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authorBjörn Gustavsson <[email protected]>2016-02-08 07:06:31 +0100
committerBjörn Gustavsson <[email protected]>2016-02-08 08:08:55 +0100
commitabde1d03db03536af19fdb274f1119bbfaba262b (patch)
treefc7eb2311be3f3aa458fb298a5a23803b7bbfe67
parenta03b7add86b92d0d7d2d744e5555314bedbc2197 (diff)
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Eliminate crash because of unsafe delaying of sub-binary creation
The following code would fail to compile: decode(<<Code/integer, Bin/binary>>) -> <<C1/integer, B1/binary>> = Bin, case C1 of X when X =:= 1 orelse X =:= 2 -> Bin2 = <<>>; _ -> Bin2 = B1 end, case Code of 1 -> decode(Bin2); _ -> Bin2 end. The error message would be: t: function decode/1+28: Internal consistency check failed - please report this bug. Instruction: return Error: {match_context,{x,0}}: The beam_bsm pass would delay the creation of a sub-binary when it was unsafe to do so. The culprit was the btb_follow_branch/3 function that for performance reasons cached labels that had already been checked. The problem was the safety of a label also depends on the contents of the registers. Therefore, the key for caching needs to be both the label and the register contents. Reported-by: José Valim
-rw-r--r--lib/compiler/src/beam_bsm.erl5
-rw-r--r--lib/compiler/test/bs_match_SUITE.erl32
2 files changed, 33 insertions, 4 deletions
diff --git a/lib/compiler/src/beam_bsm.erl b/lib/compiler/src/beam_bsm.erl
index 4f76350269..62356928ae 100644
--- a/lib/compiler/src/beam_bsm.erl
+++ b/lib/compiler/src/beam_bsm.erl
@@ -421,7 +421,8 @@ btb_follow_branches([], _, D) -> D.
btb_follow_branch(0, _Regs, D) -> D;
btb_follow_branch(Lbl, Regs, #btb{ok_br=Br0,index=Li}=D) ->
- case gb_sets:is_member(Lbl, Br0) of
+ Key = {Lbl,Regs},
+ case gb_sets:is_member(Key, Br0) of
true ->
%% We have already followed this branch and it was OK.
D;
@@ -432,7 +433,7 @@ btb_follow_branch(Lbl, Regs, #btb{ok_br=Br0,index=Li}=D) ->
btb_reaches_match_1(Is, Regs, D),
%% Since we got back, this branch is OK.
- D#btb{ok_br=gb_sets:insert(Lbl, Br),must_not_save=MustNotSave,
+ D#btb{ok_br=gb_sets:insert(Key, Br),must_not_save=MustNotSave,
must_save=MustSave}
end.
diff --git a/lib/compiler/test/bs_match_SUITE.erl b/lib/compiler/test/bs_match_SUITE.erl
index b4601b0798..7fb0a16540 100644
--- a/lib/compiler/test/bs_match_SUITE.erl
+++ b/lib/compiler/test/bs_match_SUITE.erl
@@ -36,7 +36,8 @@
match_string/1,zero_width/1,bad_size/1,haystack/1,
cover_beam_bool/1,matched_out_size/1,follow_fail_branch/1,
no_partition/1,calling_a_binary/1,binary_in_map/1,
- match_string_opt/1,map_and_binary/1]).
+ match_string_opt/1,map_and_binary/1,
+ unsafe_branch_caching/1]).
-export([coverage_id/1,coverage_external_ignore/2]).
@@ -62,7 +63,8 @@ groups() ->
otp_7498,match_string,zero_width,bad_size,haystack,
cover_beam_bool,matched_out_size,follow_fail_branch,
no_partition,calling_a_binary,binary_in_map,
- match_string_opt,map_and_binary]}].
+ match_string_opt,map_and_binary,
+ unsafe_branch_caching]}].
init_per_suite(Config) ->
@@ -1243,6 +1245,32 @@ do_map_and_binary(#{time := _} = T) ->
do_map_and_binary(#{hour := Hour, min := Min} = T) ->
{Hour, Min, T}.
+%% Unsafe caching of branch outcomes in beam_bsm would cause the
+%% delayed creation of sub-binaries optimization to be applied even
+%% when it was unsafe.
+
+unsafe_branch_caching(_Config) ->
+ <<>> = do_unsafe_branch_caching(<<42,1>>),
+ <<>> = do_unsafe_branch_caching(<<42,2>>),
+ <<>> = do_unsafe_branch_caching(<<42,3>>),
+ <<17,18>> = do_unsafe_branch_caching(<<42,3,17,18>>),
+ <<>> = do_unsafe_branch_caching(<<1,3,42,2>>),
+
+ ok.
+
+do_unsafe_branch_caching(<<Code/integer, Bin/binary>>) ->
+ <<C1/integer, B1/binary>> = Bin,
+ case C1 of
+ X when X =:= 1 orelse X =:= 2 ->
+ Bin2 = <<>>;
+ _ ->
+ Bin2 = B1
+ end,
+ case Code of
+ 1 -> do_unsafe_branch_caching(Bin2);
+ _ -> Bin2
+ end.
+
check(F, R) ->
R = F().