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, 12 insertions, 3 deletions

diff --git a/erts/emulator/beam/ops.tab b/erts/emulator/beam/ops.tab
index d71594235e..d859c4bb24 100644
--- a/erts/emulator/beam/ops.tab
+++ b/erts/emulator/beam/ops.tab
@@ -483,9 +483,16 @@ is_eq f? s s
 is_ne f? s s
 
 #
-# Putting things.
+# Putting tuples.
+#
+# Code compiled with OTP 22 and later uses put_tuple2 to
+# to construct a tuple.
+#
+# Code compiled before OTP 22 uses put_tuple + one put instruction
+# per element. Translate to put_tuple2.
 #
 
+i_put_tuple/2
 put_tuple Arity Dst => i_put_tuple Dst u
 
 i_put_tuple Dst Arity Puts=* | put S1 | put S2 | \
@@ -495,11 +502,13 @@ i_put_tuple Dst Arity Puts=* | put S1 | put S2 | \
 i_put_tuple Dst Arity Puts=* | put S => \
 	    tuple_append_put(Arity, Dst, Puts, S)
 
-i_put_tuple/2
+i_put_tuple Dst Arity Puts=* => put_tuple2 Dst Arity Puts
 
-i_put_tuple xy I
+put_tuple2 xy I
 
 #
+# Putting lists.
+#
 # The instruction "put_list Const [] Dst" were generated in rare
 # circumstances up to and including OTP 18. Starting with OTP 19,
 # AFAIK, it should never be generated.