don't test non-null args

For lots of core functions:

if a function parameter has been declared NN in embed.fnc, don't test for
nullness at the start of the function, i.e. eliminate code like

    if (!foo) ...

On debugging builds the test is redundant, as the PERL_ARGS_ASSERT_FOO
at the start of the function will already have croaked.

On optimised builds, it will skip the check (and so be slightly faster),
but if actually passed a null arg, will now crash with a null-deref SEGV
rather than doing whatever the check used to do (e.g. croak, or silently
return and let the caller's code logic to go awry). But hopefully  this
should never happen as such instances will already have been detected on
debugging builds.

It also has the advantage of shutting up recent clangs which spew forth
lots of stuff like:

    sv.c:6308:10: warning: nonnull parameter 'bigstr' will evaluate to
    'true' on first encounter [-Wpointer-bool-conversion]
        if (!bigstr)

The only exception was in dump.c, where rather than skipping the null
test, I instead changed the function def in embed.fnc to allow a null arg,
on the basis that dump functions are often used for debugging (where
pointers may unexpectedly become NULL) and it's better there to display
that this item is null than to SEGV.

See the p5p thread starting at 20150224112829.GG28599@iabyn.com.

dump.c

@@ -1090,9 +1090,6 @@ Perl_gv_dump(pTHX_ GV *gv)
     const char* name;
     SV *sv, *tmp = newSVpvs_flags("", SVs_TEMP);
 
-
-    PERL_ARGS_ASSERT_GV_DUMP;
-
     if (!gv) {
 	PerlIO_printf(Perl_debug_log, "{}\n");
 	return;

embed.fnc

@@ -445,7 +445,7 @@ Ap	|void	|dump_all
 p	|void	|dump_all_perl	|bool justperl
 Ap	|void	|dump_eval
 Ap	|void	|dump_form	|NN const GV* gv
-Ap	|void	|gv_dump	|NN GV* gv
+Ap	|void	|gv_dump	|NULLOK GV* gv
 Ap	|void	|op_dump	|NN const OP *o
 Ap	|void	|pmop_dump	|NULLOK PMOP* pm
 Ap	|void	|dump_packsubs	|NN const HV* stash
@@ -1770,7 +1770,7 @@ Ap	|void	|do_gvgv_dump	|I32 level|NN PerlIO *file|NN const char *name\
 				|NULLOK GV *sv
 Ap	|void	|do_hv_dump	|I32 level|NN PerlIO *file|NN const char *name\
 				|NULLOK HV *sv
-Ap	|void	|do_magic_dump	|I32 level|NN PerlIO *file|NN const MAGIC *mg|I32 nest \
+Ap	|void	|do_magic_dump	|I32 level|NN PerlIO *file|NULLOK const MAGIC *mg|I32 nest \
 				|I32 maxnest|bool dumpops|STRLEN pvlim
 Ap	|void	|do_op_dump	|I32 level|NN PerlIO *file|NULLOK const OP *o
 Ap	|void	|do_pmop_dump	|I32 level|NN PerlIO *file|NULLOK const PMOP *pm

hv.c

@@ -2096,11 +2096,6 @@ Perl_hv_iterinit(pTHX_ HV *hv)
 {
     PERL_ARGS_ASSERT_HV_ITERINIT;
 
-    /* FIXME: Are we not NULL, or do we croak? Place bets now! */
-
-    if (!hv)
-	Perl_croak(aTHX_ "Bad hash");
-
     if (SvOOK(hv)) {
 	struct xpvhv_aux * iter = HvAUX(hv);
 	HE * const entry = iter->xhv_eiter; /* HvEITER(hv) */
@@ -2128,9 +2123,6 @@ Perl_hv_riter_p(pTHX_ HV *hv) {
 
     PERL_ARGS_ASSERT_HV_RITER_P;
 
-    if (!hv)
-	Perl_croak(aTHX_ "Bad hash");
-
     iter = SvOOK(hv) ? HvAUX(hv) : hv_auxinit(hv);
     return &(iter->xhv_riter);
 }
@@ -2141,9 +2133,6 @@ Perl_hv_eiter_p(pTHX_ HV *hv) {
 
     PERL_ARGS_ASSERT_HV_EITER_P;
 
-    if (!hv)
-	Perl_croak(aTHX_ "Bad hash");
-
     iter = SvOOK(hv) ? HvAUX(hv) : hv_auxinit(hv);
     return &(iter->xhv_eiter);
 }
@@ -2154,9 +2143,6 @@ Perl_hv_riter_set(pTHX_ HV *hv, I32 riter) {
 
