From 9b0122b65bdcafbae2a3cfd3299903da0948acab Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Tue, 28 Nov 2017 07:28:25 +0100
Subject: Don't build a stacktrace if it's only passed to erlang:raise/3

Consider the following function:

    function({function,Name,Arity,CLabel,Is0}, Lc0) ->
      try
        %% Optimize the code for the function.
      catch
        Class:Error:Stack ->
          io:format("Function: ~w/~w\n", [Name,Arity]),
          erlang:raise(Class, Error, Stack)
      end.

The stacktrace is retrieved, but it is only used in the call
to erlang:raise/3. There is no need to build a stacktrace
in this function. We can avoid the building if we introduce
an instruction called raw_raise/3 that works exactly like
the erlang:raise/3 BIF except that its third argument must
be a raw stacktrace.
---
 lib/compiler/test/trycatch_SUITE.erl | 108 ++++++++++++++++++++++++++++++++++-
 1 file changed, 106 insertions(+), 2 deletions(-)

(limited to 'lib/compiler/test/trycatch_SUITE.erl')

diff --git a/lib/compiler/test/trycatch_SUITE.erl b/lib/compiler/test/trycatch_SUITE.erl
index 8cf7928cc4..d5a1dc642f 100644
--- a/lib/compiler/test/trycatch_SUITE.erl
+++ b/lib/compiler/test/trycatch_SUITE.erl
@@ -27,7 +27,7 @@
 	 nested_horrid/1,last_call_optimization/1,bool/1,
 	 plain_catch_coverage/1,andalso_orelse/1,get_in_try/1,
 	 hockey/1,handle_info/1,catch_in_catch/1,grab_bag/1,
-         stacktrace/1,nested_stacktrace/1]).
+         stacktrace/1,nested_stacktrace/1,raise/1]).
 
 -include_lib("common_test/include/ct.hrl").
 
@@ -44,7 +44,7 @@ groups() ->
        nested_after,nested_horrid,last_call_optimization,
        bool,plain_catch_coverage,andalso_orelse,get_in_try,
        hockey,handle_info,catch_in_catch,grab_bag,
-       stacktrace,nested_stacktrace]}].
+       stacktrace,nested_stacktrace,raise]}].
 
 
 init_per_suite(Config) ->
@@ -117,6 +117,16 @@ basic(Conf) when is_list(Conf) ->
 	 catch nisse -> erro
 	 end,
 
+    %% Unmatchable clauses.
+    try
+        throw(thrown)
+    catch
+        {a,b}={a,b,c} ->                        %Intentionally no match.
+            ok;
+        thrown ->
+            ok
+    end,
+
     ok.
 
 after_call() ->
@@ -1159,5 +1169,99 @@ nested_stacktrace_1({X1,C1,V1}, {X2,C2,V2}) ->
             {caught1,S1,T2}
     end.
 
+raise(_Config) ->
+    test_raise(fun() -> exit({exit,tuple}) end),
+    test_raise(fun() -> abs(id(x)) end),
+    test_raise(fun() -> throw({was,thrown}) end),
+
+    badarg = bad_raise(fun() -> abs(id(x)) end),
+
+    ok.
+
+bad_raise(Expr) ->
+    try
+        Expr()
+    catch
+        _:E:Stk ->
+            erlang:raise(bad_class, E, Stk)
+    end.
+
+test_raise(Expr) ->
+    test_raise_1(Expr),
+    test_raise_2(Expr),
+    test_raise_3(Expr).
+
+test_raise_1(Expr) ->
+    erase(exception),
+    try
+        do_test_raise_1(Expr)
+    catch
+        C:E:Stk ->
+            {C,E,Stk} = erase(exception)
+    end.
+
+do_test_raise_1(Expr) ->
+    try
+        Expr()
+    catch
+        C:E:Stk ->
+            %% Here the stacktrace must be built.
+            put(exception, {C,E,Stk}),
+            erlang:raise(C, E, Stk)
+    end.
+
+test_raise_2(Expr) ->
+    erase(exception),
+    try
+        do_test_raise_2(Expr)
+    catch
+        C:E:Stk ->
+            {C,E} = erase(exception),
+            try
+                Expr()
+            catch
+                _:_:S ->
+                    [StkTop|_] = S,
+                    [StkTop|_] = Stk
+            end
+    end.
+
+do_test_raise_2(Expr) ->
+    try
+        Expr()
+    catch
+        C:E:Stk ->
+            %% Here it is possible to replace erlang:raise/3 with
+            %% the raw_raise/3 instruction since the stacktrace is
+            %% not actually used.
+            put(exception, {C,E}),
+            erlang:raise(C, E, Stk)
+    end.
+
+test_raise_3(Expr) ->
+    try
+        do_test_raise_3(Expr)
+    catch
+        exit:{exception,C,E}:Stk ->
+            try
+                Expr()
+            catch
+                C:E:S ->
+                    [StkTop|_] = S,
+                    [StkTop|_] = Stk
+            end
+    end.
+
+do_test_raise_3(Expr) ->
+    try
+        Expr()
+    catch
+        C:E:Stk ->
+            %% Here it is possible to replace erlang:raise/3 with
+            %% the raw_raise/3 instruction since the stacktrace is
+            %% not actually used.
+            erlang:raise(exit, {exception,C,E}, Stk)
+    end.
+
 
 id(I) -> I.
-- 
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