From 2f432a4399544baa346ffa9b0dd18a7ab717dd53 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Thu, 28 Feb 2019 10:25:02 +0100
Subject: Combine is_nonempty_list with get_hd/get_tl

The is_nonempty_list test is very frequently followed by
get_tl, and frequently followed by get_hd.
---
 erts/emulator/beam/instrs.tab | 12 ++++++++++++
 erts/emulator/beam/ops.tab    | 10 ++++++++++
 2 files changed, 22 insertions(+)

diff --git a/erts/emulator/beam/instrs.tab b/erts/emulator/beam/instrs.tab
index 14ca07f97e..fc88cab22f 100644
--- a/erts/emulator/beam/instrs.tab
+++ b/erts/emulator/beam/instrs.tab
@@ -678,6 +678,18 @@ is_nonempty_list_get_list(Fail, Src, Hd, Tl) {
     $get_list($Src, $Hd, $Tl);
 }
 
+is_nonempty_list_get_hd(Fail, Src, Hd) {
+    //| -no_prefetch
+    $is_nonempty_list($Fail, $Src);
+    $get_hd($Src, $Hd);
+}
+
+is_nonempty_list_get_tl(Fail, Src, Tl) {
+    //| -no_prefetch
+    $is_nonempty_list($Fail, $Src);
+    $get_tl($Src, $Tl);
+}
+
 jump(Fail) {
     $JUMP($Fail);
 }
diff --git a/erts/emulator/beam/ops.tab b/erts/emulator/beam/ops.tab
index 47a8e566b2..3cfc685336 100644
--- a/erts/emulator/beam/ops.tab
+++ b/erts/emulator/beam/ops.tab
@@ -679,8 +679,18 @@ is_nonempty_list Fail=f S=x | allocate Need Rs => is_nonempty_list_allocate Fail
 is_nonempty_list Fail=f S=x | get_list S D1=x D2=x => \
   is_nonempty_list_get_list Fail S D1 D2
 
+is_nonempty_list Fail=f S=x | get_hd S Dst=x => \
+  is_nonempty_list_get_hd Fail S Dst
+
+is_nonempty_list Fail=f S=x | get_tl S Dst=x => \
+  is_nonempty_list_get_tl Fail S Dst
+
 is_nonempty_list_allocate f? rx t t
+
 is_nonempty_list_get_list f? rx x x
+is_nonempty_list_get_hd f? x x
+is_nonempty_list_get_tl f? x x
+
 is_nonempty_list f? xy
 
 is_atom f? x
-- 
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