1 files changed, 30 insertions, 2 deletions
diff --git a/lib/compiler/src/beam_dead.erl b/lib/compiler/src/beam_dead.erl
index 3606af9d75..9087586b58 100644
--- a/lib/compiler/src/beam_dead.erl
+++ b/lib/compiler/src/beam_dead.erl
@@ -266,12 +266,30 @@ backward([{jump,{f,To0}},{move,Src,Reg}=Move|Is], D, Acc) ->
 	false -> backward([Move|Is], D, [Jump|Acc]);
 	true -> backward([Jump|Is], D, Acc)
     end;
-backward([{jump,{f,To}}=J|[{bif,Op,_,Ops,Reg}|Is]=Is0], D, Acc) ->
+backward([{jump,{f,To}}=J|[{bif,Op,{f,BifFail},Ops,Reg}|Is]=Is0], D, Acc) ->
     try replace_comp_op(To, Reg, Op, Ops, D) of
 	I -> backward(Is, D, I++Acc)
     catch
-	throw:not_possible -> backward(Is0, D, [J|Acc])
+	throw:not_possible ->
+	    case To =:= BifFail of
+		true ->
+		    %% The bif instruction is redundant. See the comment
+		    %% in the next clause for why there is no need to
+		    %% test for liveness of Reg at label To.
+		    backward([J|Is], D, Acc);
+		false ->
+		    backward(Is0, D, [J|Acc])
+	    end
     end;
+backward([{jump,{f,To}}=J|[{gc_bif,_,{f,To},_,_,_Dst}|Is]], D, Acc) ->
+    %% The gc_bif instruction is redundant, since either the gc_bif
+    %% instruction itself or the jump instruction will transfer control
+    %% to label To. Note that a gc_bif instruction does not assign its
+    %% destination register if the failure branch is taken; therefore,
+    %% the code at label To is not allowed to assume that the destination
+    %% register is initialized, and it is therefore no need to test
+    %% for liveness of the destination register at label To.
+    backward([J|Is], D, Acc);
 backward([{test,bs_start_match2,F,Live,[R,_]=Args,Ctxt}|Is], D,
 	 [{test,bs_match_string,F,[Ctxt,Bs]},
 	  {test,bs_test_tail2,F,[Ctxt,0]}|Acc0]=Acc) ->
@@ -361,6 +379,14 @@ backward([{kill,_}=I|Is], D, [{line,_},Exit|_]=Acc) ->
 	false -> backward(Is, D, [I|Acc]);
 	true -> backward(Is, D, Acc)
     end;
+backward([{bif,'or',{f,To0},[Dst,{atom,false}],Dst}=I|Is], D,
+	 [{test,is_eq_exact,{f,To},[Dst,{atom,true}]}|_]=Acc) ->
+    case shortcut_label(To0, D) of
+	To ->
+	    backward(Is, D, Acc);
+	_ ->
+	    backward(Is, D, [I|Acc])
+    end;
 backward([I|Is], D, Acc) ->
     backward(Is, D, [I|Acc]);
 backward([], _D, Acc) -> Acc.
@@ -379,6 +405,8 @@ shortcut_select_list([Lit,{f,To0}|T], Reg, D, Acc) ->
     shortcut_select_list(T, Reg, D, [{f,To},Lit|Acc]);
 shortcut_select_list([], _, _, Acc) -> reverse(Acc).
 
+shortcut_label(0, _) ->
+    0;
 shortcut_label(To0, D) ->
     case beam_utils:code_at(To0, D) of
   	[{jump,{f,To}}|_] -> shortcut_label(To, D);