From f63b503f9c7ea4d5824899dc5b287075e261e6a8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Mon, 10 Aug 2015 14:27:50 +0200
Subject: Move rewriting of select_val to is_boolean from beam_peep to
 beam_dead

We can rewrite more instances of select_val to is_boolean because
it is not necessary that a particular label follows the select_val.
---
 lib/compiler/src/beam_dead.erl | 24 +++++++++++++++++++++---
 lib/compiler/src/beam_peep.erl | 28 ----------------------------
 2 files changed, 21 insertions(+), 31 deletions(-)

diff --git a/lib/compiler/src/beam_dead.erl b/lib/compiler/src/beam_dead.erl
index ead88b57e9..0cb5040177 100644
--- a/lib/compiler/src/beam_dead.erl
+++ b/lib/compiler/src/beam_dead.erl
@@ -242,8 +242,15 @@ backward([{select,select_val,Reg,{f,Fail0},List0}|Is], D, Acc) ->
     List = shortcut_select_list(List0, Reg, D, []),
     Fail1 = shortcut_label(Fail0, D),
     Fail = shortcut_bs_test(Fail1, Is, D),
-    Sel = {select,select_val,Reg,{f,Fail},List},
-    backward(Is, D, [Sel|Acc]);
+    case List of
+	[{atom,B1},F,{atom,B2},F] when B1 =:= not B2 ->
+	    Test = {test,is_boolean,{f,Fail},[Reg]},
+	    Jump = {jump,F},
+	    backward([Jump,Test|Is], D, Acc);
+	[_|_] ->
+	    Sel = {select,select_val,Reg,{f,Fail},List},
+	    backward(Is, D, [Sel|Acc])
+    end;
 backward([{jump,{f,To0}},{move,Src,Reg}=Move|Is], D, Acc) ->
     To = shortcut_select_label(To0, Reg, Src, D),
     Jump = {jump,{f,To}},
@@ -295,7 +302,18 @@ backward([{test,Op,{f,To0},Ops0}|Is], D, Acc) ->
 	    is_eq_exact -> combine_eqs(To, Ops0, D, Acc);
 	    _ -> {test,Op,{f,To},Ops0}
 	end,
-    backward(Is, D, [I|Acc]);
+    case {I,Acc} of
+	{{test,is_atom,Fail,Ops0},[{test,is_boolean,Fail,Ops0}|_]} ->
+	    %% An is_atom test before an is_boolean test (with the
+	    %% same failure label) is redundant.
+	    backward(Is, D, Acc);
+	{{test,_,_,_},_} ->
+	    %% Still a test instruction. Done.
+	    backward(Is, D, [I|Acc]);
+	{_,_} ->
+	    %% Rewritten to a select_val. Rescan.
+	    backward([I|Is], D, Acc)
+    end;
 backward([{test,Op,{f,To0},Live,Ops0,Dst}|Is], D, Acc) ->
     To1 = shortcut_bs_test(To0, Is, D),
     To2 = shortcut_label(To1, D),
diff --git a/lib/compiler/src/beam_peep.erl b/lib/compiler/src/beam_peep.erl
index 17fd2e502a..75be86b83f 100644
--- a/lib/compiler/src/beam_peep.erl
+++ b/lib/compiler/src/beam_peep.erl
@@ -65,18 +65,6 @@ function({function,Name,Arity,CLabel,Is0}) ->
 %%      InEncoding =:= latin1, OutEncoding =:= unicode; 
 %%      InEncoding =:= latin1, OutEncoding =:= utf8 ->
 %%
-%% (2) A select_val/4 instruction that only verifies that
-%%     its argument is either 'true' or 'false' can be
-%%     be replaced with an is_boolean/2 instruction. That is:
-%%
-%%          select_val Reg Fail   [ true Next false Next ]
-%%        Next: ...
-%%         
-%%     can be rewritten to
-%%
-%%          is_boolean Fail Reg
-%%        Next: ...
-%%
 
 peep(Is) ->
     peep(Is, gb_sets:empty(), []).
@@ -95,12 +83,6 @@ peep([{gc_bif,_,_,_,_,Dst}=I|Is], SeenTests0, Acc) ->
     %% Kill all remembered tests that depend on the destination register.
     SeenTests = kill_seen(Dst, SeenTests0),
     peep(Is, SeenTests, [I|Acc]);
-peep([{test,is_boolean,{f,Fail},Ops}|_]=Is, SeenTests,
-     [{test,is_atom,{f,Fail},Ops}|Acc]) ->
-    %% The previous is_atom/2 test (with the same failure label) is redundant.
-    %% (If is_boolean(Src) is true, is_atom(Src) is also true, so it is
-    %% OK to still remember that we have seen is_atom/1.)
-    peep(Is, SeenTests, Acc);
 peep([{test,Op,_,Ops}=I|Is], SeenTests0, Acc) ->
     case beam_utils:is_pure_test(I) of
 	false ->
@@ -121,16 +103,6 @@ peep([{test,Op,_,Ops}=I|Is], SeenTests0, Acc) ->
 		    peep(Is, SeenTests, [I|Acc])
 	    end
     end;
-peep([{select,select_val,Src,Fail,
-       [{atom,false},{f,L},{atom,true},{f,L}]}|
-      [{label,L}|_]=Is], SeenTests, Acc) ->
-    I = {test,is_boolean,Fail,[Src]},
-    peep([I|Is], SeenTests, Acc);
-peep([{select,select_val,Src,Fail,
-       [{atom,true},{f,L},{atom,false},{f,L}]}|
-      [{label,L}|_]=Is], SeenTests, Acc) ->
-    I = {test,is_boolean,Fail,[Src]},
-    peep([I|Is], SeenTests, Acc);
 peep([I|Is], _, Acc) ->
     %% An unknown instruction. Throw away all information we
     %% have collected about test instructions.
-- 
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