Store GvGP in the SV head union. For all the common lookups [eg GvCV()]

this avoids 1 pointer dereference and the associated risk of a CPU
cache miss. Although this patch looks deceptively small, I fear its
CBV(*) might be rather high.
(* Crack By Volume)

p4raw-id: //depot/perl@27323

1 files changed, 3 insertions, 0 deletions

diff --git a/pp_hot.c b/pp_hot.c
index 8d590caa63..d26d8f0c9c 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -1611,6 +1611,9 @@ Perl_do_readline(pTHX)
 	sv = TARG;
 	if (SvROK(sv))
 	    sv_unref(sv);
+	else if (isGV_with_GP(sv)) {
+	    SvPV_force_nolen(sv);
+	}
 	SvUPGRADE(sv, SVt_PV);
 	tmplen = SvLEN(sv);	/* remember if already alloced */
 	if (!tmplen && !SvREADONLY(sv))