From 50d8a8b1b0b46d35564ca1c949039ec903cd0937 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micha=C5=82=20Muska=C5=82a?= <michal@muskala.eu>
Date: Sun, 13 Aug 2017 18:24:54 +0200
Subject: Enhance optimisations in beam_peep

When cleaning selects, it might happen we're left with only one pair. In such
case convert to a regular test + jump.
---
 lib/compiler/src/beam_peep.erl    | 28 +++++++++++++++--
 lib/compiler/test/match_SUITE.erl | 64 +++++++++++++++++++++++++++++++++++++--
 2 files changed, 87 insertions(+), 5 deletions(-)

(limited to 'lib')

diff --git a/lib/compiler/src/beam_peep.erl b/lib/compiler/src/beam_peep.erl
index 6df5c02334..9436c20b36 100644
--- a/lib/compiler/src/beam_peep.erl
+++ b/lib/compiler/src/beam_peep.erl
@@ -89,15 +89,37 @@ peep([{gc_bif,_,_,_,_,Dst}=I|Is], SeenTests0, Acc) ->
 peep([{jump,{f,L}},{label,L}=I|Is], _, Acc) ->
     %% Sometimes beam_jump has missed this optimization.
     peep(Is, gb_sets:empty(), [I|Acc]);
-peep([{select,Op,R,F,Vls0}|Is], _, Acc) ->
+peep([{select,Op,R,F,Vls0}|Is], SeenTests0, Acc0) ->
     case prune_redundant_values(Vls0, F) of
 	[] ->
 	    %% No values left. Must convert to plain jump.
 	    I = {jump,F},
-	    peep(Is, gb_sets:empty(), [I|Acc]);
+	    peep([I|Is], gb_sets:empty(), Acc0);
+        [{atom,_}=Value,Lbl] when Op =:= select_val ->
+            %% Single value left. Convert to regular test and pop redundant tests.
+            Is1 = [{test,is_eq_exact,F,[R,Value]},{jump,Lbl}|Is],
+            case Acc0 of
+                [{test,is_atom,F,[R]}|Acc] ->
+                    peep(Is1, SeenTests0, Acc);
+                _ ->
+                    peep(Is1, SeenTests0, Acc0)
+            end;
+        [{integer,_}=Value,Lbl] when Op =:= select_val ->
+            %% Single value left. Convert to regular test and pop redundant tests.
+            Is1 = [{test,is_eq_exact,F,[R,Value]},{jump,Lbl}|Is],
+            case Acc0 of
+                [{test,is_integer,F,[R]}|Acc] ->
+                    peep(Is1, SeenTests0, Acc);
+                _ ->
+                    peep(Is1, SeenTests0, Acc0)
+            end;
+        [Arity,Lbl] when Op =:= select_tuple_arity ->
+            %% Single value left. Convert to regular test
+            Is1 = [{test,test_arity,F,[R,Arity]},{jump,Lbl}|Is],
+            peep(Is1, SeenTests0, Acc0);
 	[_|_]=Vls ->
 	    I = {select,Op,R,F,Vls},
-	    peep(Is, gb_sets:empty(), [I|Acc])
+	    peep(Is, gb_sets:empty(), [I|Acc0])
     end;
 peep([{test,Op,_,Ops}=I|Is], SeenTests0, Acc) ->
     case beam_utils:is_pure_test(I) of
diff --git a/lib/compiler/test/match_SUITE.erl b/lib/compiler/test/match_SUITE.erl
index 52b2da05f7..c31695be24 100644
--- a/lib/compiler/test/match_SUITE.erl
+++ b/lib/compiler/test/match_SUITE.erl
@@ -23,7 +23,7 @@
 	 init_per_group/2,end_per_group/2,
 	 pmatch/1,mixed/1,aliases/1,non_matching_aliases/1,
 	 match_in_call/1,untuplify/1,shortcut_boolean/1,letify_guard/1,
-	 selectify/1,underscore/1,match_map/1,map_vars_used/1,
+	 selectify/1,deselectify/1,underscore/1,match_map/1,map_vars_used/1,
 	 coverage/1,grab_bag/1,literal_binary/1]).
 	 
 -include_lib("common_test/include/ct.hrl").
@@ -38,7 +38,7 @@ groups() ->
     [{p,[parallel],
       [pmatch,mixed,aliases,non_matching_aliases,
        match_in_call,untuplify,
-       shortcut_boolean,letify_guard,selectify,
+       shortcut_boolean,letify_guard,selectify,deselectify,
        underscore,match_map,map_vars_used,coverage,
        grab_bag,literal_binary]}].
 
@@ -466,6 +466,66 @@ sel_same_value2(V) when V =:= 42; V =:= 43 ->
 sel_same_value2(_) ->
     error.
 
+%% Test deconstruction of select_val instructions in beam_peep into
+%% regular tests with just one possible value left. Hitting proper cases
+%% in beam_peep relies on unification of labels by beam_jump.
+
+deselectify(Config) when is_list(Config) ->
+    one_or_other = desel_tuple_arity({1}),
+    two = desel_tuple_arity({1,1}),
+    one_or_other = desel_tuple_arity({1,1,1}),
+
+    one_or_other = dsel_integer(1),
+    two = dsel_integer(2),
+    one_or_other = dsel_integer(3),
+
+    one_or_other = dsel_integer_typecheck(1),
+    two = dsel_integer_typecheck(2),
+    one_or_other = dsel_integer_typecheck(3),
+
+    one_or_other = dsel_atom(one),
+    two = dsel_atom(two),
+    one_or_other = dsel_atom(three),
+
+    one_or_other = dsel_atom_typecheck(one),
+    two = dsel_atom_typecheck(two),
+    one_or_other = dsel_atom_typecheck(three).
+
+desel_tuple_arity(Tuple) when is_tuple(Tuple) ->
+    case Tuple of
+        {_} -> one_or_other;
+        {_,_} -> two;
+        _ -> one_or_other
+    end.
+
+dsel_integer(Val) ->
+    case Val of
+        1 -> one_or_other;
+        2 -> two;
+        _ -> one_or_other
+    end.
+
+dsel_integer_typecheck(Val) when is_integer(Val) ->
+    case Val of
+        1 -> one_or_other;
+        2 -> two;
+        _ -> one_or_other
+    end.
+
+dsel_atom(Val) ->
+    case Val of
+        one -> one_or_other;
+        two -> two;
+        _ -> one_or_other
+    end.
+
+dsel_atom_typecheck(Val) when is_atom(Val) ->
+    case Val of
+        one -> one_or_other;
+        two -> two;
+        _ -> one_or_other
+    end.
+
 underscore(Config) when is_list(Config) ->
     case Config of
 	[] ->
-- 
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