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authorBjörn Gustavsson <[email protected]>2018-11-15 10:21:11 +0100
committerBjörn Gustavsson <[email protected]>2018-11-15 14:07:50 +0100
commit4534b73552bdb405808154f01f9b051cacb4ff3e (patch)
tree3fff3a75f8ac0c6cf36c9e2ec30f8aa1db39b488
parent64a15f2979c4644298cdad1319919fe84103484e (diff)
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beam_ssa_dead: Speed up optimization of switch instructions
`beam_ssa_dead` can waste a lot of time trying to optimize an unoptimizable `switch` instruction. By being a little bit smarter when optimizing `switch` instructions, the runtime for the beam_ssa_dead pass was reduced approximately by half on my computer for this module: https://github.com/aggelgian/cuter/blob/master/src/cuter_binlib.erl Noticed-by: Kostis Sagonas
-rw-r--r--lib/compiler/src/beam_ssa_dead.erl59
1 files changed, 31 insertions, 28 deletions
diff --git a/lib/compiler/src/beam_ssa_dead.erl b/lib/compiler/src/beam_ssa_dead.erl
index c20652580d..067d9a6741 100644
--- a/lib/compiler/src/beam_ssa_dead.erl
+++ b/lib/compiler/src/beam_ssa_dead.erl
@@ -135,7 +135,8 @@ shortcut_terminator(Last, _Is, _Bs, _St) ->
Last.
shortcut_switch([{Lit,L0}|T], Bool, Bs, St0) ->
- St = St0#st{rel_op=normalize_op({bif,'=:='}, [Bool,Lit])},
+ RelOp = {'=:=',Bool,Lit},
+ St = St0#st{rel_op=RelOp},
#b_br{bool=#b_literal{val=true},succ=L} =
shortcut(L0, bind_var(Bool, Lit, Bs), St#st{target=one_way}),
[{Lit,L}|shortcut_switch(T, Bool, Bs, St0)];
@@ -388,41 +389,43 @@ eval_terminator(#b_switch{arg=Arg,fail=Fail,list=List}=Sw, Bs, St) ->
%% Literal argument. Simplify to a `br`.
beam_ssa:normalize(Sw#b_switch{arg=Val});
#b_var{} ->
- case St of
- #st{rel_op=none} ->
- %% No previous relational operator is stored.
- %% Give up.
+ %% Try optimizing the switch.
+ case eval_switch(List, Arg, St, Fail) of
+ none ->
none;
- #st{} ->
- %% There is a previous relational operator stored.
- %% Try optimizing the switch.
- case eval_switch(List, Arg, St, Fail) of
- none ->
- none;
- To when is_integer(To) ->
- %% Either one of the values in the switch
- %% matched a previous value in a '=:=' test, or
- %% none of the values matched a previous test.
- #b_br{bool=#b_literal{val=true},succ=To,fail=To}
- end
+ To when is_integer(To) ->
+ %% Either one of the values in the switch
+ %% matched a previous value in a '=:=' test, or
+ %% none of the values matched a previous test.
+ #b_br{bool=#b_literal{val=true},succ=To,fail=To}
end
end;
eval_terminator(#b_ret{}, _Bs, _St) ->
none.
-eval_switch([{Lit,Lbl}|T], Arg, St, Fail) ->
- case eval_rel_op({bif,'=:='}, [Arg,Lit], St) of
- none ->
- %% This label could be reached.
- eval_switch(T, Arg, St, none);
- #b_literal{val=false} ->
- %% This branch will never be taken.
- eval_switch(T, Arg, St, Fail);
- #b_literal{val=true} ->
+eval_switch(List, Arg, #st{rel_op={_,Arg,_}=PrevOp}, Fail) ->
+ %% There is a previous relational operator testing the same variable.
+ %% Optimization may be possible.
+ eval_switch_1(List, Arg, PrevOp, Fail);
+eval_switch(_, _, _, _) ->
+ %% There is either no previous relational operator, or it tests
+ %% a different variable. Nothing to optimize.
+ none.
+
+eval_switch_1([{Lit,Lbl}|T], Arg, PrevOp, Fail) ->
+ RelOp = {'=:=',Arg,Lit},
+ case will_succeed(PrevOp, RelOp) of
+ yes ->
%% Success. This branch will always be taken.
- Lbl
+ Lbl;
+ no ->
+ %% This branch will never be taken.
+ eval_switch_1(T, Arg, PrevOp, Fail);
+ maybe ->
+ %% This label could be reached.
+ eval_switch_1(T, Arg, PrevOp, none)
end;
-eval_switch([], _Arg, _St, Fail) ->
+eval_switch_1([], _Arg, _PrevOp, Fail) ->
%% Fail is now either the failure label or 'none'.
Fail.