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, 18 insertions, 0 deletions

diff --git a/pp_hot.c b/pp_hot.c
index e1e151bc6e..528817fed9 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -991,6 +991,9 @@ S_padhv_rv2hv_common(pTHX_ HV *hv, U8 gimme, bool is_keys, bool has_targ)
         /* 'keys %h' masquerading as '%h': reset iterator */
         (void)hv_iterinit(hv);
 
+    if (gimme == G_VOID)
+        return NORMAL;
+
     is_bool = (     PL_op->op_private & OPpTRUEBOOL
               || (  PL_op->op_private & OPpMAYBE_TRUEBOOL
                   && block_gimme() == G_VOID));
@@ -1022,6 +1025,21 @@ S_padhv_rv2hv_common(pTHX_ HV *hv, U8 gimme, bool is_keys, bool has_targ)
                 PUSHi(i);
             }
             else
+#ifdef PERL_OP_PARENT
+            if (is_keys) {
+                /* parent op should be an unused OP_KEYS whose targ we can
+                 * use */
+                dTARG;
+                OP *k;
+
+                assert(!OpHAS_SIBLING(PL_op));
+                k = PL_op->op_sibparent;
+                assert(k->op_type == OP_KEYS);
+                TARG = PAD_SV(k->op_targ);
+                PUSHi(i);
+            }
+            else
+#endif
                 mPUSHi(i);
         }
     }