Merge pull request #1596 from bjorng/bjorn/enhance-try-catch

(Slightly) optimize catch and try/catch

OTP-14683

6 files changed, 37 insertions, 11 deletions

diff --git a/erts/emulator/beam/instrs.tab b/erts/emulator/beam/instrs.tab
index 07cc4bd527..20d356a81d 100644
--- a/erts/emulator/beam/instrs.tab
+++ b/erts/emulator/beam/instrs.tab
@@ -857,8 +857,7 @@ catch(Y, Fail) {
 }
 
 catch_end(Y) {
-    c_p->catches--;
-    make_blank($Y);
+    $try_end($Y);
     if (is_non_value(r(0))) {
         c_p->fvalue = NIL;
         if (x(1) == am_throw) {
@@ -888,12 +887,15 @@ catch_end(Y) {
 try_end(Y) {
     c_p->catches--;
     make_blank($Y);
-    if (is_non_value(r(0))) {
-        c_p->fvalue = NIL;
-        r(0) = x(1);
-        x(1) = x(2);
-        x(2) = x(3);
-    }
+}
+
+try_case(Y) {
+    $try_end($Y);
+    ASSERT(is_non_value(r(0)));
+    c_p->fvalue = NIL;
+    r(0) = x(1);
+    x(1) = x(2);
+    x(2) = x(3);
 }
 
 try_case_end(Src) {
diff --git a/erts/emulator/beam/ops.tab b/erts/emulator/beam/ops.tab
index 4a915c7762..7a2c39b3a8 100644
--- a/erts/emulator/beam/ops.tab
+++ b/erts/emulator/beam/ops.tab
@@ -188,7 +188,8 @@ catch_end y
 
 # Try/catch.
 try Y F => catch Y F
-try_case Y => try_end Y
+
+try_case y
 try_end y
 
 %cold
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) ->
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/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),
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) ->