     PERL_ARGS_ASSERT_HV_RITER_SET;
 
-    if (!hv)
-	Perl_croak(aTHX_ "Bad hash");
-
     if (SvOOK(hv)) {
 	iter = HvAUX(hv);
     } else {
@@ -2175,9 +2161,6 @@ Perl_hv_rand_set(pTHX_ HV *hv, U32 new_xhv_rand) {
     PERL_ARGS_ASSERT_HV_RAND_SET;
 
 #ifdef PERL_HASH_RANDOMIZE_KEYS
-    if (!hv)
-        Perl_croak(aTHX_ "Bad hash");
-
     if (SvOOK(hv)) {
         iter = HvAUX(hv);
     } else {
@@ -2195,9 +2178,6 @@ Perl_hv_eiter_set(pTHX_ HV *hv, HE *eiter) {
 
     PERL_ARGS_ASSERT_HV_EITER_SET;
 
-    if (!hv)
-	Perl_croak(aTHX_ "Bad hash");
-
     if (SvOOK(hv)) {
 	iter = HvAUX(hv);
     } else {
@@ -2515,9 +2495,6 @@ Perl_hv_iternext_flags(pTHX_ HV *hv, I32 flags)
 
     PERL_ARGS_ASSERT_HV_ITERNEXT_FLAGS;
 
-    if (!hv)
-	Perl_croak(aTHX_ "Bad hash");
-
     xhv = (XPVHV*)SvANY(hv);
 
     if (!SvOOK(hv)) {

mro.c

@@ -685,7 +685,7 @@ S_mro_clean_isarev(pTHX_ HV * const isa, const char * const name,
     PERL_ARGS_ASSERT_MRO_CLEAN_ISAREV;
 
     /* Delete our name from our former parents' isarevs. */
-    if(isa && HvARRAY(isa) && hv_iterinit(isa)) {
+    if(HvARRAY(isa) && hv_iterinit(isa)) {
         SV **svp;
         while((iter = hv_iternext(isa))) {
             I32 klen;

op.c

@@ -400,7 +400,7 @@ Perl_opslab_free(pTHX_ OPSLAB *slab)
     PERL_UNUSED_CONTEXT;
     DEBUG_S_warn((aTHX_ "freeing slab %p", (void*)slab));
     assert(slab->opslab_refcnt == 1);
-    for (; slab; slab = slab2) {
+    do {
 	slab2 = slab->opslab_next;
 #ifdef DEBUGGING
 	slab->opslab_refcnt = ~(size_t)0;
@@ -415,7 +415,8 @@ Perl_opslab_free(pTHX_ OPSLAB *slab)
 #else
 	PerlMemShared_free(slab);
 #endif
-    }
+        slab = slab2;
+    } while (slab);
 }
 
 void
@@ -3236,7 +3237,7 @@ Perl_doref(pTHX_ OP *o, I32 type, bool set_op_ref)
 
     PERL_ARGS_ASSERT_DOREF;
 
-    if (!o || (PL_parser && PL_parser->error_count))
+    if (PL_parser && PL_parser->error_count)
 	return o;
 
     switch (o->op_type) {
@@ -8390,7 +8391,7 @@ Perl_newMYSUB(pTHX_ I32 floor, OP *o, OP *proto, OP *attrs, OP *block)
     if (slab)
 	Slab_to_ro(slab);
 #endif
-    if (o) op_free(o);
+    op_free(o);
     return cv;
 }
 
@@ -9080,9 +9081,7 @@ Perl_newXS_len_flags(pTHX_ const char *name, STRLEN len,
     bool interleave = FALSE;
 
     PERL_ARGS_ASSERT_NEWXS_LEN_FLAGS;
-    if (!subaddr)
-	Perl_croak_nocontext("panic: no address for '%s' in '%s'",
-	    name, filename ? filename : PL_xsubfilename);
+
     {
         GV * const gv = gv_fetchpvn(
 			    name ? name : PL_curstash ? "__ANON__" : "__ANON__::__ANON__",

perl.c

@@ -2601,13 +2601,11 @@ Perl_call_argv(pTHX_ const char *sub_name, I32 flags, char **argv)
     PERL_ARGS_ASSERT_CALL_ARGV;
 
     PUSHMARK(SP);
-    if (argv) {
-	while (*argv) {
-	    mXPUSHs(newSVpv(*argv,0));
-	    argv++;
-	}
-	PUTBACK;
+    while (*argv) {
+        mXPUSHs(newSVpv(*argv,0));
+        argv++;
     }
+    PUTBACK;
     return call_pv(sub_name, flags);
 }
 

pp_sys.c

@@ -4806,7 +4806,7 @@ S_space_join_names_mortal(pTHX_ char *const *array)
 
