From 282fb67730e1bafe722e7149a35e272398f88b34 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Wed, 4 Apr 2018 15:14:54 +0200
Subject: Fix unsafe optimization of record test
beam_record would make an unsafe optimization for the
not_used_p/4 function added to beam_utils_SUITE in this
commit. The bug is in beam_utils, which would falsely
report that {x,4} was unused when it in fact was used.
The bug was in the function not_used/1. The purpose of
not_used/1 is to return a 'not_used' result unless the
actual result is 'used'. Unfortunately it was not
implemented in that way. It would let a 'transparent'
result slip through, which the caller in this case would
convert to 'killed' (because the register was killed on
all other paths).
Reported-by: Richard Carlsson
---
lib/compiler/src/beam_utils.erl | 5 ++---
lib/compiler/test/beam_utils_SUITE.erl | 24 ++++++++++++++++++++++--
2 files changed, 24 insertions(+), 5 deletions(-)
diff --git a/lib/compiler/src/beam_utils.erl b/lib/compiler/src/beam_utils.erl
index 047cd5a569..1ddad30328 100644
--- a/lib/compiler/src/beam_utils.erl
+++ b/lib/compiler/src/beam_utils.erl
@@ -655,9 +655,8 @@ check_liveness_at(R, Lbl, #live{lbl=Ll,res=ResMemorized}=St0) ->
{Res,St#live{res=gb_trees:insert(Lbl, Res, St#live.res)}}
end.
-not_used({exit_not_used,St}) -> {not_used,St};
-not_used({killed,St}) -> {not_used,St};
-not_used({_,_}=Res) -> Res.
+not_used({used,_}=Res) -> Res;
+not_used({_,St}) -> {not_used,St}.
check_liveness_ret(R, R, St) -> {used,St};
check_liveness_ret(_, _, St) -> {killed,St}.
diff --git a/lib/compiler/test/beam_utils_SUITE.erl b/lib/compiler/test/beam_utils_SUITE.erl
index 7686e69b63..b2a5cada3d 100644
--- a/lib/compiler/test/beam_utils_SUITE.erl
+++ b/lib/compiler/test/beam_utils_SUITE.erl
@@ -25,7 +25,7 @@
is_not_killed/1,is_not_used_at/1,
select/1,y_catch/1,otp_8949_b/1,liveopt/1,coverage/1,
y_registers/1,user_predef/1,scan_f/1,cafu/1,
- receive_label/1,read_size_file_version/1]).
+ receive_label/1,read_size_file_version/1,not_used/1]).
-export([id/1]).
suite() -> [{ct_hooks,[ts_install_cth]}].
@@ -51,7 +51,8 @@ groups() ->
user_predef,
scan_f,
cafu,
- read_size_file_version
+ read_size_file_version,
+ not_used
]}].
init_per_suite(Config) ->
@@ -507,5 +508,24 @@ do_read_size_file_version(E) ->
{ok,MaxFiles}
end.
+-record(s, { a, b }).
+-record(k, { v }).
+
+not_used(_Config) ->
+ [] = not_used_p(any, #s{b=true}, #k{}, ignored),
+ #k{v=42} = not_used_p(any, #s{b=false}, #k{v=42}, ignored),
+ #k{v=42} = not_used_p(any, #s{b=bad}, #k{v=42}, ignored),
+ ok.
+
+not_used_p(_C, S, K, L) when is_record(K, k) ->
+ if ((S#s.b) and
+ (S#s.b)) ->
+ [];
+ true ->
+ id(L),
+ id(K#k.v),
+ id(K)
+ end.
+
%% The identity function.
id(I) -> I.
--
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