convert last small purpose of builtin.pm to C and NOOP require's I/O

builtin.c

@@ -447,7 +447,7 @@ static OP *ck_builtin_func1(pTHX_ OP *entersubop, GV *namegv, SV *ckobj)
 
     entersubop = ck_entersub_args_proto(entersubop, namegv, prototype);
 
-    OPCODE opcode = builtin->ckval;
+    OPCODE opcode = (OPCODE)builtin->ckval;
     if(!opcode)
         return entersubop;
 
@@ -752,7 +752,7 @@ XS(XS_builtin_import)
             if(!S_parse_version(sympv + 1, sympv + symlen, &vmajor, &vminor))
                 Perl_croak(aTHX_ "Invalid version bundle %" SVf_QUOTEDPREFIX, sym);
 
-            U16 want_ver = SHORTVER(vmajor, vminor);
+            U16 want_ver = (U16)SHORTVER(vmajor, vminor);
 
             if(want_ver < SHORTVER(5,39) ||
                     /* round up devel version to next major release; e.g. 5.39 => 5.40 */
@@ -789,7 +789,7 @@ Perl_boot_core_builtin(pTHX)
         SV *name = newSVpvs_flags("builtin::", SVs_TEMP);
         sv_catpv(name, builtin->name);
         CV *cv = newXS_flags(SvPV_nolen(name), builtin->xsub, __FILE__, proto, 0);
-        XSANY.any_i32 = builtin->ckval;
+        XSANY.any_i32 = (I32)builtin->ckval;
 
         if (   builtin->xsub == &XS_builtin_func1_void
             || builtin->xsub == &XS_builtin_func1_scalar)
@@ -807,6 +807,14 @@ Perl_boot_core_builtin(pTHX)
     }
 
     newXS_flags("builtin::import", &XS_builtin_import, __FILE__, NULL, 0);
+
+    HV * inc_hv = GvHVn(PL_incgv);
+    hv_stores(inc_hv, "builtin.pm", newSVpvs(__FILE__));
+
+    GV * ver_gv = gv_fetchpvs("builtin::VERSION", GV_ADDMULTI, SVt_PV);
+    SV * ver_sv = GvSV(ver_gv);
+    /* Remember to keep $VERSION in this file and $VERSION in builtin.pm synced. */
+    sv_setpvs(ver_sv, "0.016");
 }
 
 /*

lib/builtin.pm

@@ -1,10 +1,16 @@
-package builtin 0.015;
+package builtin 0.016;
 
 use v5.40;
 
 # All code, including &import, is implemented by always-present
-# functions in the perl interpreter itself.
-# See also `builtin.c` in perl source
+# functions in the perl interpreter itself in `builtin.c`.
+#
+# $builtin::VERSION and %INC are also set by the interpreter in `builtin.c`
+# since this file is a NOOP.  Therefore this file is unlikely to ever execute
+# and primarily serves as POD.
+#
+# Remember to keep $VERSION in this file and $VERSION in builtin.c synced!
+
 
 __END__
 

lib/builtin.t

@@ -645,6 +645,13 @@ EOS
     }
 }
 
+like($INC{'builtin.pm'}, qr/builtin\.c/, 'check that \'builtin.pm\' is in %INC');
+{
+    my $xsv = $builtin::VERSION;
+    delete $INC{'builtin.pm'};
+    eval "use builtin;";
+    is($xsv, $builtin::VERSION, 'XS $VERSION matches PP $VERSION');
+}
 # vim: tabstop=4 shiftwidth=4 expandtab autoindent softtabstop=4
 
 done_testing();

pod/perldelta.pod

@@ -123,11 +123,22 @@ XXX Remove this section if F<Porting/corelist-perldelta.pl> did not add any cont
 
 =over 4
 
-=item *
-
-L<XXX> has been upgraded from version A.xx to B.yy.
-
-XXX If there was something important to note about this change, include that here.
+=item builtin.pm
+
+L<builtin.pm|/builtin.pm> has been upgraded from version 0.015 to 0.016.
+As an optimization the C<builtin::> package and module is now fully
+implemented in C to save on file system I/O and startup time.
+
+Specifically the C<use builtin;> statement  and any permutations of
+C<use builtin;> will not internally perform a per process first time
+C<require;> anymore and C<$INC{'builtin.pm'}> is already filled in at
+process startup.  All C<.pm> functionality is embedded in the interpreter at
+startup now.  This optimization removes all I/O calls and time overhead of
+parsing the C<builtin.pm> file.  The C<builtin.pm> file will remain as
+documentation.
+
+C<builtin::>'s C<import()>, C<$VERSION>, and all available subroutines/APIs
+have not changed.  No changes are required to previously written code.
 
 =back