gv)
     Newxz(gp, 1, GP);
     gp->gp_egv = gv; /* allow compiler to reuse gv after this */
 #ifndef PERL_DONT_CREATE_GVSV
-    gp->gp_sv = newSV(0);
+    gp->gp_sv = newSV_type(SVt_NULL);
 #endif
 
     /* PL_curcop may be null here.  E.g.,
@@ -294,7 +294,7 @@ Perl_cvgv_from_hek(pTHX_ CV *cv)
     if (!CvSTASH(cv)) return NULL;
     ASSUME(CvNAME_HEK(cv));
     svp = hv_fetchhek(CvSTASH(cv), CvNAME_HEK(cv), 0);
-    gv = MUTABLE_GV(svp && *svp ? *svp : newSV(0));
+    gv = MUTABLE_GV(svp && *svp ? *svp : newSV_type(SVt_NULL));
     if (!isGV(gv))
         gv_init_pvn(gv, CvSTASH(cv), HEK_KEY(CvNAME_HEK(cv)),
                 HEK_LEN(CvNAME_HEK(cv)),
@@ -580,7 +580,7 @@ S_maybe_add_coresub(pTHX_ HV * const stash, GV *gv,
         ampable = FALSE;
     }
     if (!gv) {
-        gv = (GV *)newSV(0);
+        gv = (GV *)newSV_type(SVt_NULL);
         gv_init(gv, stash, name, len, TRUE);
     }
     GvMULTI_on(gv);
@@ -1359,7 +1359,7 @@ Perl_gv_autoload_pvn(pTHX_ HV *stash, const char *name, STRLEN len, U32 flags)
     if (!isGV(vargv)) {
         gv_init_pvn(vargv, varstash, S_autoload, S_autolen, 0);
 #ifdef PERL_DONT_CREATE_GVSV
-        GvSV(vargv) = newSV(0);
+        GvSV(vargv) = newSV_type(SVt_NULL);
 #endif
     }
     LEAVE;
@@ -2516,7 +2516,7 @@ Perl_gv_fetchpvn_flags(pTHX_ const char *nambeg, STRLEN full_len, I32 flags,
     /* By this point we should have a stash and a name */
     gvp = (GV**)hv_fetch(stash,name,is_utf8 ? -(I32)len : (I32)len,add);
     if (!gvp || *gvp == (const GV *)&PL_sv_undef) {
-        if (addmg) gv = (GV *)newSV(0);     /* tentatively */
+        if (addmg) gv = (GV *)newSV_type(SVt_NULL);     /* tentatively */
         else return NULL;
     }
     else gv = *gvp, addmg = 0;

hv.c

@@ -480,7 +480,7 @@ Perl_hv_common(pTHX_ HV *hv, SV *keysv, const char *key, STRLEN klen,
                                                HV_FETCH_ISSTORE
                                                | HV_DISABLE_UVAR_XKEY
                                                | return_svp,
-                                               newSV(0), hash);
+                                               newSV_type(SVt_NULL), hash);
                         } else {
                             if (flags & HVhek_FREEKEY)
                                 Safefree(key);
@@ -739,7 +739,7 @@ Perl_hv_common(pTHX_ HV *hv, SV *keysv, const char *key, STRLEN klen,
                         break;
                     }
                     /* LVAL fetch which actually needs a store.  */
-                    val = newSV(0);
+                    val = newSV_type(SVt_NULL);
                     HvPLACEHOLDERS(hv)--;
                 } else {
                     /* store */
@@ -793,7 +793,7 @@ Perl_hv_common(pTHX_ HV *hv, SV *keysv, const char *key, STRLEN klen,
         return NULL;
     }
     if (action & HV_FETCH_LVALUE) {
-        val = action & HV_FETCH_EMPTY_HE ? NULL : newSV(0);
+        val = action & HV_FETCH_EMPTY_HE ? NULL : newSV_type(SVt_NULL);
         if (SvMAGICAL(hv)) {
             /* At this point the old hv_fetch code would call to hv_store,
                which in turn might do some tied magic. So we need to make that
@@ -3247,7 +3247,7 @@ S_refcounted_he_value(pTHX_ const struct refcounted_he *he)
 
     switch(he->refcounted_he_data[0] & HVrhek_typemask) {
     case HVrhek_undef:
-        value = newSV(0);
+        value = newSV_type(SVt_NULL);
         break;
     case HVrhek_delete:
         value = &PL_sv_placeholder;

inline.h

@@ -134,7 +134,7 @@ Perl_av_fetch_simple(pTHX_ AV *av, SSize_t key, I32 lval)
     assert(key > -1);
 
