diff --git a/gv.c b/gv.c
index 9856e03a2b7a..b640979efed7 100644
--- a/gv.c
+++ b/gv.c
@@ -669,7 +669,7 @@ S_maybe_add_coresub(pTHX_ HV * const stash, GV *gv,
            get hairy. */
         cv = MUTABLE_CV(newSV_type(SVt_PVCV));
         GvCV_set(gv,cv);
-        GvCVGEN(gv) = 0;
+        assert(GvCVGEN(gv) == 0);
         CvISXSUB_on(cv);
         CvXSUB(cv) = core_xsub;
         PoisonPADLIST(cv);
diff --git a/hv.c b/hv.c
index 11e8c3eafd6c..7959ec10acfb 100644
--- a/hv.c
+++ b/hv.c
@@ -3570,7 +3570,7 @@ S_refcounted_he_value(pTHX_ const struct refcounted_he *he)
         SvPV_set(value, (char *) he->refcounted_he_data + 1);
         SvCUR_set(value, he->refcounted_he_val.refcounted_he_u_len);
         /* This stops anything trying to free it  */
-        SvLEN_set(value, 0);
+        assert(SvLEN(value) == 0);
         SvPOK_on(value);
         SvREADONLY_on(value);
         if ((he->refcounted_he_data[0] & HVrhek_typemask) == HVrhek_PV_UTF8)
diff --git a/op.c b/op.c
index 890acc37285f..1d01d0f203ce 100644
--- a/op.c
+++ b/op.c
@@ -12320,7 +12320,7 @@ Perl_newSTUB(pTHX_ GV *gv, bool fake)
     PERL_ARGS_ASSERT_NEWSTUB;
     assert(!GvCVu(gv));
     GvCV_set(gv, cv);
-    GvCVGEN(gv) = 0;
+    assert(GvCVGEN(gv) == 0);
     if (!fake && GvSTASH(gv) && HvENAME_HEK(GvSTASH(gv)))
         gv_method_changed(gv);
     if (SvFAKE(gv)) {
diff --git a/pp.c b/pp.c
index ed6155f8810b..a754dd64f754 100644
--- a/pp.c
+++ b/pp.c
@@ -3855,7 +3855,7 @@ PP(pp_index)
                  * the routine that contains the new byte string, and donate it
                  * to temp to ensure it will get free()d */
                 if (free_little_p) {
-                    little = temp = newSV_type(SVt_NULL);
+                    little = temp = newSV_type(SVt_PV);
                     sv_usepvn(temp, (char *) little_p, llen);
                     little_p = SvPVX_const(little);
                 }
diff --git a/pp_ctl.c b/pp_ctl.c
index 90853e010029..6516005c8348 100644
--- a/pp_ctl.c
+++ b/pp_ctl.c
@@ -3753,7 +3753,7 @@ S_save_lines(pTHX_ AV *array, SV *sv)
 
         sv_setpvn_fresh(tmpstr, s, t - s);
         /* not breakable until we compile a COP for it */
-        SvIV_set(tmpstr, 0);
+        assert(SvIVX(tmpstr) == 0);
         SvIOK_on(tmpstr);
         av_store(array, line++, tmpstr);
         s = t;
diff --git a/regcomp_invlist.c b/regcomp_invlist.c
index 658ece56c960..247c0ab56d4e 100644
--- a/regcomp_invlist.c
+++ b/regcomp_invlist.c
@@ -357,8 +357,8 @@ Perl__new_invlist_C_array(pTHX_ const UV* const list)
      * of the list proper, so start it just after them */
     SvPV_set(invlist, (char *) (list + HEADER_LENGTH));
 
-    SvLEN_set(invlist, 0);  /* Means we own the contents, and the system
-                               shouldn't touch it */
+    assert(SvLEN(invlist) == 0);  /* Means we own the contents, and the system
+                                     shouldn't touch it */
 
     *(get_invlist_offset_addr(invlist)) = offset;
 
diff --git a/regexec.c b/regexec.c
index be9ec2cf338f..2016903a81a7 100644
--- a/regexec.c
+++ b/regexec.c
@@ -3863,10 +3863,8 @@ Perl_regexec_flags(pTHX_ REGEXP * const rx, char *stringarg, char *strend,
            S_cleanup_regmatch_info_aux has executed (registered by
            SAVEDESTRUCTOR_X below).  S_cleanup_regmatch_info_aux modifies
            magic belonging to this SV.
-           Not newSVsv, either, as it does not COW.
         */
-        reginfo->sv = newSV_type(SVt_NULL);
-        SvSetSV_nosteal(reginfo->sv, sv);
+        reginfo->sv = newSVsv_flags(sv, SV_GMAGIC|SV_NOSTEAL|SV_DO_COW_SVSETSV);
         SAVEFREESV(reginfo->sv);
     }
 
diff --git a/sv.c b/sv.c
index af145738def1..a60f056665d9 100644
--- a/sv.c
+++ b/sv.c
@@ -1500,12 +1500,13 @@ Perl_sv_grow_fresh(pTHX_ SV *const sv, STRLEN newlen)
     if (newlen < PERL_STRLEN_NEW_MIN)
         newlen = PERL_STRLEN_NEW_MIN;
 
