Merge branch 'bjorn/compiler/dup-bug-fix/OTP-12453'

* bjorn/compiler/dup-bug-fix/OTP-12453:
  Teach case_opt/3 to avoid unnecessary building
  sys_core_fold: Optimize let statements more aggressively
  Suppress warnings for expressions that are assigned to '_'
  trace_bif_SUITE: Ensure that a call to time/0 is not removed

5 files changed, 91 insertions, 11 deletions

diff --git a/lib/compiler/test/compilation_SUITE.erl b/lib/compiler/test/compilation_SUITE.erl
index 8711f35e8e..296774e083 100644
--- a/lib/compiler/test/compilation_SUITE.erl
+++ b/lib/compiler/test/compilation_SUITE.erl
@@ -611,12 +611,10 @@ otp_7345(Config) when is_list(Config) ->
 
 otp_7345(ObjRef, _RdEnv, Args) ->
     Cid = ObjRef#contextId.cid,
-    _DpRef =
-	#dpRef{cid = Cid,
+    _ =	#dpRef{cid = Cid,
 		     ms_device_context_id = cid_id,
 		     tlli = #ptmsi{value = 0}},
-    _QosProfile =
-	#qosProfileBssgp{peak_bit_rate_msb = 0,
+    _ =	#qosProfileBssgp{peak_bit_rate_msb = 0,
 			 peak_bit_rate_lsb = 80,
 			 t_a_precedence = 49},
     [Cpdu|_] = Args,
diff --git a/lib/compiler/test/core_fold_SUITE.erl b/lib/compiler/test/core_fold_SUITE.erl
index 1358e002e2..40a5ba2b17 100644
--- a/lib/compiler/test/core_fold_SUITE.erl
+++ b/lib/compiler/test/core_fold_SUITE.erl
@@ -23,7 +23,8 @@
 	 t_element/1,setelement/1,t_length/1,append/1,t_apply/1,bifs/1,
 	 eq/1,nested_call_in_case/1,guard_try_catch/1,coverage/1,
 	 unused_multiple_values_error/1,unused_multiple_values/1,
-	 multiple_aliases/1,redundant_boolean_clauses/1,mixed_matching_clauses/1]).
+	 multiple_aliases/1,redundant_boolean_clauses/1,
+	 mixed_matching_clauses/1,unnecessary_building/1]).
 
 -export([foo/0,foo/1,foo/2,foo/3]).
 
@@ -40,7 +41,8 @@ groups() ->
       [t_element,setelement,t_length,append,t_apply,bifs,
        eq,nested_call_in_case,guard_try_catch,coverage,
        unused_multiple_values_error,unused_multiple_values,
-       multiple_aliases,redundant_boolean_clauses,mixed_matching_clauses]}].
+       multiple_aliases,redundant_boolean_clauses,
+       mixed_matching_clauses,unnecessary_building]}].
 
 
 init_per_suite(Config) ->
@@ -252,6 +254,8 @@ do_guard_try_catch(K, V) ->
 	    false
     end.
 
+-record(cover_opt_guard_try, {list=[]}).
+
 coverage(Config) when is_list(Config) ->
     ?line {'EXIT',{{case_clause,{a,b,c}},_}} =
 	(catch cover_will_match_list_type({a,b,c})),
@@ -261,6 +265,9 @@ coverage(Config) when is_list(Config) ->
     ?line error = cover_will_match_lit_list(),
     {ok,[a]} = cover_is_safe_bool_expr(a),
 
+    ok = cover_opt_guard_try(#cover_opt_guard_try{list=[a]}),
+    error = cover_opt_guard_try(#cover_opt_guard_try{list=[]}),
+
     %% Make sure that we don't attempt to make literals
     %% out of pids. (Putting a pid into a #c_literal{}
     %% would crash later compiler passes.)
@@ -314,6 +321,14 @@ cover_is_safe_bool_expr(X) ->
 	    false
     end.
 
+cover_opt_guard_try(Msg) ->
+    if
+	length(Msg#cover_opt_guard_try.list) =/= 1 ->
+	    error;
+	true ->
+	    ok
+    end.
+
 bsm_an_inlined(<<_:8>>, _) -> ok;
 bsm_an_inlined(_, _) -> error.
 
@@ -400,4 +415,29 @@ mixed_matching_clauses(Config) when is_list(Config) ->
       end,
   ok.
 
+unnecessary_building(Config) when is_list(Config) ->
+    Term1 = do_unnecessary_building_1(test_lib:id(a)),
+    [{a,a},{a,a}] = Term1,
+    7 = erts_debug:size(Term1),
+
+    %% The Input term should not be rebuilt (thus, it should
+    %% only be counted once in the size of the combined term).
+    Input = test_lib:id({a,b,c}),
+    Term2 = test_lib:id(do_unnecessary_building_2(Input)),
+    {b,[{a,b,c},none],x} = Term2,
+    4+4+4+2 = erts_debug:size([Term2|Input]),
+
+    ok.
+
+do_unnecessary_building_1(S) ->
+    %% The tuple must only be built once.
+    F0 = F1 = {S,S},
+    [F0,F1].
+
+do_unnecessary_building_2({a,_,_}=T) ->
+    %% The T term should not be rebuilt.
+    {b,
+     [_,_] = [T,none],
+     x}.
+
 id(I) -> I.
diff --git a/lib/compiler/test/test_lib.erl b/lib/compiler/test/test_lib.erl
index e06e42276a..e8f469c5b4 100644
--- a/lib/compiler/test/test_lib.erl
+++ b/lib/compiler/test/test_lib.erl
@@ -20,9 +20,11 @@
 
