From 7e44a4b8eaad7d7d6fadf933794d3a0d05790b23 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Tue, 12 Mar 2019 07:20:43 +0100
Subject: Combine move with trim

It is relatively common to move something from a Y register to
an X register before trimming.
---
 erts/emulator/beam/instrs.tab | 7 +++++++
 erts/emulator/beam/ops.tab    | 3 +++
 2 files changed, 10 insertions(+)

diff --git a/erts/emulator/beam/instrs.tab b/erts/emulator/beam/instrs.tab
index aeb47c3b0f..7fa1df64ff 100644
--- a/erts/emulator/beam/instrs.tab
+++ b/erts/emulator/beam/instrs.tab
@@ -477,6 +477,13 @@ i_make_fun(FunP, NumFree) {
     HEAVY_SWAPIN;
 }
 
+move_trim(Src, Dst, Words) {
+    Uint cp = E[0];
+    $Dst = $Src;
+    E += $Words;
+    E[0] = cp;
+}
+
 i_trim(Words) {
     Uint cp = E[0];
     E += $Words;
diff --git a/erts/emulator/beam/ops.tab b/erts/emulator/beam/ops.tab
index a6f5ba347c..4f57e8d9d5 100644
--- a/erts/emulator/beam/ops.tab
+++ b/erts/emulator/beam/ops.tab
@@ -106,7 +106,10 @@ init y
 allocate_zero t t?
 allocate_heap_zero t I t?
 
+move Src=y Dst=x | trim N Remaining => move_trim Src Dst N
 trim N Remaining => i_trim N
+
+move_trim y x t
 i_trim t
 
 test_heap I t?
-- 
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