From 34c8b06de52ac81e2938e93ed7a219d7611c16f9 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= Date: Fri, 6 Oct 2017 09:06:24 +0200 Subject: 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 --- lib/hipe/icode/hipe_beam_to_icode.erl | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'lib/hipe/icode/hipe_beam_to_icode.erl') 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) -> -- cgit v1.2.3