make scalar(keys(%lexical)) less slow.

A recent commit in this branch made OP_PADHV / OP_RV2HV in void/scalar
context, followed by OP_KEYS, optimise away the OP_KEYS op and set the
OPpPADHV_ISKEYS or OPpRV2HV_ISKEYS flag on the OP_PADHV / OP_RV2HV op.

However, in scalar but non-boolean context with OP_PADHV, this actually
makes it slower, because the OP_KEYS op has a target, while the OP_PADHV
op doesn't, thus it has to create a new mortal each time to return the
integer value.

This commit fixes that by, in the case of scalar padhv, retaining the
OP_KEYS node (although still not keeping it in the execution path), then
at runtime using that op's otherwise unused target.

This only works on PERL_OP_PARENT builds (now the default) as the OP_KEYS
is the parent of the OP_PADHV, so would be hard to find at runtime
otherwise.

This commit also fixes pp_padhv/pp_rv2hv in void context - formerly it
was needlessly pushing a scalar-valued count like scalar context.

1 files changed, 7 insertions, 1 deletions

diff --git a/lib/B/Deparse.pm b/lib/B/Deparse.pm
index f214081a7b..fe4e24960d 100644
--- a/lib/B/Deparse.pm
+++ b/lib/B/Deparse.pm
@@ -4115,7 +4115,13 @@ sub pp_padav { pp_padsv(@_) }
 
 sub pp_padhv {
     my $op = $_[1];
-    (($op->private & OPpPADHV_ISKEYS) ? 'keys ' : '') . pp_padsv(@_);
+    my $keys = '';
+    # with OPpPADHV_ISKEYS the keys op is optimised away, except
+    # in scalar context the old op is kept (but not executed) so its targ
+    # can be used.
+    $keys = 'keys ' if (     ($op->private & OPpPADHV_ISKEYS)
+                            && !(($op->flags & OPf_WANT) == OPf_WANT_SCALAR));
+    $keys . pp_padsv(@_);
 }
 
 sub gv_or_padgv {