File 2330-Optimize-encoding-of-simple-literals.patch of Package erlang
From 6a9ed8508d4025c68b90aab44679551655967908 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Sun, 14 Apr 2019 09:07:40 +0200
Subject: [PATCH] Optimize encoding of simple literals
`beam_asm` would encode `{literal,[]}`, `{literal,erlang}`, and
`{literal,42}` in a less efficient way than the equivalent values
`nil`, `{atom,erlang}`, and `{integer,42}`. That would increase the
size of BEAM files and could increase the loaded code size. It would
probably not harm performance, because `literal` was only used this
way in code that generates `badmatch` and `case_clause` exceptions.
---
lib/compiler/src/beam_asm.erl | 26 +++++++++++++++++++-------
1 file changed, 19 insertions(+), 7 deletions(-)
diff --git a/lib/compiler/src/beam_asm.erl b/lib/compiler/src/beam_asm.erl
index bc1290f6fd..df09dcb06c 100644
--- a/lib/compiler/src/beam_asm.erl
+++ b/lib/compiler/src/beam_asm.erl
@@ -407,14 +407,14 @@ encode_arg({atom, Atom}, Dict0) when is_atom(Atom) ->
{Index, Dict} = beam_dict:atom(Atom, Dict0),
{encode(?tag_a, Index), Dict};
encode_arg({integer, N}, Dict) ->
- %% Conservatily assume that all integers whose absolute
+ %% Conservatively assume that all integers whose absolute
%% value is greater than 1 bsl 128 will be bignums in
%% the runtime system.
if
N >= 1 bsl 128 ->
- encode_arg({literal, N}, Dict);
+ encode_literal(N, Dict);
N =< -(1 bsl 128) ->
- encode_arg({literal, N}, Dict);
+ encode_literal(N, Dict);
true ->
{encode(?tag_i, N), Dict}
end;
@@ -434,7 +434,7 @@ encode_arg({list, List}, Dict0) ->
{L, Dict} = encode_list(List, Dict0, []),
{[encode(?tag_z, 1), encode(?tag_u, length(List))|L], Dict};
encode_arg({float, Float}, Dict) when is_float(Float) ->
- encode_arg({literal,Float}, Dict);
+ encode_literal(Float, Dict);
encode_arg({fr,Fr}, Dict) ->
{[encode(?tag_z, 2),encode(?tag_u, Fr)], Dict};
encode_arg({field_flags,Flags0}, Dict) ->
@@ -442,12 +442,24 @@ encode_arg({field_flags,Flags0}, Dict) ->
{encode(?tag_u, Flags), Dict};
encode_arg({alloc,List}, Dict) ->
encode_alloc_list(List, Dict);
-encode_arg({literal,Lit}, Dict0) ->
- {Index,Dict} = beam_dict:literal(Lit, Dict0),
- {[encode(?tag_z, 4),encode(?tag_u, Index)],Dict};
+encode_arg({literal,Lit}, Dict) ->
+ if
+ Lit =:= [] ->
+ encode_arg(nil, Dict);
+ is_atom(Lit) ->
+ encode_arg({atom,Lit}, Dict);
+ is_integer(Lit) ->
+ encode_arg({integer,Lit}, Dict);
+ true ->
+ encode_literal(Lit, Dict)
+ end;
encode_arg(Int, Dict) when is_integer(Int) ->
{encode(?tag_u, Int),Dict}.
+encode_literal(Literal, Dict0) ->
+ {Index,Dict} = beam_dict:literal(Literal, Dict0),
+ {[encode(?tag_z, 4),encode(?tag_u, Index)],Dict}.
+
%%flag_to_bit(aligned) -> 16#01; %% No longer useful.
flag_to_bit(little) -> 16#02;
flag_to_bit(big) -> 16#00;
--
2.16.4