diff options
Diffstat (limited to 'lib/compiler/src/beam_block.erl')
| -rw-r--r-- | lib/compiler/src/beam_block.erl | 35 |
1 files changed, 21 insertions, 14 deletions
diff --git a/lib/compiler/src/beam_block.erl b/lib/compiler/src/beam_block.erl index 9c6f835ab0..c45874597a 100644 --- a/lib/compiler/src/beam_block.erl +++ b/lib/compiler/src/beam_block.erl @@ -36,12 +36,13 @@ function({function,Name,Arity,CLabel,Is0}, Lc0) -> %% Collect basic blocks and optimize them. Is2 = blockify(Is1), - Is3 = beam_utils:live_opt(Is2), - Is4 = opt_blocks(Is3), - Is5 = beam_utils:delete_live_annos(Is4), + Is3 = move_allocates(Is2), + Is4 = beam_utils:live_opt(Is3), + Is5 = opt_blocks(Is4), + Is6 = beam_utils:delete_live_annos(Is5), %% Optimize bit syntax. - {Is,Lc} = bsm_opt(Is5, Lc0), + {Is,Lc} = bsm_opt(Is6, Lc0), %% Done. {{function,Name,Arity,CLabel,Is},Lc} @@ -156,11 +157,7 @@ opt_blocks([I|Is]) -> opt_blocks([]) -> []. opt_block(Is0) -> - %% We explicitly move any allocate instruction upwards before optimising - %% moves, to avoid any potential problems with the calculation of live - %% registers. - Is1 = move_allocates(Is0), - Is = find_fixpoint(fun opt/1, Is1), + Is = find_fixpoint(fun opt/1, Is0), opt_alloc(Is). find_fixpoint(OptFun, Is0) -> @@ -170,11 +167,21 @@ find_fixpoint(OptFun, Is0) -> end. %% move_allocates(Is0) -> Is -%% Move allocates upwards in the instruction stream, in the hope of -%% getting more possibilities for optimizing away moves later. - -move_allocates(Is) -> - move_allocates_1(reverse(Is), []). +%% Move allocate instructions upwards in the instruction stream, in the +%% hope of getting more possibilities for optimizing away moves later. +%% +%% NOTE: Moving allocation instructions is only safe because it is done +%% immediately after code generation so that we KNOW that if {x,X} is +%% initialized, all x registers with lower numbers are also initialized. +%% That assumption may not be true after other optimizations, such as +%% the beam_utils:live_opt/1 optimization. + +move_allocates([{block,Bl0}|Is]) -> + Bl = move_allocates_1(reverse(Bl0), []), + [{block,Bl}|move_allocates(Is)]; +move_allocates([I|Is]) -> + [I|move_allocates(Is)]; +move_allocates([]) -> []. move_allocates_1([{set,[],[],{alloc,_,_}=Alloc}|Is0], Acc0) -> {Is,Acc} = move_allocates_2(Alloc, Is0, Acc0), |