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, 17 insertions, 0 deletions

diff --git a/lib/compiler/src/beam_disasm.erl b/lib/compiler/src/beam_disasm.erl
index 6cee9acae4..d0be39f520 100644
--- a/lib/compiler/src/beam_disasm.erl
+++ b/lib/compiler/src/beam_disasm.erl
@@ -373,6 +373,8 @@ disasm_instr(B, Bs, Atoms, Literals) ->
 	    disasm_map_inst(get_map_elements, Arity, Bs, Atoms, Literals);
 	has_map_fields ->
 	    disasm_map_inst(has_map_fields, Arity, Bs, Atoms, Literals);
+	put_tuple2 ->
+	    disasm_put_tuple2(Bs, Atoms, Literals);
 	_ ->
 	    try decode_n_args(Arity, Bs, Atoms, Literals) of
 		{Args, RestBs} ->
@@ -413,6 +415,14 @@ disasm_map_inst(Inst, Arity, Bs0, Atoms, Literals) ->
     {List, RestBs} = decode_n_args(Len, Bs2, Atoms, Literals),
     {{Inst, Args ++ [{Z,U,List}]}, RestBs}.
 
+disasm_put_tuple2(Bs, Atoms, Literals) ->
+    {X, Bs1} = decode_arg(Bs, Atoms, Literals),
+    {Z, Bs2} = decode_arg(Bs1, Atoms, Literals),
+    {U, Bs3} = decode_arg(Bs2, Atoms, Literals),
+    {u, Len} = U,
+    {List, RestBs} = decode_n_args(Len, Bs3, Atoms, Literals),
+    {{put_tuple2, [X,{Z,U,List}]}, RestBs}.
+
 %%-----------------------------------------------------------------------
 %% decode_arg([Byte]) -> {Arg, [Byte]}
 %%
@@ -1096,6 +1106,13 @@ resolve_inst({get_tl,[Src,Dst]},_,_,_) ->
     {get_tl,Src,Dst};
 
 %%
+%% OTP 22.
+%%
+resolve_inst({put_tuple2,[Dst,{{z,1},{u,_},List0}]},_,_,_) ->
+    List = resolve_args(List0),
+    {put_tuple2,Dst,{list,List}};
+
+%%
 %% Catches instructions that are not yet handled.
 %%
 resolve_inst(X,_,_,_) -> ?exit({resolve_inst,X}).