From e93a66110aa27a5b8228fb46a3459a6de0e626d0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Mon, 7 Dec 2015 16:12:21 +0100
Subject: Introduce a 'rename' instruction

Introduce a 'rename' instruction that can be used to optimize
simple renaming with unchanged operands such as:

  get_tuple_element Reg P Dst => i_get_tuple_element Reg P Dst

By allowing it to lower the arity of instruction, transformations
such as the following can be handled:

  trim N Remaining => i_trim N

All in all, currently 67 transformations can be optimized in this
way, including some commonly used ones.
---
 erts/emulator/beam/beam_load.c   |  6 +++++
 erts/emulator/utils/beam_makeops | 55 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+)

(limited to 'erts')

diff --git a/erts/emulator/beam/beam_load.c b/erts/emulator/beam/beam_load.c
index 5d03c98657..ad174664ae 100644
--- a/erts/emulator/beam/beam_load.c
+++ b/erts/emulator/beam/beam_load.c
@@ -5077,6 +5077,12 @@ transform_engine(LoaderState* st)
 	    instr->arity = gen_opc[op].arity;
 	    ap = 0;
 	    break;
+#ifdef TOP_rename
+	case TOP_rename:
+	    instr->op = op = *pc++;
+	    instr->arity = gen_opc[op].arity;
+	    return TE_OK;
+#endif
 	case TOP_store_type:
 	    i = *pc++;
 	    instr->a[ap].type = i;
diff --git a/erts/emulator/utils/beam_makeops b/erts/emulator/utils/beam_makeops
index 8f99fdb201..3d4213d55d 100755
--- a/erts/emulator/utils/beam_makeops
+++ b/erts/emulator/utils/beam_makeops
@@ -1718,6 +1718,8 @@ sub tr_gen_to {
     push(@code, make_op('', 'end'))
 	unless is_instr($code[$#code], 'call_end');
 
+    tr_maybe_rename(\@code);
+
     #
     # Chain together all codes segments having the same first operation.
     #
@@ -1743,6 +1745,59 @@ sub tr_gen_to {
     push(@{$gen_transform{$key}}, @code),
 }
 
+sub tr_maybe_rename {
+    my($ref) = @_;
+    my $s = 'left';
+    my $a = 0;
+    my $num_args = 0;
+    my $new_instr;
+    my $first;
+    my $i;
+
+    for ($i = 1; $i < @$ref; $i++) {
+	my $instr = $$ref[$i];
+	my($size, $instr_ref, $comment) = @$instr;
+	my($op, @args) = @$instr_ref;
+
+	if ($s eq 'left') {
+	    if ($op eq 'set_var_next_arg') {
+		if ($num_args == $a and $args[0] == $a) {
+		    $num_args++;
+		}
+		$a++;
+	    } elsif ($op eq 'next_arg') {
+		$a++;
+	    } elsif ($op eq 'commit') {
+		$a = 0;
+		$first = $i;
+		$s = 'committed';
+	    } elsif ($op eq 'next_instr') {
+		return;
+	    }
+	} elsif ($s eq 'committed') {
+	    if ($op eq 'new_instr') {
+		$new_instr = $args[0];
+		$a = 0;
+		$s = 'right';
+	    } else {
+		return;
+	    }
+	} elsif ($s eq 'right') {
+	    if ($op eq 'store_var_next_arg' && $args[0] == $a) {
+		$a++;
+	    } elsif ($op eq 'end' && $a <= $num_args) {
+		my $name = $gen_opname[$new_instr];
+		my $arity = $gen_arity[$new_instr];
+		my $new_op = make_op("$name/$arity", 'rename', $new_instr);
+		splice @$ref, $first, $i-$first+1, ($new_op);
+		return;
+	    } else {
+		return;
+	    }
+	}
+    }
+}
+
 sub tr_code_len {
     my($sum) = 0;
     my($ref);
-- 
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