File 3281-Do-strength-reduction-of-is_tagged_tuple-a... of Package erlang

Overview Repositories Revisions Requests Users Attributes Meta

File 3281-Do-strength-reduction-of-is_tagged_tuple-and-is_list.patch of Package erlang (Revision 04547a2f7d9bbb4ead58b93b0932096a)

Currently displaying revision 04547a2f7d9bbb4ead58b93b0932096a , Show latest

From d3beb34700543298b12e5420a63c618356fab1f2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Mon, 28 Jun 2021 21:44:53 +0200
Subject: [PATCH] Do strength reduction of is_tagged_tuple and is_list

There is an instruction called `is_tagged_tuple` that is used for
matching a tuple whose first element is a literal atom. Here is
an example where this instruction will be used:

f(X) ->
        case some_function(X) of
            {ok,Result} -> Result;
            Error -> Error
        end.

The following BEAM code will be generated:

{allocate,0,1}.
        {call,1,{f,5}}.
        {test,is_tagged_tuple,{f,3},[{x,0},2,{atom,ok}]}.
        {get_tuple_element,{x,0},1,{x,0}}.
        {deallocate,0}.
        return.
      {label,3}.
        {deallocate,0}.
        return.

Better code can be generated if the compiler's type analysis has
figured out that the type of the return value of `some_function/1` is:

{'ok', any()} | 'error'

If that is the case, since the return value of `some_function/1` is
either a tuple or the atom `error`, the `is_tagged_tuple` instruction
can be replaced with the less expensive (slightly faster and slightly
smaller) `is_tuple` instruction:

{allocate,0,1}.
        {call,1,{f,5}}.
        {test,is_tuple,{f,3},[{x,0}]}.
        {get_tuple_element,{x,0},1,{x,0}}.
        {deallocate,0}.
        return.
      {label,3}.
        {deallocate,0}.
        return.

If the compiler has figured out that the type is:

{'ok', any()} | {'error', any(), any()}

then `is_tagged_tuple` can be replaced with `test_arity`:

{allocate,0,1}.
       {call,1,{f,5}}. % some_function/1
       {test,test_arity,{f,3},[{x,0},2]}.
       {get_tuple_element,{x,0},1,{x,0}}.
       {deallocate,0}.
       return.
     {label,3}.
       {deallocate,0}.
       return.

Unfortunately, if the type is:

{'ok', any()} | {'error', any()}

which is not uncommon, there does not exist any alternative sequence
of instructions that would be guaranteed to be less expensive, so we
will keep `is_tagged_tuple`.

Also replace the `is_list/1` guard BIF with a less expensive instruction
when we have knowledge of the argument.
---
 lib/compiler/src/beam_ssa_codegen.erl | 16 ++++++--
 lib/compiler/src/beam_ssa_type.erl    | 55 ++++++++++++++++++++++++++-
 2 files changed, 67 insertions(+), 4 deletions(-)

