add SvREFCNT_dec_NN()

Like SvREFCNT_dec(), but skips the not null check, making code potentially
smaller and faster.

Also as proof of concept, updates the SvREFCNT_dec's in scope.c where
it's obvious the value can't be NULL. There are still 500+ uses in the
perl core that need evaluating!

1 files changed, 10 insertions, 0 deletions

diff --git a/inline.h b/inline.h
index 5e11b69122..776a30499e 100644
--- a/inline.h
+++ b/inline.h
@@ -64,6 +64,16 @@ S_SvREFCNT_dec(pTHX_ SV *sv)
 }
 
 PERL_STATIC_INLINE void
+S_SvREFCNT_dec_NN(pTHX_ SV *sv)
+{
+    U32 rc = SvREFCNT(sv);
+    if (rc > 1)
+	SvREFCNT(sv) = rc - 1;
+    else
+	Perl_sv_free2(aTHX_ sv, rc);
+}
+
+PERL_STATIC_INLINE void
 SvAMAGIC_on(SV *sv)
 {
     assert(SvROK(sv));