From 47a2ff39ac75c69b41f90f05a63fd9a2e6c0b36a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Sat, 1 Sep 2018 10:57:33 +0200
Subject: Introduce a put_tuple2 instruction

Sometimes when building a tuple, there is no way to avoid an
extra `move` instruction. Consider this code:

    make_tuple(A) -> {ok,A}.

The corresponding BEAM code looks like this:

    {test_heap,3,1}.
    {put_tuple,2,{x,1}}.
    {put,{atom,ok}}.
    {put,{x,0}}.
    {move,{x,1},{x,0}}.
    return.

To avoid overwriting the source register `{x,0}`, a `move`
instruction is necessary.

The problem doesn't exist when building a list:

    %% build_list(A) -> [A].
    {test_heap,2,1}.
    {put_list,{x,0},nil,{x,0}}.
    return.

Introduce a new `put_tuple2` instruction that builds a tuple in a
single instruction, so that the `move` instruction can be eliminated:

    %% make_tuple(A) -> {ok,A}.
    {test_heap,3,1}.
    {put_tuple2,{x,0},{list,[{atom,ok},{x,0}]}}.
    return.

Note that the BEAM loader already combines `put_tuple` and `put`
instructions into an internal instruction similar to `put_tuple2`.
Therefore the introduction of the new instruction will not speed up
execution of tuple building itself, but it will be less work for
the loader to load the new instruction.
---
 lib/hipe/icode/hipe_beam_to_icode.erl | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

(limited to 'lib/hipe')

diff --git a/lib/hipe/icode/hipe_beam_to_icode.erl b/lib/hipe/icode/hipe_beam_to_icode.erl
index 4f099baab3..ffe81ef9b8 100644
--- a/lib/hipe/icode/hipe_beam_to_icode.erl
+++ b/lib/hipe/icode/hipe_beam_to_icode.erl
@@ -647,6 +647,13 @@ trans_fun([{put_tuple,_Size,Reg}|Instructions], Env) ->
   Primop = hipe_icode:mk_primop(Dest,mktuple,Src),
   Moves ++ [Primop | trans_fun(Instructions2,Env2)];
 %%--- put --- SHOULD NOT REALLY EXIST HERE; put INSTRUCTIONS ARE HANDLED ABOVE.
+%%--- put_tuple2 ---
+trans_fun([{put_tuple2,Reg,{list,Elements}}|Instructions], Env) ->
+  Dest = [mk_var(Reg)],
+  {Moves,Vars,Env2} = trans_elements(Elements, [], [], Env),
+  Src = lists:reverse(Vars),
+  Primop = hipe_icode:mk_primop(Dest, mktuple, Src),
+  Moves ++ [Primop | trans_fun(Instructions, Env2)];
 %%--- badmatch ---
 trans_fun([{badmatch,Arg}|Instructions], Env) ->
   BadVar = trans_arg(Arg),
@@ -1699,6 +1706,19 @@ trans_puts([{put,X}|Code], Vars, Moves, Env) ->
 trans_puts(Code, Vars, Moves, Env) ->    %% No more put operations
   {Moves, Code, Vars, Env}.
 
+trans_elements([X|Code], Vars, Moves, Env) ->
+  case type(X) of
+    var ->
+      Var = mk_var(X),
+      trans_elements(Code, [Var|Vars], Moves, Env);
+    #beam_const{value=C} ->
+      Var = mk_var(new),
+      Move = hipe_icode:mk_move(Var, hipe_icode:mk_const(C)),
+      trans_elements(Code, [Var|Vars], [Move|Moves], Env)
+  end;
+trans_elements([], Vars, Moves, Env) ->
+  {Moves, Vars, Env}.
+
 %%-----------------------------------------------------------------------
 %% The code for this instruction is a bit large because we are treating
 %% different cases differently.  We want to use the icode `type' 
-- 
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