sys_core_fold: Fix opt_guard_try/1

opt_guard_try/1 assumed that it was only operating on guards, and
implicitly assumed that any function call was to BIFs without
any side effects.

2 files changed, 37 insertions, 8 deletions

diff --git a/lib/compiler/src/sys_core_fold.erl b/lib/compiler/src/sys_core_fold.erl
index 620b4e8847..c92ee86e07 100644
--- a/lib/compiler/src/sys_core_fold.erl
+++ b/lib/compiler/src/sys_core_fold.erl
@@ -150,14 +150,26 @@ guard(Expr, Sub) ->
 opt_guard_try(#c_seq{arg=Arg,body=Body0}=Seq) ->
     Body = opt_guard_try(Body0),
     case {Arg,Body} of
-	{#c_call{},#c_literal{val=false}} ->
-	    %% We have sequence consisting of a call (evaluted
-	    %% for a possible exception only), followed by 'false'.
-	    %% Since the sequence is inside a try block that will
+	{#c_call{module=#c_literal{val=Mod},
+		 name=#c_literal{val=Name},
+		 args=Args},#c_literal{val=false}} ->
+	    %% We have sequence consisting of a call (evaluated
+	    %% for a possible exception and/or side effect only),
+	    %% followed by 'false'.
+	    %%   Since the sequence is inside a try block that will
 	    %% default to 'false' if any exception occurs, not
 	    %% evalutating the call will not change the behaviour
-	    %% of the guard.
-	    Body;
+	    %% provided that the call has no side effects.
+	    case erl_bifs:is_pure(Mod, Name, length(Args)) of
+		false ->
+		    %% Not a pure BIF (meaning that this is not
+		    %% a guard and that we must keep the call).
+		    Seq#c_seq{body=Body};
+		true ->
+		    %% The BIF has no side effects, so it can
+		    %% be safely removed.
+		    Body
+	    end;
 	{_,_} ->
 	    Seq#c_seq{body=Body}
     end;
diff --git a/lib/compiler/test/core_fold_SUITE.erl b/lib/compiler/test/core_fold_SUITE.erl
index fb5ec88c9f..54bd52947e 100644
--- a/lib/compiler/test/core_fold_SUITE.erl
+++ b/lib/compiler/test/core_fold_SUITE.erl
@@ -21,7 +21,7 @@
 -export([all/0, suite/0,groups/0,init_per_suite/1, end_per_suite/1, 
 	 init_per_group/2,end_per_group/2,
 	 t_element/1,setelement/1,t_length/1,append/1,t_apply/1,bifs/1,
-	 eq/1,nested_call_in_case/1,coverage/1]).
+	 eq/1,nested_call_in_case/1,guard_try_catch/1,coverage/1]).
 
 -export([foo/0,foo/1,foo/2,foo/3]).
 
@@ -32,7 +32,7 @@ suite() -> [{ct_hooks,[ts_install_cth]}].
 all() -> 
     test_lib:recompile(?MODULE),
     [t_element, setelement, t_length, append, t_apply, bifs,
-     eq, nested_call_in_case, coverage].
+     eq, nested_call_in_case, guard_try_catch, coverage].
 
 groups() -> 
     [].
@@ -207,6 +207,23 @@ nested_call_in_case(Config) when is_list(Config) ->
     ?line {'EXIT',_} = (catch Mod:a(not_a_list, 42)),
     ok.
 
+guard_try_catch(_Config) ->
+    false = do_guard_try_catch(key, value),
+    value = get(key),
+    ok.
+
+do_guard_try_catch(K, V) ->
+    %% This try...catch block looks like a guard.
+    %% Make sure that it is not optimized like a guard
+    %% (the put/2 call must not be optimized away).
+    try
+	put(K, V),
+	false
+    catch
+	_:_ ->
+	    false
+    end.
+
 coverage(Config) when is_list(Config) ->
     ?line {'EXIT',{{case_clause,{a,b,c}},_}} =
 	(catch cover_will_match_list_type({a,b,c})),