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authorBjörn Gustavsson <[email protected]>2017-10-06 09:06:24 +0200
committerBjörn Gustavsson <[email protected]>2017-10-11 09:59:41 +0200
commit34c8b06de52ac81e2938e93ed7a219d7611c16f9 (patch)
tree0ed2df8a4aa99368ee5bf483c056cf808d34fd25
parent4fe3f3b8be4825726fab6d4ea7515adf5b5df1ac (diff)
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Optimize try/catch that ignores the return value
If a try/catch is used to ignore the potential exception caused by some expression with a side effect such as: try side_effect() catch _Class:_Reason -> ok end, . . . the generated code will be wasteful: try YReg TryLabel %% call side_effect() here try_end Yreg jump GoodLabel TryLabel: try_case YReg %% try_case has set up registers as follows: %% x(0) -> error | exit | throw %% x(1) -> reason %% x(2) -> raw stack trace data GoodLabel: %% This code does not use any x registers. There will be two code paths that both end up at GoodLabel, and the try_case instruction will set up registers that are never used. We can do better by replacing try_case with try_end to obtain this code: try YReg TryLabel %% call side_effect() here try_end Yreg jump GoodLabel TryLabel: try_end YReg GoodLabel: The jump optimizer (beam_jump) can further optimize this code like this: try YReg TryLabel %% call side_effect() here TryLabel: try_end YReg
-rw-r--r--lib/compiler/src/beam_utils.erl10
-rw-r--r--lib/hipe/icode/hipe_beam_to_icode.erl6
2 files changed, 14 insertions, 2 deletions
diff --git a/lib/compiler/src/beam_utils.erl b/lib/compiler/src/beam_utils.erl
index a4c65397df..00f396c246 100644
--- a/lib/compiler/src/beam_utils.erl
+++ b/lib/compiler/src/beam_utils.erl
@@ -825,8 +825,14 @@ live_opt([{select,_,Src,Fail,List}=I|Is], Regs0, D, Acc) ->
Regs1 = x_live([Src], Regs0),
Regs = live_join_labels([Fail|List], D, Regs1),
live_opt(Is, Regs, D, [I|Acc]);
-live_opt([{try_case,_}=I|Is], _, D, Acc) ->
- live_opt(Is, live_call(1), D, [I|Acc]);
+live_opt([{try_case,Y}=I|Is], Regs0, D, Acc) ->
+ Regs = live_call(1),
+ case Regs0 of
+ 0 ->
+ live_opt(Is, Regs, D, [{try_end,Y}|Acc]);
+ _ ->
+ live_opt(Is, live_call(1), D, [I|Acc])
+ end;
live_opt([{loop_rec,_Fail,_Dst}=I|Is], _, D, Acc) ->
live_opt(Is, 0, D, [I|Acc]);
live_opt([timeout=I|Is], _, D, Acc) ->
diff --git a/lib/hipe/icode/hipe_beam_to_icode.erl b/lib/hipe/icode/hipe_beam_to_icode.erl
index 2abecf7f18..167f5c67bb 100644
--- a/lib/hipe/icode/hipe_beam_to_icode.erl
+++ b/lib/hipe/icode/hipe_beam_to_icode.erl
@@ -2296,6 +2296,12 @@ split_code([First|Code], Label, Instr) ->
split_code([Instr|Code], Label, Instr, Prev, As) when Prev =:= Label ->
split_code_final(Code, As); % drop both label and instruction
+split_code([{icode_end_try}|_]=Code, Label, {try_case,_}, Prev, As)
+ when Prev =:= Label ->
+ %% The try_case has been replaced with try_end as an optimization.
+ %% Keep this instruction, since it might be the only try_end instruction
+ %% for this try/catch block.
+ split_code_final(Code, As); % drop label
split_code([Other|_Code], Label, Instr, Prev, _As) when Prev =:= Label ->
?EXIT({missing_instr_after_label, Label, Instr, [Other, Prev | _As]});
split_code([Other|Code], Label, Instr, Prev, As) ->