aboutsummaryrefslogtreecommitdiffstats
diff options
context:
space:
mode:
-rw-r--r--lib/compiler/src/beam_block.erl113
-rw-r--r--lib/compiler/test/beam_block_SUITE.erl62
2 files changed, 167 insertions, 8 deletions
diff --git a/lib/compiler/src/beam_block.erl b/lib/compiler/src/beam_block.erl
index 18f325f172..d0536e0669 100644
--- a/lib/compiler/src/beam_block.erl
+++ b/lib/compiler/src/beam_block.erl
@@ -43,12 +43,13 @@ function({function,Name,Arity,CLabel,Is0}, Blockify) ->
false ->
Is0
end,
- Is3 = beam_utils:anno_defs(Is2),
- Is4 = move_allocates(Is3),
- Is5 = beam_utils:live_opt(Is4),
- Is6 = opt_blocks(Is5),
- Is7 = beam_utils:delete_annos(Is6),
- Is = opt_allocs(Is7),
+ Is3 = local_cse(Is2),
+ Is4 = beam_utils:anno_defs(Is3),
+ Is5 = move_allocates(Is4),
+ Is6 = beam_utils:live_opt(Is5),
+ Is7 = opt_blocks(Is6),
+ Is8 = beam_utils:delete_annos(Is7),
+ Is = opt_allocs(Is8),
%% Done.
{function,Name,Arity,CLabel,Is}
@@ -564,3 +565,103 @@ defined_regs([{set,Ds,_,{alloc,Live,_}}|_], Regs) ->
x_live(Ds, Regs bor ((1 bsl Live) - 1));
defined_regs([{set,Ds,_,_}|Is], Regs) ->
defined_regs(Is, x_live(Ds, Regs)).
+
+%%%
+%%% Do local common sub expression elimination (CSE) in each block.
+%%%
+
+local_cse([{block,Bl0}|Is]) ->
+ Bl = cse_block(Bl0, orddict:new(), []),
+ [{block,Bl}|local_cse(Is)];
+local_cse([I|Is]) ->
+ [I|local_cse(Is)];
+local_cse([]) -> [].
+
+cse_block([I|Is], Es0, Acc0) ->
+ Es1 = cse_clear(I, Es0),
+ case cse_expr(I) of
+ none ->
+ %% Instruction is not suitable for CSE.
+ cse_block(Is, Es1, [I|Acc0]);
+ {ok,D,Expr} ->
+ %% Suitable instruction. First update the dictionary of
+ %% suitable expressions for the next iteration.
+ Es = cse_add(D, Expr, Es1),
+
+ %% Search for a previous identical expression.
+ case cse_find(Expr, Es0) of
+ error ->
+ %% Nothing found
+ cse_block(Is, Es, [I|Acc0]);
+ Src ->
+ %% Use the previously calculated result.
+ %% Also eliminate any line instruction.
+ Move = {set,[D],[Src],move},
+ case Acc0 of
+ [{set,_,_,{line,_}}|Acc] ->
+ cse_block(Is, Es, [Move|Acc]);
+ [_|_] ->
+ cse_block(Is, Es, [Move|Acc0])
+ end
+ end
+ end;
+cse_block([], _, Acc) ->
+ reverse(Acc).
+
+%% cse_find(Expr, Expressions) -> error | Register.
+%% Find a previously evaluated expression whose result can be reused,
+%% or return 'error' if no such expression is found.
+
+cse_find(Expr, Es) ->
+ case orddict:find(Expr, Es) of
+ {ok,{Src,_}} -> Src;
+ error -> error
+ end.
+
+cse_expr({set,[D],Ss,{bif,N,_}}) ->
+ {ok,D,{{bif,N},Ss}};
+cse_expr({set,[D],Ss,{alloc,_,{gc_bif,N,_}}}) ->
+ {ok,D,{{gc_bif,N},Ss}};
+cse_expr({set,[D],Ss,put_list}) ->
+ {ok,D,{put_list,Ss}};
+cse_expr(_) -> none.
+
+%% cse_clear(Instr, Expressions0) -> Expressions.
+%% Remove all previous expressions that will become
+%% invalid when this instruction is executed. Basically,
+%% an expression is no longer safe to reuse when the
+%% register it has been stored to has been modified, killed,
+%% or if any of the source operands have changed.
+
+cse_clear({set,Ds,_,{alloc,Live,_}}, Es) ->
+ cse_clear_1(Es, Live, Ds);
+cse_clear({set,Ds,_,_}, Es) ->
+ cse_clear_1(Es, all, Ds).
