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-rw-r--r--lib/compiler/src/beam_block.erl168
1 files changed, 146 insertions, 22 deletions
diff --git a/lib/compiler/src/beam_block.erl b/lib/compiler/src/beam_block.erl
index 39ae8d5347..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}
@@ -231,7 +232,7 @@ alloc_may_pass({set,_,_,_}) -> true.
%% Optimize the instruction stream inside a basic block.
opt([{set,[X],[X],move}|Is]) -> opt(Is);
-opt([{set,[X],_,move},{set,[X],_,move}=I|Is]) ->
+opt([{set,[Dst],_,move},{set,[Dst],[Src],move}=I|Is]) when Dst =/= Src ->
opt([I|Is]);
opt([{set,[{x,0}],[S1],move}=I1,{set,[D2],[{x,0}],move}|Is]) ->
opt([I1,{set,[D2],[S1],move}|Is]);
@@ -289,7 +290,7 @@ opt_move(Dest, Is) ->
opt_move_1(R, [{set,[D],[R],move}|Is0], Acc) ->
%% Provided that the source register is killed by instructions
%% that follow, the optimization is safe.
- case eliminate_use_of_from_reg(Is0, R, D, []) of
+ case eliminate_use_of_from_reg(Is0, R, D) of
{yes,Is} -> opt_move_rev(D, Acc, Is);
no -> not_possible
end;
@@ -347,7 +348,7 @@ opt_tuple_element_1([{set,_,_,{alloc,_,_}}|_], _, _, _) ->
opt_tuple_element_1([{set,_,_,{try_catch,_,_}}|_], _, _, _) ->
no;
opt_tuple_element_1([{set,[D],[S],move}|Is0], I0, {_,S}, Acc) ->
- case eliminate_use_of_from_reg(Is0, S, D, []) of
+ case eliminate_use_of_from_reg(Is0, S, D) of
no ->
no;
{yes,Is} ->
@@ -389,6 +390,14 @@ is_killed_or_used(R, {set,Ss,Ds,_}) ->
%% that FromRegister is still used and that the optimization is not
%% possible.
+eliminate_use_of_from_reg(Is, From, To) ->
+ try
+ eliminate_use_of_from_reg(Is, From, To, [])
+ catch
+ throw:not_possible ->
+ no
+ end.
+
eliminate_use_of_from_reg([{set,_,_,{alloc,Live,_}}|_]=Is0, {x,X}, _, Acc) ->
if
X < Live ->
@@ -397,21 +406,32 @@ eliminate_use_of_from_reg([{set,_,_,{alloc,Live,_}}|_]=Is0, {x,X}, _, Acc) ->
{yes,reverse(Acc, Is0)}
end;
eliminate_use_of_from_reg([{set,Ds,Ss0,Op}=I0|Is], From, To, Acc) ->
+ ensure_safe_tuple(I0, To),
I = case member(From, Ss0) of
- true ->
- Ss = [case S of
- From -> To;
- _ -> S
- end || S <- Ss0],
- {set,Ds,Ss,Op};
- false ->
- I0
- end,
+ true ->
+ Ss = [case S of
+ From -> To;
+ _ -> S
+ end || S <- Ss0],
+ {set,Ds,Ss,Op};
+ false ->
+ I0
+ end,
case member(From, Ds) of
- true ->
- {yes,reverse(Acc, [I|Is])};
- false ->
- eliminate_use_of_from_reg(Is, From, To, [I|Acc])
+ true ->
+ {yes,reverse(Acc, [I|Is])};
+ false ->
+ case member(To, Ds) of
+ true ->
+ case beam_utils:is_killed_block(From, Is) of
+ true ->
+ {yes,reverse(Acc, [I|Is])};
+ false ->
+ no
+ end;
+ false ->
+ eliminate_use_of_from_reg(Is, From, To, [I|Acc])
+ end
end;
eliminate_use_of_from_reg([I]=Is, From, _To, Acc) ->
case beam_utils:is_killed_block(From, [I]) of
@@ -421,6 +441,10 @@ eliminate_use_of_from_reg([I]=Is, From, _To, Acc) ->
no
end.
+ensure_safe_tuple({set,[To],[],{put_tuple,_}}, To) ->
+ throw(not_possible);
+ensure_safe_tuple(_, _) -> ok.
+
%% opt_allocs(Instructions) -> Instructions. Optimize allocate
%% instructions inside blocks. If safe, replace an allocate_zero
%% instruction with the slightly cheaper allocate instruction.
@@ -541,3 +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.
generated by cgit v1.2.3 (git 2.25.1) at 2024-11-03 09:30:19 +0000