Only allocate entries for @_ when the subroutine is first called.

Previously, @_ was allocated for every subroutine at compile time, with a
default sized AV, hence space for 4 entries. We don't actually need to
allocate the space for entries, as there is already a check at call time as to
whether @_ is long enough.

valgrind suggests that this saves allocating 23K (on a 64 bit platform) when
running pod2man on perlfunc.pod. As well as the absolute saving, there is also
benefit in deferring allocation for subroutines actually called - for a program
which forks, @_ is less likely to be in pages shared COW with the parent.

Resolves RT #72416.

diff --git a/pad.c b/pad.c
index 8015154..f297e54 100644 (file)
--- a/pad.c
+++ b/pad.c
@@ -200,7 +200,6 @@ Perl_pad_new(pTHX_ int flags)
         */
 
         AV * const a0 = newAV();                       /* will be @_ */
-       av_extend(a0, 0);
        av_store(pad, 0, MUTABLE_SV(a0));
        AvREIFY_only(a0);
     }
@@ -1299,7 +1298,6 @@ Perl_pad_tidy(pTHX_ padtidy_type type)
     else if (type == padtidy_SUB) {
        /* XXX DAPM this same bit of code keeps appearing !!! Rationalise? */
        AV * const av = newAV();                        /* Will be @_ */
-       av_extend(av, 0);
        av_store(PL_comppad, 0, MUTABLE_SV(av));
        AvREIFY_only(av);
     }
@@ -1742,7 +1740,6 @@ Perl_pad_push(pTHX_ PADLIST *padlist, int depth)
            }
        }
        av = newAV();
-       av_extend(av, 0);
        av_store(newpad, 0, MUTABLE_SV(av));
        AvREIFY_only(av);