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-rw-r--r--lib/compiler/src/beam_dead.erl55
1 files changed, 51 insertions, 4 deletions
diff --git a/lib/compiler/src/beam_dead.erl b/lib/compiler/src/beam_dead.erl
index 6f6d742293..9087586b58 100644
--- a/lib/compiler/src/beam_dead.erl
+++ b/lib/compiler/src/beam_dead.erl
@@ -266,20 +266,42 @@ 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([{test,bs_start_match2,F,_,[R,_],Ctxt}=I|Is], D,
+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) ->
+ {f,To0} = F,
case beam_utils:is_killed(Ctxt, Acc0, D) of
true ->
- Eq = {test,is_eq_exact,F,[R,{literal,Bs}]},
+ To = shortcut_bs_context_to_binary(To0, R, D),
+ Eq = {test,is_eq_exact,{f,To},[R,{literal,Bs}]},
backward(Is, D, [Eq|Acc0]);
false ->
+ To = shortcut_bs_start_match(To0, R, D),
+ I = {test,bs_start_match2,{f,To},Live,Args,Ctxt},
backward(Is, D, [I|Acc])
end;
backward([{test,bs_start_match2,{f,To0},Live,[Src|_]=Info,Dst}|Is], D, Acc) ->
@@ -357,6 +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.
@@ -375,6 +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);
@@ -551,6 +583,21 @@ shortcut_bs_start_match_1([{test,bs_start_match2,{f,To},_,[Reg|_],_}|_],
shortcut_bs_start_match_1(_, _, To, _) ->
To.
+%% shortcut_bs_context_to_binary(TargetLabel, Reg) -> TargetLabel
+%% If a bs_start_match2 instruction has been eliminated, the
+%% bs_context_to_binary instruction can be eliminated too.
+
+shortcut_bs_context_to_binary(To, Reg, D) ->
+ shortcut_bs_ctb_1(beam_utils:code_at(To, D), Reg, To, D).
+
+shortcut_bs_ctb_1([{bs_context_to_binary,Reg}|Is], Reg, To, D) ->
+ shortcut_bs_ctb_1(Is, Reg, To, D);
+shortcut_bs_ctb_1([{jump,{f,To}}|_], Reg, _, D) ->
+ Code = beam_utils:code_at(To, D),
+ shortcut_bs_ctb_1(Code, Reg, To, D);
+shortcut_bs_ctb_1(_, _, To, _) ->
+ To.
+
%% shortcut_rel_op(FailLabel, Operator, [Operand], D) -> FailLabel'
%% Try to shortcut the given test instruction. Example:
%%