     if ( (key > AvFILLp(av)) || !AvARRAY(av)[key]) {
-        return lval ? av_store_simple(av,key,newSV(0)) : NULL;
+        return lval ? av_store_simple(av,key,newSV_type(SVt_NULL)) : NULL;
     } else {
         return &AvARRAY(av)[key];
     }

op.c

@@ -10964,7 +10964,7 @@ S_op_const_sv(pTHX_ const OP *o, CV *cv, bool allow_lex)
         if (type == OP_CONST && cSVOPo->op_sv)
             sv = cSVOPo->op_sv;
         else if (type == OP_UNDEF && !o->op_private) {
-            sv = newSV(0);
+            sv = newSV_type(SVt_NULL);
             SAVEFREESV(sv);
         }
         else if (allow_lex && type == OP_PADSV) {
@@ -13623,7 +13623,7 @@ Perl_ck_glob(pTHX_ OP *o)
         LEAVE;
     }
 #endif /* !PERL_EXTERNAL_GLOB */
-    gv = (GV *)newSV(0);
+    gv = (GV *)newSV_type(SVt_NULL);
     gv_init(gv, 0, "", 0, 0);
     gv_IOadd(gv);
     op_append_elem(OP_GLOB, o, newGVOP(OP_GV, 0, gv));
@@ -13689,7 +13689,7 @@ Perl_ck_index(pTHX_ OP *o)
             if (   (!SvPOK(sv) || SvNIOKp(sv) || isREGEXP(sv))
                 && SvOK(sv) && !SvROK(sv))
             {
-                sv = newSV(0);
+                sv = newSV_type(SVt_NULL);
                 sv_copypv(sv, kSVOP->op_sv);
                 SvREFCNT_dec_NN(kSVOP->op_sv);
                 kSVOP->op_sv = sv;

pad.c

@@ -719,7 +719,7 @@ Perl_pad_alloc(pTHX_ I32 optype, U32 tmptype)
         pad_reset();
     if (tmptype == SVs_PADMY) { /* Not & because this ‘flag’ is 0.  */
         /* For a my, simply push a null SV onto the end of PL_comppad. */
-        sv = *av_store_simple(PL_comppad, AvFILLp(PL_comppad) + 1, newSV(0));
+        sv = *av_store_simple(PL_comppad, AvFILLp(PL_comppad) + 1, newSV_type(SVt_NULL));
         retval = (PADOFFSET)AvFILLp(PL_comppad);
     }
     else {
@@ -1565,7 +1565,7 @@ Perl_pad_swipe(pTHX_ PADOFFSET po, bool refadjust)
     /* if pad tmps aren't shared between ops, then there's no need to
      * create a new tmp when an existing op is freed */
 #ifdef USE_PAD_RESET
-    PL_curpad[po] = newSV(0);
+    PL_curpad[po] = newSV_type(SVt_NULL);
     SvPADTMP_on(PL_curpad[po]);
 #else
     PL_curpad[po] = NULL;
@@ -2030,7 +2030,7 @@ S_cv_clone_pad(pTHX_ CV *proto, CV *cv, CV *outside, HV *cloned,
                 else if (sigil == '%')
                     sv = MUTABLE_SV(newHV());
                 else
-                    sv = newSV(0);
+                    sv = newSV_type(SVt_NULL);
                 /* reset the 'assign only once' flag on each state var */
                 if (sigil != '&' && SvPAD_STATE(namesv))
                     SvPADSTALE_on(sv);
@@ -2041,7 +2041,7 @@ S_cv_clone_pad(pTHX_ CV *proto, CV *cv, CV *outside, HV *cloned,
             sv = SvREFCNT_inc_NN(ppad[ix]);
         }
         else {
-            sv = newSV(0);
+            sv = newSV_type(SVt_NULL);
             SvPADTMP_on(sv);
         }
         PL_curpad[ix] = sv;
@@ -2435,15 +2435,15 @@ Perl_pad_push(pTHX_ PADLIST *padlist, int depth)
                     else if (sigil == '%')
                         sv = MUTABLE_SV(newHV());
                     else
-                        sv = newSV(0);
+                        sv = newSV_type(SVt_NULL);
                 }
             }
             else if (PadnamePV(names[ix])) {
                 sv = SvREFCNT_inc_NN(oldpad[ix]);
             }
             else {
                 /* save temporaries on recursion? */
-                sv = newSV(0);
+                sv = newSV_type(SVt_NULL);
                 SvPADTMP_on(sv);
             }
             AvARRAY(newpad)[ix] = sv;
@@ -2543,7 +2543,7 @@ Perl_padlist_dup(pTHX_ PADLIST *srcpad, CLONE_PARAMS *param)
                             else if (sigil == '%')
                                 sv = MUTABLE_SV(newHV());
                             else
-                                sv = newSV(0);
+                                sv = newSV_type(SVt_NULL);
                             pad1a[ix] = sv;
                         }
                     }
@@ -2554,7 +2554,7 @@ Perl_padlist_dup(pTHX_ PADLIST *srcpad, CLONE_PARAMS *param)
                 }
                 else {
                     /* save temporaries on recursion? */
-                    SV * const sv = newSV(0);
+                    SV * const sv = newSV_type(SVt_NULL);
                     pad1a[ix] = sv;
 
