optimize SV creation funcs in sv.c

In Perl_newSV, the sv_upgrade is redundant, except to protect against a
segv in blindly SV body derefing SvGROW (but not in sv_grow). sv_grow has
always upgraded a non-PV SV to PV. So don't it here. Since a new SV will
never have be a COW, have a SvLEN or a body, all of which SvGROW uses,
just call sv_grow. Less branching, and smaller code that way.

In Perl_newSV_type, give a hint to compiler that if a platform's
symbol visibility allows inlining, and newSV_type's arg is the base type
(currently SVt_NULL, maybe SVt_IV in future (see ML)), to possibly inline
new_SV into the caller and remove the sv_upgrade call. Also don't call
sv_upgrade if it isn't needed (SVt_NULL) in the public symbol version.

The redundant sv_upgrade then sv_grow goes to commit 79072805bf
"perl 5.0 alpha 2". VC 2003 -01 32 bit threaded machine code size in bytes
of 2 functions
Perl_newSV_type before 0x2f after 0x29
Perl_newSV  before 0x48 after 0x28

1 files changed, 3 insertions, 0 deletions

diff --git a/sv.h b/sv.h
index 5e0139086e..8c751dcd2b 100644
--- a/sv.h
+++ b/sv.h
@@ -176,6 +176,9 @@ typedef enum {
 #if defined(PERL_IN_HV_C) || defined(PERL_IN_XS_APITEST)
 #define HE_SVSLOT	SVt_NULL
 #endif
+#ifdef PERL_IN_SV_C
+#  define SVt_FIRST SVt_NULL	/* the type of SV that new_SV() in sv.c returns */
+#endif
 
 #define PERL_ARENA_ROOTS_SIZE	(SVt_LAST)