Merge pull request #2115 from bjorng/bjorn/compiler/opt-function_clause

Enhance optimization of function_clause exceptions

2 files changed, 44 insertions, 19 deletions

diff --git a/lib/compiler/src/beam_except.erl b/lib/compiler/src/beam_except.erl
index 26b193a35b..254a716b81 100644
--- a/lib/compiler/src/beam_except.erl
+++ b/lib/compiler/src/beam_except.erl
@@ -31,7 +31,7 @@
 %%% erlang:error(function_clause, Args)  => jump FuncInfoLabel
 %%%
 
--import(lists, [reverse/1,seq/2,splitwith/2]).
+-import(lists, [reverse/1,reverse/2,seq/2,splitwith/2]).
 
 -spec module(beam_utils:module_code(), [compile:option()]) ->
                     {'ok',beam_utils:module_code()}.
@@ -53,7 +53,7 @@ function({function,Name,Arity,CLabel,Is0}) ->
 -record(st,
 	{lbl :: beam_asm:label(),              %func_info label
 	 loc :: [_],                           %location for func_info
-	 arity :: arity()                       %arity for function
+	 arity :: arity()                      %arity for function
 	 }).
 
 function_1(Is0) ->
@@ -150,10 +150,15 @@ dig_out_fc(Arity, Is0) ->
                              (_) -> true
                           end, Is0),
     {Regs,Acc} = dig_out_fc_1(reverse(Is), Regs0, Acc0),
-    case is_fc(Arity, Regs) of
-        true ->
-            {yes,function_clause,Acc};
-        false ->
+    case Regs of
+        #{{x,0}:={atom,function_clause},{x,1}:=Args} ->
+            case moves_from_stack(Args, 0, []) of
+                {Moves,Arity} ->
+                    {yes,function_clause,reverse(Moves, Acc)};
+                {_,_} ->
+                    no
+            end;
+        #{} ->
             no
     end.
 
@@ -187,22 +192,30 @@ dig_out_fc_block([], Regs) -> Regs.
 prune_xregs(Live, Regs) ->
     maps:filter(fun({x,X}, _) -> X < Live end, Regs).
 
-is_fc(Arity, Regs) ->
-    case Regs of
-        #{{x,0}:={atom,function_clause},{x,1}:=Args} ->
-            is_fc_1(Args, 0) =:= Arity;
-        #{} ->
-            false
-    end.
-
-is_fc_1({cons,{arg,I},T}, I) ->
-    is_fc_1(T, I+1);
-is_fc_1(nil, I) ->
-    I;
-is_fc_1(_, _) -> -1.
+moves_from_stack({cons,{arg,N},_}, I, _Acc) when N =/= I ->
+    %% Wrong argument. Give up.
+    {[],-1};
+moves_from_stack({cons,H,T}, I, Acc) ->
+    case H of
+        {arg,I} ->
+            moves_from_stack(T, I+1, Acc);
+        _ ->
+            moves_from_stack(T, I+1, [{move,H,{x,I}}|Acc])
+    end;
+moves_from_stack(nil, I, Acc) ->
+    {reverse(Acc),I};
+moves_from_stack({literal,[H|T]}, I, Acc) ->
+    Cons = {cons,tag_literal(H),tag_literal(T)},
+    moves_from_stack(Cons, I, Acc).
 
 get_reg(R, Regs) ->
     case Regs of
         #{R:=Val} -> Val;
         #{} -> R
     end.
+
+tag_literal([]) -> nil;
+tag_literal(T) when is_atom(T) -> {atom,T};
+tag_literal(T) when is_float(T) -> {float,T};
+tag_literal(T) when is_integer(T) -> {integer,T};
+tag_literal(T) -> {literal,T}.
diff --git a/lib/compiler/test/beam_except_SUITE.erl b/lib/compiler/test/beam_except_SUITE.erl
index da61931136..49acad2bc5 100644
--- a/lib/compiler/test/beam_except_SUITE.erl
+++ b/lib/compiler/test/beam_except_SUITE.erl
@@ -88,8 +88,17 @@ coverage(_) ->
     {'EXIT',{{strange,Self},[{?MODULE,foo,[any],[File,{line,14}]}|_]}} =
         (catch foo(any)),
 
+    {ok,succeed,1,2} = foobar(succeed, 1, 2),
+    {'EXIT',{function_clause,[{?MODULE,foobar,[[fail],1,2],
+                               [{file,"fake.erl"},{line,16}]}|_]}} =
+        (catch foobar([fail], 1, 2)),
+    {'EXIT',{function_clause,[{?MODULE,fake_function_clause,[{a,b},42.0],_}|_]}} =
+        (catch fake_function_clause({a,b})),
+
     ok.
 
+fake_function_clause(A) -> error(function_clause, [A,42.0]).
+
 -file("fake.erl", 1).
 fc(a) ->	                                %Line 2
     ok;						%Line 3
@@ -104,3 +113,6 @@ bar(X) ->					%Line 8
 %% Cover collection code for function_clause exceptions.
 foo(A) ->                                       %Line 13
     error({strange,self()}, [A]).               %Line 14
+%% Cover beam_except:tag_literal/1.
+foobar(A, B, C) when is_atom(A) ->              %Line 16
+    {ok,A,B,C}.                                 %Line 17