From 34c8b06de52ac81e2938e93ed7a219d7611c16f9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
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/compiler/src/beam_utils.erl | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
(limited to 'lib/compiler')
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) ->
--
cgit v1.2.3
From 5fa3ac7e10f45ad433ac6a44f32f9b5e96b56fcd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Fri, 6 Oct 2017 09:22:00 +0200
Subject: Do the receive optimization in the presence of try/catch
Improve the receive optimization to be able to handle code
such as this:
Ref = make_ref(),
try
side_effect()
catch _:_ ->
ok
end,
receive
%% Clauses that all match Ref.
.
.
.
end
---
lib/compiler/src/beam_receive.erl | 2 ++
1 file changed, 2 insertions(+)
(limited to 'lib/compiler')
diff --git a/lib/compiler/src/beam_receive.erl b/lib/compiler/src/beam_receive.erl
index 1403e1e05e..468460eedf 100644
--- a/lib/compiler/src/beam_receive.erl
+++ b/lib/compiler/src/beam_receive.erl
@@ -207,6 +207,8 @@ opt_update_regs({label,Lbl}, R, L) ->
%% A catch label for a previously seen catch instruction is OK.
{R,L}
end;
+opt_update_regs({'try',_,{f,Lbl}}, R, L) ->
+ {R,gb_sets:add(Lbl, L)};
opt_update_regs({try_end,_}, R, L) ->
{R,L};
opt_update_regs({line,_}, R, L) ->
--
cgit v1.2.3
From 119713b4d9ad6649aa5f1d0bf492e2f35a0ced01 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Fri, 6 Oct 2017 09:25:53 +0200
Subject: Optimize a catch whose return value is ignored
Rewrite a catch expression like this:
catch side_effect(),
...
to:
try
side_effect()
catch
_:_ ->
ok
end,
...
A try/catch is more efficient since no stack trace will be built
when an exception occurs.
---
lib/compiler/src/sys_core_fold.erl | 9 +++++++++
1 file changed, 9 insertions(+)
(limited to 'lib/compiler')
diff --git a/lib/compiler/src/sys_core_fold.erl b/lib/compiler/src/sys_core_fold.erl
index f3f315935a..df880ff784 100644
--- a/lib/compiler/src/sys_core_fold.erl
+++ b/lib/compiler/src/sys_core_fold.erl
@@ -418,6 +418,15 @@ expr(#c_call{module=M0,name=N0}=Call0, Ctxt, Sub) ->
expr(#c_primop{args=As0}=Prim, _, Sub) ->
As1 = expr_list(As0, value, Sub),
Prim#c_primop{args=As1};
+expr(#c_catch{anno=Anno,body=B}, effect, Sub) ->
+ %% When the return value of the 'catch' is ignored, we can replace it
+ %% with a try/catch to avoid building a stack trace when an exception
+ %% occurs.
+ Var = #c_var{name='catch_value'},
+ Evs = [#c_var{name='Class'},#c_var{name='Reason'},#c_var{name='Stk'}],
+ Try = #c_try{anno=Anno,arg=B,vars=[Var],body=Var,
+ evars=Evs,handler=void()},
+ expr(Try, effect, Sub);
expr(#c_catch{body=B0}=Catch, _, Sub) ->
%% We can remove catch if the value is simple
B1 = body(B0, value, Sub),
--
cgit v1.2.3