From 72b503485b0d029f615c80c3e64680419cd690d9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Tue, 26 Feb 2019 13:31:16 +0100
Subject: beam_ssa_opt: Use is_tagged_tuple more

Consider this code:

    foo(X) ->
       case X of
         {ok,A} -> A;
         error -> X
    end.

The `is_tagged_tuple` instruction would not be used
because not all instructions in the tuple matching
sequence had the same failure label:

    function t:foo(_0) {
    0:
      @ssa_bool:7 = bif:is_tuple _0
      br @ssa_bool:7, label 8, label 4

    8:
      @ssa_arity = bif:tuple_size _0
      @ssa_bool:9 = bif:'=:=' @ssa_arity, literal 2
      br @ssa_bool:9, label 6, label 3

    6:
      _4 = get_tuple_element _0, literal 0
      @ssa_bool = bif:'=:=' _4, literal ok
      br @ssa_bool, label 5, label 3

    5:
      _3 = get_tuple_element _0, literal 1
      ret _3

    4:
      @ssa_bool:11 = bif:'=:=' _0, literal error
      br @ssa_bool:11, label 10, label 3

    10:
      ret _0

    3:
      _2 = put_tuple literal case_clause, _0

      %% t.erl:5
      @ssa_ret:12 = call remote (literal erlang):(literal error)/1, _2
      ret @ssa_ret:12
    }

Enhance the ssa_opt_record optimization to use
`is_tagged_tuple` even if all failure labels are not the
same:

    function t:foo(_0) {
    0:
      @ssa_bool:7 = bif:is_tuple _0
      br @ssa_bool:7, label 8, label 4

    8:
      @ssa_bool:9 = is_tagged_tuple _0, literal 2, literal ok
      br @ssa_bool:9, label 6, label 3

    6:
      _3 = get_tuple_element _0, literal 1
      ret _3

    4:
      @ssa_bool:11 = bif:'=:=' _0, literal error
      br @ssa_bool:11, label 10, label 3

    10:
      ret _0

    3:
      _2 = put_tuple literal case_clause, _0

      %% t.erl:5
      @ssa_ret:12 = call remote (literal erlang):(literal error)/1, _2
      ret @ssa_ret:12
    }

The tuple test will be repeated, but since four instructions
are replaced by two instructions, the code will still be faster
and smaller.
---
 lib/compiler/src/beam_ssa_opt.erl | 51 +++++++++++++++++++++++----------------
 1 file changed, 30 insertions(+), 21 deletions(-)

(limited to 'lib/compiler')

diff --git a/lib/compiler/src/beam_ssa_opt.erl b/lib/compiler/src/beam_ssa_opt.erl
index ff9d562d67..bcf55f3fda 100644
--- a/lib/compiler/src/beam_ssa_opt.erl
+++ b/lib/compiler/src/beam_ssa_opt.erl
@@ -683,6 +683,14 @@ record_opt_is([#b_set{op={bif,is_tuple},dst=Bool,args=[Tuple]}=Set],
         no ->
             [Set]
     end;
+record_opt_is([I|Is]=Is0, #b_br{bool=Bool}=Last, Blocks) ->
+    case is_tagged_tuple_1(Is0, Last, Blocks) of
+        {yes,_Fail,Tuple,Arity,Tag} ->
+            Args = [Tuple,Arity,Tag],
+            [I#b_set{op=is_tagged_tuple,dst=Bool,args=Args}];
+        no ->
+            [I|record_opt_is(Is, Last, Blocks)]
+    end;
 record_opt_is([I|Is], Last, Blocks) ->
     [I|record_opt_is(Is, Last, Blocks)];
 record_opt_is([], _Last, _Blocks) -> [].
@@ -690,29 +698,30 @@ record_opt_is([], _Last, _Blocks) -> [].
 is_tagged_tuple(#b_var{}=Tuple, Bool,
                 #b_br{bool=Bool,succ=Succ,fail=Fail},
                 Blocks) ->
-    SuccBlk = map_get(Succ, Blocks),
-    is_tagged_tuple_1(SuccBlk, Tuple, Fail, Blocks);
+    #b_blk{is=Is,last=Last} = map_get(Succ, Blocks),
+    case is_tagged_tuple_1(Is, Last, Blocks) of
+        {yes,Fail,Tuple,Arity,Tag} ->
+            {yes,Arity,Tag};
+        _ ->
+            no
+    end;
 is_tagged_tuple(_, _, _, _) -> no.
 
-is_tagged_tuple_1(#b_blk{is=Is,last=Last}, Tuple, Fail, Blocks) ->
-    case Is of
-        [#b_set{op={bif,tuple_size},dst=ArityVar,
-                args=[#b_var{}=Tuple]},
-         #b_set{op={bif,'=:='},
-                dst=Bool,
-                args=[ArityVar, #b_literal{val=ArityVal}=Arity]}]
-        when is_integer(ArityVal) ->
-            case Last of
-                #b_br{bool=Bool,succ=Succ,fail=Fail} ->
-                    SuccBlk = map_get(Succ, Blocks),
-                    case is_tagged_tuple_2(SuccBlk, Tuple, Fail) of
-                        no ->
-                            no;
-                        {yes,Tag} ->
-                            {yes,Arity,Tag}
-                    end;
-                _ ->
-                    no
+is_tagged_tuple_1(Is, Last, Blocks) ->
+    case {Is,Last} of
+        {[#b_set{op={bif,tuple_size},dst=ArityVar,
+                 args=[#b_var{}=Tuple]},
+          #b_set{op={bif,'=:='},
+                 dst=Bool,
+                 args=[ArityVar, #b_literal{val=ArityVal}=Arity]}],
+         #b_br{bool=Bool,succ=Succ,fail=Fail}}
+          when is_integer(ArityVal) ->
+            SuccBlk = map_get(Succ, Blocks),
+            case is_tagged_tuple_2(SuccBlk, Tuple, Fail) of
+                no ->
+                    no;
+                {yes,Tag} ->
+                    {yes,Fail,Tuple,Arity,Tag}
             end;
         _ ->
             no
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