Various functions - when a field is already zero, don't set it to zero.

SV bodies are Zero()ed when allocated/uprooted from an arena for use.
This commit changes instances where a fresh body field is unnecessarily
assigned a zero/NULL value into an assertion that the field already
contains the desired value.

Author: richardleach

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);

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)

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)) {

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;

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;