diff options
| -rw-r--r-- | lib/compiler/src/beam_block.erl | 89 |
1 files changed, 60 insertions, 29 deletions
diff --git a/lib/compiler/src/beam_block.erl b/lib/compiler/src/beam_block.erl index c640af224d..f799147da1 100644 --- a/lib/compiler/src/beam_block.erl +++ b/lib/compiler/src/beam_block.erl @@ -37,13 +37,14 @@ function({function,Name,Arity,CLabel,Is0}) -> %% Collect basic blocks and optimize them. Is1 = blockify(Is0), Is2 = embed_lines(Is1), - Is3 = move_allocates(Is2), - Is4 = beam_utils:live_opt(Is3), - Is5 = opt_blocks(Is4), - Is6 = beam_utils:delete_live_annos(Is5), - - %% Done. - {function,Name,Arity,CLabel,Is6} + Is3 = beam_utils:anno_defs(Is2), + Is4 = move_allocates(Is3), + Is5 = beam_utils:live_opt(Is4), + Is6 = opt_blocks(Is5), + Is = beam_utils:delete_live_annos(Is6), + + %% Done. + {function,Name,Arity,CLabel,Is} catch Class:Error -> Stack = erlang:get_stacktrace(), @@ -173,7 +174,7 @@ find_fixpoint(OptFun, Is0) -> %% safe to assume that if x(N) is initialized, then all lower-numbered %% x registers are also initialized. %% -%% For example, in general it is not safe to transform the following +%% For example, we must be careful when transforming the following %% instructions: %% %% get_tuple_element x(0) Element => x(1) @@ -185,13 +186,9 @@ find_fixpoint(OptFun, Is0) -> %% get_tuple_element x(0) Element => x(1) %% %% The transformation is safe if and only if x(1) has been -%% initialized previously. Unfortunately, beam_reorder may have moved -%% a get_tuple_element instruction so that x(1) is not always -%% initialized when this code is reached. To find whether or not x(1) -%% is initialized, we would need to analyze all code preceding these -%% two instructions (across branches). Since we currently don't have -%% any practical mechanism for doing that, we will have to -%% conservatively assume that the transformation is unsafe. +%% initialized previously. We will use the annotations added by +%% beam_utils:anno_defs/1 to determine whether x(a) has been +%% initialized. move_allocates([{block,Bl0}|Is]) -> Bl = move_allocates_1(reverse(Bl0), []), @@ -200,15 +197,20 @@ move_allocates([I|Is]) -> [I|move_allocates(Is)]; move_allocates([]) -> []. +move_allocates_1([{'%def',_}|Is], Acc) -> + move_allocates_1(Is, Acc); move_allocates_1([I|Is], [{set,[],[],{alloc,Live0,Info}}|Acc]=Acc0) -> - case {alloc_may_pass(I),alloc_live_regs(I, Live0)} of - {false,_} -> - move_allocates_1(Is, [I|Acc0]); - {true,not_possible} -> - move_allocates_1(Is, [I|Acc0]); - {true,Live} when is_integer(Live) -> - A = {set,[],[],{alloc,Live,Info}}, - move_allocates_1(Is, [A,I|Acc]) + case alloc_may_pass(I) of + false -> + move_allocates_1(Is, [I|Acc0]); + true -> + case alloc_live_regs(I, Is, Live0) of + not_possible -> + move_allocates_1(Is, [I|Acc0]); + Live when is_integer(Live) -> + A = {set,[],[],{alloc,Live,Info}}, + move_allocates_1(Is, [A,I|Acc]) + end end; move_allocates_1([I|Is], Acc) -> move_allocates_1(Is, [I|Acc]); @@ -472,16 +474,34 @@ count_ones(Bits, Acc) -> %% Calculate the new number of live registers when we move an allocate %% instruction upwards, passing a 'set' instruction. -alloc_live_regs({set,Ds,Ss,_}, Regs0) -> +alloc_live_regs({set,Ds,Ss,_}, Is, Regs0) -> Rset = x_live(Ss, x_dead(Ds, (1 bsl Regs0)-1)), - live_regs(0, Rset). + Live = live_regs(0, Rset), + case ensure_contiguous(Rset, Live) of + not_possible -> + %% Liveness information (looking forward in the + %% instruction stream) can't prove that moving this + %% allocation instruction is safe. Now use the annotation + %% of defined registers at the beginning of the current + %% block to see whether moving would be safe. + Def0 = defined_regs(Is, 0), + Def = Def0 band ((1 bsl Live) - 1), + ensure_contiguous(Rset bor Def, Live); + Live -> + %% Safe based on liveness information. + Live + end. live_regs(N, 0) -> N; -live_regs(N, Regs) when Regs band 1 =:= 1 -> - live_regs(N+1, Regs bsr 1); -live_regs(_, _) -> - not_possible. +live_regs(N, Regs) -> + live_regs(N+1, Regs bsr 1). + +ensure_contiguous(Regs, Live) -> + case (1 bsl Live) - 1 of + Regs -> Live; + _ -> not_possible + end. x_dead([{x,N}|Rs], Regs) -> x_dead(Rs, Regs band (bnot (1 bsl N))); x_dead([_|Rs], Regs) -> x_dead(Rs, Regs); @@ -490,3 +510,14 @@ x_dead([], Regs) -> Regs. x_live([{x,N}|Rs], Regs) -> x_live(Rs, Regs bor (1 bsl N)); x_live([_|Rs], Regs) -> x_live(Rs, Regs); x_live([], Regs) -> Regs. + +%% defined_regs(ReversedInstructions) -> RegBitmap. +%% Given a reversed instruction stream, determine the +%% the registers that are defined. + +defined_regs([{'%def',Def}|_], Regs) -> + Def bor Regs; +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)). |