Merge branch 'bjorn/compiler/opt/OTP-12951'

* bjorn/compiler/opt/OTP-12951:
  beam_block: Eliminate unsafe optimization

3 files changed, 76 insertions, 3 deletions

diff --git a/lib/compiler/src/beam_block.erl b/lib/compiler/src/beam_block.erl
index 10dbaf462c..d1052303e0 100644
--- a/lib/compiler/src/beam_block.erl
+++ b/lib/compiler/src/beam_block.erl
@@ -58,6 +58,13 @@ blockify(Is) ->
 blockify([{loop_rec,{f,Fail},{x,0}},{loop_rec_end,_Lbl},{label,Fail}|Is], Acc) ->
     %% Useless instruction sequence.
     blockify(Is, Acc);
+blockify([{get_map_elements,F,S,{list,Gets}}|Is0], Acc) ->
+    %% A get_map_elements instruction is only safe at the beginning of
+    %% a block because of the failure label.
+    {Ss,Ds} = beam_utils:split_even(Gets),
+    I = {set,Ds,[S|Ss],{get_map_elements,F}},
+    {Block,Is} = collect_block(Is0, [I]),
+    blockify(Is, [{block,Block}|Acc]);
 blockify([I|Is0]=IsAll, Acc) ->
     case collect(I) of
 	error -> blockify(Is0, [I|Acc]);
@@ -101,9 +108,6 @@ collect({get_list,S,D1,D2})  -> {set,[D1,D2],[S],get_list};
 collect(remove_message)      -> {set,[],[],remove_message};
 collect({put_map,F,Op,S,D,R,{list,Puts}}) ->
     {set,[D],[S|Puts],{alloc,R,{put_map,Op,F}}};
-collect({get_map_elements,F,S,{list,Gets}}) ->
-    {Ss,Ds} = beam_utils:split_even(Gets),
-    {set,Ds,[S|Ss],{get_map_elements,F}};
 collect({'catch'=Op,R,L}) ->
     {set,[R],[],{try_catch,Op,L}};
 collect({'try'=Op,R,L}) ->
diff --git a/lib/compiler/test/Makefile b/lib/compiler/test/Makefile
index c2d757da4d..85118502e3 100644
--- a/lib/compiler/test/Makefile
+++ b/lib/compiler/test/Makefile
@@ -8,6 +8,7 @@ include $(ERL_TOP)/make/$(TARGET)/otp.mk
 MODULES= \
 	andor_SUITE \
 	apply_SUITE \
+	beam_block_SUITE \
 	beam_validator_SUITE \
 	beam_disasm_SUITE \
 	beam_except_SUITE \
@@ -44,6 +45,7 @@ MODULES= \
 NO_OPT= \
 	andor \
 	apply \
+	beam_block \
 	beam_except \
 	beam_reorder \
 	beam_type \
@@ -67,6 +69,7 @@ NO_OPT= \
 INLINE= \
 	andor \
 	apply \
+	beam_block \
 	beam_utils \
 	bs_bincomp \
 	bs_bit_binaries \
diff --git a/lib/compiler/test/beam_block_SUITE.erl b/lib/compiler/test/beam_block_SUITE.erl
new file mode 100644
index 0000000000..7b6f2066be
--- /dev/null
+++ b/lib/compiler/test/beam_block_SUITE.erl
@@ -0,0 +1,66 @@
+%%
+%% %CopyrightBegin%
+%%
+%% Copyright Ericsson AB 2015. All Rights Reserved.
+%%
+%% Licensed under the Apache License, Version 2.0 (the "License");
+%% you may not use this file except in compliance with the License.
+%% You may obtain a copy of the License at
+%%
+%%     http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+%%
+%% %CopyrightEnd%
+%%
+-module(beam_block_SUITE).
+
+-export([all/0,suite/0,groups/0,init_per_suite/1,end_per_suite/1,
+	 init_per_group/2,end_per_group/2,
+	 get_map_elements/1]).
+
+suite() -> [{ct_hooks,[ts_install_cth]}].
+
+all() ->
+    test_lib:recompile(?MODULE),
+    [{group,p}].
+
+groups() ->
+    [{p,[parallel],
+      [get_map_elements
+      ]}].
+
+init_per_suite(Config) ->
+    Config.
+
+end_per_suite(_Config) ->
+    ok.
+
+init_per_group(_GroupName, Config) ->
+    Config.
+
+end_per_group(_GroupName, Config) ->
+    Config.
+
+get_map_elements(_Config) ->
+    [{pred,var}] = get_map_elements([{pred,var}], #{}, []),
+    [{pred,var}] = get_map_elements([{pred,var}], #{pred=>[]}, []),
+    acc = get_map_elements([], #{pred=>[]}, acc),
+    ok.
+
+get_map_elements([{Pred,Var}|Left], Map, Acc) ->
+    case Map of
+        #{Var := List} ->
+            case lists:keyfind(Pred, 1, List) of
+                false ->
+                    get_map_elements(Left, Map, [{Pred,Var}|Acc])
+            end;
+        #{} ->
+            get_map_elements(Left, Map, [{Pred,Var}|Acc])
+    end;
+get_map_elements([], _Map, Acc) ->
+    Acc.