From beb15397b746cb20d00f6585e115ac2a112b18ad Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Wed, 13 Dec 2017 10:39:22 +0100
Subject: beam_utils: Improve precision for is_not_used/3

---
 lib/compiler/src/beam_utils.erl        | 13 ++++++---
 lib/compiler/test/beam_utils_SUITE.erl | 48 ++++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+), 3 deletions(-)

(limited to 'lib/compiler')

diff --git a/lib/compiler/src/beam_utils.erl b/lib/compiler/src/beam_utils.erl
index bd1423cb40..6f20fc94de 100644
--- a/lib/compiler/src/beam_utils.erl
+++ b/lib/compiler/src/beam_utils.erl
@@ -380,9 +380,16 @@ check_liveness(R, [{bs_init,_,_,none,Ss,Dst}|Is], St) ->
 check_liveness(R, [{bs_init,_,_,Live,Ss,Dst}|Is], St) ->
     case R of
 	{x,X} ->
-	    case X < Live orelse member(R, Ss) of
-		true -> {used,St};
-		false -> {killed,St}
+            case member(R, Ss) of
+                true ->
+                    {used,St};
+                false ->
+                    if
+                        X < Live ->
+                            not_used(check_liveness(R, Is, St));
+                        true ->
+                            {killed,St}
+                    end
 	    end;
 	{y,_} ->
 	    case member(R, Ss) of
diff --git a/lib/compiler/test/beam_utils_SUITE.erl b/lib/compiler/test/beam_utils_SUITE.erl
index d516b0c3c7..7686e69b63 100644
--- a/lib/compiler/test/beam_utils_SUITE.erl
+++ b/lib/compiler/test/beam_utils_SUITE.erl
@@ -122,6 +122,15 @@ bs_init(_Config) ->
     {'EXIT',{badarg,_}} = (catch do_bs_init_2([0.5])),
     {'EXIT',{badarg,_}} = (catch do_bs_init_2([-1])),
     {'EXIT',{badarg,_}} = (catch do_bs_init_2([1 bsl 32])),
+
+    <<>> = do_bs_init_3({tag,0}, 0, 0),
+    <<0>> = do_bs_init_3({tag,0}, 2, 1),
+
+    <<"_build/shared">> = do_bs_init_4([], false),
+    <<"abc/shared">> = do_bs_init_4(<<"abc">>, false),
+    <<"foo/foo">> = do_bs_init_4(<<"foo">>, true),
+    error = do_bs_init_4([], not_boolean),
+
     ok.
 
 do_bs_init_1([?MODULE], Sz) ->
@@ -139,6 +148,45 @@ do_bs_init_2(SigNos) ->
 	    erlang:error(badarg)
     >>.
 
+do_bs_init_3({tag,Pos}, Offset, Len) ->
+    N0 = Offset - Pos,
+    N = if N0 > Len -> Len;
+           true -> N0
+        end,
+    <<0:N/unit:8>>.
+
+do_bs_init_4(Arg1, Arg2) ->
+    Build =
+        case id(Arg1) of
+            X when X =:= [] orelse X =:= false -> <<"_build">>;
+            X -> X
+        end,
+    case id(Arg2) of
+        true ->
+            id(<<case Build of
+                     Rewrite when is_binary(Rewrite) ->
+                         Rewrite;
+                     Rewrite ->
+                         id(Rewrite)
+                 end/binary,
+                 "/",
+                 case id(<<"foo">>) of
+                     Rewrite when is_binary(Rewrite) ->
+                         Rewrite;
+                     Rewrite ->
+                         id(Rewrite)
+                 end/binary>>);
+        false ->
+            id(<<case Build of
+                     Rewrite when is_binary(Rewrite) ->
+                         Rewrite;
+                     Rewrite ->
+                         id(Rewrite)
+                 end/binary,
+                 "/shared">>);
+        Other ->
+            error
+    end.
 
 bs_save(_Config) ->
     {a,30,<<>>} = do_bs_save(<<1:1,30:5>>),
-- 
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