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.

1 files changed, 1 insertions, 0 deletions

diff --git a/lib/compiler/src/beam_flatten.erl b/lib/compiler/src/beam_flatten.erl
index 9a1c5a1021..973d16a1bc 100644
--- a/lib/compiler/src/beam_flatten.erl
+++ b/lib/compiler/src/beam_flatten.erl
@@ -65,6 +65,7 @@ norm({set,[D],[S],move})          -> {move,S,D};
 norm({set,[D],[S],fmove})         -> {fmove,S,D};
 norm({set,[D],[S],fconv})         -> {fconv,S,D};
 norm({set,[D],[S1,S2],put_list})  -> {put_list,S1,S2,D};
+norm({set,[D],Els,put_tuple2})    -> {put_tuple2,D,{list,Els}};
 norm({set,[D],[],{put_tuple,A}})  -> {put_tuple,A,D};
 norm({set,[],[S],put})            -> {put,S};
 norm({set,[D],[S],{get_tuple_element,I}}) -> {get_tuple_element,S,I,D};