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-rw-r--r--lib/compiler/src/beam_dead.erl24
1 files changed, 21 insertions, 3 deletions
diff --git a/lib/compiler/src/beam_dead.erl b/lib/compiler/src/beam_dead.erl
index ead88b57e9..0cb5040177 100644
--- a/lib/compiler/src/beam_dead.erl
+++ b/lib/compiler/src/beam_dead.erl
@@ -242,8 +242,15 @@ backward([{select,select_val,Reg,{f,Fail0},List0}|Is], D, Acc) ->
List = shortcut_select_list(List0, Reg, D, []),
Fail1 = shortcut_label(Fail0, D),
Fail = shortcut_bs_test(Fail1, Is, D),
- Sel = {select,select_val,Reg,{f,Fail},List},
- backward(Is, D, [Sel|Acc]);
+ case List of
+ [{atom,B1},F,{atom,B2},F] when B1 =:= not B2 ->
+ Test = {test,is_boolean,{f,Fail},[Reg]},
+ Jump = {jump,F},
+ backward([Jump,Test|Is], D, Acc);
+ [_|_] ->
+ Sel = {select,select_val,Reg,{f,Fail},List},
+ backward(Is, D, [Sel|Acc])
+ end;
backward([{jump,{f,To0}},{move,Src,Reg}=Move|Is], D, Acc) ->
To = shortcut_select_label(To0, Reg, Src, D),
Jump = {jump,{f,To}},
@@ -295,7 +302,18 @@ backward([{test,Op,{f,To0},Ops0}|Is], D, Acc) ->
is_eq_exact -> combine_eqs(To, Ops0, D, Acc);
_ -> {test,Op,{f,To},Ops0}
end,
- backward(Is, D, [I|Acc]);
+ case {I,Acc} of
+ {{test,is_atom,Fail,Ops0},[{test,is_boolean,Fail,Ops0}|_]} ->
+ %% An is_atom test before an is_boolean test (with the
+ %% same failure label) is redundant.
+ backward(Is, D, Acc);
+ {{test,_,_,_},_} ->
+ %% Still a test instruction. Done.
+ backward(Is, D, [I|Acc]);
+ {_,_} ->
+ %% Rewritten to a select_val. Rescan.
+ backward([I|Is], D, Acc)
+ end;
backward([{test,Op,{f,To0},Live,Ops0,Dst}|Is], D, Acc) ->
To1 = shortcut_bs_test(To0, Is, D),
To2 = shortcut_label(To1, D),