beam_type: Improve optimization by keeping track of integers

The ASN.1 compiler often generates code similar to:

  f(<<0:1,...>>) -> ...;
  f(<<1:1,...>>) -> ....

Internally that will be rewritten to (conceptually):

  f(<<B:1,Tail/binary>>) ->
    case B of
      0 ->
        case Tail of ... end;
      1 ->
        case Tail of ... end;
      _ ->
        error(case_clause)
   end.

Since B comes from a bit field of one bit, we know that the only
possible values are 0 and 1. Therefore the error clause can be
eliminated like this:

  f(<<B:1,Tail/binary>>) ->
    case B of
      0 ->
        case Tail of ... end;
      _ ->
        case Tail of ... end
   end.

Similarly, we can also a deduce the range for an integer from
a 'band' operation with a literal integer.

While we are at it, also add a test case to improve the coverage.

1 files changed, 87 insertions, 0 deletions

diff --git a/lib/compiler/test/beam_type_SUITE.erl b/lib/compiler/test/beam_type_SUITE.erl
new file mode 100644
index 0000000000..8d99d76180
--- /dev/null
+++ b/lib/compiler/test/beam_type_SUITE.erl
@@ -0,0 +1,87 @@
+%%
+%% %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_type_SUITE).
+
+-export([all/0,suite/0,groups/0,init_per_suite/1,end_per_suite/1,
+	 init_per_group/2,end_per_group/2,
+	 integers/1,coverage/1]).
+
+suite() -> [{ct_hooks,[ts_install_cth]}].
+
+all() ->
+    test_lib:recompile(?MODULE),
+    [{group,p}].
+
+groups() ->
+    [{p,[parallel],
+      [integers,
+       coverage
+      ]}].
+
+init_per_suite(Config) ->
+    Config.
+
+end_per_suite(_Config) ->
+    ok.
+
+init_per_group(_GroupName, Config) ->
+    Config.
+
+end_per_group(_GroupName, Config) ->
+    Config.
+
+integers(_Config) ->
+    a = do_integers_1(2#11000),
+    b = do_integers_1(2#11001),
+
+    a = do_integers_2(<<0:1>>),
+    {'EXIT',{{case_clause,-1},_}} = (catch do_integers_2(<<1:1>>)),
+
+    ok.
+
+do_integers_1(B0) ->
+    B = B0 band 1,
+    case B band 15 of
+	0 -> a;
+	1 -> b
+    end.
+
+do_integers_2(Bin) ->
+    <<B:1/signed>> = Bin,
+    case B of
+	0 -> a;
+	1 -> b
+    end.
+
+coverage(_Config) ->
+    {'EXIT',{badarith,_}} = (catch id(1) bsl 0.5),
+    {'EXIT',{badarith,_}} = (catch id(2.0) bsl 2),
+    {'EXIT',{badarith,_}} = (catch a + 0.5),
+    {'EXIT',{badarith,_}} = (catch 2.0 * b),
+
+    {'EXIT',{badarith,_}} = (catch id(42.0) / (1 bsl 2000)),
+
+    id(id(42) band 387439739874298734983787934283479243879),
+    id(-1 band id(13)),
+
+    ok.
+
+id(I) ->
+    I.