 -include("test_server.hrl").
 -compile({no_auto_import,[binary_part/2]}).
--export([recompile/1,parallel/0,uniq/0,opt_opts/1,get_data_dir/1,
+-export([id/1,recompile/1,parallel/0,uniq/0,opt_opts/1,get_data_dir/1,
 	 smoke_disasm/1,p_run/2,binary_part/2]).
 
+id(I) -> I.
+
 recompile(Mod) when is_atom(Mod) ->
     case whereis(cover_server) of
  	undefined -> ok;
diff --git a/lib/compiler/test/trycatch_SUITE.erl b/lib/compiler/test/trycatch_SUITE.erl
index b490257a6e..8ab618bb01 100644
--- a/lib/compiler/test/trycatch_SUITE.erl
+++ b/lib/compiler/test/trycatch_SUITE.erl
@@ -790,7 +790,6 @@ nested_after_1({X1,C1,V1},
 
 
 nested_horrid(Config) when is_list(Config) ->
-    _V = {make_ref(),nested_horrid,4.711},
     {[true,true],{[true,1.0],1.0}} =
 	nested_horrid_1({true,void,void}, 1.0),
     ok.
diff --git a/lib/compiler/test/warnings_SUITE.erl b/lib/compiler/test/warnings_SUITE.erl
index 6e5a7d35e9..6663985ad7 100644
--- a/lib/compiler/test/warnings_SUITE.erl
+++ b/lib/compiler/test/warnings_SUITE.erl
@@ -39,7 +39,7 @@
 	 guard/1,bad_arith/1,bool_cases/1,bad_apply/1,
          files/1,effect/1,bin_opt_info/1,bin_construction/1,
 	 comprehensions/1,maps/1,redundant_boolean_clauses/1,
-	 latin1_fallback/1]).
+	 latin1_fallback/1,underscore/1]).
 
 % Default timetrap timeout (set in init_per_testcase).
 -define(default_timeout, ?t:minutes(2)).
@@ -64,7 +64,8 @@ groups() ->
       [pattern,pattern2,pattern3,pattern4,guard,
        bad_arith,bool_cases,bad_apply,files,effect,
        bin_opt_info,bin_construction,comprehensions,maps,
-       redundant_boolean_clauses,latin1_fallback]}].
+       redundant_boolean_clauses,latin1_fallback,
+       underscore]}].
 
 init_per_suite(Config) ->
     Config.
@@ -280,11 +281,12 @@ bad_arith(Config) when is_list(Config) ->
 	     {3,sys_core_fold,{eval_failure,badarith}},
 	     {9,sys_core_fold,nomatch_guard},
 	     {9,sys_core_fold,{eval_failure,badarith}},
+	     {9,sys_core_fold,{no_effect,{erlang,is_integer,1}}},
 	     {10,sys_core_fold,nomatch_guard},
 	     {10,sys_core_fold,{eval_failure,badarith}},
 	     {15,sys_core_fold,{eval_failure,badarith}}
 	    ] }}],
-    ?line [] = run(Config, Ts),
+    [] = run(Config, Ts),
     ok.
 
 bool_cases(Config) when is_list(Config) ->
@@ -678,6 +680,45 @@ latin1_fallback(Conf) when is_list(Conf) ->
 
     ok.
 
+underscore(Config) when is_list(Config) ->
+    S0 = <<"f(A) ->
+              _VAR1 = <<A>>,
+              _VAR2 = {ok,A},
+              _VAR3 = [A],
+              ok.
+	    g(A) ->
+              _VAR1 = A/0,
+              _VAR2 = date(),
+	      ok.
+            h() ->
+               _VAR1 = fun() -> ok end,
+	      ok.
+            i(A) ->
+               _VAR1 = #{A=>42},
+	      ok.
+	 ">>,
+    Ts0 = [{underscore0,
+	    S0,
+	    [],
+	    {warnings,[{2,sys_core_fold,useless_building},
+		       {3,sys_core_fold,useless_building},
+		       {4,sys_core_fold,useless_building},
+		       {7,sys_core_fold,result_ignored},
+		       {8,sys_core_fold,{no_effect,{erlang,date,0}}},
+		       {11,sys_core_fold,useless_building},
+		       {14,sys_core_fold,useless_building}
+		      ]}}],
+    [] = run(Config, Ts0),
+
+    %% Replace all "_VAR<digit>" variables with a plain underscore.
+    %% Now there should be no warnings.
+    S1 = re:replace(S0, "_VAR\\d+", "_", [global]),
+    io:format("~s\n", [S1]),
+    Ts1 = [{underscore1,S1,[],[]}],
+    [] = run(Config, Ts1),
+
+    ok.
+
 %%%
 %%% End of test cases.
 %%%