                     /* SvREFCNT(oldpad[ix]) != 1 for some code in threads.xs

pp.c

@@ -130,7 +130,7 @@ S_rv2gv(pTHX_ SV *sv, const bool vivify_sv, const bool strict,
                     HV *stash;
                     if (SvREADONLY(sv))
                         Perl_croak_no_modify();
-                    gv = MUTABLE_GV(newSV(0));
+                    gv = MUTABLE_GV(newSV_type(SVt_NULL));
                     stash = CopSTASH(PL_curcop);
                     if (SvTYPE(stash) != SVt_PVHV) stash = NULL;
                     if (cUNOP->op_targ) {
@@ -938,7 +938,7 @@ PP(pp_undef)
             Newxz(gp, 1, GP);
             GvGP_set(sv, gp_ref(gp));
 #ifndef PERL_DONT_CREATE_GVSV
-            GvSV(sv) = newSV(0);
+            GvSV(sv) = newSV_type(SVt_NULL);
 #endif
             GvLINE(sv) = CopLINE(PL_curcop);
             GvEGV(sv) = MUTABLE_GV(sv);
@@ -3499,7 +3499,7 @@ PP(pp_index)
 
             /* At this point, pv is a malloc()ed string. So donate it to temp
                to ensure it will get free()d  */
-            little = temp = newSV(0);
+            little = temp = newSV_type(SVt_NULL);
             sv_usepvn(temp, pv, llen);
             little_p = SvPVX(little);
         } else {
@@ -5534,13 +5534,13 @@ PP(pp_anonhash)
         {
             MARK++;
             SvGETMAGIC(*MARK);
-            val = newSV(0);
+            val = newSV_type(SVt_NULL);
             sv_setsv_nomg(val, *MARK);
         }
         else
         {
             Perl_ck_warner(aTHX_ packWARN(WARN_MISC), "Odd number of elements in anonymous hash");
-            val = newSV(0);
+            val = newSV_type(SVt_NULL);
         }
         (void)hv_store_ent(hv,key,val,0);
     }
@@ -5791,7 +5791,7 @@ PP(pp_push)
         for (++MARK; MARK <= SP; MARK++) {
             SV *sv;
             if (*MARK) SvGETMAGIC(*MARK);
-            sv = newSV(0);
+            sv = newSV_type(SVt_NULL);
             if (*MARK)
                 sv_setsv_nomg(sv, *MARK);
             av_store(ary, AvFILLp(ary)+1, sv);
@@ -7026,7 +7026,7 @@ PP(pp_argelem)
             SV *tmpsv;
             SV **svp = av_fetch(defav, ix + i, FALSE);
             SV *val = svp ? *svp : &PL_sv_undef;
-            tmpsv = newSV(0);
+            tmpsv = newSV_type(SVt_NULL);
             sv_setsv(tmpsv, val);
             av_store((AV*)targ, i++, tmpsv);
             TAINT_NOT;
@@ -7042,7 +7042,7 @@ PP(pp_argelem)
             /* see "target should usually be empty" comment above */
             for (i = 0; i < argc; i++) {
                 SV **svp = av_fetch(defav, ix + i, FALSE);
-                SV *newsv = newSV(0);
+                SV *newsv = newSV_type(SVt_NULL);
                 sv_setsv_flags(newsv,
                                 svp ? *svp : &PL_sv_undef,
                                 (SV_DO_COW_SVSETSV|SV_NOSTEAL));
@@ -7071,7 +7071,7 @@ PP(pp_argelem)
             argc -= 2;
             if (UNLIKELY(SvGMAGICAL(key)))
                 key = sv_mortalcopy(key);
-            tmpsv = newSV(0);
+            tmpsv = newSV_type(SVt_NULL);
             sv_setsv(tmpsv, val);
             hv_store_ent((HV*)targ, key, tmpsv, 0);
             TAINT_NOT;

