diff options
| -rw-r--r-- | lib/compiler/src/beam_block.erl | 53 |
1 files changed, 46 insertions, 7 deletions
diff --git a/lib/compiler/src/beam_block.erl b/lib/compiler/src/beam_block.erl index 58e8f77a2c..af1bf8fd08 100644 --- a/lib/compiler/src/beam_block.erl +++ b/lib/compiler/src/beam_block.erl @@ -291,13 +291,12 @@ opt_moves(Ds, Is) -> opt_move(Dest, Is) -> opt_move_1(Dest, Is, []). -opt_move_1(R, [{set,[D],[R],move}|Is], Acc) -> - %% Check whether this instruction can be safely eliminated. - %% First check that the source (R) is not used by the - %% instructions that follow. - case beam_utils:is_killed_block(R, Is) of - true -> opt_move_rev(D, Acc, Is); - false -> not_possible +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 + {yes,Is} -> opt_move_rev(D, Acc, Is); + no -> not_possible end; opt_move_1({x,_}, [{set,_,_,{alloc,_,_}}|_], _) -> %% The optimization is not possible. If the X register is not @@ -333,6 +332,46 @@ opt_move_rev(D, [], Acc) -> {D,Acc}. is_killed_or_used(R, {set,Ss,Ds,_}) -> member(R, Ds) orelse member(R, Ss). +%% eliminate_use_of_from_reg([Instruction], FromRegister, ToRegister, Acc) -> +%% {yes,Is} | no +%% Eliminate any use of FromRegister in the instruction sequence +%% by replacing uses of FromRegister with ToRegister. If FromRegister +%% is referenced by an allocation instruction, return 'no' to indicate +%% that FromRegister is still used and that the optimization is not +%% possible. + +eliminate_use_of_from_reg([{set,_,_,{alloc,Live,_}}|_]=Is0, {x,X}, _, Acc) -> + if + X < Live -> + no; + true -> + {yes,reverse(Acc, Is0)} + end; +eliminate_use_of_from_reg([{set,Ds,Ss0,Op}=I0|Is], From, To, Acc) -> + I = case member(From, Ss0) of + 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]) + end; +eliminate_use_of_from_reg([I]=Is, From, _To, Acc) -> + case beam_utils:is_killed_block(From, [I]) of + true -> + {yes,reverse(Acc, Is)}; + false -> + no + end. + %% opt_alloc(Instructions) -> Instructions' %% Optimises all allocate instructions. |