From: Nicholas Clark <nick@ccl4.org>
Date: Sun, 30 May 2010 10:51:15 +0000 (+0100)
Subject: Only allocate entries for @_ when the subroutine is first called.
X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=commitdiff_plain;h=77bac227771c643a8a6e305b2bac4665a8f772d1;p=p5sagit%2Fp5-mst-13.2.git

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
--- 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);