pp_ctl.c

@@ -4386,7 +4386,7 @@ S_require_file(pTHX_ SV *sv)
            than hanging another SV from it. In turn, filter_add() optionally
            takes the SV to use as the filter (or creates a new SV if passed
            NULL), so simply pass in whatever value filter_cache has.  */
-        SV * const fc = filter_cache ? newSV(0) : NULL;
+        SV * const fc = filter_cache ? newSV_type(SVt_NULL) : NULL;
         SV *datasv;
         if (fc) sv_copypv(fc, filter_cache);
         datasv = filter_add(S_run_user_filter, fc);

pp_hot.c

@@ -4895,7 +4895,7 @@ Perl_leave_adjust_stacks(pTHX_ SV **from_sp, SV **to_sp, U8 gimme, int pass)
                  *    ++PL_tmps_ix, moving the previous occupant there
                  *    instead.
                  */
-                SV *newsv = newSV(0);
+                SV *newsv = newSV_type(SVt_NULL);
 
                 PL_tmps_stack[++PL_tmps_ix] = *tmps_basep;
                 /* put it on the tmps stack early so it gets freed if we die */
@@ -5510,7 +5510,7 @@ Perl_vivify_ref(pTHX_ SV *sv, U32 to_what)
         prepare_SV_for_RV(sv);
         switch (to_what) {
         case OPpDEREF_SV:
-            SvRV_set(sv, newSV(0));
+            SvRV_set(sv, newSV_type(SVt_NULL));
             break;
         case OPpDEREF_AV:
             SvRV_set(sv, MUTABLE_SV(newAV()));

regexec.c

@@ -3712,7 +3712,7 @@ Perl_regexec_flags(pTHX_ REGEXP * const rx, char *stringarg, char *strend,
            magic belonging to this SV.
            Not newSVsv, either, as it does not COW.
         */
-        reginfo->sv = newSV(0);
+        reginfo->sv = newSV_type(SVt_NULL);
         SvSetSV_nosteal(reginfo->sv, sv);
         SAVEFREESV(reginfo->sv);
     }

scope.c

@@ -232,7 +232,7 @@ S_save_scalar_at(pTHX_ SV **sptr, const U32 flags)
     if (flags & SAVEf_KEEPOLDELEM)
         sv = osv;
     else {
-        sv  = (*sptr = newSV(0));
+        sv  = (*sptr = newSV_type(SVt_NULL));
         if (SvTYPE(osv) >= SVt_PVMG && SvMAGIC(osv))
             mg_localize(osv, sv, cBOOL(flags & SAVEf_SETMAGIC));
     }
@@ -1264,7 +1264,7 @@ Perl_leave_scope(pTHX_ I32 base)
                         CvLEXICAL_on(*svp);
                         break;
                     }
-                    default:	*svp = newSV(0);		break;
+                    default:	*svp = newSV_type(SVt_NULL);		break;
                     }
                     SvREFCNT_dec_NN(sv); /* Cast current value to the winds. */
                     /* preserve pad nature, but also mark as not live

sv.c

@@ -8361,7 +8361,7 @@ Perl_sv_collxfrm_flags(pTHX_ SV *const sv, STRLEN *const nxp, const I32 flags)
 static char *
 S_sv_gets_append_to_utf8(pTHX_ SV *const sv, PerlIO *const fp, I32 append)
 {
-    SV * const tsv = newSV(0);
+    SV * const tsv = newSV_type(SVt_NULL);
     ENTER;
     SAVEFREESV(tsv);
     sv_gets(tsv, fp, 0);
@@ -16308,7 +16308,7 @@ Perl_varname(pTHX_ const GV *const gv, const char gvtype, PADOFFSET targ,
     }
 
     if (subscript_type == FUV_SUBSCRIPT_HASH) {
-        SV * const sv = newSV(0);
+        SV * const sv = newSV_type(SVt_NULL);
         STRLEN len;
         const char * const pv = SvPV_nomg_const((SV*)keyname, len);
 

toke.c

@@ -2382,7 +2382,7 @@ S_force_strict_version(pTHX_ char *s)
         s++;
 
     if (is_STRICT_VERSION(s,&errstr)) {
-        SV *ver = newSV(0);
+        SV *ver = newSV_type(SVt_NULL);
         s = (char *)scan_version(s, ver, 0);
         version = newSVOP(OP_CONST, 0, ver);
     }