     PERL_ARGS_ASSERT_SPACE_JOIN_NAMES_MORTAL;
 
-    if (array && *array) {
+    if (*array) {
 	target = newSVpvs_flags("", SVs_TEMP);
 	while (1) {
 	    sv_catpv(target, *array);

proto.h

@@ -986,10 +986,9 @@ PERL_CALLCONV void	Perl_do_join(pTHX_ SV *sv, SV *delim, SV **mark, SV **sp)
 	assert(sv); assert(delim); assert(mark); assert(sp)
 
 PERL_CALLCONV void	Perl_do_magic_dump(pTHX_ I32 level, PerlIO *file, const MAGIC *mg, I32 nest, I32 maxnest, bool dumpops, STRLEN pvlim)
-			__attribute__nonnull__(pTHX_2)
-			__attribute__nonnull__(pTHX_3);
+			__attribute__nonnull__(pTHX_2);
 #define PERL_ARGS_ASSERT_DO_MAGIC_DUMP	\
-	assert(file); assert(mg)
+	assert(file)
 
 PERL_CALLCONV I32	Perl_do_ncmp(pTHX_ SV *const left, SV *const right)
 			__attribute__warn_unused_result__
@@ -1427,11 +1426,7 @@ PERL_CALLCONV SV*	Perl_gv_const_sv(pTHX_ GV* gv)
 #define PERL_ARGS_ASSERT_GV_CONST_SV	\
 	assert(gv)
 
-PERL_CALLCONV void	Perl_gv_dump(pTHX_ GV* gv)
-			__attribute__nonnull__(pTHX_1);
-#define PERL_ARGS_ASSERT_GV_DUMP	\
-	assert(gv)
-
+PERL_CALLCONV void	Perl_gv_dump(pTHX_ GV* gv);
 PERL_CALLCONV void	Perl_gv_efullname(pTHX_ SV* sv, const GV* gv)
 			__attribute__nonnull__(pTHX_1)
 			__attribute__nonnull__(pTHX_2);

regexec.c

@@ -2783,7 +2783,7 @@ Perl_regexec_flags(pTHX_ REGEXP * const rx, char *stringarg, char *strend,
     PERL_UNUSED_ARG(data);
 
     /* Be paranoid... */
-    if (prog == NULL || stringarg == NULL) {
+    if (prog == NULL) {
 	Perl_croak(aTHX_ "NULL regexp parameter");
     }
 
@@ -2802,7 +2802,7 @@ Perl_regexec_flags(pTHX_ REGEXP * const rx, char *stringarg, char *strend,
         reginfo->ganch =
             (flags & REXEC_IGNOREPOS)
             ? stringarg /* use start pos rather than pos() */
-            : (sv && (mg = mg_find_mglob(sv)) && mg->mg_len >= 0)
+            : ((mg = mg_find_mglob(sv)) && mg->mg_len >= 0)
               /* Defined pos(): */
             ? strbeg + MgBYTEPOS(mg, sv, strbeg, strend-strbeg)
             : strbeg; /* pos() not defined; use start of string */

sv.c

@@ -6306,8 +6306,6 @@ Perl_sv_insert_flags(pTHX_ SV *const bigstr, const STRLEN offset, const STRLEN l
 
     PERL_ARGS_ASSERT_SV_INSERT_FLAGS;
 
-    if (!bigstr)
-	Perl_croak(aTHX_ "Can't modify nonexistent substring");
     SvPV_force_flags(bigstr, curlen, flags);
     (void)SvPOK_only_UTF8(bigstr);
     if (offset + len > curlen) {
@@ -15352,7 +15350,7 @@ Perl_sv_cat_decode(pTHX_ SV *dsv, SV *encoding,
 
     PERL_ARGS_ASSERT_SV_CAT_DECODE;
 
-    if (SvPOK(ssv) && SvPOK(dsv) && SvROK(encoding) && offset) {
+    if (SvPOK(ssv) && SvPOK(dsv) && SvROK(encoding)) {
 	SV *offsv;
 	dSP;
 	ENTER;

util.c

@@ -556,10 +556,6 @@ Perl_instr(const char *big, const char *little)
 
     PERL_ARGS_ASSERT_INSTR;
 
-    /* libc prior to 4.6.27 (late 1994) did not work properly on a NULL
-     * 'little' */
-    if (!little)
-	return (char*)big;
     return strstr((char*)big, (char*)little);
 }