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/compiler/test/compile_SUITE.erl | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

(limited to 'lib/compiler/test')

diff --git a/lib/compiler/test/compile_SUITE.erl b/lib/compiler/test/compile_SUITE.erl
index 85f0b7dc46..8d8fc23027 100644
--- a/lib/compiler/test/compile_SUITE.erl
+++ b/lib/compiler/test/compile_SUITE.erl
@@ -1476,18 +1476,22 @@ bc_options(Config) ->
     101 = highest_opcode(DataDir, small_float, [no_get_hd_tl,no_line_info]),
 
     103 = highest_opcode(DataDir, big,
-                         [no_get_hd_tl,no_ssa_opt_record,
+                         [no_put_tuple2,
+                          no_get_hd_tl,no_ssa_opt_record,
                           no_line_info,no_stack_trimming]),
 
     125 = highest_opcode(DataDir, small_float,
                          [no_get_hd_tl,no_line_info,no_ssa_opt_float]),
 
     132 = highest_opcode(DataDir, small,
-                         [no_get_hd_tl,no_ssa_opt_record,no_ssa_opt_float,no_line_info]),
+                         [no_put_tuple2,no_get_hd_tl,no_ssa_opt_record,
+                          no_ssa_opt_float,no_line_info]),
 
-    136 = highest_opcode(DataDir, big, [no_get_hd_tl,no_ssa_opt_record,no_line_info]),
+    136 = highest_opcode(DataDir, big, [no_put_tuple2,no_get_hd_tl,
+                                        no_ssa_opt_record,no_line_info]),
 
-    153 = highest_opcode(DataDir, big, [no_get_hd_tl,no_ssa_opt_record]),
+    153 = highest_opcode(DataDir, big, [no_put_tuple2,no_get_hd_tl,
+                                        no_ssa_opt_record]),
     153 = highest_opcode(DataDir, big, [r16]),
     153 = highest_opcode(DataDir, big, [r17]),
     153 = highest_opcode(DataDir, big, [r18]),
@@ -1499,9 +1503,10 @@ bc_options(Config) ->
     158 = highest_opcode(DataDir, small_maps, [r18]),
     158 = highest_opcode(DataDir, small_maps, [r19]),
     158 = highest_opcode(DataDir, small_maps, [r20]),
-    158 = highest_opcode(DataDir, small_maps, []),
+    158 = highest_opcode(DataDir, small_maps, [r21]),
 
-    163 = highest_opcode(DataDir, big, []),
+    164 = highest_opcode(DataDir, small_maps, []),
+    164 = highest_opcode(DataDir, big, []),
 
     ok.
 
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