+
+cse_clear_1(Es, Live, Ds0) ->
+ Ds = ordsets:from_list(Ds0),
+ [E || E <- Es, cse_is_safe(E, Live, Ds)].
+
+cse_is_safe({_,{Dst,Interfering}}, Live, Ds) ->
+ ordsets:is_disjoint(Interfering, Ds) andalso
+ case Dst of
+ {x,X} ->
+ X < Live;
+ _ ->
+ true
+ end.
+
+%% cse_add(Dest, Expr, Expressions0) -> Expressions.
+%% Provided that it is safe, add a new expression to the dictionary
+%% of already evaluated expressions.
+
+cse_add(D, {_,Ss}=Expr, Es) ->
+ case member(D, Ss) of
+ false ->
+ Interfering = ordsets:from_list([D|Ss]),
+ orddict:store(Expr, {D,Interfering}, Es);
+ true ->
+ %% Unsafe because the instruction overwrites one of
+ %% source operands.
+ Es
+ end.
diff --git a/lib/compiler/test/beam_block_SUITE.erl b/lib/compiler/test/beam_block_SUITE.erl
index 55d5f2dbe8..fac18789e0 100644
--- a/lib/compiler/test/beam_block_SUITE.erl
+++ b/lib/compiler/test/beam_block_SUITE.erl
@@ -22,7 +22,7 @@
-export([all/0,suite/0,groups/0,init_per_suite/1,end_per_suite/1,
init_per_group/2,end_per_group/2,
get_map_elements/1,otp_7345/1,move_opt_across_gc_bif/1,
- erl_202/1,repro/1]).
+ erl_202/1,repro/1,local_cse/1]).
%% The only test for the following functions is that
%% the code compiles and is accepted by beam_validator.
@@ -40,7 +40,8 @@ groups() ->
otp_7345,
move_opt_across_gc_bif,
erl_202,
- repro
+ repro,
+ local_cse
]}].
init_per_suite(Config) ->
@@ -237,6 +238,63 @@ find_operands(Cfg,XsiGraph,ActiveList,Count) ->
[Count+1, length(NewActiveList), length(digraph:vertices(XsiGraph))],
find_operands(NewCfg,XsiGraph,NewActiveList,Count+1).
+%% Some tests of local common subexpression elimination (CSE).
+
+local_cse(_Config) ->
+ {Self,{ok,Self}} = local_cse_1(),
+
+ local_cse_2([]),
+ local_cse_2(lists:seq(1, 512)),
+ local_cse_2(?MODULE:module_info()),
+
+ {[b],[a,b]} = local_cse_3(a, b),
+
+ {2000,Self,{Self,write_cache}} = local_cse_4(),
+
+ ok.
+
+local_cse_1() ->
+ %% Cover handling of unsafe tuple construction in
+ %% eliminate_use_of_from_reg/4. It became necessary to handle
+ %% unsafe tuples when local CSE was introduced.
+
+ {self(),{ok,self()}}.
+
+local_cse_2(Term) ->
+ case cse_make_binary(Term) of
+ <<Size:8,BinTerm:Size/binary>> ->
+ Term = binary_to_term(BinTerm);
+ <<Size:8,SizeTerm:Size/binary,BinTerm/binary>> ->
+ {'$size',TermSize} = binary_to_term(SizeTerm),
+ TermSize = byte_size(BinTerm),
+ Term = binary_to_term(BinTerm)
+ end.
+
+%% Copy of observer_backend:ttb_make_binary/1. During development of
+%% the local CSE optimization this function was incorrectly optimized.
+
+cse_make_binary(Term) ->
+ B = term_to_binary(Term),
+ SizeB = byte_size(B),
+ if SizeB > 255 ->
+ SB = term_to_binary({'$size',SizeB}),
+ <<(byte_size(SB)):8, SB/binary, B/binary>>;
+ true ->
+ <<SizeB:8, B/binary>>
+ end.
+
+local_cse_3(X, Y) ->
+ %% The following expression was incorrectly transformed to {[X,Y],[X,Y]}
+ %% during development of the local CSE optimization.
+
+ {[Y],[X,Y]}.
+
+local_cse_4() ->
+ do_local_cse_4(2000, self(), {self(), write_cache}).
+
+do_local_cse_4(X, Y, Z) ->
+ {X,Y,Z}.
+
%%%
%%% Common functions.
%%%