diff --git a/lib/compiler/src/beam_ssa_codegen.erl b/lib/compiler/src/beam_ssa_codegen.erl
index e38a2265d5..f80d7b5bb1 100644
--- a/lib/compiler/src/beam_ssa_codegen.erl
+++ b/lib/compiler/src/beam_ssa_codegen.erl
@@ -1209,9 +1209,19 @@ cg_block([#cg_set{op=Op,dst=Dst0,args=Args0}=I,
 cg_block([#cg_set{op=bs_test_tail,dst=Bool,args=Args0}], {Bool,Fail}, St) ->
     [Ctx,{integer,Bits}] = beam_args(Args0, St),
     {[{test,bs_test_tail2,bif_fail(Fail),[Ctx,Bits]}],St};
-cg_block([#cg_set{op=is_tagged_tuple,dst=Bool,args=Args0}], {Bool,Fail}, St) ->
-    [Src,{integer,Arity},Tag] = beam_args(Args0, St),
-    {[{test,is_tagged_tuple,ensure_label(Fail, St),[Src,Arity,Tag]}],St};
+cg_block([#cg_set{op=is_tagged_tuple,anno=Anno,dst=Bool,args=Args0}], {Bool,Fail}, St) ->
+    case Anno of
+        #{constraints := arity} ->
+            [Src,{integer,Arity},_Tag] = beam_args(Args0, St),
+            {[{test,test_arity,ensure_label(Fail, St),[Src,Arity]}],St};
+        #{constraints := tuple_arity} ->
+            [Src,{integer,Arity},_Tag] = beam_args(Args0, St),
+            {[{test,is_tuple,ensure_label(Fail, St),[Src]},
+              {test,test_arity,ensure_label(Fail, St),[Src,Arity]}],St};
+        #{} ->
+            [Src,{integer,Arity},Tag] = beam_args(Args0, St),
+            {[{test,is_tagged_tuple,ensure_label(Fail, St),[Src,Arity,Tag]}],St}
+    end;
 cg_block([#cg_set{op=is_nonempty_list,dst=Bool,args=Args0}], {Bool,Fail}, St) ->
     Args = beam_args(Args0, St),
     {[{test,is_nonempty_list,ensure_label(Fail, St),Args}],St};
diff --git a/lib/compiler/src/beam_ssa_type.erl b/lib/compiler/src/beam_ssa_type.erl
index 2fa8f0dcf5..8ab7473139 100644
--- a/lib/compiler/src/beam_ssa_type.erl
+++ b/lib/compiler/src/beam_ssa_type.erl
@@ -886,6 +886,15 @@ simplify(#b_set{op={bif,'=:='},args=[LHS,RHS]}=I, Ts) ->
                     eval_bif(I, Ts)
             end
     end;
+simplify(#b_set{op={bif,is_list},args=[Src]}=I, Ts) ->
+    case raw_type(Src, Ts) of
+        #t_union{list=#t_cons{}} ->
+            I#b_set{op=is_nonempty_list,args=[Src]};
+        #t_union{list=nil} ->
+            I#b_set{op={bif,'=:='},args=[Src,#b_literal{val=[]}]};
+        _ ->
+            eval_bif(I, Ts)
+    end;
 simplify(#b_set{op={bif,Op},args=Args}=I, Ts) ->
     Types = normalized_types(Args, Ts),
     case is_float_op(Op, Types) of
@@ -945,7 +954,51 @@ simplify(#b_set{op=is_nonempty_list,args=[Src]}=I, Ts) ->
     end;
 simplify(#b_set{op=is_tagged_tuple,
                 args=[Src,#b_literal{val=Size},#b_literal{}=Tag]}=I, Ts) ->
-    simplify_is_record(I, normalized_type(Src, Ts), Size, Tag, Ts);
+    case raw_type(Src, Ts) of
+        #t_union{tuple_set=TupleSet}=U ->
+            %% A union of different types, one of them (probably)
+            %% a tuple. Dig out the tuple type from the union and
+            %% find out whether it will match.
+            TupleOnlyType = #t_union{tuple_set=TupleSet},
+            TT = beam_types:normalize(TupleOnlyType),
+            case simplify_is_record(I, TT, Size, Tag, Ts) of
+                #b_literal{val=true} ->
+                    %% The tuple part of the union will always match.
+                    %% A simple is_tuple/1 test will be sufficient to
+                    %% distinguish the tuple from the other types in
+                    %% the union.
+                    I#b_set{op={bif,is_tuple},args=[Src]};
+                #b_literal{val=false}=False ->
+                    %% Src is never a tuple.
+                    False;
+                _ ->
+                    %% More than one type of tuple can match. Find out
+                    %% whether the possible tuples can be
+                    %% distinguished by size.
+                    TupleArityType = #t_tuple{size=Size,exact=true},
+                    TTT = beam_types:meet(TupleArityType, TupleOnlyType),
+                    case simplify_is_record(I, TTT, Size, Tag, Ts) of
+                        #b_literal{val=true} ->
+                            %% The possible tuple types have different sizes.
+                            %% Example: {ok, _} | {error, _, _}.
+                            case beam_types:normalize(U) of
+                                #t_tuple{} ->
+                                    %% Src is known to be a tuple, so it will
+                                    %% be sufficient to test the arity.
+                                    beam_ssa:add_anno(constraints, arity, I);
+                                any ->
+                                    %% Src might not be a tuple. Must
+                                    %% test for a tuple with a given
+                                    %% arity.
+                                    beam_ssa:add_anno(constraints, tuple_arity, I)
+                            end;
+                        _ ->
+                            I
+                    end
+            end;
+        SimpleType ->
+            simplify_is_record(I, SimpleType, Size, Tag, Ts)
+    end;
 simplify(#b_set{op=put_list,args=[#b_literal{val=H},
                                   #b_literal{val=T}]}, _Ts) ->
     #b_literal{val=[H|T]};
-- 
2.31.1

Places

File 3281-Do-strength-reduction-of-is_tagged_tuple-and-is_list.patch of Package erlang (Revision 04547a2f7d9bbb4ead58b93b0932096a)

Places