-    s = (char*)safemalloc(newlen);
-    SvPV_set(sv, s);
-
     /* No PERL_UNWARANTED_CHUMMINESS_WITH_MALLOC here, since many strings */
     /* will never be grown once set. Let the real sv_grow worry about that. */
     SvLEN_set(sv, newlen);
+
+    s = (char*)safemalloc(newlen);
+    SvPV_set(sv, s);
+
     return s;
 }
 
@@ -6275,10 +6276,14 @@ Perl_newSV(pTHX_ const STRLEN len)
 {
     SV *sv;
 
-    if (!len)
-        new_SV(sv);
-    else {
-        sv = newSV_type(SVt_PV);
+    new_SV(sv);
+    if (len) {
+        SvFLAGS(sv) = SVt_PV;
+        SvANY(sv) = new_XPV();
+
+        SvCUR_set(sv, 0);
+        SvLEN_set(sv, 0);
+
         sv_grow_fresh(sv, len + 1);
     }
     return sv;
@@ -6301,6 +6306,11 @@ Perl_newSVpvz(pTHX_ const STRLEN len)
 {
     SV *sv = newSV_type(SVt_PV);
     sv_grow_fresh(sv, len + 1);
+
+    /* Some ASSUMEs which may help the compiler avoid unnecessary work */
+    ASSUME(SvCUR(sv) == 0);
+    ASSUME(SvFLAGS(sv) == SVt_PV);
+    ASSUME(!TAINT_get);
     (void) sv_setpv_freshbuf(sv);
 
     return sv;
@@ -9143,7 +9153,7 @@ 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, SSize_t append)
 {
-    SV * const tsv = newSV_type(SVt_NULL);
+    SV * const tsv = newSV_type(SVt_PV);
     ENTER;
     SAVEFREESV(tsv);
     sv_gets(tsv, fp, 0);
@@ -10286,54 +10296,45 @@ SV if C<hek> is NULL.
 SV *
 Perl_newSVhek(pTHX_ const HEK *const hek)
 {
-    if (!hek) {
-        SV *sv;
-
-        new_SV(sv);
-        return sv;
-    }
-
-    if (HEK_LEN(hek) == HEf_SVKEY) {
-        return newSVsv(*(SV**)HEK_KEY(hek));
-    } else {
-        const int flags = HEK_FLAGS(hek);
-        if (flags & HVhek_WASUTF8) {
-            /* Trouble :-)
-               Andreas would like keys he put in as utf8 to come back as utf8
-            */
-            STRLEN utf8_len = HEK_LEN(hek);
-            SV * const sv = newSV_type(SVt_PV);
-            char *as_utf8 = (char *)bytes_to_utf8 ((U8*)HEK_KEY(hek), &utf8_len);
-            /* bytes_to_utf8() allocates a new string, which we can repurpose: */
-            sv_usepvn_flags(sv, as_utf8, utf8_len, SV_HAS_TRAILING_NUL);
-            SvUTF8_on (sv);
-            return sv;
-        } else if (flags & HVhek_NOTSHARED) {
-            /* A hash that isn't using shared hash keys has to have
-               the flag in every key so that we know not to try to call
-               share_hek_hek on it.  */
+    SV *sv = newSV_type(SVt_PV);
 
-            SV * const sv = newSVpvn (HEK_KEY(hek), HEK_LEN(hek));
-            if (HEK_UTF8(hek))
+    if (LIKELY(hek)) {
+        if (HEK_LEN(hek) != HEf_SVKEY) {
+            const int flags = HEK_FLAGS(hek);
+            if (LIKELY(!(flags & (HVhek_WASUTF8|HVhek_NOTSHARED)))) {
+                /* This will be overwhelmingly the most common case.  */
+                /* Inline most of newSVpvn_share(), because share_hek_hek() is far
+                   more efficient than sharepvn().  */
+                SvFLAGS(sv) = SVt_PV | SVf_POK | SVp_POK | SVf_IsCOW |
+                               (HEK_UTF8(hek) ? SVf_UTF8 : 0);
+                SvCUR_set(sv, HEK_LEN(hek));
+                SvPV_set(sv, (char *)HEK_KEY(share_hek_hek(hek)));
+                assert(SvLEN(sv) == 0); /* SVt_PV should be initialized with this value */
+                return sv;
+            } else if (flags & HVhek_WASUTF8) {
+                /* Trouble :-)
+                   Andreas would like keys he put in as utf8 to come back as utf8
+                */
+                STRLEN utf8_len = HEK_LEN(hek);
+                char *as_utf8 = (char *)bytes_to_utf8 ((U8*)HEK_KEY(hek), &utf8_len);
+                /* bytes_to_utf8() allocates a new string, which we can repurpose: */
+                sv_usepvn_flags(sv, as_utf8, utf8_len, SV_HAS_TRAILING_NUL);
                 SvUTF8_on (sv);
-            return sv;
-        }
-        /* This will be overwhelmingly the most common case.  */
-        {
-            /* Inline most of newSVpvn_share(), because share_hek_hek() is far
-               more efficient than sharepvn().  */
-            SV *sv = newSV_type(SVt_PV);
-
-            SvPV_set(sv, (char *)HEK_KEY(share_hek_hek(hek)));
-            SvCUR_set(sv, HEK_LEN(hek));
-            SvLEN_set(sv, 0);
-            SvIsCOW_on(sv);
-            SvPOK_on(sv);
-            if (HEK_UTF8(hek))
-                SvUTF8_on(sv);
+                return sv;
+            } else {
+                assert(flags & HVhek_NOTSHARED);
+                sv_setpvn_fresh(sv,HEK_KEY(hek),HEK_LEN(hek));
+                if (HEK_UTF8(hek))
+                    SvUTF8_on (sv);
+                return sv;
+            }
+        } else {
+            /* (HEK_LEN(hek) == HEf_SVKEY) is comparatively more rare nowadays */
+            sv_setsv_flags(sv, *(SV**)HEK_KEY(hek), SV_GMAGIC|SV_NOSTEAL);
             return sv;
         }
     }
+    return sv;
 }
 
