From 6f45ff73583aa7d0352b8a16df78872f47defd35 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Sat, 9 Sep 2017 12:01:14 +0200
Subject: Optimize i_select_tuple_arity2 and is_select_lins

Don't save a pointer to the default failure label. That could
relieve register pressure. Instead, if we'll need to signal an
error in i_select_tuple_arity2, delay to the execution phase.
That should be a clear win because i_select_tuple_arity2 very
rarely fails because of the term being selected is not a tuple.
---
 erts/emulator/beam/select_instrs.tab | 43 ++++++++++++++----------------------
 1 file changed, 16 insertions(+), 27 deletions(-)

diff --git a/erts/emulator/beam/select_instrs.tab b/erts/emulator/beam/select_instrs.tab
index 4a8d9cce96..f5ce5d5a32 100644
--- a/erts/emulator/beam/select_instrs.tab
+++ b/erts/emulator/beam/select_instrs.tab
@@ -75,66 +75,55 @@ select_val_bins.select(Fail, NumElements) {
     $JUMP($Fail);
 }
 
-i_select_tuple_arity2 := select_val2.src.ta_fail.execute;
-i_select_val2 := select_val2.src.fail.execute;
+i_select_tuple_arity2 := select_val2.src.get_arity.execute;
+i_select_val2 := select_val2.src.execute;
 
 select_val2.head() {
     Eterm select_val2;
-    BeamInstr* select_fail;
 }
 
 select_val2.src(Src) {
     select_val2 = $Src;
 }
 
-select_val2.ta_fail(Fail) {
-    select_fail = &$Fail;
-    if (is_not_tuple(select_val2)) {
-        $FAIL(*select_fail);
+select_val2.get_arity() {
+    if (ERTS_LIKELY(is_tuple(select_val2))) {
+        select_val2 = *tuple_val(select_val2);
+    } else {
+        select_val2 = NIL;
     }
-    select_val2 = *tuple_val(select_val2);
-}
-
-select_val2.fail(Fail) {
-    select_fail = &$Fail;
 }
 
-select_val2.execute(T1, T2, D1, D2) {
+select_val2.execute(Fail, T1, T2, D1, D2) {
     if (select_val2 == $T1) {
         $JUMP($D1);
     } else if (select_val2 == $T2) {
         $JUMP($D2);
     } else {
-        $FAIL(*select_fail);
+        $FAIL($Fail);
     }
 }
 
-i_select_tuple_arity := select_val_lin.fetch.ta_fail.execute;
-i_select_val_lins := select_val_lin.fetch.fail.execute;
+i_select_tuple_arity := select_val_lin.fetch.get_arity.execute;
+i_select_val_lins := select_val_lin.fetch.execute;
 
 select_val_lin.head() {
     Eterm select_val;
-    BeamInstr* select_fail;
 }
 
 select_val_lin.fetch(Src) {
     select_val = $Src;
 }
 
-select_val_lin.ta_fail(Fail) {
-    select_fail = &$Fail;
-    if (is_tuple(select_val)) {
+select_val_lin.get_arity() {
+    if (ERTS_LIKELY(is_tuple(select_val))) {
         select_val = *tuple_val(select_val);
     } else {
-        $JUMP(*select_fail);
+        select_val = NIL;
     }
 }
 
-select_val_lin.fail(Fail) {
-    select_fail = &$Fail;
-}
-
-select_val_lin.execute(N) {
+select_val_lin.execute(Fail, N) {
     BeamInstr* vs = $NEXT_INSTRUCTION;
     int ix = 0;
 
@@ -155,7 +144,7 @@ select_val_lin.execute(N) {
         Eterm offset = jump_tab[ix];
         $JUMP(offset);
     } else {
-        $JUMP(*select_fail);
+        $JUMP($Fail);
     }
 }
 
-- 
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