Very few PAD[HA]Vs are "LVALUE": branch predictor hints

In a nutshell, very few PADHV and PADAV OPs are executed that have
the OPpLVAL_INTRO flag set. To wit, "my %h" does whereas "$h{foo}" and
similar (also "$h{foo} = 1") do not. Also, traditional lexicals greatly
outnumber state variables, so pessimize "state" slightly.

This was determined with a nifty new trick. With a Perl compiled with
-DPERL_TRACE_OPS, we get a summary of all executed op counts by type at
the end of the program execution. The above was figured out (naively) by
adding the following:

--- a/dump.c
+++ b/dump.c
@@ -2215,6 +2215,8 @@ Perl_runops_debug(pTHX)
     do {
 #ifdef PERL_TRACE_OPS
         ++PL_op_exec_cnt[PL_op->op_type];
+        if (PL_op->op_type == OP_PADHV && PL_op->op_private & OPpLVAL_INTRO)
+            ++PL_op_exec_cnt[OP_max+1];
 #endif
        if (PL_debug) {
            if (PL_watchaddr && (*PL_watchaddr != PL_watchok))

Which adds a special case (OP_max+1) to the OP report. Dividing that
count by the total PADHV count gives a diminishingly small percentage.

1 files changed, 4 insertions, 4 deletions

diff --git a/pp.c b/pp.c
index dce5ccb418..e7e06fffdf 100644
--- a/pp.c
+++ b/pp.c
@@ -68,8 +68,8 @@ PP(pp_padav)
     dVAR; dSP; dTARGET;
     I32 gimme;
     assert(SvTYPE(TARG) == SVt_PVAV);
-    if (PL_op->op_private & OPpLVAL_INTRO)
-	if (!(PL_op->op_private & OPpPAD_STATE))
+    if (UNLIKELY( PL_op->op_private & OPpLVAL_INTRO ))
+	if (LIKELY( !(PL_op->op_private & OPpPAD_STATE) ))
 	    SAVECLEARSV(PAD_SVl(PL_op->op_targ));
     EXTEND(SP, 1);
     if (PL_op->op_flags & OPf_REF) {
@@ -118,8 +118,8 @@ PP(pp_padhv)
 
     assert(SvTYPE(TARG) == SVt_PVHV);
     XPUSHs(TARG);
-    if (PL_op->op_private & OPpLVAL_INTRO)
-	if (!(PL_op->op_private & OPpPAD_STATE))
+    if (UNLIKELY( PL_op->op_private & OPpLVAL_INTRO ))
+	if (LIKELY( !(PL_op->op_private & OPpPAD_STATE) ))
 	    SAVECLEARSV(PAD_SVl(PL_op->op_targ));
     if (PL_op->op_flags & OPf_REF)
 	RETURN;