 /*
@@ -10375,13 +10376,11 @@ Perl_newSVpvn_share(pTHX_ const char *src, I32 len, U32 hash)
     sv = newSV_type(SVt_PV);
     /* The logic for this is inlined in S_mro_get_linear_isa_dfs(), so if it
        changes here, update it there too.  */
-    SvPV_set(sv, sharepvn(src, is_utf8?-len:len, hash));
+    SvFLAGS(sv) |= SVf_POK | SVp_POK | SVf_IsCOW |
+                   (is_utf8 ? SVf_UTF8 : 0);
     SvCUR_set(sv, len);
-    SvLEN_set(sv, 0);
-    SvIsCOW_on(sv);
-    SvPOK_on(sv);
-    if (is_utf8)
-        SvUTF8_on(sv);
+    assert(SvLEN(sv) ==0);
+    SvPV_set(sv, sharepvn(src, is_utf8?-len:len, hash));
     return sv;
 }
 
@@ -10563,9 +10562,7 @@ SV *
 Perl_newSVbool(pTHX_ bool bool_val)
 {
     PERL_ARGS_ASSERT_NEWSVBOOL;
-    SV *sv = newSVsv(bool_val ? &PL_sv_yes : &PL_sv_no);
-
-    return sv;
+    return (bool_val ? newSV_true() : newSV_false());
 }
 
 /*
@@ -10579,7 +10576,18 @@ SV *
 Perl_newSV_true(pTHX)
 {
     PERL_ARGS_ASSERT_NEWSV_TRUE;
-    SV *sv = newSVsv(&PL_sv_yes);
+
+    /* Equivalent to: SV *sv = newSVsv(&PL_sv_yes); */
+    SV *sv;
+    new_SV(sv);
+    SvFLAGS(sv) = SVt_PVNV|SVf_IOK|SVp_IOK|SVf_NOK|SVp_NOK
+            |SVf_POK|SVp_POK|SVf_IsCOW|SVppv_STATIC;
+    SvPV_set(sv, (char*)PL_Yes);
+    SvANY(sv) = new_XPVNV();
+    SvCUR_set(sv, 1);
+    SvLEN_set(sv, 0);
+    SvIV_set(sv, 1);
+    SvNV_set(sv, 1);
 
     return sv;
 }
@@ -10596,7 +10604,18 @@ SV *
 Perl_newSV_false(pTHX)
 {
     PERL_ARGS_ASSERT_NEWSV_FALSE;
-    SV *sv = newSVsv(&PL_sv_no);
+
+    /* Equivalent to: SV *sv = newSVsv(&PL_sv_no); */
+    SV *sv;
+    new_SV(sv);
+    SvFLAGS(sv) = SVt_PVNV|SVf_IOK|SVp_IOK|SVf_NOK|SVp_NOK
+            |SVf_POK|SVp_POK|SVf_IsCOW|SVppv_STATIC;
+    SvPV_set(sv, (char*)PL_No);
+    SvANY(sv) = new_XPVNV();
+    SvCUR_set(sv, 0);
+    SvLEN_set(sv, 0);
+    SvIV_set(sv, 0);
+    SvNV_set(sv, 0);
 
     return sv;
 }
@@ -11175,10 +11194,11 @@ Perl_newSVrv(pTHX_ SV *const rv, const char *const classname)
         const U32 refcnt = SvREFCNT(rv);
         SvREFCNT(rv) = 0;
         sv_clear(rv);
-        SvFLAGS(rv) = 0;
+        SvFLAGS(rv) = SVt_IV;
         SvREFCNT(rv) = refcnt;
 
-        sv_upgrade(rv, SVt_IV);
+        SET_SVANY_FOR_BODYLESS_IV(rv);
+        SvIV_set(rv, 0);
     } else if (SvROK(rv)) {
         SvREFCNT_dec(SvRV(rv));
     } else {